From 5205e2f8b8094a5f3d0205593820391dfe481808 Mon Sep 17 00:00:00 2001
From: Taylor Cramer <cramertaylorj@gmail.com>
Date: Wed, 15 Feb 2017 14:52:27 -0800
Subject: [PATCH 1/5] Normalize labeled and unlabeled breaks

---
 src/librustc/cfg/construct.rs                 |  15 +--
 src/librustc/hir/intravisit.rs                |  20 +--
 src/librustc/hir/lowering.rs                  | 115 ++++++++++++------
 src/librustc/hir/mod.rs                       |   9 +-
 src/librustc/hir/print.rs                     |  12 +-
 src/librustc/middle/liveness.rs               |  25 +---
 .../calculate_svh/svh_visitor.rs              |   6 +-
 src/librustc_mir/build/scope.rs               |  22 ++--
 src/librustc_mir/hair/cx/expr.rs              |   4 +-
 src/librustc_mir/hair/mod.rs                  |   4 +-
 src/librustc_passes/loops.rs                  |  23 ++--
 src/librustc_typeck/check/mod.rs              |  14 +--
 src/test/run-pass/loop-break-value.rs         |   8 --
 13 files changed, 138 insertions(+), 139 deletions(-)

diff --git a/src/librustc/cfg/construct.rs b/src/librustc/cfg/construct.rs
index 595059332895d..bc3da13ccf82d 100644
--- a/src/librustc/cfg/construct.rs
+++ b/src/librustc/cfg/construct.rs
@@ -579,17 +579,12 @@ impl<'a, 'tcx> CFGBuilder<'a, 'tcx> {
 
     fn find_scope(&self,
                   expr: &hir::Expr,
-                  label: Option<hir::Label>) -> LoopScope {
-        match label {
-            None => *self.loop_scopes.last().unwrap(),
-            Some(label) => {
-                for l in &self.loop_scopes {
-                    if l.loop_id == label.loop_id {
-                        return *l;
-                    }
-                }
-                span_bug!(expr.span, "no loop scope for id {}", label.loop_id);
+                  label: hir::Label) -> LoopScope {
+        for l in &self.loop_scopes {
+            if l.loop_id == label.loop_id {
+                return *l;
             }
         }
+        span_bug!(expr.span, "no loop scope for id {}", label.loop_id);
     }
 }
diff --git a/src/librustc/hir/intravisit.rs b/src/librustc/hir/intravisit.rs
index 1df6761506993..03b59aaf319c6 100644
--- a/src/librustc/hir/intravisit.rs
+++ b/src/librustc/hir/intravisit.rs
@@ -1006,18 +1006,18 @@ pub fn walk_expr<'v, V: Visitor<'v>>(visitor: &mut V, expression: &'v Expr) {
         ExprPath(ref qpath) => {
             visitor.visit_qpath(qpath, expression.id, expression.span);
         }
-        ExprBreak(None, ref opt_expr) => {
+        ExprBreak(label, ref opt_expr) => {
+            label.ident.map(|ident| {
+                visitor.visit_def_mention(Def::Label(label.loop_id));
+                visitor.visit_name(ident.span, ident.node.name);
+            });
             walk_list!(visitor, visit_expr, opt_expr);
         }
-        ExprBreak(Some(label), ref opt_expr) => {
-            visitor.visit_def_mention(Def::Label(label.loop_id));
-            visitor.visit_name(label.span, label.name);
-            walk_list!(visitor, visit_expr, opt_expr);
-        }
-        ExprAgain(None) => {}
-        ExprAgain(Some(label)) => {
-            visitor.visit_def_mention(Def::Label(label.loop_id));
-            visitor.visit_name(label.span, label.name);
+        ExprAgain(label) => {
+            label.ident.map(|ident| {
+                visitor.visit_def_mention(Def::Label(label.loop_id));
+                visitor.visit_name(ident.span, ident.node.name);
+            });
         }
         ExprRet(ref optional_expression) => {
             walk_list!(visitor, visit_expr, optional_expression);
diff --git a/src/librustc/hir/lowering.rs b/src/librustc/hir/lowering.rs
index 8a4acb3d03880..d6f99327d4fa2 100644
--- a/src/librustc/hir/lowering.rs
+++ b/src/librustc/hir/lowering.rs
@@ -50,6 +50,7 @@ use util::nodemap::{DefIdMap, NodeMap, FxHashMap};
 
 use std::collections::BTreeMap;
 use std::iter;
+use std::mem;
 
 use syntax::attr;
 use syntax::ast::*;
@@ -79,6 +80,8 @@ pub struct LoweringContext<'a> {
     impl_items: BTreeMap<hir::ImplItemId, hir::ImplItem>,
     bodies: FxHashMap<hir::BodyId, hir::Body>,
 
