Auto merge of rust-lang#62233 - matthewjasper:exit-arm-scopes, r=pnkfelix

Exit arm scopes

Due to a bug in the HIR CFG construction, borrows for arm scopes were incorrectly leaking into other arms.
This PR also includes some drive-by improvements to `-Zunpretty=hir,identified` that would have been helpful while investigating this.

Closes rust-lang#62107

Author: bors

src/librustc/cfg/construct.rs

@@ -371,7 +371,8 @@ impl<'a, 'tcx> CFGBuilder<'a, 'tcx> {
         let expr_exit = self.add_ast_node(id, &[]);
 
         // Keep track of the previous guard expressions
-        let mut prev_guards = Vec::new();
+        let mut prev_guard = None;
+        let match_scope = region::Scope { id, data: region::ScopeData::Node };
 
         for arm in arms {
             // Add an exit node for when we've visited all the
@@ -389,23 +390,23 @@ impl<'a, 'tcx> CFGBuilder<'a, 'tcx> {
                     let guard_start = self.add_dummy_node(&[pat_exit]);
                     // Visit the guard expression
                     let guard_exit = match guard {
-                        hir::Guard::If(ref e) => self.expr(e, guard_start),
+                        hir::Guard::If(ref e) => (&**e, self.expr(e, guard_start)),
                     };
                     // #47295: We used to have very special case code
                     // here for when a pair of arms are both formed
                     // solely from constants, and if so, not add these
                     // edges.  But this was not actually sound without
                     // other constraints that we stopped enforcing at
                     // some point.
-                    while let Some(prev) = prev_guards.pop() {
-                        self.add_contained_edge(prev, guard_start);
+                    if let Some((prev_guard, prev_index)) = prev_guard.take() {
+                        self.add_exiting_edge(prev_guard, prev_index, match_scope, guard_start);
                     }
 
                     // Push the guard onto the list of previous guards
-                    prev_guards.push(guard_exit);
+                    prev_guard = Some(guard_exit);
 
                     // Update the exit node for the pattern
-                    pat_exit = guard_exit;
+                    pat_exit = guard_exit.1;
                 }
 
                 // Add an edge from the exit of this pattern to the

src/librustc/hir/print.rs

@@ -27,6 +27,7 @@ pub enum AnnNode<'a> {
     SubItem(hir::HirId),
     Expr(&'a hir::Expr),
     Pat(&'a hir::Pat),
+    Arm(&'a hir::Arm),
 }
 
 pub enum Nested {
@@ -1821,6 +1822,7 @@ impl<'a> State<'a> {
             self.s.space();
         }
         self.cbox(indent_unit);
+        self.ann.pre(self, AnnNode::Arm(arm));
         self.ibox(0);
         self.print_outer_attributes(&arm.attrs);
         let mut first = true;
@@ -1865,6 +1867,7 @@ impl<'a> State<'a> {
                 self.s.word(",");
             }
         }
+        self.ann.post(self, AnnNode::Arm(arm));
         self.end() // close enclosing cbox
     }
 

src/librustc_borrowck/dataflow.rs

@@ -109,7 +109,8 @@ impl<'tcx, O: DataFlowOperator> pprust::PpAnn for DataFlowContext<'tcx, O> {
             pprust::AnnNode::Block(blk) => blk.hir_id.local_id,
             pprust::AnnNode::Item(_) |
             pprust::AnnNode::SubItem(_) => return,
-            pprust::AnnNode::Pat(pat) => pat.hir_id.local_id
+            pprust::AnnNode::Pat(pat) => pat.hir_id.local_id,
+            pprust::AnnNode::Arm(arm) => arm.hir_id.local_id,
         };
 
         if !self.has_bitset_for_local_id(id) {

src/librustc_driver/pretty.rs

@@ -387,28 +387,28 @@ impl<'hir> pprust_hir::PpAnn for IdentifiedAnnotation<'hir> {
             pprust_hir::AnnNode::Name(_) => {},
             pprust_hir::AnnNode::Item(item) => {
                 s.s.space();
-                s.synth_comment(format!("hir_id: {} hir local_id: {}",
-                                        item.hir_id, item.hir_id.local_id.as_u32()))
+                s.synth_comment(format!("hir_id: {}", item.hir_id));
             }
             pprust_hir::AnnNode::SubItem(id) => {
                 s.s.space();
-                s.synth_comment(id.to_string())
+                s.synth_comment(id.to_string());
             }
             pprust_hir::AnnNode::Block(blk) => {
                 s.s.space();
-                s.synth_comment(format!("block hir_id: {} hir local_id: {}",
-                                        blk.hir_id, blk.hir_id.local_id.as_u32()))
+                s.synth_comment(format!("block hir_id: {}", blk.hir_id));
             }
             pprust_hir::AnnNode::Expr(expr) => {
                 s.s.space();
-                s.synth_comment(format!("expr hir_id: {} hir local_id: {}",
-                                        expr.hir_id, expr.hir_id.local_id.as_u32()));
-                s.pclose()
+                s.synth_comment(format!("expr hir_id: {}", expr.hir_id));
+                s.pclose();
             }
             pprust_hir::AnnNode::Pat(pat) => {
                 s.s.space();
-                s.synth_comment(format!("pat hir_id: {} hir local_id: {}",
-                                        pat.hir_id, pat.hir_id.local_id.as_u32()))
+                s.synth_comment(format!("pat hir_id: {}", pat.hir_id));
+            }
+            pprust_hir::AnnNode::Arm(arm) => {
+                s.s.space();
+                s.synth_comment(format!("arm hir_id: {}", arm.hir_id));
             }
         }
     }

src/test/ui/borrowck/issue-62107-match-arm-scopes.rs

@@ -0,0 +1,12 @@
+fn main() {
+    let e: i32;
+    match e {
+        //~^ ERROR use of possibly uninitialized variable
+        ref u if true => {}
+        ref v if true => {
+            let tx = 0;
+            &tx;
+        }
+        _ => (),
+    }
+}

src/test/ui/borrowck/issue-62107-match-arm-scopes.stderr

@@ -0,0 +1,9 @@
+error[E0381]: use of possibly uninitialized variable: `e`
+  --> $DIR/issue-62107-match-arm-scopes.rs:3:11
+   |
+LL |     match e {
+   |           ^ use of possibly uninitialized `e`
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0381`.