Auto merge of #76136 - CDirkx:const-result, r=dtolnay

Stabilize some Result methods as const

Stabilize the following methods of Result as const:
 - `is_ok`
 - `is_err`
 - `as_ref`

A test is also included, analogous to the test for `const_option`.

These methods are currently const under the unstable feature `const_result` (tracking issue: #67520).
I believe these methods to be eligible for stabilization because of the stabilization of #49146 (Allow if and match in constants) and the trivial implementations, see also: [PR#75463](https://github.com/rust-lang/rust/pull/75463) and [PR#76135](https://github.com/rust-lang/rust/pull/76135).

Note: these methods are the only methods currently under the `const_result` feature, thus this PR results in the removal of the feature.

Related: #76225

library/core/src/lib.rs

@@ -87,7 +87,6 @@
 #![feature(const_ptr_offset)]
 #![feature(const_ptr_offset_from)]
 #![feature(const_raw_ptr_comparison)]
-#![feature(const_result)]
 #![feature(const_slice_from_raw_parts)]
 #![feature(const_slice_ptr_len)]
 #![feature(const_size_of_val)]

library/core/src/result.rs

@@ -273,7 +273,7 @@ impl<T, E> Result<T, E> {
     /// assert_eq!(x.is_ok(), false);
     /// ```
     #[must_use = "if you intended to assert that this is ok, consider `.unwrap()` instead"]
-    #[rustc_const_unstable(feature = "const_result", issue = "67520")]
+    #[rustc_const_stable(feature = "const_result", since = "1.48.0")]
     #[inline]
     #[stable(feature = "rust1", since = "1.0.0")]
     pub const fn is_ok(&self) -> bool {
@@ -294,7 +294,7 @@ impl<T, E> Result<T, E> {
     /// assert_eq!(x.is_err(), true);
     /// ```
     #[must_use = "if you intended to assert that this is err, consider `.unwrap_err()` instead"]
-    #[rustc_const_unstable(feature = "const_result", issue = "67520")]
+    #[rustc_const_stable(feature = "const_result", since = "1.48.0")]
     #[inline]
     #[stable(feature = "rust1", since = "1.0.0")]
     pub const fn is_err(&self) -> bool {
@@ -438,7 +438,7 @@ impl<T, E> Result<T, E> {
     /// assert_eq!(x.as_ref(), Err(&"Error"));
     /// ```
     #[inline]
-    #[rustc_const_unstable(feature = "const_result", issue = "67520")]
+    #[rustc_const_stable(feature = "const_result", since = "1.48.0")]
     #[stable(feature = "rust1", since = "1.0.0")]
     pub const fn as_ref(&self) -> Result<&T, &E> {
         match *self {

library/core/tests/result.rs

@@ -304,3 +304,19 @@ fn test_result_as_deref_mut() {
     let expected_result = Result::Err::<&mut u32, &mut Vec<i32>>(&mut expected_vec);
     assert_eq!(mut_err.as_deref_mut(), expected_result);
 }
+
+#[test]
+fn result_const() {
+    // test that the methods of `Result` are usable in a const context
+
+    const RESULT: Result<usize, bool> = Ok(32);
+
+    const REF: Result<&usize, &bool> = RESULT.as_ref();
+    assert_eq!(REF, Ok(&32));
+
+    const IS_OK: bool = RESULT.is_ok();
+    assert!(IS_OK);
+
+    const IS_ERR: bool = RESULT.is_err();
+    assert!(!IS_ERR)
+}

src/tools/clippy/clippy_lints/src/matches.rs

@@ -1469,10 +1469,10 @@ mod redundant_pattern_match {
         keyword: &'static str,
     ) {
         fn find_suggestion(cx: &LateContext<'_>, hir_id: HirId, path: &QPath<'_>) -> Option<&'static str> {
-            if match_qpath(path, &paths::RESULT_OK) && can_suggest(cx, hir_id, sym!(result_type), "is_ok") {
+            if match_qpath(path, &paths::RESULT_OK) {
                 return Some("is_ok()");
             }
-            if match_qpath(path, &paths::RESULT_ERR) && can_suggest(cx, hir_id, sym!(result_type), "is_err") {
+            if match_qpath(path, &paths::RESULT_ERR) {
                 return Some("is_err()");
             }
             if match_qpath(path, &paths::OPTION_SOME) && can_suggest(cx, hir_id, sym!(option_type), "is_some") {
@@ -1562,8 +1562,8 @@ mod redundant_pattern_match {
                             &paths::RESULT_ERR,
                             "is_ok()",
                             "is_err()",
-                            || can_suggest(cx, hir_id, sym!(result_type), "is_ok"),
-                            || can_suggest(cx, hir_id, sym!(result_type), "is_err"),
+                            || true,
+                            || true,
                         )
                     } else {
                         None

