Rollup merge of #34355 - jseyfried:paren_expression_ids_nonunique, r=nrc

Give `ast::ExprKind::Paren` no-op expressions the same ids as their children.

Having `ast::ExprKind::Paren` expressions share ids with their children
 - reduces the number of unused `NodeId`s in the hir map and
 - guarantees that `tcx.map.expect_expr(ast_expr.id)` is the hir corresponding to `ast_expr`.

This fixes the bug from #34327, which was introduced in #33296 when I assumed the above guarantee.

r? @nrc

Author: Manishearth

src/libsyntax/fold.rs

@@ -1102,7 +1102,6 @@ pub fn noop_fold_pat<T: Folder>(p: P<Pat>, folder: &mut T) -> P<Pat> {
 
 pub fn noop_fold_expr<T: Folder>(Expr {id, node, span, attrs}: Expr, folder: &mut T) -> Expr {
     Expr {
-        id: folder.new_id(id),
         node: match node {
             ExprKind::Box(e) => {
                 ExprKind::Box(folder.fold_expr(e))
@@ -1270,9 +1269,19 @@ pub fn noop_fold_expr<T: Folder>(Expr {id, node, span, attrs}: Expr, folder: &mu
                         fields.move_map(|x| folder.fold_field(x)),
                         maybe_expr.map(|x| folder.fold_expr(x)))
             },
-            ExprKind::Paren(ex) => ExprKind::Paren(folder.fold_expr(ex)),
+            ExprKind::Paren(ex) => {
+                let sub_expr = folder.fold_expr(ex);
+                return Expr {
+                    // Nodes that are equal modulo `Paren` sugar no-ops should have the same ids.
+                    id: sub_expr.id,
+                    node: ExprKind::Paren(sub_expr),
+                    span: folder.new_span(span),
+                    attrs: fold_attrs(attrs.into(), folder).into(),
+                };
+            }
             ExprKind::Try(ex) => ExprKind::Try(folder.fold_expr(ex)),
         },
+        id: folder.new_id(id),
         span: folder.new_span(span),
         attrs: fold_attrs(attrs.into(), folder).into(),
     }

src/libsyntax/parse/parser.rs

@@ -553,10 +553,6 @@ impl<'a> Parser<'a> {
         self.expect_one_of(edible, inedible)
     }
 
-    pub fn commit_stmt_expecting(&mut self, edible: token::Token) -> PResult<'a, ()> {
-        self.commit_stmt(&[edible], &[])
-    }
-
     /// returns the span of expr, if it was not interpolated or the span of the interpolated token
     fn interpolated_or_expr_span(&self,
                                  expr: PResult<'a, P<Expr>>)
@@ -4122,7 +4118,7 @@ impl<'a> Parser<'a> {
                 _ => { // all other kinds of statements:
                     let mut hi = span.hi;
                     if classify::stmt_ends_with_semi(&node) {
-                        self.commit_stmt_expecting(token::Semi)?;
+                        self.commit_stmt(&[token::Semi], &[])?;
                         hi = self.last_span.hi;
                     }