Rollup merge of rust-lang#60174 - matthewjasper:add-match-arm-scopes, r=pnkfelix

Add match arm scopes and other scope fixes

* Add drop and lint scopes for match arms.
* Lint attributes are now respected on match arms.
* Make sure we emit a StorageDead if we diverge when initializing a temporary.
* Adjust MIR pretty printing of scopes for locals.
* Don't generate duplicate lint scopes for `let statements`.
* Add some previously missing fake borrows for matches.

closes rust-lang#46525

cc @rust-lang/compiler

Author: Centril

src/librustc/cfg/construct.rs

@@ -419,7 +419,7 @@ impl<'a, 'tcx> CFGBuilder<'a, 'tcx> {
         for arm in arms {
             // Add an exit node for when we've visited all the
             // patterns and the guard (if there is one) in the arm.
-            let arm_exit = self.add_dummy_node(&[]);
+            let bindings_exit = self.add_dummy_node(&[]);
 
             for pat in &arm.pats {
                 // Visit the pattern, coming from the discriminant exit
@@ -453,14 +453,16 @@ impl<'a, 'tcx> CFGBuilder<'a, 'tcx> {
 
                 // Add an edge from the exit of this pattern to the
                 // exit of the arm
-                self.add_contained_edge(pat_exit, arm_exit);
+                self.add_contained_edge(pat_exit, bindings_exit);
             }
 
             // Visit the body of this arm
-            let body_exit = self.expr(&arm.body, arm_exit);
+            let body_exit = self.expr(&arm.body, bindings_exit);
+
+            let arm_exit = self.add_ast_node(arm.hir_id.local_id, &[body_exit]);
 
             // Link the body to the exit of the expression
-            self.add_contained_edge(body_exit, expr_exit);
+            self.add_contained_edge(arm_exit, expr_exit);
         }
 
         expr_exit

src/librustc/hir/intravisit.rs

@@ -1102,6 +1102,7 @@ pub fn walk_expr<'v, V: Visitor<'v>>(visitor: &mut V, expression: &'v Expr) {
 }
 
 pub fn walk_arm<'v, V: Visitor<'v>>(visitor: &mut V, arm: &'v Arm) {
+    visitor.visit_id(arm.hir_id);
     walk_list!(visitor, visit_pat, &arm.pats);
     if let Some(ref g) = arm.guard {
         match g {