src/tools/clippy/tests/ui/redundant_pattern_matching.fixed

@@ -77,6 +77,7 @@ fn main() {
 
     issue5504();
     issue5697();
+    issue6067();
 
     let _ = if gen_opt().is_some() {
         1
@@ -131,31 +132,14 @@ fn issue5504() {
 // None of these should be linted because none of the suggested methods
 // are `const fn` without toggling a feature.
 const fn issue5697() {
-    if let Ok(_) = Ok::<i32, i32>(42) {}
-
-    if let Err(_) = Err::<i32, i32>(42) {}
-
     if let Some(_) = Some(42) {}
 
     if let None = None::<()> {}
 
-    while let Ok(_) = Ok::<i32, i32>(10) {}
-
-    while let Err(_) = Ok::<i32, i32>(10) {}
-
     while let Some(_) = Some(42) {}
 
     while let None = None::<()> {}
 
-    match Ok::<i32, i32>(42) {
-        Ok(_) => true,
-        Err(_) => false,
-    };
-
-    match Err::<i32, i32>(42) {
-        Ok(_) => false,
-        Err(_) => true,
-    };
     match Some(42) {
         Some(_) => true,
         None => false,
@@ -166,3 +150,20 @@ const fn issue5697() {
         None => true,
     };
 }
+
+// Methods that are unstable const should not be suggested within a const context, see issue #5697.
+// However, in Rust 1.48.0 the methods `is_ok` and `is_err` of `Result` were stabilized as const,
+// so the following should be linted.
+const fn issue6067() {
+    if Ok::<i32, i32>(42).is_ok() {}
+
+    if Err::<i32, i32>(42).is_err() {}
+
+    while Ok::<i32, i32>(10).is_ok() {}
+
+    while Ok::<i32, i32>(10).is_err() {}
+
+    Ok::<i32, i32>(42).is_ok();
+
+    Err::<i32, i32>(42).is_err();
+}

src/tools/clippy/tests/ui/redundant_pattern_matching.rs

@@ -98,6 +98,7 @@ fn main() {
 
     issue5504();
     issue5697();
+    issue6067();
 
     let _ = if let Some(_) = gen_opt() {
         1
@@ -152,31 +153,14 @@ fn issue5504() {
 // None of these should be linted because none of the suggested methods
 // are `const fn` without toggling a feature.
 const fn issue5697() {
-    if let Ok(_) = Ok::<i32, i32>(42) {}
-
-    if let Err(_) = Err::<i32, i32>(42) {}
-
     if let Some(_) = Some(42) {}
 
     if let None = None::<()> {}
 
-    while let Ok(_) = Ok::<i32, i32>(10) {}
-
-    while let Err(_) = Ok::<i32, i32>(10) {}
-
     while let Some(_) = Some(42) {}
 
     while let None = None::<()> {}
 
-    match Ok::<i32, i32>(42) {
-        Ok(_) => true,
-        Err(_) => false,
-    };
-
-    match Err::<i32, i32>(42) {
-        Ok(_) => false,
-        Err(_) => true,
-    };
     match Some(42) {
         Some(_) => true,
         None => false,
@@ -187,3 +171,26 @@ const fn issue5697() {
         None => true,
     };
 }
+
+// Methods that are unstable const should not be suggested within a const context, see issue #5697.
+// However, in Rust 1.48.0 the methods `is_ok` and `is_err` of `Result` were stabilized as const,
+// so the following should be linted.
+const fn issue6067() {
+    if let Ok(_) = Ok::<i32, i32>(42) {}
+
+    if let Err(_) = Err::<i32, i32>(42) {}
+
+    while let Ok(_) = Ok::<i32, i32>(10) {}
+
+    while let Err(_) = Ok::<i32, i32>(10) {}
+
+    match Ok::<i32, i32>(42) {
+        Ok(_) => true,
+        Err(_) => false,
+    };
+
+    match Err::<i32, i32>(42) {
+        Ok(_) => false,
+        Err(_) => true,
+    };
+}

src/tools/clippy/tests/ui/redundant_pattern_matching.stderr

@@ -149,52 +149,94 @@ LL |     let x = if let Some(_) = opt { true } else { false };
    |             -------^^^^^^^------ help: try this: `if opt.is_some()`
 
 error: redundant pattern matching, consider using `is_some()`
-  --> $DIR/redundant_pattern_matching.rs:102:20
+  --> $DIR/redundant_pattern_matching.rs:103:20
    |
 LL |     let _ = if let Some(_) = gen_opt() {
    |             -------^^^^^^^------------ help: try this: `if gen_opt().is_some()`
 
