From 679dde7338281f958094b409202cc23ce1ba640c Mon Sep 17 00:00:00 2001
From: Deadbeef <ent3rm4n@gmail.com>
Date: Wed, 1 Feb 2023 05:55:48 +0000
Subject: [PATCH] fix parser mistaking const closures for const item

---
 compiler/rustc_parse/src/parser/expr.rs       |  2 +-
 compiler/rustc_parse/src/parser/mod.rs        | 21 ++++++++++++++-----
 tests/ui/parser/recover-quantified-closure.rs |  2 +-
 .../parser/recover-quantified-closure.stderr  |  4 ++--
 .../const-closure-parse-not-item.rs           | 10 +++++++++
 5 files changed, 30 insertions(+), 9 deletions(-)
 create mode 100644 tests/ui/rfc-2632-const-trait-impl/const-closure-parse-not-item.rs

diff --git a/compiler/rustc_parse/src/parser/expr.rs b/compiler/rustc_parse/src/parser/expr.rs
index dcc3059a7f4..701a2a3efcf 100644
--- a/compiler/rustc_parse/src/parser/expr.rs
+++ b/compiler/rustc_parse/src/parser/expr.rs
@@ -2108,7 +2108,7 @@ impl<'a> Parser<'a> {
             ClosureBinder::NotPresent
         };
 
-        let constness = self.parse_constness(Case::Sensitive);
+        let constness = self.parse_closure_constness(Case::Sensitive);
 
         let movability =
             if self.eat_keyword(kw::Static) { Movability::Static } else { Movability::Movable };
diff --git a/compiler/rustc_parse/src/parser/mod.rs b/compiler/rustc_parse/src/parser/mod.rs
index ffb23b50a16..bb06ad20118 100644
--- a/compiler/rustc_parse/src/parser/mod.rs
+++ b/compiler/rustc_parse/src/parser/mod.rs
@@ -739,9 +739,10 @@ impl<'a> Parser<'a> {
     fn check_const_closure(&self) -> bool {
         self.is_keyword_ahead(0, &[kw::Const])
             && self.look_ahead(1, |t| match &t.kind {
-                token::Ident(kw::Move | kw::Static | kw::Async, _)
-                | token::OrOr
-                | token::BinOp(token::Or) => true,
+                // async closures do not work with const closures, so we do not parse that here.
+                token::Ident(kw::Move | kw::Static, _) | token::OrOr | token::BinOp(token::Or) => {
+                    true
+                }
                 _ => false,
             })
     }
@@ -1203,8 +1204,18 @@ impl<'a> Parser<'a> {
 
     /// Parses constness: `const` or nothing.
     fn parse_constness(&mut self, case: Case) -> Const {
-        // Avoid const blocks to be parsed as const items
-        if self.look_ahead(1, |t| t != &token::OpenDelim(Delimiter::Brace))
+        self.parse_constness_(case, false)
+    }
+
+    /// Parses constness for closures
+    fn parse_closure_constness(&mut self, case: Case) -> Const {
+        self.parse_constness_(case, true)
+    }
+
+    fn parse_constness_(&mut self, case: Case, is_closure: bool) -> Const {
+        // Avoid const blocks and const closures to be parsed as const items
+        if (self.check_const_closure() == is_closure)
+            && self.look_ahead(1, |t| t != &token::OpenDelim(Delimiter::Brace))
             && self.eat_keyword_case(kw::Const, case)
         {
             Const::Yes(self.prev_token.uninterpolated_span())
diff --git a/tests/ui/parser/recover-quantified-closure.rs b/tests/ui/parser/recover-quantified-closure.rs
index df22f5e065c..10af39b7007 100644
--- a/tests/ui/parser/recover-quantified-closure.rs
+++ b/tests/ui/parser/recover-quantified-closure.rs
@@ -7,6 +7,6 @@ fn main() {
 enum Foo { Bar }
 fn foo(x: impl Iterator<Item = Foo>) {
     for <Foo>::Bar in x {}
-    //~^ ERROR expected one of `const`, `move`, `static`, `|`
+    //~^ ERROR expected one of `move`, `static`, `|`
     //~^^ ERROR `for<...>` binders for closures are experimental
 }
diff --git a/tests/ui/parser/recover-quantified-closure.stderr b/tests/ui/parser/recover-quantified-closure.stderr
index 9ec4d2c034d..39eec80f658 100644
--- a/tests/ui/parser/recover-quantified-closure.stderr
+++ b/tests/ui/parser/recover-quantified-closure.stderr
@@ -1,8 +1,8 @@
-error: expected one of `const`, `move`, `static`, `|`, or `||`, found `::`
+error: expected one of `move`, `static`, `|`, or `||`, found `::`
   --> $DIR/recover-quantified-closure.rs:9:14
    |
 LL |     for <Foo>::Bar in x {}
-   |              ^^ expected one of `const`, `move`, `static`, `|`, or `||`
+   |              ^^ expected one of `move`, `static`, `|`, or `||`
 
 error[E0658]: `for<...>` binders for closures are experimental
   --> $DIR/recover-quantified-closure.rs:2:5
diff --git a/tests/ui/rfc-2632-const-trait-impl/const-closure-parse-not-item.rs b/tests/ui/rfc-2632-const-trait-impl/const-closure-parse-not-item.rs
new file mode 100644
index 00000000000..2c99d8bf1c6
--- /dev/null
+++ b/tests/ui/rfc-2632-const-trait-impl/const-closure-parse-not-item.rs
@@ -0,0 +1,10 @@
+// check-pass
+
+#![feature(const_trait_impl, const_closures)]
+#![allow(incomplete_features)]
+
+const fn test() -> impl ~const Fn() {
+    const move || {}
+}
+
+fn main() {}