+    loop_scopes: Vec<NodeId>,
+
     type_def_lifetime_params: DefIdMap<usize>,
 }
 
@@ -112,6 +115,7 @@ pub fn lower_crate(sess: &Session,
         trait_items: BTreeMap::new(),
         impl_items: BTreeMap::new(),
         bodies: FxHashMap(),
+        loop_scopes: Vec::new(),
         type_def_lifetime_params: DefIdMap(),
     }.lower_crate(krate)
 }
@@ -244,6 +248,27 @@ impl<'a> LoweringContext<'a> {
         span
     }
 
+    fn with_loop_scope<T, F>(&mut self, loop_id: NodeId, f: F) -> T
+        where F: FnOnce(&mut LoweringContext) -> T
+    {
+        let len = self.loop_scopes.len();
+        self.loop_scopes.push(loop_id);
+        let result = f(self);
+        assert_eq!(len + 1, self.loop_scopes.len(),
+            "Loop scopes should be added and removed in stack order");
+        self.loop_scopes.pop().unwrap();
+        result
+    }
+
+    fn with_new_loop_scopes<T, F>(&mut self, f: F) -> T
+        where F: FnOnce(&mut LoweringContext) -> T
+    {
+        let loop_scopes = mem::replace(&mut self.loop_scopes, Vec::new());
+        let result = f(self);
+        mem::replace(&mut self.loop_scopes, loop_scopes);
+        result
+    }
+
     fn with_parent_def<T, F>(&mut self, parent_id: NodeId, f: F) -> T
         where F: FnOnce(&mut LoweringContext) -> T
     {
@@ -271,17 +296,23 @@ impl<'a> LoweringContext<'a> {
         o_id.map(|sp_ident| respan(sp_ident.span, sp_ident.node.name))
     }
 
-    fn lower_label(&mut self, id: NodeId, label: Option<Spanned<Ident>>) -> Option<hir::Label> {
-        label.map(|sp_ident| {
-            hir::Label {
-                span: sp_ident.span,
-                name: sp_ident.node.name,
+    fn lower_label(&mut self, label: Option<(NodeId, Spanned<Ident>)>) -> hir::Label {
+        match label {
+            Some((id, label_ident)) => hir::Label {
+                ident: Some(label_ident),
                 loop_id: match self.expect_full_def(id) {
                     Def::Label(loop_id) => loop_id,
                     _ => DUMMY_NODE_ID
                 }
+            },
+            None => hir::Label {
+                ident: None,
+                loop_id: match self.loop_scopes.last() {
+                    Some(innermost_loop_id) => *innermost_loop_id,
+                    _ => DUMMY_NODE_ID
+                }
             }
-        })
+        }
     }
 