 error: redundant pattern matching, consider using `is_none()`
-  --> $DIR/redundant_pattern_matching.rs:104:19
+  --> $DIR/redundant_pattern_matching.rs:105:19
    |
 LL |     } else if let None = gen_opt() {
    |            -------^^^^------------ help: try this: `if gen_opt().is_none()`
 
 error: redundant pattern matching, consider using `is_ok()`
-  --> $DIR/redundant_pattern_matching.rs:106:19
+  --> $DIR/redundant_pattern_matching.rs:107:19
    |
 LL |     } else if let Ok(_) = gen_res() {
    |            -------^^^^^------------ help: try this: `if gen_res().is_ok()`
 
 error: redundant pattern matching, consider using `is_err()`
-  --> $DIR/redundant_pattern_matching.rs:108:19
+  --> $DIR/redundant_pattern_matching.rs:109:19
    |
 LL |     } else if let Err(_) = gen_res() {
    |            -------^^^^^^------------ help: try this: `if gen_res().is_err()`
 
 error: redundant pattern matching, consider using `is_some()`
-  --> $DIR/redundant_pattern_matching.rs:141:19
+  --> $DIR/redundant_pattern_matching.rs:142:19
    |
 LL |         while let Some(_) = r#try!(result_opt()) {}
    |         ----------^^^^^^^----------------------- help: try this: `while r#try!(result_opt()).is_some()`
 
 error: redundant pattern matching, consider using `is_some()`
-  --> $DIR/redundant_pattern_matching.rs:142:16
+  --> $DIR/redundant_pattern_matching.rs:143:16
    |
 LL |         if let Some(_) = r#try!(result_opt()) {}
    |         -------^^^^^^^----------------------- help: try this: `if r#try!(result_opt()).is_some()`
 
 error: redundant pattern matching, consider using `is_some()`
-  --> $DIR/redundant_pattern_matching.rs:148:12
+  --> $DIR/redundant_pattern_matching.rs:149:12
    |
 LL |     if let Some(_) = m!() {}
    |     -------^^^^^^^------- help: try this: `if m!().is_some()`
 
 error: redundant pattern matching, consider using `is_some()`
-  --> $DIR/redundant_pattern_matching.rs:149:15
+  --> $DIR/redundant_pattern_matching.rs:150:15
    |
 LL |     while let Some(_) = m!() {}
    |     ----------^^^^^^^------- help: try this: `while m!().is_some()`
 
-error: aborting due to 29 previous errors
+error: redundant pattern matching, consider using `is_ok()`
+  --> $DIR/redundant_pattern_matching.rs:179:12
+   |
+LL |     if let Ok(_) = Ok::<i32, i32>(42) {}
+   |     -------^^^^^--------------------- help: try this: `if Ok::<i32, i32>(42).is_ok()`
+
+error: redundant pattern matching, consider using `is_err()`
+  --> $DIR/redundant_pattern_matching.rs:181:12
+   |
+LL |     if let Err(_) = Err::<i32, i32>(42) {}
+   |     -------^^^^^^---------------------- help: try this: `if Err::<i32, i32>(42).is_err()`
+
+error: redundant pattern matching, consider using `is_ok()`
+  --> $DIR/redundant_pattern_matching.rs:183:15
+   |
+LL |     while let Ok(_) = Ok::<i32, i32>(10) {}
+   |     ----------^^^^^--------------------- help: try this: `while Ok::<i32, i32>(10).is_ok()`
+
+error: redundant pattern matching, consider using `is_err()`
+  --> $DIR/redundant_pattern_matching.rs:185:15
+   |
+LL |     while let Err(_) = Ok::<i32, i32>(10) {}
+   |     ----------^^^^^^--------------------- help: try this: `while Ok::<i32, i32>(10).is_err()`
+
+error: redundant pattern matching, consider using `is_ok()`
+  --> $DIR/redundant_pattern_matching.rs:187:5
+   |
+LL | /     match Ok::<i32, i32>(42) {
+LL | |         Ok(_) => true,
+LL | |         Err(_) => false,
+LL | |     };
+   | |_____^ help: try this: `Ok::<i32, i32>(42).is_ok()`
+
+error: redundant pattern matching, consider using `is_err()`
+  --> $DIR/redundant_pattern_matching.rs:192:5
+   |
+LL | /     match Err::<i32, i32>(42) {
+LL | |         Ok(_) => false,
+LL | |         Err(_) => true,
+LL | |     };
+   | |_____^ help: try this: `Err::<i32, i32>(42).is_err()`
+
+error: aborting due to 35 previous errors
 

