Do not suggest `;` if expression is side effect free
When a tail expression isn't unit, we previously always suggested adding a trailing `;` to turn it into a statement. This suggestion isn't appropriate for any expression that doesn't have side-effects, as the user will have likely wanted to call something else or do something with the resulting value, instead of just discarding it.
This commit is contained in:
Esteban Küber
parent
020edd91a9
commit
d669882f38
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@ -1,5 +1,6 @@
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// ignore-tidy-filelength
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use crate::def::{DefKind, Namespace, Res};
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use crate::def::{CtorKind, DefKind, Namespace, Res};
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use crate::def_id::DefId;
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crate use crate::hir_id::HirId;
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use crate::{itemlikevisit, LangItem};
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@ -1554,6 +1555,63 @@ impl Expr<'_> {
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}
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expr
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}
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pub fn can_have_side_effects(&self) -> bool {
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match self.peel_drop_temps().kind {
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ExprKind::Path(_) | ExprKind::Lit(_) => false,
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ExprKind::Type(base, _)
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| ExprKind::Unary(_, base)
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| ExprKind::Field(base, _)
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| ExprKind::Index(base, _)
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| ExprKind::AddrOf(.., base)
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| ExprKind::Cast(base, _) => {
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// This isn't exactly true for `Index` and all `Unnary`, but we are using this
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// method exclusively for diagnostics and there's a *cultural* pressure against
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// them being used only for its side-effects.
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base.can_have_side_effects()
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}
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ExprKind::Struct(_, fields, init) => fields
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.iter()
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.map(|field| field.expr)
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.chain(init.into_iter())
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.all(|e| e.can_have_side_effects()),
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ExprKind::Array(args)
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| ExprKind::Tup(args)
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| ExprKind::Call(
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Expr {
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kind:
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ExprKind::Path(QPath::Resolved(
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None,
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Path { res: Res::Def(DefKind::Ctor(_, CtorKind::Fn), _), .. },
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)),
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..
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},
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args,
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) => args.iter().all(|arg| arg.can_have_side_effects()),
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ExprKind::If(..)
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| ExprKind::Match(..)
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| ExprKind::MethodCall(..)
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| ExprKind::Call(..)
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| ExprKind::Closure(..)
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| ExprKind::Block(..)
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| ExprKind::Repeat(..)
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| ExprKind::Break(..)
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| ExprKind::Continue(..)
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| ExprKind::Ret(..)
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| ExprKind::Loop(..)
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| ExprKind::Assign(..)
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| ExprKind::InlineAsm(..)
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| ExprKind::LlvmInlineAsm(..)
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| ExprKind::AssignOp(..)
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| ExprKind::ConstBlock(..)
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| ExprKind::Box(..)
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| ExprKind::Binary(..)
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| ExprKind::Yield(..)
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| ExprKind::DropTemps(..)
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| ExprKind::Err => true,
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}
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}
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}
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/// Checks if the specified expression is a built-in range literal.
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@ -1450,7 +1450,9 @@ impl<'tcx, 'exprs, E: AsCoercionSite> CoerceMany<'tcx, 'exprs, E> {
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) {
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if cond_expr.span.desugaring_kind().is_none() {
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err.span_label(cond_expr.span, "expected this to be `()`");
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fcx.suggest_semicolon_at_end(cond_expr.span, &mut err);
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if expr.can_have_side_effects() {
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fcx.suggest_semicolon_at_end(cond_expr.span, &mut err);
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}
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}
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}
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fcx.get_node_fn_decl(parent).map(|(fn_decl, _, is_main)| (fn_decl, is_main))
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@ -561,7 +561,9 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
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hir::StmtKind::Expr(ref expr) => {
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// Check with expected type of `()`.
