Rollup merge of #76135 - CDirkx:const-option, r=dtolnay,oli-obk

Stabilize some Option methods as const

Stabilize the following methods of `Option` as const:
 - `is_some`
 - `is_none`
 - `as_ref`

These methods are currently const under the unstable feature `const_option` (tracking issue: #67441).
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](#75463).

Related: #76225

Author: RalfJung

library/core/src/option.rs

@@ -175,7 +175,7 @@ impl<T> Option<T> {
     /// ```
     #[must_use = "if you intended to assert that this has a value, consider `.unwrap()` instead"]
     #[inline]
-    #[rustc_const_unstable(feature = "const_option", issue = "67441")]
+    #[rustc_const_stable(feature = "const_option", since = "1.48.0")]
     #[stable(feature = "rust1", since = "1.0.0")]
     pub const fn is_some(&self) -> bool {
         matches!(*self, Some(_))
@@ -195,7 +195,7 @@ impl<T> Option<T> {
     #[must_use = "if you intended to assert that this doesn't have a value, consider \
                   `.and_then(|| panic!(\"`Option` had a value when expected `None`\"))` instead"]
     #[inline]
-    #[rustc_const_unstable(feature = "const_option", issue = "67441")]
+    #[rustc_const_stable(feature = "const_option", since = "1.48.0")]
     #[stable(feature = "rust1", since = "1.0.0")]
     pub const fn is_none(&self) -> bool {
         !self.is_some()
@@ -254,7 +254,7 @@ impl<T> Option<T> {
     /// println!("still can print text: {:?}", text);
     /// ```
     #[inline]
-    #[rustc_const_unstable(feature = "const_option", issue = "67441")]
+    #[rustc_const_stable(feature = "const_option", since = "1.48.0")]
     #[stable(feature = "rust1", since = "1.0.0")]
     pub const fn as_ref(&self) -> Option<&T> {
         match *self {

library/core/tests/option.rs

@@ -356,3 +356,19 @@ fn test_replace() {
     assert_eq!(x, Some(3));
     assert_eq!(old, None);
 }
+
+#[test]
+fn option_const() {
+    // test that the methods of `Option` are usable in a const context
+
+    const OPTION: Option<usize> = Some(32);
+
+    const REF: Option<&usize> = OPTION.as_ref();
+    assert_eq!(REF, Some(&32));
+
+    const IS_SOME: bool = OPTION.is_some();
+    assert!(IS_SOME);
+
+    const IS_NONE: bool = OPTION.is_none();
+    assert!(!IS_NONE);
+}

src/test/ui/consts/const-option.rs

@@ -1440,15 +1440,12 @@ where
 
 mod redundant_pattern_match {
     use super::REDUNDANT_PATTERN_MATCHING;
-    use crate::utils::{in_constant, match_qpath, match_trait_method, paths, snippet, span_lint_and_then};
+    use crate::utils::{match_qpath, match_trait_method, paths, snippet, span_lint_and_then};
     use if_chain::if_chain;
     use rustc_ast::ast::LitKind;
     use rustc_errors::Applicability;
-    use rustc_hir::{Arm, Expr, ExprKind, HirId, MatchSource, PatKind, QPath};
+    use rustc_hir::{Arm, Expr, ExprKind, MatchSource, PatKind, QPath};
     use rustc_lint::LateContext;
-    use rustc_middle::ty;
-    use rustc_mir::const_eval::is_const_fn;
-    use rustc_span::source_map::Symbol;
 
     pub fn check<'tcx>(cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
         if let ExprKind::Match(op, arms, ref match_source) = &expr.kind {
@@ -1468,37 +1465,24 @@ mod redundant_pattern_match {
         arms: &[Arm<'_>],
         keyword: &'static str,
     ) {
-        fn find_suggestion(cx: &LateContext<'_>, hir_id: HirId, path: &QPath<'_>) -> Option<&'static str> {
-            if match_qpath(path, &paths::RESULT_OK) {
-                return Some("is_ok()");
-            }
-            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") {
-                return Some("is_some()");
-            }
-            if match_qpath(path, &paths::OPTION_NONE) && can_suggest(cx, hir_id, sym!(option_type), "is_none") {
-                return Some("is_none()");
-            }
-            None
-        }
-
-        let hir_id = expr.hir_id;
         let good_method = match arms[0].pat.kind {
             PatKind::TupleStruct(ref path, ref patterns, _) if patterns.len() == 1 => {
                 if let PatKind::Wild = patterns[0].kind {
-                    find_suggestion(cx, hir_id, path)
+                    if match_qpath(path, &paths::RESULT_OK) {
+                        "is_ok()"
+                    } else if match_qpath(path, &paths::RESULT_ERR) {
+                        "is_err()"
+                    } else if match_qpath(path, &paths::OPTION_SOME) {
+                        "is_some()"
+                    } else {
+                        return;
+                    }
                 } else {
-                    None
+                    return;
                 }
             },
-            PatKind::Path(ref path) => find_suggestion(cx, hir_id, path),
-            _ => None,
-        };
-        let good_method = match good_method {
-            Some(method) => method,
-            None => return,
+            PatKind::Path(ref path) if match_qpath(path, &paths::OPTION_NONE) => "is_none()",
+            _ => return,
         };
 
