Rollup merge of rust-lang#47947 - goodmanjonathan:stabilize_match_beginning_vert, r=petrochenkov

Stabilize feature(match_beginning_vert)

With this feature stabilized, match expressions can optionally have a `|` at the beginning of each arm.

Reference PR: rust-lang/reference#231

Closes rust-lang#44101

Author: kennytm

src/doc/unstable-book/src/language-features/match-beginning-vert.md

@@ -883,7 +883,6 @@ pub struct Arm {
     pub pats: Vec<P<Pat>>,
     pub guard: Option<P<Expr>>,
     pub body: P<Expr>,
-    pub beginning_vert: Option<Span>, // For RFC 1925 feature gate
 }
 
 #[derive(Clone, PartialEq, Eq, RustcEncodable, RustcDecodable, Hash, Debug)]

src/libsyntax/ast.rs

@@ -883,7 +883,6 @@ impl<'a> AstBuilder for ExtCtxt<'a> {
             pats,
             guard: None,
             body: expr,
-            beginning_vert: None,
         }
     }
 

src/libsyntax/ext/build.rs

@@ -386,9 +386,6 @@ declare_features! (
     // allow `#[must_use]` on functions and comparison operators (RFC 1940)
     (active, fn_must_use, "1.21.0", Some(43302)),
 
-    // allow '|' at beginning of match arms (RFC 1925)
-    (active, match_beginning_vert, "1.21.0", Some(44101)),
-
     // Future-proofing enums/structs with #[non_exhaustive] attribute (RFC 2008)
     (active, non_exhaustive, "1.22.0", Some(44109)),
 
@@ -545,6 +542,8 @@ declare_features! (
     (accepted, abi_sysv64, "1.24.0", Some(36167)),
     // Allows `repr(align(16))` struct attribute (RFC 1358)
     (accepted, repr_align, "1.24.0", Some(33626)),
+    // allow '|' at beginning of match arms (RFC 1925)
+    (accepted, match_beginning_vert, "1.25.0", Some(44101)),
 );
 
 // If you change this, please modify src/doc/unstable-book as well. You must
@@ -1683,11 +1682,6 @@ impl<'a> Visitor<'a> for PostExpansionVisitor<'a> {
     }
 
     fn visit_arm(&mut self, arm: &'a ast::Arm) {
-        if let Some(span) = arm.beginning_vert {
-            gate_feature_post!(&self, match_beginning_vert,
-                               span,
-                               "Use of a '|' at the beginning of a match arm is experimental")
-        }
         visit::walk_arm(self, arm)
     }
 

src/libsyntax/feature_gate.rs

@@ -340,14 +340,13 @@ pub fn fold_thin_attrs<T: Folder>(attrs: ThinVec<Attribute>, fld: &mut T) -> Thi
     fold_attrs(attrs.into(), fld).into()
 }
 
-pub fn noop_fold_arm<T: Folder>(Arm {attrs, pats, guard, body, beginning_vert}: Arm,
+pub fn noop_fold_arm<T: Folder>(Arm {attrs, pats, guard, body}: Arm,
     fld: &mut T) -> Arm {
     Arm {
         attrs: fold_attrs(attrs, fld),
         pats: pats.move_map(|x| fld.fold_pat(x)),
         guard: guard.map(|x| fld.fold_expr(x)),
         body: fld.fold_expr(body),
-        beginning_vert,
     }
 }
 

src/libsyntax/fold.rs

@@ -3398,11 +3398,7 @@ impl<'a> Parser<'a> {
 
         let attrs = self.parse_outer_attributes()?;
         // Allow a '|' before the pats (RFC 1925)
-        let beginning_vert = if self.eat(&token::BinOp(token::Or)) {
-            Some(self.prev_span)
-        } else {
-            None
-        };
+        self.eat(&token::BinOp(token::Or));
         let pats = self.parse_pats()?;
         let guard = if self.eat_keyword(keywords::If) {
             Some(self.parse_expr()?)
@@ -3426,7 +3422,6 @@ impl<'a> Parser<'a> {
             pats,
             guard,
             body: expr,
-            beginning_vert,
         })
     }
 

src/libsyntax/parse/parser.rs

@@ -0,0 +1,28 @@
+// Copyright 2018 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+enum Foo {
+    A,
+    B,
+    C,
+    D,
+    E,
+}
+use Foo::*;
+
+fn main() {
+    for foo in &[A, B, C, D, E] {
+        match *foo {
+            | A => println!("A"),
+            | B | C if 1 < 2 => println!("BC!"),
+            | _ => {},
+        }
+    }
+}