Rollup merge of #82854 - estebank:issue-82827, r=oli-obk

Account for `if (let pat = expr) {}`

Fix #82827.

compiler/rustc_ast/src/ast.rs

@@ -1129,6 +1129,14 @@ impl Expr {
         }
     }
 
+    pub fn peel_parens(&self) -> &Expr {
+        let mut expr = self;
+        while let ExprKind::Paren(inner) = &expr.kind {
+            expr = &inner;
+        }
+        expr
+    }
+
     /// Attempts to reparse as `Ty` (for diagnostic purposes).
     pub fn to_ty(&self) -> Option<P<Ty>> {
         let kind = match &self.kind {

compiler/rustc_ast_lowering/src/expr.rs

@@ -97,6 +97,23 @@ impl<'hir> LoweringContext<'_, 'hir> {
                     ExprKind::Let(ref pat, ref scrutinee) => {
                         self.lower_expr_if_let(e.span, pat, scrutinee, then, else_opt.as_deref())
                     }
+                    ExprKind::Paren(ref paren) => match paren.peel_parens().kind {
+                        ExprKind::Let(ref pat, ref scrutinee) => {
+                            // A user has written `if (let Some(x) = foo) {`, we want to avoid
+                            // confusing them with mentions of nightly features.
+                            // If this logic is changed, you will also likely need to touch
+                            // `unused::UnusedParens::check_expr`.
+                            self.if_let_expr_with_parens(cond, &paren.peel_parens());
+                            self.lower_expr_if_let(
+                                e.span,
+                                pat,
+                                scrutinee,
+                                then,
+                                else_opt.as_deref(),
+                            )
+                        }
+                        _ => self.lower_expr_if(cond, then, else_opt.as_deref()),
+                    },
                     _ => self.lower_expr_if(cond, then, else_opt.as_deref()),
                 },
                 ExprKind::While(ref cond, ref body, opt_label) => self
@@ -346,6 +363,25 @@ impl<'hir> LoweringContext<'_, 'hir> {
         hir::ExprKind::Call(f, self.lower_exprs(&real_args))
     }
 
+    fn if_let_expr_with_parens(&mut self, cond: &Expr, paren: &Expr) {
+        let start = cond.span.until(paren.span);
+        let end = paren.span.shrink_to_hi().until(cond.span.shrink_to_hi());
+        self.sess
+            .struct_span_err(
+                vec![start, end],
+                "invalid parentheses around `let` expression in `if let`",
+            )
+            .multipart_suggestion(
+                "`if let` needs to be written without parentheses",
+                vec![(start, String::new()), (end, String::new())],
+                rustc_errors::Applicability::MachineApplicable,
+            )
+            .emit();
+        // Ideally, we'd remove the feature gating of a `let` expression since we are already
+        // complaining about it here, but `feature_gate::check_crate` has already run by now:
+        // self.sess.parse_sess.gated_spans.ungate_last(sym::let_chains, paren.span);
+    }
+
     /// Emit an error and lower `ast::ExprKind::Let(pat, scrutinee)` into:
     /// ```rust
     /// match scrutinee { pats => true, _ => false }
@@ -356,8 +392,10 @@ impl<'hir> LoweringContext<'_, 'hir> {
         if self.sess.opts.unstable_features.is_nightly_build() {
             self.sess
                 .struct_span_err(span, "`let` expressions are not supported here")
-                .note("only supported directly in conditions of `if`- and `while`-expressions")
-                .note("as well as when nested within `&&` and parenthesis in those conditions")
+                .note(
+                    "only supported directly without parentheses in conditions of `if`- and \
+                     `while`-expressions, as well as in `let` chains within parentheses",
+                )
                 .emit();
         } else {
             self.sess

compiler/rustc_ast_passes/src/feature_gate.rs

@@ -638,8 +638,16 @@ pub fn check_crate(krate: &ast::Crate, sess: &Session) {
             }
         };
     }
-    gate_all!(if_let_guard, "`if let` guards are experimental");
-    gate_all!(let_chains, "`let` expressions in this position are experimental");
+    gate_all!(
+        if_let_guard,
+        "`if let` guards are experimental",
+        "you can write `if matches!(<expr>, <pattern>)` instead of `if let <pattern> = <expr>`"
+    );
+    gate_all!(
+        let_chains,
+        "`let` expressions in this position are experimental",
+        "you can write `matches!(<expr>, <pattern>)` instead of `let <pattern> = <expr>`"
+    );
     gate_all!(
         async_closure,
         "async closures are unstable",

compiler/rustc_lint/src/unused.rs

@@ -602,7 +602,7 @@ trait UnusedDelimLint {
         use rustc_ast::ExprKind::*;
         let (value, ctx, followed_by_block, left_pos, right_pos) = match e.kind {
             // Do not lint `unused_braces` in `if let` expressions.
-            If(ref cond, ref block, ..)
+            If(ref cond, ref block, _)
                 if !matches!(cond.kind, Let(_, _)) || Self::LINT_EXPR_IN_PATTERN_MATCHING_CTX =>
             {
                 let left = e.span.lo() + rustc_span::BytePos(2);
@@ -816,8 +816,33 @@ impl UnusedParens {
 
 impl EarlyLintPass for UnusedParens {
     fn check_expr(&mut self, cx: &EarlyContext<'_>, e: &ast::Expr) {
-        if let ExprKind::Let(ref pat, ..) | ExprKind::ForLoop(ref pat, ..) = e.kind {
-            self.check_unused_parens_pat(cx, pat, false, false);
+        match e.kind {
+            ExprKind::Let(ref pat, _) | ExprKind::ForLoop(ref pat, ..) => {
+                self.check_unused_parens_pat(cx, pat, false, false);
+            }
+            // We ignore parens in cases like `if (((let Some(0) = Some(1))))` because we already
+            // handle a hard error for them during AST lowering in `lower_expr_mut`, but we still
+            // want to complain about things like `if let 42 = (42)`.
+            ExprKind::If(ref cond, ref block, ref else_)
+                if matches!(cond.peel_parens().kind, ExprKind::Let(..)) =>
+            {
+                self.check_unused_delims_expr(
+                    cx,
+                    cond.peel_parens(),
+                    UnusedDelimsCtx::LetScrutineeExpr,
+                    true,
+                    None,
+                    None,
+                );
+                for stmt in &block.stmts {
+                    <Self as UnusedDelimLint>::check_stmt(self, cx, stmt);
+                }
+                if let Some(e) = else_ {
+                    <Self as UnusedDelimLint>::check_expr(self, cx, e);
+                }
+                return;
+            }
+            _ => {}
         }
 
         <Self as UnusedDelimLint>::check_expr(self, cx, e)

src/test/ui/pattern/issue-82290.stderr

@@ -4,8 +4,7 @@ error: `let` expressions are not supported here
 LL |     if true && let x = 1 {
    |                ^^^^^^^^^
    |
-   = note: only supported directly in conditions of `if`- and `while`-expressions
-   = note: as well as when nested within `&&` and parenthesis in those conditions
+   = note: only supported directly without parentheses in conditions of `if`- and `while`-expressions, as well as in `let` chains within parentheses
 
 warning: the feature `let_chains` is incomplete and may not be safe to use and/or cause compiler crashes
   --> $DIR/issue-82290.rs:1:12

src/test/ui/rfc-2294-if-let-guard/feature-gate.stderr

@@ -15,6 +15,7 @@ LL |         () if let 0 = 1 => {}
    |
    = note: see issue #51114 <https://github.com/rust-lang/rust/issues/51114> for more information
    = help: add `#![feature(if_let_guard)]` to the crate attributes to enable
+   = help: you can write `if matches!(<expr>, <pattern>)` instead of `if let <pattern> = <expr>`
 
 error[E0658]: `if let` guards are experimental
   --> $DIR/feature-gate.rs:76:12
@@ -24,6 +25,7 @@ LL |         () if let 0 = 1 => {}
    |
    = note: see issue #51114 <https://github.com/rust-lang/rust/issues/51114> for more information
    = help: add `#![feature(if_let_guard)]` to the crate attributes to enable
+   = help: you can write `if matches!(<expr>, <pattern>)` instead of `if let <pattern> = <expr>`
 
 error[E0658]: `let` expressions in this position are experimental
   --> $DIR/feature-gate.rs:10:16
@@ -33,6 +35,7 @@ LL |         () if (let 0 = 1) => {}
    |
    = note: see issue #53667 <https://github.com/rust-lang/rust/issues/53667> for more information
    = help: add `#![feature(let_chains)]` to the crate attributes to enable
+   = help: you can write `matches!(<expr>, <pattern>)` instead of `let <pattern> = <expr>`
 
 error[E0658]: `let` expressions in this position are experimental
   --> $DIR/feature-gate.rs:14:18
@@ -42,6 +45,7 @@ LL |         () if (((let 0 = 1))) => {}
    |
    = note: see issue #53667 <https://github.com/rust-lang/rust/issues/53667> for more information
    = help: add `#![feature(let_chains)]` to the crate attributes to enable
+   = help: you can write `matches!(<expr>, <pattern>)` instead of `let <pattern> = <expr>`
 
 error[E0658]: `let` expressions in this position are experimental
   --> $DIR/feature-gate.rs:18:23
@@ -51,6 +55,7 @@ LL |         () if true && let 0 = 1 => {}
    |
    = note: see issue #53667 <https://github.com/rust-lang/rust/issues/53667> for more information
    = help: add `#![feature(let_chains)]` to the crate attributes to enable
+   = help: you can write `matches!(<expr>, <pattern>)` instead of `let <pattern> = <expr>`
 
 error[E0658]: `let` expressions in this position are experimental
   --> $DIR/feature-gate.rs:22:15
@@ -60,6 +65,7 @@ LL |         () if let 0 = 1 && true => {}
    |
    = note: see issue #53667 <https://github.com/rust-lang/rust/issues/53667> for more information
    = help: add `#![feature(let_chains)]` to the crate attributes to enable
+   = help: you can write `matches!(<expr>, <pattern>)` instead of `let <pattern> = <expr>`
 
 error[E0658]: `let` expressions in this position are experimental
   --> $DIR/feature-gate.rs:26:16
@@ -69,6 +75,7 @@ LL |         () if (let 0 = 1) && true => {}
    |
    = note: see issue #53667 <https://github.com/rust-lang/rust/issues/53667> for more information
    = help: add `#![feature(let_chains)]` to the crate attributes to enable
+   = help: you can write `matches!(<expr>, <pattern>)` instead of `let <pattern> = <expr>`
 
 error[E0658]: `let` expressions in this position are experimental
   --> $DIR/feature-gate.rs:30:24
@@ -78,6 +85,7 @@ LL |         () if true && (let 0 = 1) => {}
    |
    = note: see issue #53667 <https://github.com/rust-lang/rust/issues/53667> for more information
    = help: add `#![feature(let_chains)]` to the crate attributes to enable
+   = help: you can write `matches!(<expr>, <pattern>)` instead of `let <pattern> = <expr>`
 
