Rollup merge of #133784 - dtolnay:visitspans, r=compiler-errors

Fix MutVisitor's default implementations to visit Stmt's and BinOp's spans

The `Stmt` case is a bug introduced almost certainly unintentionally by https://github.com/rust-lang/rust/pull/126993. The code _used_ to visit and mutate `span` correctly, but got changed as follows by that PR. Notice how `span` is **copied** into the output by `|kind| Stmt { id, kind, span }` which happens after the mutation in the correct code (red) and before the mutation in the incorrect code (green).

```diff
  pub fn noop_flat_map_stmt<T: MutVisitor>(
      Stmt { kind, mut span, mut id }: Stmt,
      vis: &mut T,
  ) -> SmallVec<[Stmt; 1]> {
      vis.visit_id(&mut id);
-     vis.visit_span(&mut span);
      let stmts: SmallVec<_> = noop_flat_map_stmt_kind(kind, vis)
          .into_iter()
          .map(|kind| Stmt { id, kind, span })
          .collect();
      if stmts.len() > 1 {
          panic!(...);
      }
+     vis.visit_span(&mut span);
      stmts
  }
```

2 files changed, 10 insertions, 22 deletions

diff --git a/compiler/rustc_ast/src/mut_visit.rs b/compiler/rustc_ast/src/mut_visit.rs
index 196fcc1af30..622c260868e 100644
--- a/compiler/rustc_ast/src/mut_visit.rs
+++ b/compiler/rustc_ast/src/mut_visit.rs
@@ -1625,9 +1625,10 @@ pub fn walk_expr<T: MutVisitor>(vis: &mut T, Expr { kind, id, span, attrs, token
             visit_thin_exprs(vis, call_args);
             vis.visit_span(span);
         }
-        ExprKind::Binary(_binop, lhs, rhs) => {
+        ExprKind::Binary(binop, lhs, rhs) => {
             vis.visit_expr(lhs);
             vis.visit_expr(rhs);
+            vis.visit_span(&mut binop.span);
         }
         ExprKind::Unary(_unop, ohs) => vis.visit_expr(ohs),
         ExprKind::Cast(expr, ty) => {
@@ -1785,20 +1786,21 @@ pub fn noop_filter_map_expr<T: MutVisitor>(vis: &mut T, mut e: P<Expr>) -> Optio
 
 pub fn walk_flat_map_stmt<T: MutVisitor>(
     vis: &mut T,
-    Stmt { kind, mut span, mut id }: Stmt,
+    Stmt { kind, span, mut id }: Stmt,
 ) -> SmallVec<[Stmt; 1]> {
     vis.visit_id(&mut id);
-    let stmts: SmallVec<_> = walk_flat_map_stmt_kind(vis, kind)
+    let mut stmts: SmallVec<[Stmt; 1]> = walk_flat_map_stmt_kind(vis, kind)
         .into_iter()
         .map(|kind| Stmt { id, kind, span })
         .collect();
-    if stmts.len() > 1 {
-        panic!(
+    match stmts.len() {
+        0 => {}
+        1 => vis.visit_span(&mut stmts[0].span),
+        2.. => panic!(
             "cloning statement `NodeId`s is prohibited by default, \
              the visitor should implement custom statement visiting"
-        );
+        ),
     }
-    vis.visit_span(&mut span);
     stmts
 }
 
diff --git a/tests/ui-fulldeps/pprust-parenthesis-insertion.rs b/tests/ui-fulldeps/pprust-parenthesis-insertion.rs
index fd6644d73c1..b83e576076d 100644
--- a/tests/ui-fulldeps/pprust-parenthesis-insertion.rs
+++ b/tests/ui-fulldeps/pprust-parenthesis-insertion.rs
@@ -36,12 +36,11 @@ extern crate rustc_errors;
 extern crate rustc_parse;
 extern crate rustc_session;
 extern crate rustc_span;
-extern crate smallvec;
 
 use std::mem;
 use std::process::ExitCode;
 
-use rustc_ast::ast::{DUMMY_NODE_ID, Expr, ExprKind, Stmt};
+use rustc_ast::ast::{DUMMY_NODE_ID, Expr, ExprKind};
 use rustc_ast::mut_visit::{self, DummyAstNode as _, MutVisitor};
 use rustc_ast::node_id::NodeId;
 use rustc_ast::ptr::P;
@@ -50,7 +49,6 @@ use rustc_errors::Diag;
 use rustc_parse::parser::Recovery;
 use rustc_session::parse::ParseSess;
 use rustc_span::{DUMMY_SP, FileName, Span};
-use smallvec::SmallVec;
 
 // Every parenthesis in the following expressions is re-inserted by the
 // pretty-printer.
@@ -164,18 +162,6 @@ impl MutVisitor for Normalize {
     fn visit_span(&mut self, span: &mut Span) {
         *span = DUMMY_SP;
     }
-
-    fn visit_expr(&mut self, expr: &mut P<Expr>) {
-        if let ExprKind::Binary(binop, _left, _right) = &mut expr.kind {
-            self.visit_span(&mut binop.span);
-        }
-        mut_visit::walk_expr(self, expr);
-    }
-
-    fn flat_map_stmt(&mut self, mut stmt: Stmt) -> SmallVec<[Stmt; 1]> {
-        self.visit_span(&mut stmt.span);
-        mut_visit::walk_flat_map_stmt(self, stmt)
-    }
 }
 
 fn parse_expr(psess: &ParseSess, source_code: &str) -> Option<P<Expr>> {