Change how parse_expr_force_collect works.

It now parses outer attributes before collecting tokens. This avoids the
problem where the outer attribute tokens were being stored twice -- for
the attribute tokesn, and also for the expression tokens.

Fixes #86055.

Author: nnethercote

compiler/rustc_parse/src/parser/expr.rs

@@ -98,9 +98,12 @@ impl<'a> Parser<'a> {
         self.parse_expr_res(Restrictions::empty(), attrs)
     }
 
-    /// Parses an expression, forcing tokens to be collected
+    /// Parses an expression, forcing tokens to be collected.
     pub fn parse_expr_force_collect(&mut self) -> PResult<'a, P<Expr>> {
-        self.collect_tokens_no_attrs(|this| this.parse_expr())
+        self.current_closure.take();
+
+        let attrs = self.parse_outer_attributes()?;
+        self.collect_tokens_no_attrs(|this| this.parse_expr_res(Restrictions::empty(), attrs))
     }
 
     pub fn parse_expr_anon_const(&mut self) -> PResult<'a, AnonConst> {

tests/ui/proc-macro/expr-stmt-nonterminal-tokens.stdout

@@ -1,4 +1,4 @@
-PRINT-DERIVE INPUT (DISPLAY): enum E { V = { let _ = #[allow(warnings)] #[allow(warnings)] 0; 0 }, }
+PRINT-DERIVE INPUT (DISPLAY): enum E { V = { let _ = #[allow(warnings)] 0; 0 }, }
 PRINT-DERIVE INPUT (DEBUG): TokenStream [
     Ident {
         ident: "enum",
@@ -39,31 +39,6 @@ PRINT-DERIVE INPUT (DEBUG): TokenStream [
                     Group {
                         delimiter: None,
                         stream: TokenStream [
-                            Punct {
-                                ch: '#',
-                                spacing: Alone,
-                                span: #0 bytes(543..544),
-                            },
-                            Group {
-                                delimiter: Bracket,
-                                stream: TokenStream [
-                                    Ident {
-                                        ident: "allow",
-                                        span: #0 bytes(545..550),
-                                    },
-                                    Group {
-                                        delimiter: Parenthesis,
-                                        stream: TokenStream [
-                                            Ident {
-                                                ident: "warnings",
-                                                span: #0 bytes(551..559),
-                                            },
-                                        ],
-                                        span: #0 bytes(550..560),
-                                    },
-                                ],
-                                span: #0 bytes(544..561),
-                            },
                             Punct {
                                 ch: '#',
                                 spacing: Alone,