 error[E0658]: `let` expressions in this position are experimental
   --> $DIR/feature-gate.rs:34:16
@@ -87,6 +95,7 @@ LL |         () if (let 0 = 1) && (let 0 = 1) => {}
    |
    = note: see issue #53667 <https://github.com/rust-lang/rust/issues/53667> for more information
    = help: add `#![feature(let_chains)]` to the crate attributes to enable
+   = help: you can write `matches!(<expr>, <pattern>)` instead of `let <pattern> = <expr>`
 
 error[E0658]: `let` expressions in this position are experimental
   --> $DIR/feature-gate.rs:34:31
@@ -96,6 +105,7 @@ LL |         () if (let 0 = 1) && (let 0 = 1) => {}
    |
    = note: see issue #53667 <https://github.com/rust-lang/rust/issues/53667> for more information
    = help: add `#![feature(let_chains)]` to the crate attributes to enable
+   = help: you can write `matches!(<expr>, <pattern>)` instead of `let <pattern> = <expr>`
 
 error[E0658]: `let` expressions in this position are experimental
   --> $DIR/feature-gate.rs:40:15
@@ -105,6 +115,7 @@ LL |         () if let 0 = 1 && let 1 = 2 && (let 2 = 3 && let 3 = 4 && let 4 =
    |
    = note: see issue #53667 <https://github.com/rust-lang/rust/issues/53667> for more information
    = help: add `#![feature(let_chains)]` to the crate attributes to enable
+   = help: you can write `matches!(<expr>, <pattern>)` instead of `let <pattern> = <expr>`
 
 error[E0658]: `let` expressions in this position are experimental
   --> $DIR/feature-gate.rs:40:28
@@ -114,6 +125,7 @@ LL |         () if let 0 = 1 && let 1 = 2 && (let 2 = 3 && let 3 = 4 && let 4 =
    |
    = note: see issue #53667 <https://github.com/rust-lang/rust/issues/53667> for more information
    = help: add `#![feature(let_chains)]` to the crate attributes to enable
+   = help: you can write `matches!(<expr>, <pattern>)` instead of `let <pattern> = <expr>`
 
 error[E0658]: `let` expressions in this position are experimental
   --> $DIR/feature-gate.rs:40:42
@@ -123,6 +135,7 @@ LL |         () if let 0 = 1 && let 1 = 2 && (let 2 = 3 && let 3 = 4 && let 4 =
    |
    = note: see issue #53667 <https://github.com/rust-lang/rust/issues/53667> for more information
    = help: add `#![feature(let_chains)]` to the crate attributes to enable
+   = help: you can write `matches!(<expr>, <pattern>)` instead of `let <pattern> = <expr>`
 
 error[E0658]: `let` expressions in this position are experimental
   --> $DIR/feature-gate.rs:40:55
@@ -132,6 +145,7 @@ LL |         () if let 0 = 1 && let 1 = 2 && (let 2 = 3 && let 3 = 4 && let 4 =
    |
    = note: see issue #53667 <https://github.com/rust-lang/rust/issues/53667> for more information
    = help: add `#![feature(let_chains)]` to the crate attributes to enable
+   = help: you can write `matches!(<expr>, <pattern>)` instead of `let <pattern> = <expr>`
 
 error[E0658]: `let` expressions in this position are experimental
   --> $DIR/feature-gate.rs:40:68
@@ -141,6 +155,7 @@ LL |         () if let 0 = 1 && let 1 = 2 && (let 2 = 3 && let 3 = 4 && let 4 =
    |
    = note: see issue #53667 <https://github.com/rust-lang/rust/issues/53667> for more information
    = help: add `#![feature(let_chains)]` to the crate attributes to enable
+   = help: you can write `matches!(<expr>, <pattern>)` instead of `let <pattern> = <expr>`
 
 error[E0658]: `let` expressions in this position are experimental
   --> $DIR/feature-gate.rs:52:15
@@ -150,6 +165,7 @@ LL |         () if let Range { start: _, end: _ } = (true..true) && false => {}
    |
    = note: see issue #53667 <https://github.com/rust-lang/rust/issues/53667> for more information
    = help: add `#![feature(let_chains)]` to the crate attributes to enable
+   = help: you can write `matches!(<expr>, <pattern>)` instead of `let <pattern> = <expr>`
 
 error[E0658]: `let` expressions in this position are experimental
   --> $DIR/feature-gate.rs:68:16
@@ -159,6 +175,7 @@ LL |     use_expr!((let 0 = 1 && 0 == 0));
    |
    = note: see issue #53667 <https://github.com/rust-lang/rust/issues/53667> for more information
    = help: add `#![feature(let_chains)]` to the crate attributes to enable
+   = help: you can write `matches!(<expr>, <pattern>)` instead of `let <pattern> = <expr>`
 
 error[E0658]: `let` expressions in this position are experimental
   --> $DIR/feature-gate.rs:71:16
@@ -168,6 +185,7 @@ LL |     use_expr!((let 0 = 1));
    |
    = note: see issue #53667 <https://github.com/rust-lang/rust/issues/53667> for more information
    = help: add `#![feature(let_chains)]` to the crate attributes to enable
+   = help: you can write `matches!(<expr>, <pattern>)` instead of `let <pattern> = <expr>`
 
 error: `let` expressions are not supported here
   --> $DIR/feature-gate.rs:10:16
@@ -175,8 +193,7 @@ error: `let` expressions are not supported here
 LL |         () if (let 0 = 1) => {}
    |                ^^^^^^^^^
    |
-   = note: only supported directly in conditions of `if`- and `while`-expressions
-   = note: as well as when nested within `&&` and parenthesis in those conditions
+   = note: only supported directly without parentheses in conditions of `if`- and `while`-expressions, as well as in `let` chains within parentheses
 
 error: `let` expressions are not supported here
   --> $DIR/feature-gate.rs:14:18
@@ -184,8 +201,7 @@ error: `let` expressions are not supported here
 LL |         () if (((let 0 = 1))) => {}
    |                  ^^^^^^^^^
    |
-   = note: only supported directly in conditions of `if`- and `while`-expressions
-   = note: as well as when nested within `&&` and parenthesis in those conditions
+   = note: only supported directly without parentheses in conditions of `if`- and `while`-expressions, as well as in `let` chains within parentheses
 
 error: `let` expressions are not supported here
   --> $DIR/feature-gate.rs:18:23
@@ -193,8 +209,7 @@ error: `let` expressions are not supported here
 LL |         () if true && let 0 = 1 => {}
    |                       ^^^^^^^^^
    |
-   = note: only supported directly in conditions of `if`- and `while`-expressions
-   = note: as well as when nested within `&&` and parenthesis in those conditions
+   = note: only supported directly without parentheses in conditions of `if`- and `while`-expressions, as well as in `let` chains within parentheses
 
 error: `let` expressions are not supported here
   --> $DIR/feature-gate.rs:22:15
@@ -202,8 +217,7 @@ error: `let` expressions are not supported here
 LL |         () if let 0 = 1 && true => {}
    |               ^^^^^^^^^
    |
-   = note: only supported directly in conditions of `if`- and `while`-expressions
-   = note: as well as when nested within `&&` and parenthesis in those conditions
+   = note: only supported directly without parentheses in conditions of `if`- and `while`-expressions, as well as in `let` chains within parentheses
 
 error: `let` expressions are not supported here
   --> $DIR/feature-gate.rs:26:16
@@ -211,8 +225,7 @@ error: `let` expressions are not supported here
 LL |         () if (let 0 = 1) && true => {}
    |                ^^^^^^^^^
    |
-   = note: only supported directly in conditions of `if`- and `while`-expressions
-   = note: as well as when nested within `&&` and parenthesis in those conditions
+   = note: only supported directly without parentheses in conditions of `if`- and `while`-expressions, as well as in `let` chains within parentheses
 
 error: `let` expressions are not supported here
   --> $DIR/feature-gate.rs:30:24
@@ -220,8 +233,7 @@ error: `let` expressions are not supported here
 LL |         () if true && (let 0 = 1) => {}
    |                        ^^^^^^^^^
    |
-   = note: only supported directly in conditions of `if`- and `while`-expressions
-   = note: as well as when nested within `&&` and parenthesis in those conditions
+   = note: only supported directly without parentheses in conditions of `if`- and `while`-expressions, as well as in `let` chains within parentheses
 
 error: `let` expressions are not supported here
   --> $DIR/feature-gate.rs:34:16
@@ -229,8 +241,7 @@ error: `let` expressions are not supported here
 LL |         () if (let 0 = 1) && (let 0 = 1) => {}
    |                ^^^^^^^^^
    |
-   = note: only supported directly in conditions of `if`- and `while`-expressions
-   = note: as well as when nested within `&&` and parenthesis in those conditions
+   = note: only supported directly without parentheses in conditions of `if`- and `while`-expressions, as well as in `let` chains within parentheses
 
 error: `let` expressions are not supported here
   --> $DIR/feature-gate.rs:34:31
@@ -238,8 +249,7 @@ error: `let` expressions are not supported here
 LL |         () if (let 0 = 1) && (let 0 = 1) => {}
    |                               ^^^^^^^^^
    |
-   = note: only supported directly in conditions of `if`- and `while`-expressions
-   = note: as well as when nested within `&&` and parenthesis in those conditions
+   = note: only supported directly without parentheses in conditions of `if`- and `while`-expressions, as well as in `let` chains within parentheses
 
 error: `let` expressions are not supported here
   --> $DIR/feature-gate.rs:40:15
@@ -247,8 +257,7 @@ error: `let` expressions are not supported here
 LL |         () if let 0 = 1 && let 1 = 2 && (let 2 = 3 && let 3 = 4 && let 4 = 5) => {}
    |               ^^^^^^^^^
    |
-   = note: only supported directly in conditions of `if`- and `while`-expressions
-   = note: as well as when nested within `&&` and parenthesis in those conditions
+   = note: only supported directly without parentheses in conditions of `if`- and `while`-expressions, as well as in `let` chains within parentheses
 
 error: `let` expressions are not supported here
   --> $DIR/feature-gate.rs:40:28
@@ -256,8 +265,7 @@ error: `let` expressions are not supported here
 LL |         () if let 0 = 1 && let 1 = 2 && (let 2 = 3 && let 3 = 4 && let 4 = 5) => {}
    |                            ^^^^^^^^^
    |
-   = note: only supported directly in conditions of `if`- and `while`-expressions
-   = note: as well as when nested within `&&` and parenthesis in those conditions
+   = note: only supported directly without parentheses in conditions of `if`- and `while`-expressions, as well as in `let` chains within parentheses
 
 error: `let` expressions are not supported here
   --> $DIR/feature-gate.rs:40:42
@@ -265,8 +273,7 @@ error: `let` expressions are not supported here
 LL |         () if let 0 = 1 && let 1 = 2 && (let 2 = 3 && let 3 = 4 && let 4 = 5) => {}
    |                                          ^^^^^^^^^
    |
-   = note: only supported directly in conditions of `if`- and `while`-expressions
-   = note: as well as when nested within `&&` and parenthesis in those conditions
+   = note: only supported directly without parentheses in conditions of `if`- and `while`-expressions, as well as in `let` chains within parentheses
 