         // check that `while_let_on_iterator` lint does not trigger
@@ -1547,7 +1531,6 @@ mod redundant_pattern_match {
         if arms.len() == 2 {
             let node_pair = (&arms[0].pat.kind, &arms[1].pat.kind);
 
-            let hir_id = expr.hir_id;
             let found_good_method = match node_pair {
                 (
                     PatKind::TupleStruct(ref path_left, ref patterns_left, _),
@@ -1562,8 +1545,6 @@ mod redundant_pattern_match {
                             &paths::RESULT_ERR,
                             "is_ok()",
                             "is_err()",
-                            || true,
-                            || true,
                         )
                     } else {
                         None
@@ -1582,8 +1563,6 @@ mod redundant_pattern_match {
                             &paths::OPTION_NONE,
                             "is_some()",
                             "is_none()",
-                            || can_suggest(cx, hir_id, sym!(option_type), "is_some"),
-                            || can_suggest(cx, hir_id, sym!(option_type), "is_none"),
                         )
                     } else {
                         None
@@ -1616,7 +1595,6 @@ mod redundant_pattern_match {
         }
     }
 
-    #[allow(clippy::too_many_arguments)]
     fn find_good_method_for_match<'a>(
         arms: &[Arm<'_>],
         path_left: &QPath<'_>,
@@ -1625,8 +1603,6 @@ mod redundant_pattern_match {
         expected_right: &[&str],
         should_be_left: &'a str,
         should_be_right: &'a str,
-        can_suggest_left: impl Fn() -> bool,
-        can_suggest_right: impl Fn() -> bool,
     ) -> Option<&'a str> {
         let body_node_pair = if match_qpath(path_left, expected_left) && match_qpath(path_right, expected_right) {
             (&(*arms[0].body).kind, &(*arms[1].body).kind)
@@ -1638,35 +1614,13 @@ mod redundant_pattern_match {
 
         match body_node_pair {
             (ExprKind::Lit(ref lit_left), ExprKind::Lit(ref lit_right)) => match (&lit_left.node, &lit_right.node) {
-                (LitKind::Bool(true), LitKind::Bool(false)) if can_suggest_left() => Some(should_be_left),
-                (LitKind::Bool(false), LitKind::Bool(true)) if can_suggest_right() => Some(should_be_right),
+                (LitKind::Bool(true), LitKind::Bool(false)) => Some(should_be_left),
+                (LitKind::Bool(false), LitKind::Bool(true)) => Some(should_be_right),
                 _ => None,
             },
             _ => None,
         }
     }
-
-    fn can_suggest(cx: &LateContext<'_>, hir_id: HirId, diag_item: Symbol, name: &str) -> bool {
-        if !in_constant(cx, hir_id) {
-            return true;
-        }
-
-        // Avoid suggesting calls to non-`const fn`s in const contexts, see #5697.
-        cx.tcx
-            .get_diagnostic_item(diag_item)
-            .and_then(|def_id| {
-                cx.tcx.inherent_impls(def_id).iter().find_map(|imp| {
-                    cx.tcx
-                        .associated_items(*imp)
-                        .in_definition_order()
-                        .find_map(|item| match item.kind {
-                            ty::AssocKind::Fn if item.ident.name.as_str() == name => Some(item.def_id),
-                            _ => None,
-                        })
-                })
-            })
-            .map_or(false, |def_id| is_const_fn(cx.tcx, def_id))
-    }
 }
 
 #[test]

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

@@ -76,7 +76,6 @@ fn main() {
     takes_bool(x);
 
     issue5504();
-    issue5697();
     issue6067();
 
     let _ = if gen_opt().is_some() {
@@ -129,41 +128,31 @@ fn issue5504() {
     while m!().is_some() {}
 }
 
-// None of these should be linted because none of the suggested methods
-// are `const fn` without toggling a feature.
-const fn issue5697() {
-    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,
-    };
-}
-
 // 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.
+// However, in Rust 1.48.0 the methods `is_ok` and `is_err` of `Result`, and `is_some` and `is_none`
+// of `Option` 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() {}
 
+    if Some(42).is_some() {}
+
+    if None::<()>.is_none() {}
+
     while Ok::<i32, i32>(10).is_ok() {}
 
     while Ok::<i32, i32>(10).is_err() {}
 
+    while Some(42).is_some() {}
+
+    while None::<()>.is_none() {}
+
     Ok::<i32, i32>(42).is_ok();
 
     Err::<i32, i32>(42).is_err();
+
+    Some(42).is_some();
+
+    None::<()>.is_none();
 }

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

@@ -97,7 +97,6 @@ fn main() {
     takes_bool(x);
 
     issue5504();
-    issue5697();
     issue6067();
 
     let _ = if let Some(_) = gen_opt() {
@@ -150,40 +149,26 @@ fn issue5504() {
     while let Some(_) = m!() {}
 }
 
-// None of these should be linted because none of the suggested methods
-// are `const fn` without toggling a feature.
-const fn issue5697() {
-    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,
-    };
-}
-
 // 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.
+// However, in Rust 1.48.0 the methods `is_ok` and `is_err` of `Result`, and `is_some` and `is_none`
+// of `Option` 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) {}
 
+    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,
@@ -193,4 +178,14 @@ const fn issue6067() {
         Ok(_) => false,
         Err(_) => true,
     };
+
+    match Some(42) {
+        Some(_) => true,
+        None => false,
+    };
+
+    match None::<()> {
+        Some(_) => false,
+        None => true,
+    };
 }