Split inline const to two feature gates

Author: nbdd0121

compiler/rustc_ast_passes/src/feature_gate.rs

@@ -719,6 +719,7 @@ pub fn check_crate(krate: &ast::Crate, sess: &Session) {
     gate_all!(const_trait_impl, "const trait impls are experimental");
     gate_all!(half_open_range_patterns, "half-open range patterns are unstable");
     gate_all!(inline_const, "inline-const is experimental");
+    gate_all!(inline_const_pat, "inline-const in pattern position is experimental");
     gate_all!(
         const_generics_defaults,
         "default values for const generic parameters are experimental"

compiler/rustc_feature/src/active.rs

@@ -410,6 +410,8 @@ declare_features! (
     (incomplete, inherent_associated_types, "1.52.0", Some(8995), None),
     /// Allow anonymous constants from an inline `const` block
     (incomplete, inline_const, "1.49.0", Some(76001), None),
+    /// Allow anonymous constants from an inline `const` block in pattern position
+    (incomplete, inline_const_pat, "1.58.0", Some(76001), None),
     /// Allows using `pointer` and `reference` in intra-doc links
     (active, intra_doc_pointers, "1.51.0", Some(80896), None),
     /// Allows `#[instruction_set(_)]` attribute

compiler/rustc_parse/src/parser/expr.rs

@@ -1243,7 +1243,7 @@ impl<'a> Parser<'a> {
         } else if self.eat_keyword(kw::Unsafe) {
             self.parse_block_expr(None, lo, BlockCheckMode::Unsafe(ast::UserProvided), attrs)
         } else if self.check_inline_const(0) {
-            self.parse_const_block(lo.to(self.token.span))
+            self.parse_const_block(lo.to(self.token.span), false)
         } else if self.is_do_catch_block() {
             self.recover_do_catch(attrs)
         } else if self.is_try_block() {

compiler/rustc_parse/src/parser/mod.rs

@@ -1095,8 +1095,12 @@ impl<'a> Parser<'a> {
     }
 
     /// Parses inline const expressions.
-    fn parse_const_block(&mut self, span: Span) -> PResult<'a, P<Expr>> {
-        self.sess.gated_spans.gate(sym::inline_const, span);
+    fn parse_const_block(&mut self, span: Span, pat: bool) -> PResult<'a, P<Expr>> {
+        if pat {
+            self.sess.gated_spans.gate(sym::inline_const_pat, span);
+        } else {
+            self.sess.gated_spans.gate(sym::inline_const, span);
+        }
         self.eat_keyword(kw::Const);
         let blk = self.parse_block()?;
         let anon_const = AnonConst {

compiler/rustc_parse/src/parser/pat.rs

@@ -437,7 +437,7 @@ impl<'a> Parser<'a> {
             PatKind::Box(pat)
         } else if self.check_inline_const(0) {
             // Parse `const pat`
-            let const_expr = self.parse_const_block(lo.to(self.token.span))?;
+            let const_expr = self.parse_const_block(lo.to(self.token.span), true)?;
 
             if let Some(re) = self.parse_range_end() {
                 self.parse_pat_range_begin_with(const_expr, re)?
@@ -884,7 +884,7 @@ impl<'a> Parser<'a> {
 
     fn parse_pat_range_end(&mut self) -> PResult<'a, P<Expr>> {
         if self.check_inline_const(0) {
-            self.parse_const_block(self.token.span)
+            self.parse_const_block(self.token.span, true)
         } else if self.check_path() {
             let lo = self.token.span;
             let (qself, path) = if self.eat_lt() {

compiler/rustc_span/src/symbol.rs

@@ -731,6 +731,7 @@ symbols! {
         inlateout,
         inline,
         inline_const,
+        inline_const_pat,
         inout,
         instruction_set,
         intel,

src/doc/unstable-book/src/language-features/inline-const-pat.md

@@ -0,0 +1,24 @@
+# `inline_const_pat`
+
+The tracking issue for this feature is: [#76001]
+
+See also [`inline_const`](inline-const.md)
+
+------
+
+This feature allows you to use inline constant expressions in pattern position:
+
+```rust
+#![feature(inline_const_pat)]
+
+const fn one() -> i32 { 1 }
+
+let some_int = 3;
+match some_int {
+    const { 1 + 2 } => println!("Matched 1 + 2"),
+    const { one() } => println!("Matched const fn returning 1"),
+    _ => println!("Didn't match anything :("),
+}
+```
+
+[#76001]: https://github.com/rust-lang/rust/issues/76001

src/doc/unstable-book/src/language-features/inline-const.md

@@ -2,6 +2,8 @@
 
 The tracking issue for this feature is: [#76001]
 
+See also [`inline_const_pat`](inline-const-pat.md)
+
 ------
 
 This feature allows you to use inline constant expressions. For example, you can
@@ -27,19 +29,4 @@ fn main() {
 }
 ```
 
-You can also use inline constant expressions in patterns:
-
-```rust
-#![feature(inline_const)]
-
-const fn one() -> i32 { 1 }
-
-let some_int = 3;
-match some_int {
-    const { 1 + 2 } => println!("Matched 1 + 2"),
-    const { one() } => println!("Matched const fn returning 1"),
-    _ => println!("Didn't match anything :("),
-}
-```
-
 [#76001]: https://github.com/rust-lang/rust/issues/76001

src/test/ui/feature-gates/feature-gate-inline_const_pat.rs

@@ -0,0 +1,4 @@
+fn main() {
+    let const { () } = ();
+    //~^ ERROR inline-const in pattern position is experimental [E0658]
+}

src/test/ui/feature-gates/feature-gate-inline_const_pat.stderr

@@ -0,0 +1,12 @@
+error[E0658]: inline-const in pattern position is experimental
+  --> $DIR/feature-gate-inline_const_pat.rs:2:9
+   |
+LL |     let const { () } = ();
+   |         ^^^^^
+   |
+   = note: see issue #76001 <https://github.com/rust-lang/rust/issues/76001> for more information
+   = help: add `#![feature(inline_const_pat)]` to the crate attributes to enable
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0658`.