 error: `let` expressions are not supported here
   --> $DIR/feature-gate.rs:40:55
@@ -274,8 +281,7 @@ error: `let` expressions are not supported here
 LL |         () if let 0 = 1 && let 1 = 2 && (let 2 = 3 && let 3 = 4 && let 4 = 5) => {}
    |                                                       ^^^^^^^^^
    |
-   = note: only supported directly in conditions of `if`- and `while`-expressions
-   = note: as well as when nested within `&&` and parenthesis in those conditions
+   = note: only supported directly without parentheses in conditions of `if`- and `while`-expressions, as well as in `let` chains within parentheses
 
 error: `let` expressions are not supported here
   --> $DIR/feature-gate.rs:40:68
@@ -283,8 +289,7 @@ error: `let` expressions are not supported here
 LL |         () if let 0 = 1 && let 1 = 2 && (let 2 = 3 && let 3 = 4 && let 4 = 5) => {}
    |                                                                    ^^^^^^^^^
    |
-   = note: only supported directly in conditions of `if`- and `while`-expressions
-   = note: as well as when nested within `&&` and parenthesis in those conditions
+   = note: only supported directly without parentheses in conditions of `if`- and `while`-expressions, as well as in `let` chains within parentheses
 
 error: `let` expressions are not supported here
   --> $DIR/feature-gate.rs:52:15
@@ -292,8 +297,7 @@ error: `let` expressions are not supported here
 LL |         () if let Range { start: _, end: _ } = (true..true) && false => {}
    |               ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    |
-   = note: only supported directly in conditions of `if`- and `while`-expressions
-   = note: as well as when nested within `&&` and parenthesis in those conditions
+   = note: only supported directly without parentheses in conditions of `if`- and `while`-expressions, as well as in `let` chains within parentheses
 
 error: `let` expressions are not supported here
   --> $DIR/feature-gate.rs:68:16
@@ -301,8 +305,7 @@ error: `let` expressions are not supported here
 LL |     use_expr!((let 0 = 1 && 0 == 0));
    |                ^^^^^^^^^
    |
-   = note: only supported directly in conditions of `if`- and `while`-expressions
-   = note: as well as when nested within `&&` and parenthesis in those conditions
+   = note: only supported directly without parentheses in conditions of `if`- and `while`-expressions, as well as in `let` chains within parentheses
 
 error: `let` expressions are not supported here
   --> $DIR/feature-gate.rs:71:16
@@ -310,8 +313,7 @@ error: `let` expressions are not supported here
 LL |     use_expr!((let 0 = 1));
    |                ^^^^^^^^^
    |
-   = note: only supported directly in conditions of `if`- and `while`-expressions
-   = note: as well as when nested within `&&` and parenthesis in those conditions
+   = note: only supported directly without parentheses in conditions of `if`- and `while`-expressions, as well as in `let` chains within parentheses
 
 error: aborting due to 35 previous errors
 

src/test/ui/rfc-2497-if-let-chains/disallowed-positions.stderr

@@ -15,8 +15,7 @@ error: `let` expressions are not supported here
 LL |     if &let 0 = 0 {}
    |         ^^^^^^^^^
    |
-   = note: only supported directly in conditions of `if`- and `while`-expressions
-   = note: as well as when nested within `&&` and parenthesis in those conditions
+   = note: only supported directly without parentheses in conditions of `if`- and `while`-expressions, as well as in `let` chains within parentheses
 
 error: `let` expressions are not supported here
   --> $DIR/disallowed-positions.rs:35:9
@@ -24,8 +23,7 @@ error: `let` expressions are not supported here
 LL |     if !let 0 = 0 {}
    |         ^^^^^^^^^
    |
-   = note: only supported directly in conditions of `if`- and `while`-expressions
-   = note: as well as when nested within `&&` and parenthesis in those conditions
+   = note: only supported directly without parentheses in conditions of `if`- and `while`-expressions, as well as in `let` chains within parentheses
 
 error: `let` expressions are not supported here
   --> $DIR/disallowed-positions.rs:36:9
@@ -33,8 +31,7 @@ error: `let` expressions are not supported here
 LL |     if *let 0 = 0 {}
    |         ^^^^^^^^^
    |
-   = note: only supported directly in conditions of `if`- and `while`-expressions
-   = note: as well as when nested within `&&` and parenthesis in those conditions
+   = note: only supported directly without parentheses in conditions of `if`- and `while`-expressions, as well as in `let` chains within parentheses
 
 error: `let` expressions are not supported here
   --> $DIR/disallowed-positions.rs:38:9
@@ -42,8 +39,7 @@ error: `let` expressions are not supported here
 LL |     if -let 0 = 0 {}
    |         ^^^^^^^^^
    |
-   = note: only supported directly in conditions of `if`- and `while`-expressions
-   = note: as well as when nested within `&&` and parenthesis in those conditions
+   = note: only supported directly without parentheses in conditions of `if`- and `while`-expressions, as well as in `let` chains within parentheses
 
 error: `let` expressions are not supported here
   --> $DIR/disallowed-positions.rs:46:9
@@ -51,8 +47,7 @@ error: `let` expressions are not supported here
 LL |     if (let 0 = 0)? {}
    |         ^^^^^^^^^
    |
-   = note: only supported directly in conditions of `if`- and `while`-expressions
-   = note: as well as when nested within `&&` and parenthesis in those conditions
+   = note: only supported directly without parentheses in conditions of `if`- and `while`-expressions, as well as in `let` chains within parentheses
 
 error: `let` expressions are not supported here
   --> $DIR/disallowed-positions.rs:50:16
@@ -60,8 +55,7 @@ error: `let` expressions are not supported here
 LL |     if true || let 0 = 0 {}
    |                ^^^^^^^^^
    |
-   = note: only supported directly in conditions of `if`- and `while`-expressions
-   = note: as well as when nested within `&&` and parenthesis in those conditions
+   = note: only supported directly without parentheses in conditions of `if`- and `while`-expressions, as well as in `let` chains within parentheses
 
 error: `let` expressions are not supported here
   --> $DIR/disallowed-positions.rs:51:17
@@ -69,8 +63,7 @@ error: `let` expressions are not supported here
 LL |     if (true || let 0 = 0) {}
    |                 ^^^^^^^^^
    |
-   = note: only supported directly in conditions of `if`- and `while`-expressions
-   = note: as well as when nested within `&&` and parenthesis in those conditions
+   = note: only supported directly without parentheses in conditions of `if`- and `while`-expressions, as well as in `let` chains within parentheses
 
 error: `let` expressions are not supported here
   --> $DIR/disallowed-positions.rs:52:25
@@ -78,8 +71,7 @@ error: `let` expressions are not supported here
 LL |     if true && (true || let 0 = 0) {}
    |                         ^^^^^^^^^
    |
-   = note: only supported directly in conditions of `if`- and `while`-expressions
-   = note: as well as when nested within `&&` and parenthesis in those conditions
+   = note: only supported directly without parentheses in conditions of `if`- and `while`-expressions, as well as in `let` chains within parentheses
 
 error: `let` expressions are not supported here
   --> $DIR/disallowed-positions.rs:53:25
@@ -87,8 +79,7 @@ error: `let` expressions are not supported here
 LL |     if true || (true && let 0 = 0) {}
    |                         ^^^^^^^^^
    |
-   = note: only supported directly in conditions of `if`- and `while`-expressions
-   = note: as well as when nested within `&&` and parenthesis in those conditions
+   = note: only supported directly without parentheses in conditions of `if`- and `while`-expressions, as well as in `let` chains within parentheses
 
 error: `let` expressions are not supported here
   --> $DIR/disallowed-positions.rs:56:12
@@ -96,8 +87,7 @@ error: `let` expressions are not supported here
 LL |     if x = let 0 = 0 {}
    |            ^^^^^^^^^
    |
-   = note: only supported directly in conditions of `if`- and `while`-expressions
-   = note: as well as when nested within `&&` and parenthesis in those conditions
+   = note: only supported directly without parentheses in conditions of `if`- and `while`-expressions, as well as in `let` chains within parentheses
 
 error: `let` expressions are not supported here
   --> $DIR/disallowed-positions.rs:59:15
@@ -105,8 +95,7 @@ error: `let` expressions are not supported here
 LL |     if true..(let 0 = 0) {}
    |               ^^^^^^^^^
    |
-   = note: only supported directly in conditions of `if`- and `while`-expressions
-   = note: as well as when nested within `&&` and parenthesis in those conditions
+   = note: only supported directly without parentheses in conditions of `if`- and `while`-expressions, as well as in `let` chains within parentheses
 
 error: `let` expressions are not supported here
   --> $DIR/disallowed-positions.rs:61:11
@@ -114,8 +103,7 @@ error: `let` expressions are not supported here
 LL |     if ..(let 0 = 0) {}
    |           ^^^^^^^^^
    |
-   = note: only supported directly in conditions of `if`- and `while`-expressions
-   = note: as well as when nested within `&&` and parenthesis in those conditions
+   = note: only supported directly without parentheses in conditions of `if`- and `while`-expressions, as well as in `let` chains within parentheses
 
 error: `let` expressions are not supported here
   --> $DIR/disallowed-positions.rs:63:9
@@ -123,8 +111,7 @@ error: `let` expressions are not supported here
 LL |     if (let 0 = 0).. {}
    |         ^^^^^^^^^
    |
-   = note: only supported directly in conditions of `if`- and `while`-expressions
-   = note: as well as when nested within `&&` and parenthesis in those conditions
+   = note: only supported directly without parentheses in conditions of `if`- and `while`-expressions, as well as in `let` chains within parentheses
 
 error: `let` expressions are not supported here
   --> $DIR/disallowed-positions.rs:67:8
@@ -132,8 +119,7 @@ error: `let` expressions are not supported here
 LL |     if let Range { start: _, end: _ } = true..true && false {}
    |        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    |
-   = note: only supported directly in conditions of `if`- and `while`-expressions
-   = note: as well as when nested within `&&` and parenthesis in those conditions
+   = note: only supported directly without parentheses in conditions of `if`- and `while`-expressions, as well as in `let` chains within parentheses
 
 error: `let` expressions are not supported here
   --> $DIR/disallowed-positions.rs:71:8
@@ -141,8 +127,7 @@ error: `let` expressions are not supported here
 LL |     if let Range { start: _, end: _ } = true..true || false {}
    |        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    |
-   = note: only supported directly in conditions of `if`- and `while`-expressions
-   = note: as well as when nested within `&&` and parenthesis in those conditions
+   = note: only supported directly without parentheses in conditions of `if`- and `while`-expressions, as well as in `let` chains within parentheses
 
 error: `let` expressions are not supported here
   --> $DIR/disallowed-positions.rs:78:8
@@ -150,8 +135,7 @@ error: `let` expressions are not supported here
 LL |     if let Range { start: F, end } = F..|| true {}
    |        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    |
-   = note: only supported directly in conditions of `if`- and `while`-expressions
-   = note: as well as when nested within `&&` and parenthesis in those conditions
+   = note: only supported directly without parentheses in conditions of `if`- and `while`-expressions, as well as in `let` chains within parentheses
 