src/tools/clippy/tests/ui/redundant_pattern_matching_const_result.fixed

@@ -1,44 +0,0 @@
-// run-rustfix
-
-#![feature(const_result)]
-#![warn(clippy::redundant_pattern_matching)]
-#![allow(clippy::match_like_matches_macro, unused)]
-
-// Test that results are linted with the feature enabled.
-
-const fn issue_5697() {
-    if Ok::<i32, i32>(42).is_ok() {}
-
-    if Err::<i32, i32>(42).is_err() {}
-
-    while Ok::<i32, i32>(10).is_ok() {}
-
-    while Ok::<i32, i32>(10).is_err() {}
-
-    Ok::<i32, i32>(42).is_ok();
-
-    Err::<i32, i32>(42).is_err();
-
-    // These should not be linted until `const_option` is implemented.
-    // See https://github.com/rust-lang/rust/issues/67441
-
-    if let Some(_) = Some(42) {}
-
-    if let None = None::<()> {}
-
-    while let Some(_) = Some(42) {}
-
-    while let None = None::<()> {}
-
-    match Some(42) {
-        Some(_) => true,
-        None => false,
-    };
-
-    match None::<()> {
-        Some(_) => false,
-        None => true,
-    };
-}
-
-fn main() {}

src/tools/clippy/tests/ui/redundant_pattern_matching_const_result.rs

@@ -1,50 +0,0 @@
-// run-rustfix
-
-#![feature(const_result)]
-#![warn(clippy::redundant_pattern_matching)]
-#![allow(clippy::match_like_matches_macro, unused)]
-
-// Test that results are linted with the feature enabled.
-
-const fn issue_5697() {
-    if let Ok(_) = Ok::<i32, i32>(42) {}
-
-    if let Err(_) = Err::<i32, i32>(42) {}
-
-    while let Ok(_) = Ok::<i32, i32>(10) {}
-
-    while let Err(_) = Ok::<i32, i32>(10) {}
-
-    match Ok::<i32, i32>(42) {
-        Ok(_) => true,
-        Err(_) => false,
-    };
-
-    match Err::<i32, i32>(42) {
-        Ok(_) => false,
-        Err(_) => true,
-    };
-
-    // These should not be linted until `const_option` is implemented.
-    // See https://github.com/rust-lang/rust/issues/67441
-
-    if let Some(_) = Some(42) {}
-
-    if let None = None::<()> {}
-
-    while let Some(_) = Some(42) {}
-
-    while let None = None::<()> {}
-
-    match Some(42) {
-        Some(_) => true,
-        None => false,
-    };
-
-    match None::<()> {
-        Some(_) => false,
-        None => true,
-    };
-}
-
-fn main() {}

src/tools/clippy/tests/ui/redundant_pattern_matching_const_result.stderr

@@ -1,46 +0,0 @@
-error: redundant pattern matching, consider using `is_ok()`
-  --> $DIR/redundant_pattern_matching_const_result.rs:10:12
-   |
-LL |     if let Ok(_) = Ok::<i32, i32>(42) {}
-   |     -------^^^^^--------------------- help: try this: `if Ok::<i32, i32>(42).is_ok()`
-   |
-   = note: `-D clippy::redundant-pattern-matching` implied by `-D warnings`
-
-error: redundant pattern matching, consider using `is_err()`
-  --> $DIR/redundant_pattern_matching_const_result.rs:12:12
-   |
-LL |     if let Err(_) = Err::<i32, i32>(42) {}
-   |     -------^^^^^^---------------------- help: try this: `if Err::<i32, i32>(42).is_err()`
-
-error: redundant pattern matching, consider using `is_ok()`
-  --> $DIR/redundant_pattern_matching_const_result.rs:14:15
-   |
-LL |     while let Ok(_) = Ok::<i32, i32>(10) {}
-   |     ----------^^^^^--------------------- help: try this: `while Ok::<i32, i32>(10).is_ok()`
-
-error: redundant pattern matching, consider using `is_err()`
-  --> $DIR/redundant_pattern_matching_const_result.rs:16:15
-   |
-LL |     while let Err(_) = Ok::<i32, i32>(10) {}
-   |     ----------^^^^^^--------------------- help: try this: `while Ok::<i32, i32>(10).is_err()`
-
-error: redundant pattern matching, consider using `is_ok()`
-  --> $DIR/redundant_pattern_matching_const_result.rs:18:5
-   |
-LL | /     match Ok::<i32, i32>(42) {
-LL | |         Ok(_) => true,
-LL | |         Err(_) => false,
-LL | |     };
-   | |_____^ help: try this: `Ok::<i32, i32>(42).is_ok()`
-
-error: redundant pattern matching, consider using `is_err()`
-  --> $DIR/redundant_pattern_matching_const_result.rs:23:5
-   |
-LL | /     match Err::<i32, i32>(42) {
-LL | |         Ok(_) => false,
-LL | |         Err(_) => true,
-LL | |     };
-   | |_____^ help: try this: `Err::<i32, i32>(42).is_err()`
-
-error: aborting due to 6 previous errors
-