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self.check_expr_has_type_or_error(&expr, self.tcx.mk_unit(), |err| {
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self.suggest_semicolon_at_end(expr.span, err);
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if expr.can_have_side_effects() {
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self.suggest_semicolon_at_end(expr.span, err);
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}
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});
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}
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hir::StmtKind::Semi(ref expr) => {
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@ -44,11 +44,14 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
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blk_id: hir::HirId,
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) -> bool {
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let expr = expr.peel_drop_temps();
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self.suggest_missing_semicolon(err, expr, expected, cause_span);
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if expr.can_have_side_effects() {
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self.suggest_missing_semicolon(err, expr, expected, cause_span);
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}
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let mut pointing_at_return_type = false;
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if let Some((fn_decl, can_suggest)) = self.get_fn_decl(blk_id) {
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pointing_at_return_type =
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self.suggest_missing_return_type(err, &fn_decl, expected, found, can_suggest);
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self.suggest_missing_return_expr(err, expr, &fn_decl, expected, found);
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}
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pointing_at_return_type
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}
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@ -392,7 +395,9 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
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| ExprKind::Loop(..)
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| ExprKind::If(..)
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| ExprKind::Match(..)
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| ExprKind::Block(..) => {
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| ExprKind::Block(..)
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if expression.can_have_side_effects() =>
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{
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err.span_suggestion(
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cause_span.shrink_to_hi(),
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"consider using a semicolon here",
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@ -14,9 +14,7 @@ LL | | true
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| | ^^^^ expected `()`, found `bool`
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LL | |
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LL | | }
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| | -- help: consider using a semicolon here
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| |_____|
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| expected this to be `()`
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| |_____- expected this to be `()`
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error: aborting due to previous error; 1 warning emitted
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@ -7,10 +7,6 @@ LL | if let Some(x) = a { true } else { false }
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| | expected `()`, found `bool`
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| expected this to be `()`
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help: consider using a semicolon here
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LL | if let Some(x) = a { true } else { false };
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| ^
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help: you might have meant to return this value
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LL | if let Some(x) = a { return true; } else { false }
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@ -25,10 +21,6 @@ LL | if let Some(x) = a { true } else { false }
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| | expected `()`, found `bool`
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| expected this to be `()`
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help: consider using a semicolon here
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LL | if let Some(x) = a { true } else { false };
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| ^
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help: you might have meant to return this value
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LL | if let Some(x) = a { true } else { return false; }
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@ -57,7 +57,7 @@ error[E0308]: mismatched types
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--> $DIR/struct-literal-variant-in-if.rs:10:20
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LL | if x == E::V { field } {}
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| ---------------^^^^^--- help: consider using a semicolon here
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| ---------------^^^^^--
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| | |
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| | expected `()`, found `bool`
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| expected this to be `()`
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@ -9,14 +9,6 @@ LL | | }
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= note: expected unit type `()`
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found enum `std::result::Result<_, {integer}>`
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help: consider using a semicolon here
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LL | Err(42);
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| ^
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help: consider using a semicolon here
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LL | };
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| ^
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help: you might have meant to return this value
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LL | return Err(42);
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@ -1,18 +0,0 @@
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// check-only
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// run-rustfix
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fn main() {
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match 3 {
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4 => 1,
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3 => {
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2 //~ ERROR mismatched types
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}
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_ => 2
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};
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match 3 { //~ ERROR mismatched types
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4 => 1,
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3 => 2,
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_ => 2
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};
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let _ = ();
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}
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@ -1,11 +1,10 @@
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// check-only
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// run-rustfix
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fn main() {
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match 3 {
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4 => 1,
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3 => {
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2 //~ ERROR mismatched types
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foo() //~ ERROR mismatched types
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}
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_ => 2
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}
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@ -16,3 +15,7 @@ fn main() {
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}
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let _ = ();
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}
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fn foo() -> i32 {
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42
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}
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@ -1,20 +1,27 @@
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error[E0308]: mismatched types
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--> $DIR/match-needing-semi.rs:8:13
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--> $DIR/match-needing-semi.rs:7:13
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LL | / match 3 {
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LL | | 4 => 1,
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LL | | 3 => {
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LL | | 2
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| | ^ expected `()`, found integer
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LL | | foo()
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| | ^^^^^ expected `()`, found `i32`
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LL | | }
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LL | | _ => 2
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LL | | }
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| | -- help: consider using a semicolon here
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| |_____|
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| expected this to be `()`
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| |_____- expected this to be `()`
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help: consider using a semicolon here
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LL | foo();
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| ^
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help: consider using a semicolon here
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LL | };
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| ^
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error[E0308]: mismatched types
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--> $DIR/match-needing-semi.rs:12:5
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--> $DIR/match-needing-semi.rs:11:5
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LL | / match 3 {
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LL | | 4 => 1,
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