 error: `let` expressions are not supported here
   --> $DIR/disallowed-positions.rs:86:8
@@ -159,8 +143,7 @@ error: `let` expressions are not supported here
 LL |     if let Range { start: true, end } = t..&&false {}
    |        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    |
-   = note: only supported directly in conditions of `if`- and `while`-expressions
-   = note: as well as when nested within `&&` and parenthesis in those conditions
+   = note: only supported directly without parentheses in conditions of `if`- and `while`-expressions, as well as in `let` chains within parentheses
 
 error: `let` expressions are not supported here
   --> $DIR/disallowed-positions.rs:92:19
@@ -168,8 +151,7 @@ error: `let` expressions are not supported here
 LL |     if let true = let true = true {}
    |                   ^^^^^^^^^^^^^^^
    |
-   = note: only supported directly in conditions of `if`- and `while`-expressions
-   = note: as well as when nested within `&&` and parenthesis in those conditions
+   = note: only supported directly without parentheses in conditions of `if`- and `while`-expressions, as well as in `let` chains within parentheses
 
 error: `let` expressions are not supported here
   --> $DIR/disallowed-positions.rs:96:12
@@ -177,8 +159,7 @@ error: `let` expressions are not supported here
 LL |     while &let 0 = 0 {}
    |            ^^^^^^^^^
    |
-   = note: only supported directly in conditions of `if`- and `while`-expressions
-   = note: as well as when nested within `&&` and parenthesis in those conditions
+   = note: only supported directly without parentheses in conditions of `if`- and `while`-expressions, as well as in `let` chains within parentheses
 
 error: `let` expressions are not supported here
   --> $DIR/disallowed-positions.rs:99:12
@@ -186,8 +167,7 @@ error: `let` expressions are not supported here
 LL |     while !let 0 = 0 {}
    |            ^^^^^^^^^
    |
-   = note: only supported directly in conditions of `if`- and `while`-expressions
-   = note: as well as when nested within `&&` and parenthesis in those conditions
+   = note: only supported directly without parentheses in conditions of `if`- and `while`-expressions, as well as in `let` chains within parentheses
 
 error: `let` expressions are not supported here
   --> $DIR/disallowed-positions.rs:100:12
@@ -195,8 +175,7 @@ error: `let` expressions are not supported here
 LL |     while *let 0 = 0 {}
    |            ^^^^^^^^^
    |
-   = note: only supported directly in conditions of `if`- and `while`-expressions
-   = note: as well as when nested within `&&` and parenthesis in those conditions
+   = note: only supported directly without parentheses in conditions of `if`- and `while`-expressions, as well as in `let` chains within parentheses
 
 error: `let` expressions are not supported here
   --> $DIR/disallowed-positions.rs:102:12
@@ -204,8 +183,7 @@ error: `let` expressions are not supported here
 LL |     while -let 0 = 0 {}
    |            ^^^^^^^^^
    |
-   = note: only supported directly in conditions of `if`- and `while`-expressions
-   = note: as well as when nested within `&&` and parenthesis in those conditions
+   = note: only supported directly without parentheses in conditions of `if`- and `while`-expressions, as well as in `let` chains within parentheses
 
 error: `let` expressions are not supported here
   --> $DIR/disallowed-positions.rs:110:12
@@ -213,8 +191,7 @@ error: `let` expressions are not supported here
 LL |     while (let 0 = 0)? {}
    |            ^^^^^^^^^
    |
-   = note: only supported directly in conditions of `if`- and `while`-expressions
-   = note: as well as when nested within `&&` and parenthesis in those conditions
+   = note: only supported directly without parentheses in conditions of `if`- and `while`-expressions, as well as in `let` chains within parentheses
 
 error: `let` expressions are not supported here
   --> $DIR/disallowed-positions.rs:114:19
@@ -222,8 +199,7 @@ error: `let` expressions are not supported here
 LL |     while true || let 0 = 0 {}
    |                   ^^^^^^^^^
    |
-   = note: only supported directly in conditions of `if`- and `while`-expressions
-   = note: as well as when nested within `&&` and parenthesis in those conditions
+   = note: only supported directly without parentheses in conditions of `if`- and `while`-expressions, as well as in `let` chains within parentheses
 
 error: `let` expressions are not supported here
   --> $DIR/disallowed-positions.rs:115:20
@@ -231,8 +207,7 @@ error: `let` expressions are not supported here
 LL |     while (true || let 0 = 0) {}
    |                    ^^^^^^^^^
    |
-   = note: only supported directly in conditions of `if`- and `while`-expressions
-   = note: as well as when nested within `&&` and parenthesis in those conditions
+   = note: only supported directly without parentheses in conditions of `if`- and `while`-expressions, as well as in `let` chains within parentheses
 
 error: `let` expressions are not supported here
   --> $DIR/disallowed-positions.rs:116:28
@@ -240,8 +215,7 @@ error: `let` expressions are not supported here
 LL |     while true && (true || let 0 = 0) {}
    |                            ^^^^^^^^^
    |
-   = note: only supported directly in conditions of `if`- and `while`-expressions
-   = note: as well as when nested within `&&` and parenthesis in those conditions
+   = note: only supported directly without parentheses in conditions of `if`- and `while`-expressions, as well as in `let` chains within parentheses
 
 error: `let` expressions are not supported here
   --> $DIR/disallowed-positions.rs:117:28
@@ -249,8 +223,7 @@ error: `let` expressions are not supported here
 LL |     while true || (true && let 0 = 0) {}
    |                            ^^^^^^^^^
    |
-   = note: only supported directly in conditions of `if`- and `while`-expressions
-   = note: as well as when nested within `&&` and parenthesis in those conditions
+   = note: only supported directly without parentheses in conditions of `if`- and `while`-expressions, as well as in `let` chains within parentheses
 
 error: `let` expressions are not supported here
   --> $DIR/disallowed-positions.rs:120:15
@@ -258,8 +231,7 @@ error: `let` expressions are not supported here
 LL |     while x = let 0 = 0 {}
    |               ^^^^^^^^^
    |
-   = note: only supported directly in conditions of `if`- and `while`-expressions
-   = note: as well as when nested within `&&` and parenthesis in those conditions
+   = note: only supported directly without parentheses in conditions of `if`- and `while`-expressions, as well as in `let` chains within parentheses
 
 error: `let` expressions are not supported here
   --> $DIR/disallowed-positions.rs:123:18
@@ -267,8 +239,7 @@ error: `let` expressions are not supported here
 LL |     while true..(let 0 = 0) {}
    |                  ^^^^^^^^^
    |
-   = note: only supported directly in conditions of `if`- and `while`-expressions
-   = note: as well as when nested within `&&` and parenthesis in those conditions
+   = note: only supported directly without parentheses in conditions of `if`- and `while`-expressions, as well as in `let` chains within parentheses
 
 error: `let` expressions are not supported here
   --> $DIR/disallowed-positions.rs:125:14
@@ -276,8 +247,7 @@ error: `let` expressions are not supported here
 LL |     while ..(let 0 = 0) {}
    |              ^^^^^^^^^
    |
-   = note: only supported directly in conditions of `if`- and `while`-expressions
-   = note: as well as when nested within `&&` and parenthesis in those conditions
+   = note: only supported directly without parentheses in conditions of `if`- and `while`-expressions, as well as in `let` chains within parentheses
 
 error: `let` expressions are not supported here
   --> $DIR/disallowed-positions.rs:127:12
@@ -285,8 +255,7 @@ error: `let` expressions are not supported here
 LL |     while (let 0 = 0).. {}
    |            ^^^^^^^^^
    |
-   = note: only supported directly in conditions of `if`- and `while`-expressions
-   = note: as well as when nested within `&&` and parenthesis in those conditions
+   = note: only supported directly without parentheses in conditions of `if`- and `while`-expressions, as well as in `let` chains within parentheses
 
 error: `let` expressions are not supported here
   --> $DIR/disallowed-positions.rs:131:11
@@ -294,8 +263,7 @@ error: `let` expressions are not supported here
 LL |     while let Range { start: _, end: _ } = true..true && false {}
    |           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    |
-   = note: only supported directly in conditions of `if`- and `while`-expressions
-   = note: as well as when nested within `&&` and parenthesis in those conditions
+   = note: only supported directly without parentheses in conditions of `if`- and `while`-expressions, as well as in `let` chains within parentheses
 
 error: `let` expressions are not supported here
   --> $DIR/disallowed-positions.rs:135:11
@@ -303,8 +271,7 @@ error: `let` expressions are not supported here
 LL |     while let Range { start: _, end: _ } = true..true || false {}
    |           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    |
-   = note: only supported directly in conditions of `if`- and `while`-expressions
-   = note: as well as when nested within `&&` and parenthesis in those conditions
+   = note: only supported directly without parentheses in conditions of `if`- and `while`-expressions, as well as in `let` chains within parentheses
 
 error: `let` expressions are not supported here
   --> $DIR/disallowed-positions.rs:142:11
@@ -312,8 +279,7 @@ error: `let` expressions are not supported here
 LL |     while let Range { start: F, end } = F..|| true {}
    |           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    |
-   = note: only supported directly in conditions of `if`- and `while`-expressions
-   = note: as well as when nested within `&&` and parenthesis in those conditions
+   = note: only supported directly without parentheses in conditions of `if`- and `while`-expressions, as well as in `let` chains within parentheses
 
 error: `let` expressions are not supported here
   --> $DIR/disallowed-positions.rs:150:11
@@ -321,8 +287,7 @@ error: `let` expressions are not supported here
 LL |     while let Range { start: true, end } = t..&&false {}
    |           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    |
-   = note: only supported directly in conditions of `if`- and `while`-expressions
-   = note: as well as when nested within `&&` and parenthesis in those conditions
+   = note: only supported directly without parentheses in conditions of `if`- and `while`-expressions, as well as in `let` chains within parentheses
 
 error: `let` expressions are not supported here
   --> $DIR/disallowed-positions.rs:156:22
@@ -330,8 +295,7 @@ error: `let` expressions are not supported here
 LL |     while let true = let true = true {}
    |                      ^^^^^^^^^^^^^^^
    |
-   = note: only supported directly in conditions of `if`- and `while`-expressions
-   = note: as well as when nested within `&&` and parenthesis in those conditions
+   = note: only supported directly without parentheses in conditions of `if`- and `while`-expressions, as well as in `let` chains within parentheses
 
 error: `let` expressions are not supported here
   --> $DIR/disallowed-positions.rs:170:6
@@ -339,8 +303,7 @@ error: `let` expressions are not supported here
 LL |     &let 0 = 0;
    |      ^^^^^^^^^
    |
-   = note: only supported directly in conditions of `if`- and `while`-expressions
-   = note: as well as when nested within `&&` and parenthesis in those conditions
+   = note: only supported directly without parentheses in conditions of `if`- and `while`-expressions, as well as in `let` chains within parentheses
 
 error: `let` expressions are not supported here
   --> $DIR/disallowed-positions.rs:172:6
@@ -348,8 +311,7 @@ error: `let` expressions are not supported here
 LL |     !let 0 = 0;
    |      ^^^^^^^^^
    |
-   = note: only supported directly in conditions of `if`- and `while`-expressions
-   = note: as well as when nested within `&&` and parenthesis in those conditions
+   = note: only supported directly without parentheses in conditions of `if`- and `while`-expressions, as well as in `let` chains within parentheses
 
 error: `let` expressions are not supported here
   --> $DIR/disallowed-positions.rs:173:6
@@ -357,8 +319,7 @@ error: `let` expressions are not supported here
 LL |     *let 0 = 0;
    |      ^^^^^^^^^
    |
-   = note: only supported directly in conditions of `if`- and `while`-expressions
-   = note: as well as when nested within `&&` and parenthesis in those conditions
+   = note: only supported directly without parentheses in conditions of `if`- and `while`-expressions, as well as in `let` chains within parentheses
 
 error: `let` expressions are not supported here
   --> $DIR/disallowed-positions.rs:175:6
@@ -366,8 +327,7 @@ error: `let` expressions are not supported here
 LL |     -let 0 = 0;
    |      ^^^^^^^^^
    |
-   = note: only supported directly in conditions of `if`- and `while`-expressions
-   = note: as well as when nested within `&&` and parenthesis in those conditions
+   = note: only supported directly without parentheses in conditions of `if`- and `while`-expressions, as well as in `let` chains within parentheses
 
 error: `let` expressions are not supported here
   --> $DIR/disallowed-positions.rs:183:6
@@ -375,8 +335,7 @@ error: `let` expressions are not supported here
 LL |     (let 0 = 0)?;
    |      ^^^^^^^^^
    |
-   = note: only supported directly in conditions of `if`- and `while`-expressions
-   = note: as well as when nested within `&&` and parenthesis in those conditions
+   = note: only supported directly without parentheses in conditions of `if`- and `while`-expressions, as well as in `let` chains within parentheses
 
 error: `let` expressions are not supported here
   --> $DIR/disallowed-positions.rs:187:13
@@ -384,8 +343,7 @@ error: `let` expressions are not supported here
 LL |     true || let 0 = 0;
    |             ^^^^^^^^^
    |
-   = note: only supported directly in conditions of `if`- and `while`-expressions
-   = note: as well as when nested within `&&` and parenthesis in those conditions
+   = note: only supported directly without parentheses in conditions of `if`- and `while`-expressions, as well as in `let` chains within parentheses
 
 error: `let` expressions are not supported here
   --> $DIR/disallowed-positions.rs:188:14
@@ -393,8 +351,7 @@ error: `let` expressions are not supported here
 LL |     (true || let 0 = 0);
    |              ^^^^^^^^^
    |
-   = note: only supported directly in conditions of `if`- and `while`-expressions
-   = note: as well as when nested within `&&` and parenthesis in those conditions
+   = note: only supported directly without parentheses in conditions of `if`- and `while`-expressions, as well as in `let` chains within parentheses
 
 error: `let` expressions are not supported here
   --> $DIR/disallowed-positions.rs:189:22
@@ -402,8 +359,7 @@ error: `let` expressions are not supported here
 LL |     true && (true || let 0 = 0);
    |                      ^^^^^^^^^
    |
-   = note: only supported directly in conditions of `if`- and `while`-expressions
-   = note: as well as when nested within `&&` and parenthesis in those conditions
+   = note: only supported directly without parentheses in conditions of `if`- and `while`-expressions, as well as in `let` chains within parentheses
 
 error: `let` expressions are not supported here
   --> $DIR/disallowed-positions.rs:192:9
@@ -411,8 +367,7 @@ error: `let` expressions are not supported here
 LL |     x = let 0 = 0;
    |         ^^^^^^^^^
    |
-   = note: only supported directly in conditions of `if`- and `while`-expressions
-   = note: as well as when nested within `&&` and parenthesis in those conditions
+   = note: only supported directly without parentheses in conditions of `if`- and `while`-expressions, as well as in `let` chains within parentheses
 
 error: `let` expressions are not supported here
   --> $DIR/disallowed-positions.rs:194:12
@@ -420,8 +375,7 @@ error: `let` expressions are not supported here
 LL |     true..(let 0 = 0);
    |            ^^^^^^^^^
    |
-   = note: only supported directly in conditions of `if`- and `while`-expressions
-   = note: as well as when nested within `&&` and parenthesis in those conditions
+   = note: only supported directly without parentheses in conditions of `if`- and `while`-expressions, as well as in `let` chains within parentheses
 
 error: `let` expressions are not supported here
   --> $DIR/disallowed-positions.rs:195:8
@@ -429,8 +383,7 @@ error: `let` expressions are not supported here
 LL |     ..(let 0 = 0);
    |        ^^^^^^^^^
    |
-   = note: only supported directly in conditions of `if`- and `while`-expressions
-   = note: as well as when nested within `&&` and parenthesis in those conditions
+   = note: only supported directly without parentheses in conditions of `if`- and `while`-expressions, as well as in `let` chains within parentheses
 
 error: `let` expressions are not supported here
   --> $DIR/disallowed-positions.rs:196:6
@@ -438,8 +391,7 @@ error: `let` expressions are not supported here
 LL |     (let 0 = 0)..;
    |      ^^^^^^^^^
    |
-   = note: only supported directly in conditions of `if`- and `while`-expressions
-   = note: as well as when nested within `&&` and parenthesis in those conditions
+   = note: only supported directly without parentheses in conditions of `if`- and `while`-expressions, as well as in `let` chains within parentheses
 
 error: `let` expressions are not supported here
   --> $DIR/disallowed-positions.rs:198:6
@@ -447,8 +399,7 @@ error: `let` expressions are not supported here
 LL |     (let Range { start: _, end: _ } = true..true || false);
    |      ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    |
-   = note: only supported directly in conditions of `if`- and `while`-expressions
-   = note: as well as when nested within `&&` and parenthesis in those conditions
+   = note: only supported directly without parentheses in conditions of `if`- and `while`-expressions, as well as in `let` chains within parentheses
 
 error: `let` expressions are not supported here
   --> $DIR/disallowed-positions.rs:202:6
@@ -456,8 +407,7 @@ error: `let` expressions are not supported here
 LL |     (let true = let true = true);
    |      ^^^^^^^^^^^^^^^^^^^^^^^^^^
    |
-   = note: only supported directly in conditions of `if`- and `while`-expressions
-   = note: as well as when nested within `&&` and parenthesis in those conditions
+   = note: only supported directly without parentheses in conditions of `if`- and `while`-expressions, as well as in `let` chains within parentheses
 
 error: `let` expressions are not supported here
   --> $DIR/disallowed-positions.rs:202:17
@@ -465,8 +415,7 @@ error: `let` expressions are not supported here
 LL |     (let true = let true = true);
    |                 ^^^^^^^^^^^^^^^
    |
-   = note: only supported directly in conditions of `if`- and `while`-expressions
-   = note: as well as when nested within `&&` and parenthesis in those conditions
+   = note: only supported directly without parentheses in conditions of `if`- and `while`-expressions, as well as in `let` chains within parentheses
 
 error: `let` expressions are not supported here
   --> $DIR/disallowed-positions.rs:207:6
@@ -474,8 +423,7 @@ error: `let` expressions are not supported here
 LL |     &let 0 = 0
    |      ^^^^^^^^^
    |
-   = note: only supported directly in conditions of `if`- and `while`-expressions
-   = note: as well as when nested within `&&` and parenthesis in those conditions
+   = note: only supported directly without parentheses in conditions of `if`- and `while`-expressions, as well as in `let` chains within parentheses
 
 error: `let` expressions are not supported here
   --> $DIR/disallowed-positions.rs:218:17
@@ -483,8 +431,7 @@ error: `let` expressions are not supported here
 LL |         true && let 1 = 1
    |                 ^^^^^^^^^
    |
-   = note: only supported directly in conditions of `if`- and `while`-expressions
-   = note: as well as when nested within `&&` and parenthesis in those conditions
+   = note: only supported directly without parentheses in conditions of `if`- and `while`-expressions, as well as in `let` chains within parentheses
 
 error: `let` expressions are not supported here
   --> $DIR/disallowed-positions.rs:222:17
@@ -492,8 +439,7 @@ error: `let` expressions are not supported here
 LL |         true && let 1 = 1
    |                 ^^^^^^^^^
    |
-   = note: only supported directly in conditions of `if`- and `while`-expressions
-   = note: as well as when nested within `&&` and parenthesis in those conditions
+   = note: only supported directly without parentheses in conditions of `if`- and `while`-expressions, as well as in `let` chains within parentheses
 
 error: `let` expressions are not supported here
   --> $DIR/disallowed-positions.rs:226:17
@@ -501,8 +447,7 @@ error: `let` expressions are not supported here
 LL |         true && let 1 = 1
    |                 ^^^^^^^^^
    |
-   = note: only supported directly in conditions of `if`- and `while`-expressions
-   = note: as well as when nested within `&&` and parenthesis in those conditions
+   = note: only supported directly without parentheses in conditions of `if`- and `while`-expressions, as well as in `let` chains within parentheses
 
 error: `let` expressions are not supported here
   --> $DIR/disallowed-positions.rs:236:17
@@ -510,8 +455,7 @@ error: `let` expressions are not supported here
 LL |         true && let 1 = 1
    |                 ^^^^^^^^^
    |
-   = note: only supported directly in conditions of `if`- and `while`-expressions
-   = note: as well as when nested within `&&` and parenthesis in those conditions
+   = note: only supported directly without parentheses in conditions of `if`- and `while`-expressions, as well as in `let` chains within parentheses
 
 warning: the feature `const_generics` is incomplete and may not be safe to use and/or cause compiler crashes
   --> $DIR/disallowed-positions.rs:20:12

src/test/ui/rfc-2497-if-let-chains/feature-gate.rs

@@ -13,11 +13,11 @@ fn _if() {
 
     if (let 0 = 1) {}
     //~^ ERROR `let` expressions in this position are experimental [E0658]
-    //~| ERROR `let` expressions are not supported here
+    //~| ERROR invalid parentheses around `let` expression in `if let`
 
     if (((let 0 = 1))) {}
     //~^ ERROR `let` expressions in this position are experimental [E0658]
-    //~| ERROR `let` expressions are not supported here
+    //~| ERROR invalid parentheses around `let` expression in `if let`
 
     if true && let 0 = 1 {}
     //~^ ERROR `let` expressions in this position are experimental [E0658]
@@ -126,7 +126,7 @@ fn _macros() {
     //~| ERROR `let` expressions are not supported here
     use_expr!((let 0 = 1));
     //~^ ERROR `let` expressions in this position are experimental [E0658]
-    //~| ERROR `let` expressions are not supported here
+    //~| ERROR invalid parentheses around `let` expression in `if let`
     //~| ERROR `let` expressions are not supported here
     #[cfg(FALSE)] (let 0 = 1);
     //~^ ERROR `let` expressions in this position are experimental [E0658]

src/test/ui/rfc-2497-if-let-chains/feature-gate.stderr

@@ -15,6 +15,7 @@ LL |     if (let 0 = 1) {}
    |
    = note: see issue #53667 <https://github.com/rust-lang/rust/issues/53667> for more information
    = help: add `#![feature(let_chains)]` to the crate attributes to enable
+   = help: you can write `matches!(<expr>, <pattern>)` instead of `let <pattern> = <expr>`
 
 error[E0658]: `let` expressions in this position are experimental
   --> $DIR/feature-gate.rs:18:11
@@ -24,6 +25,7 @@ LL |     if (((let 0 = 1))) {}
    |
    = note: see issue #53667 <https://github.com/rust-lang/rust/issues/53667> for more information
    = help: add `#![feature(let_chains)]` to the crate attributes to enable
+   = help: you can write `matches!(<expr>, <pattern>)` instead of `let <pattern> = <expr>`
 
 error[E0658]: `let` expressions in this position are experimental
   --> $DIR/feature-gate.rs:22:16
@@ -33,6 +35,7 @@ LL |     if true && let 0 = 1 {}
    |
    = note: see issue #53667 <https://github.com/rust-lang/rust/issues/53667> for more information
    = help: add `#![feature(let_chains)]` to the crate attributes to enable
+   = help: you can write `matches!(<expr>, <pattern>)` instead of `let <pattern> = <expr>`
 
 error[E0658]: `let` expressions in this position are experimental
   --> $DIR/feature-gate.rs:26:8
@@ -42,6 +45,7 @@ LL |     if let 0 = 1 && true {}
    |
    = note: see issue #53667 <https://github.com/rust-lang/rust/issues/53667> for more information
    = help: add `#![feature(let_chains)]` to the crate attributes to enable
+   = help: you can write `matches!(<expr>, <pattern>)` instead of `let <pattern> = <expr>`
 
 error[E0658]: `let` expressions in this position are experimental
   --> $DIR/feature-gate.rs:30:9
@@ -51,6 +55,7 @@ LL |     if (let 0 = 1) && true {}
    |
    = note: see issue #53667 <https://github.com/rust-lang/rust/issues/53667> for more information
    = help: add `#![feature(let_chains)]` to the crate attributes to enable
+   = help: you can write `matches!(<expr>, <pattern>)` instead of `let <pattern> = <expr>`
 
 error[E0658]: `let` expressions in this position are experimental
   --> $DIR/feature-gate.rs:34:17
@@ -60,6 +65,7 @@ LL |     if true && (let 0 = 1) {}
    |
    = note: see issue #53667 <https://github.com/rust-lang/rust/issues/53667> for more information
    = help: add `#![feature(let_chains)]` to the crate attributes to enable
+   = help: you can write `matches!(<expr>, <pattern>)` instead of `let <pattern> = <expr>`
 
 error[E0658]: `let` expressions in this position are experimental
   --> $DIR/feature-gate.rs:38:9
@@ -69,6 +75,7 @@ LL |     if (let 0 = 1) && (let 0 = 1) {}
    |
    = note: see issue #53667 <https://github.com/rust-lang/rust/issues/53667> for more information
    = help: add `#![feature(let_chains)]` to the crate attributes to enable
+   = help: you can write `matches!(<expr>, <pattern>)` instead of `let <pattern> = <expr>`
 
 error[E0658]: `let` expressions in this position are experimental
   --> $DIR/feature-gate.rs:38:24
@@ -78,6 +85,7 @@ LL |     if (let 0 = 1) && (let 0 = 1) {}
    |
    = note: see issue #53667 <https://github.com/rust-lang/rust/issues/53667> for more information
    = help: add `#![feature(let_chains)]` to the crate attributes to enable
+   = help: you can write `matches!(<expr>, <pattern>)` instead of `let <pattern> = <expr>`
 
 error[E0658]: `let` expressions in this position are experimental
   --> $DIR/feature-gate.rs:44:8
@@ -87,6 +95,7 @@ LL |     if let 0 = 1 && let 1 = 2 && (let 2 = 3 && let 3 = 4 && let 4 = 5) {}
    |
    = note: see issue #53667 <https://github.com/rust-lang/rust/issues/53667> for more information
    = help: add `#![feature(let_chains)]` to the crate attributes to enable
+   = help: you can write `matches!(<expr>, <pattern>)` instead of `let <pattern> = <expr>`
 
 error[E0658]: `let` expressions in this position are experimental
   --> $DIR/feature-gate.rs:44:21
@@ -96,6 +105,7 @@ LL |     if let 0 = 1 && let 1 = 2 && (let 2 = 3 && let 3 = 4 && let 4 = 5) {}
    |
    = note: see issue #53667 <https://github.com/rust-lang/rust/issues/53667> for more information
    = help: add `#![feature(let_chains)]` to the crate attributes to enable
+   = help: you can write `matches!(<expr>, <pattern>)` instead of `let <pattern> = <expr>`
 
 error[E0658]: `let` expressions in this position are experimental
   --> $DIR/feature-gate.rs:44:35
@@ -105,6 +115,7 @@ LL |     if let 0 = 1 && let 1 = 2 && (let 2 = 3 && let 3 = 4 && let 4 = 5) {}
    |
    = note: see issue #53667 <https://github.com/rust-lang/rust/issues/53667> for more information
    = help: add `#![feature(let_chains)]` to the crate attributes to enable
+   = help: you can write `matches!(<expr>, <pattern>)` instead of `let <pattern> = <expr>`
 
 error[E0658]: `let` expressions in this position are experimental
   --> $DIR/feature-gate.rs:44:48
@@ -114,6 +125,7 @@ LL |     if let 0 = 1 && let 1 = 2 && (let 2 = 3 && let 3 = 4 && let 4 = 5) {}
    |
    = note: see issue #53667 <https://github.com/rust-lang/rust/issues/53667> for more information
    = help: add `#![feature(let_chains)]` to the crate attributes to enable
+   = help: you can write `matches!(<expr>, <pattern>)` instead of `let <pattern> = <expr>`
 
 error[E0658]: `let` expressions in this position are experimental
   --> $DIR/feature-gate.rs:44:61
@@ -123,6 +135,7 @@ LL |     if let 0 = 1 && let 1 = 2 && (let 2 = 3 && let 3 = 4 && let 4 = 5) {}
    |
    = note: see issue #53667 <https://github.com/rust-lang/rust/issues/53667> for more information
    = help: add `#![feature(let_chains)]` to the crate attributes to enable
+   = help: you can write `matches!(<expr>, <pattern>)` instead of `let <pattern> = <expr>`
 
 error[E0658]: `let` expressions in this position are experimental
   --> $DIR/feature-gate.rs:56:8
@@ -132,6 +145,7 @@ LL |     if let Range { start: _, end: _ } = (true..true) && false {}
    |
    = note: see issue #53667 <https://github.com/rust-lang/rust/issues/53667> for more information
    = help: add `#![feature(let_chains)]` to the crate attributes to enable
+   = help: you can write `matches!(<expr>, <pattern>)` instead of `let <pattern> = <expr>`
 
 error[E0658]: `let` expressions in this position are experimental
   --> $DIR/feature-gate.rs:64:12
@@ -141,6 +155,7 @@ LL |     while (let 0 = 1) {}
    |
    = note: see issue #53667 <https://github.com/rust-lang/rust/issues/53667> for more information
    = help: add `#![feature(let_chains)]` to the crate attributes to enable
+   = help: you can write `matches!(<expr>, <pattern>)` instead of `let <pattern> = <expr>`
 
 error[E0658]: `let` expressions in this position are experimental
   --> $DIR/feature-gate.rs:68:14
@@ -150,6 +165,7 @@ LL |     while (((let 0 = 1))) {}
    |
    = note: see issue #53667 <https://github.com/rust-lang/rust/issues/53667> for more information
    = help: add `#![feature(let_chains)]` to the crate attributes to enable
+   = help: you can write `matches!(<expr>, <pattern>)` instead of `let <pattern> = <expr>`
 
 error[E0658]: `let` expressions in this position are experimental
   --> $DIR/feature-gate.rs:72:19
@@ -159,6 +175,7 @@ LL |     while true && let 0 = 1 {}
    |
    = note: see issue #53667 <https://github.com/rust-lang/rust/issues/53667> for more information
    = help: add `#![feature(let_chains)]` to the crate attributes to enable
+   = help: you can write `matches!(<expr>, <pattern>)` instead of `let <pattern> = <expr>`
 
 error[E0658]: `let` expressions in this position are experimental
   --> $DIR/feature-gate.rs:76:11
@@ -168,6 +185,7 @@ LL |     while let 0 = 1 && true {}
    |
    = note: see issue #53667 <https://github.com/rust-lang/rust/issues/53667> for more information
    = help: add `#![feature(let_chains)]` to the crate attributes to enable
+   = help: you can write `matches!(<expr>, <pattern>)` instead of `let <pattern> = <expr>`
 
 error[E0658]: `let` expressions in this position are experimental
   --> $DIR/feature-gate.rs:80:12
@@ -177,6 +195,7 @@ LL |     while (let 0 = 1) && true {}
    |
    = note: see issue #53667 <https://github.com/rust-lang/rust/issues/53667> for more information
    = help: add `#![feature(let_chains)]` to the crate attributes to enable
+   = help: you can write `matches!(<expr>, <pattern>)` instead of `let <pattern> = <expr>`
 
 error[E0658]: `let` expressions in this position are experimental
   --> $DIR/feature-gate.rs:84:20
@@ -186,6 +205,7 @@ LL |     while true && (let 0 = 1) {}
    |
    = note: see issue #53667 <https://github.com/rust-lang/rust/issues/53667> for more information
    = help: add `#![feature(let_chains)]` to the crate attributes to enable
+   = help: you can write `matches!(<expr>, <pattern>)` instead of `let <pattern> = <expr>`
 
 error[E0658]: `let` expressions in this position are experimental
   --> $DIR/feature-gate.rs:88:12
@@ -195,6 +215,7 @@ LL |     while (let 0 = 1) && (let 0 = 1) {}
    |
    = note: see issue #53667 <https://github.com/rust-lang/rust/issues/53667> for more information
    = help: add `#![feature(let_chains)]` to the crate attributes to enable
+   = help: you can write `matches!(<expr>, <pattern>)` instead of `let <pattern> = <expr>`
 
 error[E0658]: `let` expressions in this position are experimental
   --> $DIR/feature-gate.rs:88:27
@@ -204,6 +225,7 @@ LL |     while (let 0 = 1) && (let 0 = 1) {}
    |
    = note: see issue #53667 <https://github.com/rust-lang/rust/issues/53667> for more information
    = help: add `#![feature(let_chains)]` to the crate attributes to enable
+   = help: you can write `matches!(<expr>, <pattern>)` instead of `let <pattern> = <expr>`
 
 error[E0658]: `let` expressions in this position are experimental
   --> $DIR/feature-gate.rs:94:11
@@ -213,6 +235,7 @@ LL |     while let 0 = 1 && let 1 = 2 && (let 2 = 3 && let 3 = 4 && let 4 = 5) {
    |
    = note: see issue #53667 <https://github.com/rust-lang/rust/issues/53667> for more information
    = help: add `#![feature(let_chains)]` to the crate attributes to enable
+   = help: you can write `matches!(<expr>, <pattern>)` instead of `let <pattern> = <expr>`
 
 error[E0658]: `let` expressions in this position are experimental
   --> $DIR/feature-gate.rs:94:24
@@ -222,6 +245,7 @@ LL |     while let 0 = 1 && let 1 = 2 && (let 2 = 3 && let 3 = 4 && let 4 = 5) {
    |
    = note: see issue #53667 <https://github.com/rust-lang/rust/issues/53667> for more information
    = help: add `#![feature(let_chains)]` to the crate attributes to enable
+   = help: you can write `matches!(<expr>, <pattern>)` instead of `let <pattern> = <expr>`
 
 error[E0658]: `let` expressions in this position are experimental
   --> $DIR/feature-gate.rs:94:38
@@ -231,6 +255,7 @@ LL |     while let 0 = 1 && let 1 = 2 && (let 2 = 3 && let 3 = 4 && let 4 = 5) {
    |
    = note: see issue #53667 <https://github.com/rust-lang/rust/issues/53667> for more information
    = help: add `#![feature(let_chains)]` to the crate attributes to enable
+   = help: you can write `matches!(<expr>, <pattern>)` instead of `let <pattern> = <expr>`
 
 error[E0658]: `let` expressions in this position are experimental
   --> $DIR/feature-gate.rs:94:51
@@ -240,6 +265,7 @@ LL |     while let 0 = 1 && let 1 = 2 && (let 2 = 3 && let 3 = 4 && let 4 = 5) {
    |
    = note: see issue #53667 <https://github.com/rust-lang/rust/issues/53667> for more information
    = help: add `#![feature(let_chains)]` to the crate attributes to enable
+   = help: you can write `matches!(<expr>, <pattern>)` instead of `let <pattern> = <expr>`
 
 error[E0658]: `let` expressions in this position are experimental
   --> $DIR/feature-gate.rs:94:64
@@ -249,6 +275,7 @@ LL |     while let 0 = 1 && let 1 = 2 && (let 2 = 3 && let 3 = 4 && let 4 = 5) {
    |
    = note: see issue #53667 <https://github.com/rust-lang/rust/issues/53667> for more information
    = help: add `#![feature(let_chains)]` to the crate attributes to enable
+   = help: you can write `matches!(<expr>, <pattern>)` instead of `let <pattern> = <expr>`
 
 error[E0658]: `let` expressions in this position are experimental
   --> $DIR/feature-gate.rs:106:11
@@ -258,6 +285,7 @@ LL |     while let Range { start: _, end: _ } = (true..true) && false {}
    |
    = note: see issue #53667 <https://github.com/rust-lang/rust/issues/53667> for more information
    = help: add `#![feature(let_chains)]` to the crate attributes to enable
+   = help: you can write `matches!(<expr>, <pattern>)` instead of `let <pattern> = <expr>`
 
 error[E0658]: `let` expressions in this position are experimental
   --> $DIR/feature-gate.rs:131:20
@@ -267,6 +295,7 @@ LL |     #[cfg(FALSE)] (let 0 = 1);
    |
    = note: see issue #53667 <https://github.com/rust-lang/rust/issues/53667> for more information
    = help: add `#![feature(let_chains)]` to the crate attributes to enable
+   = help: you can write `matches!(<expr>, <pattern>)` instead of `let <pattern> = <expr>`
 
 error[E0658]: `let` expressions in this position are experimental
   --> $DIR/feature-gate.rs:114:17
@@ -276,6 +305,7 @@ LL |     noop_expr!((let 0 = 1));
    |
    = note: see issue #53667 <https://github.com/rust-lang/rust/issues/53667> for more information
    = help: add `#![feature(let_chains)]` to the crate attributes to enable
+   = help: you can write `matches!(<expr>, <pattern>)` instead of `let <pattern> = <expr>`
 
 error[E0658]: `let` expressions in this position are experimental
   --> $DIR/feature-gate.rs:123:16
@@ -285,6 +315,7 @@ LL |     use_expr!((let 0 = 1 && 0 == 0));
    |
    = note: see issue #53667 <https://github.com/rust-lang/rust/issues/53667> for more information
    = help: add `#![feature(let_chains)]` to the crate attributes to enable
+   = help: you can write `matches!(<expr>, <pattern>)` instead of `let <pattern> = <expr>`
 
 error[E0658]: `let` expressions in this position are experimental
   --> $DIR/feature-gate.rs:127:16
@@ -294,24 +325,29 @@ LL |     use_expr!((let 0 = 1));
    |
    = note: see issue #53667 <https://github.com/rust-lang/rust/issues/53667> for more information
    = help: add `#![feature(let_chains)]` to the crate attributes to enable
+   = help: you can write `matches!(<expr>, <pattern>)` instead of `let <pattern> = <expr>`
 
-error: `let` expressions are not supported here
-  --> $DIR/feature-gate.rs:14:9
+error: invalid parentheses around `let` expression in `if let`
+  --> $DIR/feature-gate.rs:14:8
    |
 LL |     if (let 0 = 1) {}
-   |         ^^^^^^^^^
+   |        ^         ^
    |
-   = note: only supported directly in conditions of `if`- and `while`-expressions
-   = note: as well as when nested within `&&` and parenthesis in those conditions
+help: `if let` needs to be written without parentheses
+   |
+LL |     if let 0 = 1 {}
+   |       --       --
 
-error: `let` expressions are not supported here
-  --> $DIR/feature-gate.rs:18:11
+error: invalid parentheses around `let` expression in `if let`
+  --> $DIR/feature-gate.rs:18:8
    |
 LL |     if (((let 0 = 1))) {}
-   |           ^^^^^^^^^
+   |        ^^^         ^^^
    |
-   = note: only supported directly in conditions of `if`- and `while`-expressions
-   = note: as well as when nested within `&&` and parenthesis in those conditions
+help: `if let` needs to be written without parentheses
+   |
+LL |     if let 0 = 1 {}
+   |       --       --
 
 error: `let` expressions are not supported here
   --> $DIR/feature-gate.rs:22:16
@@ -319,8 +355,7 @@ error: `let` expressions are not supported here
 LL |     if true && let 0 = 1 {}
    |                ^^^^^^^^^
    |
-   = note: only supported directly in conditions of `if`- and `while`-expressions
-   = note: as well as when nested within `&&` and parenthesis in those conditions
+   = note: only supported directly without parentheses in conditions of `if`- and `while`-expressions, as well as in `let` chains within parentheses
 
 error: `let` expressions are not supported here
   --> $DIR/feature-gate.rs:26:8
@@ -328,8 +363,7 @@ error: `let` expressions are not supported here
 LL |     if let 0 = 1 && true {}
    |        ^^^^^^^^^
    |
-   = note: only supported directly in conditions of `if`- and `while`-expressions
-   = note: as well as when nested within `&&` and parenthesis in those conditions
+   = note: only supported directly without parentheses in conditions of `if`- and `while`-expressions, as well as in `let` chains within parentheses
 
 error: `let` expressions are not supported here
   --> $DIR/feature-gate.rs:30:9
@@ -337,8 +371,7 @@ error: `let` expressions are not supported here
 LL |     if (let 0 = 1) && true {}
    |         ^^^^^^^^^
    |
-   = note: only supported directly in conditions of `if`- and `while`-expressions
-   = note: as well as when nested within `&&` and parenthesis in those conditions
+   = note: only supported directly without parentheses in conditions of `if`- and `while`-expressions, as well as in `let` chains within parentheses
 
 error: `let` expressions are not supported here
   --> $DIR/feature-gate.rs:34:17
@@ -346,8 +379,7 @@ error: `let` expressions are not supported here
 LL |     if true && (let 0 = 1) {}
    |                 ^^^^^^^^^
    |
-   = note: only supported directly in conditions of `if`- and `while`-expressions
-   = note: as well as when nested within `&&` and parenthesis in those conditions
+   = note: only supported directly without parentheses in conditions of `if`- and `while`-expressions, as well as in `let` chains within parentheses
 
 error: `let` expressions are not supported here
   --> $DIR/feature-gate.rs:38:9
@@ -355,8 +387,7 @@ error: `let` expressions are not supported here
 LL |     if (let 0 = 1) && (let 0 = 1) {}
    |         ^^^^^^^^^
    |
-   = note: only supported directly in conditions of `if`- and `while`-expressions
-   = note: as well as when nested within `&&` and parenthesis in those conditions
+   = note: only supported directly without parentheses in conditions of `if`- and `while`-expressions, as well as in `let` chains within parentheses
 
 error: `let` expressions are not supported here
   --> $DIR/feature-gate.rs:38:24
@@ -364,8 +395,7 @@ error: `let` expressions are not supported here
 LL |     if (let 0 = 1) && (let 0 = 1) {}
    |                        ^^^^^^^^^
    |
-   = note: only supported directly in conditions of `if`- and `while`-expressions
-   = note: as well as when nested within `&&` and parenthesis in those conditions
+   = note: only supported directly without parentheses in conditions of `if`- and `while`-expressions, as well as in `let` chains within parentheses
 
 error: `let` expressions are not supported here
   --> $DIR/feature-gate.rs:44:8
@@ -373,8 +403,7 @@ error: `let` expressions are not supported here
 LL |     if let 0 = 1 && let 1 = 2 && (let 2 = 3 && let 3 = 4 && let 4 = 5) {}
    |        ^^^^^^^^^
    |
-   = note: only supported directly in conditions of `if`- and `while`-expressions
-   = note: as well as when nested within `&&` and parenthesis in those conditions
+   = note: only supported directly without parentheses in conditions of `if`- and `while`-expressions, as well as in `let` chains within parentheses
 
 error: `let` expressions are not supported here
   --> $DIR/feature-gate.rs:44:21
@@ -382,8 +411,7 @@ error: `let` expressions are not supported here
 LL |     if let 0 = 1 && let 1 = 2 && (let 2 = 3 && let 3 = 4 && let 4 = 5) {}
    |                     ^^^^^^^^^
    |
-   = note: only supported directly in conditions of `if`- and `while`-expressions
-   = note: as well as when nested within `&&` and parenthesis in those conditions
+   = note: only supported directly without parentheses in conditions of `if`- and `while`-expressions, as well as in `let` chains within parentheses
 
 error: `let` expressions are not supported here
   --> $DIR/feature-gate.rs:44:35
@@ -391,8 +419,7 @@ error: `let` expressions are not supported here
 LL |     if let 0 = 1 && let 1 = 2 && (let 2 = 3 && let 3 = 4 && let 4 = 5) {}
    |                                   ^^^^^^^^^
    |
-   = note: only supported directly in conditions of `if`- and `while`-expressions
-   = note: as well as when nested within `&&` and parenthesis in those conditions
+   = note: only supported directly without parentheses in conditions of `if`- and `while`-expressions, as well as in `let` chains within parentheses
 
 error: `let` expressions are not supported here
   --> $DIR/feature-gate.rs:44:48
@@ -400,8 +427,7 @@ error: `let` expressions are not supported here
 LL |     if let 0 = 1 && let 1 = 2 && (let 2 = 3 && let 3 = 4 && let 4 = 5) {}
    |                                                ^^^^^^^^^
    |
-   = note: only supported directly in conditions of `if`- and `while`-expressions
-   = note: as well as when nested within `&&` and parenthesis in those conditions
+   = note: only supported directly without parentheses in conditions of `if`- and `while`-expressions, as well as in `let` chains within parentheses
 
 error: `let` expressions are not supported here
   --> $DIR/feature-gate.rs:44:61
@@ -409,8 +435,7 @@ error: `let` expressions are not supported here
 LL |     if let 0 = 1 && let 1 = 2 && (let 2 = 3 && let 3 = 4 && let 4 = 5) {}
    |                                                             ^^^^^^^^^
    |
-   = note: only supported directly in conditions of `if`- and `while`-expressions
-   = note: as well as when nested within `&&` and parenthesis in those conditions
+   = note: only supported directly without parentheses in conditions of `if`- and `while`-expressions, as well as in `let` chains within parentheses
 
 error: `let` expressions are not supported here
   --> $DIR/feature-gate.rs:56:8
@@ -418,8 +443,7 @@ error: `let` expressions are not supported here
 LL |     if let Range { start: _, end: _ } = (true..true) && false {}
    |        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    |
-   = note: only supported directly in conditions of `if`- and `while`-expressions
-   = note: as well as when nested within `&&` and parenthesis in those conditions
+   = note: only supported directly without parentheses in conditions of `if`- and `while`-expressions, as well as in `let` chains within parentheses
 
 error: `let` expressions are not supported here
   --> $DIR/feature-gate.rs:64:12
@@ -427,8 +451,7 @@ error: `let` expressions are not supported here
 LL |     while (let 0 = 1) {}
    |            ^^^^^^^^^
    |
-   = note: only supported directly in conditions of `if`- and `while`-expressions
-   = note: as well as when nested within `&&` and parenthesis in those conditions
+   = note: only supported directly without parentheses in conditions of `if`- and `while`-expressions, as well as in `let` chains within parentheses
 
 error: `let` expressions are not supported here
   --> $DIR/feature-gate.rs:68:14
@@ -436,8 +459,7 @@ error: `let` expressions are not supported here
 LL |     while (((let 0 = 1))) {}
    |              ^^^^^^^^^
    |
-   = note: only supported directly in conditions of `if`- and `while`-expressions
-   = note: as well as when nested within `&&` and parenthesis in those conditions
+   = note: only supported directly without parentheses in conditions of `if`- and `while`-expressions, as well as in `let` chains within parentheses
 
 error: `let` expressions are not supported here
   --> $DIR/feature-gate.rs:72:19
@@ -445,8 +467,7 @@ error: `let` expressions are not supported here
 LL |     while true && let 0 = 1 {}
    |                   ^^^^^^^^^
    |
-   = note: only supported directly in conditions of `if`- and `while`-expressions
-   = note: as well as when nested within `&&` and parenthesis in those conditions
+   = note: only supported directly without parentheses in conditions of `if`- and `while`-expressions, as well as in `let` chains within parentheses
 
 error: `let` expressions are not supported here
   --> $DIR/feature-gate.rs:76:11
@@ -454,8 +475,7 @@ error: `let` expressions are not supported here
 LL |     while let 0 = 1 && true {}
    |           ^^^^^^^^^
    |
-   = note: only supported directly in conditions of `if`- and `while`-expressions
-   = note: as well as when nested within `&&` and parenthesis in those conditions
+   = note: only supported directly without parentheses in conditions of `if`- and `while`-expressions, as well as in `let` chains within parentheses
 
 error: `let` expressions are not supported here
   --> $DIR/feature-gate.rs:80:12
@@ -463,8 +483,7 @@ error: `let` expressions are not supported here
 LL |     while (let 0 = 1) && true {}
    |            ^^^^^^^^^
    |
-   = note: only supported directly in conditions of `if`- and `while`-expressions
-   = note: as well as when nested within `&&` and parenthesis in those conditions
+   = note: only supported directly without parentheses in conditions of `if`- and `while`-expressions, as well as in `let` chains within parentheses
 
 error: `let` expressions are not supported here
   --> $DIR/feature-gate.rs:84:20
@@ -472,8 +491,7 @@ error: `let` expressions are not supported here
 LL |     while true && (let 0 = 1) {}
    |                    ^^^^^^^^^
    |
-   = note: only supported directly in conditions of `if`- and `while`-expressions
-   = note: as well as when nested within `&&` and parenthesis in those conditions
+   = note: only supported directly without parentheses in conditions of `if`- and `while`-expressions, as well as in `let` chains within parentheses
 
 error: `let` expressions are not supported here
   --> $DIR/feature-gate.rs:88:12
@@ -481,8 +499,7 @@ error: `let` expressions are not supported here
 LL |     while (let 0 = 1) && (let 0 = 1) {}
    |            ^^^^^^^^^
    |
-   = note: only supported directly in conditions of `if`- and `while`-expressions
-   = note: as well as when nested within `&&` and parenthesis in those conditions
+   = note: only supported directly without parentheses in conditions of `if`- and `while`-expressions, as well as in `let` chains within parentheses
 
 error: `let` expressions are not supported here
   --> $DIR/feature-gate.rs:88:27
@@ -490,8 +507,7 @@ error: `let` expressions are not supported here
 LL |     while (let 0 = 1) && (let 0 = 1) {}
    |                           ^^^^^^^^^
    |
-   = note: only supported directly in conditions of `if`- and `while`-expressions
-   = note: as well as when nested within `&&` and parenthesis in those conditions
+   = note: only supported directly without parentheses in conditions of `if`- and `while`-expressions, as well as in `let` chains within parentheses
 
 error: `let` expressions are not supported here
   --> $DIR/feature-gate.rs:94:11
@@ -499,8 +515,7 @@ error: `let` expressions are not supported here
 LL |     while let 0 = 1 && let 1 = 2 && (let 2 = 3 && let 3 = 4 && let 4 = 5) {}
    |           ^^^^^^^^^
    |
-   = note: only supported directly in conditions of `if`- and `while`-expressions
-   = note: as well as when nested within `&&` and parenthesis in those conditions
+   = note: only supported directly without parentheses in conditions of `if`- and `while`-expressions, as well as in `let` chains within parentheses
 
 error: `let` expressions are not supported here
   --> $DIR/feature-gate.rs:94:24
@@ -508,8 +523,7 @@ error: `let` expressions are not supported here
 LL |     while let 0 = 1 && let 1 = 2 && (let 2 = 3 && let 3 = 4 && let 4 = 5) {}
    |                        ^^^^^^^^^
    |
-   = note: only supported directly in conditions of `if`- and `while`-expressions
-   = note: as well as when nested within `&&` and parenthesis in those conditions
+   = note: only supported directly without parentheses in conditions of `if`- and `while`-expressions, as well as in `let` chains within parentheses
 
 error: `let` expressions are not supported here
   --> $DIR/feature-gate.rs:94:38
@@ -517,8 +531,7 @@ error: `let` expressions are not supported here
 LL |     while let 0 = 1 && let 1 = 2 && (let 2 = 3 && let 3 = 4 && let 4 = 5) {}
    |                                      ^^^^^^^^^
    |
-   = note: only supported directly in conditions of `if`- and `while`-expressions
-   = note: as well as when nested within `&&` and parenthesis in those conditions
+   = note: only supported directly without parentheses in conditions of `if`- and `while`-expressions, as well as in `let` chains within parentheses
 
 error: `let` expressions are not supported here
   --> $DIR/feature-gate.rs:94:51
@@ -526,8 +539,7 @@ error: `let` expressions are not supported here
 LL |     while let 0 = 1 && let 1 = 2 && (let 2 = 3 && let 3 = 4 && let 4 = 5) {}
    |                                                   ^^^^^^^^^
    |
-   = note: only supported directly in conditions of `if`- and `while`-expressions
-   = note: as well as when nested within `&&` and parenthesis in those conditions
+   = note: only supported directly without parentheses in conditions of `if`- and `while`-expressions, as well as in `let` chains within parentheses
 
 error: `let` expressions are not supported here
   --> $DIR/feature-gate.rs:94:64
@@ -535,8 +547,7 @@ error: `let` expressions are not supported here
 LL |     while let 0 = 1 && let 1 = 2 && (let 2 = 3 && let 3 = 4 && let 4 = 5) {}
    |                                                                ^^^^^^^^^
    |
-   = note: only supported directly in conditions of `if`- and `while`-expressions
-   = note: as well as when nested within `&&` and parenthesis in those conditions
+   = note: only supported directly without parentheses in conditions of `if`- and `while`-expressions, as well as in `let` chains within parentheses
 
 error: `let` expressions are not supported here
   --> $DIR/feature-gate.rs:106:11
@@ -544,8 +555,7 @@ error: `let` expressions are not supported here
 LL |     while let Range { start: _, end: _ } = (true..true) && false {}
    |           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    |
-   = note: only supported directly in conditions of `if`- and `while`-expressions
-   = note: as well as when nested within `&&` and parenthesis in those conditions
+   = note: only supported directly without parentheses in conditions of `if`- and `while`-expressions, as well as in `let` chains within parentheses
 
 error: `let` expressions are not supported here
   --> $DIR/feature-gate.rs:123:16
@@ -553,8 +563,7 @@ error: `let` expressions are not supported here
 LL |     use_expr!((let 0 = 1 && 0 == 0));
    |                ^^^^^^^^^
    |
-   = note: only supported directly in conditions of `if`- and `while`-expressions
-   = note: as well as when nested within `&&` and parenthesis in those conditions
+   = note: only supported directly without parentheses in conditions of `if`- and `while`-expressions, as well as in `let` chains within parentheses
 
 error: `let` expressions are not supported here
   --> $DIR/feature-gate.rs:123:16
@@ -562,8 +571,18 @@ error: `let` expressions are not supported here
 LL |     use_expr!((let 0 = 1 && 0 == 0));
    |                ^^^^^^^^^
    |
-   = note: only supported directly in conditions of `if`- and `while`-expressions
-   = note: as well as when nested within `&&` and parenthesis in those conditions
+   = note: only supported directly without parentheses in conditions of `if`- and `while`-expressions, as well as in `let` chains within parentheses
+
+error: invalid parentheses around `let` expression in `if let`
+  --> $DIR/feature-gate.rs:127:15
+   |
+LL |     use_expr!((let 0 = 1));
+   |               ^         ^
+   |
+help: `if let` needs to be written without parentheses
+   |
+LL |     use_expr!(let 0 = 1);
+   |              --       --
 
 error: `let` expressions are not supported here
   --> $DIR/feature-gate.rs:127:16
@@ -571,17 +590,7 @@ error: `let` expressions are not supported here
 LL |     use_expr!((let 0 = 1));
    |                ^^^^^^^^^
    |
-   = note: only supported directly in conditions of `if`- and `while`-expressions
-   = note: as well as when nested within `&&` and parenthesis in those conditions
-
-error: `let` expressions are not supported here
-  --> $DIR/feature-gate.rs:127:16
-   |
-LL |     use_expr!((let 0 = 1));
-   |                ^^^^^^^^^
-   |
-   = note: only supported directly in conditions of `if`- and `while`-expressions
-   = note: as well as when nested within `&&` and parenthesis in those conditions
+   = note: only supported directly without parentheses in conditions of `if`- and `while`-expressions, as well as in `let` chains within parentheses
 
 error: aborting due to 65 previous errors