     fn lower_attrs(&mut self, attrs: &Vec<Attribute>) -> hir::HirVec<Attribute> {
@@ -992,15 +1023,17 @@ impl<'a> LoweringContext<'a> {
                                self.record_body(value, None))
             }
             ItemKind::Fn(ref decl, unsafety, constness, abi, ref generics, ref body) => {
-                let body = self.lower_block(body);
-                let body = self.expr_block(body, ThinVec::new());
-                let body_id = self.record_body(body, Some(decl));
-                hir::ItemFn(self.lower_fn_decl(decl),
-                            self.lower_unsafety(unsafety),
-                            self.lower_constness(constness),
-                            abi,
-                            self.lower_generics(generics),
-                            body_id)
+                self.with_new_loop_scopes(|this| {
+                    let body = this.lower_block(body);
+                    let body = this.expr_block(body, ThinVec::new());
+                    let body_id = this.record_body(body, Some(decl));
+                    hir::ItemFn(this.lower_fn_decl(decl),
+                                              this.lower_unsafety(unsafety),
+                                              this.lower_constness(constness),
+                                              abi,
+                                              this.lower_generics(generics),
+                                              body_id)
+                })
             }
             ItemKind::Mod(ref m) => hir::ItemMod(self.lower_mod(m)),
             ItemKind::ForeignMod(ref nm) => hir::ItemForeignMod(self.lower_foreign_mod(nm)),
@@ -1562,13 +1595,17 @@ impl<'a> LoweringContext<'a> {
                     hir::ExprIf(P(self.lower_expr(cond)), self.lower_block(blk), else_opt)
                 }
                 ExprKind::While(ref cond, ref body, opt_ident) => {
-                    hir::ExprWhile(P(self.lower_expr(cond)), self.lower_block(body),
-                                   self.lower_opt_sp_ident(opt_ident))
+                    self.with_loop_scope(e.id, |this|
+                        hir::ExprWhile(
+                            P(this.lower_expr(cond)),
+                            this.lower_block(body),
+                            this.lower_opt_sp_ident(opt_ident)))
                 }
                 ExprKind::Loop(ref body, opt_ident) => {
-                    hir::ExprLoop(self.lower_block(body),
-                                  self.lower_opt_sp_ident(opt_ident),
-                                  hir::LoopSource::Loop)
+                    self.with_loop_scope(e.id, |this|
+                        hir::ExprLoop(this.lower_block(body),
+                                      this.lower_opt_sp_ident(opt_ident),
+                                      hir::LoopSource::Loop))
                 }
                 ExprKind::Match(ref expr, ref arms) => {
                     hir::ExprMatch(P(self.lower_expr(expr)),
@@ -1576,12 +1613,14 @@ impl<'a> LoweringContext<'a> {
                                    hir::MatchSource::Normal)
                 }
                 ExprKind::Closure(capture_clause, ref decl, ref body, fn_decl_span) => {
-                    self.with_parent_def(e.id, |this| {
-                        let expr = this.lower_expr(body);
-                        hir::ExprClosure(this.lower_capture_clause(capture_clause),
-                                         this.lower_fn_decl(decl),
-                                         this.record_body(expr, Some(decl)),
-                                         fn_decl_span)
+                    self.with_new_loop_scopes(|this| {
+                        this.with_parent_def(e.id, |this| {
+                            let expr = this.lower_expr(body);
+                            hir::ExprClosure(this.lower_capture_clause(capture_clause),
+                                             this.lower_fn_decl(decl),
+                                             this.record_body(expr, Some(decl)),
+                                             fn_decl_span)
+                        })
                     })
                 }
                 ExprKind::Block(ref blk) => hir::ExprBlock(self.lower_block(blk)),
@@ -1660,10 +1699,13 @@ impl<'a> LoweringContext<'a> {
                     hir::ExprPath(self.lower_qpath(e.id, qself, path, ParamMode::Optional))
                 }
                 ExprKind::Break(opt_ident, ref opt_expr) => {
-                    hir::ExprBreak(self.lower_label(e.id, opt_ident),
+                    hir::ExprBreak(
+                        self.lower_label(opt_ident.map(|ident| (e.id, ident))),
                                    opt_expr.as_ref().map(|x| P(self.lower_expr(x))))
                 }
-                ExprKind::Continue(opt_ident) => hir::ExprAgain(self.lower_label(e.id, opt_ident)),
+                ExprKind::Continue(opt_ident) =>
+                    hir::ExprAgain(
+                        self.lower_label(opt_ident.map(|ident| (e.id, ident)))),
                 ExprKind::Ret(ref e) => hir::ExprRet(e.as_ref().map(|x| P(self.lower_expr(x)))),
                 ExprKind::InlineAsm(ref asm) => {
                     let hir_asm = hir::InlineAsm {
@@ -1804,9 +1846,14 @@ impl<'a> LoweringContext<'a> {
                     //     }
                     //   }
 
+                    let (body, break_expr, sub_expr) = self.with_loop_scope(e.id, |this| (
+                        this.lower_block(body),
+                        this.expr_break(e.span, ThinVec::new()),
+                        P(this.lower_expr(sub_expr)),
+                    ));
+
                     // `<pat> => <body>`
                     let pat_arm = {
-                        let body = self.lower_block(body);
                         let body_expr = P(self.expr_block(body, ThinVec::new()));
                         let pat = self.lower_pat(pat);
                         self.arm(hir_vec![pat], body_expr)
@@ -1815,13 +1862,11 @@ impl<'a> LoweringContext<'a> {
                     // `_ => break`
                     let break_arm = {
                         let pat_under = self.pat_wild(e.span);
-                        let break_expr = self.expr_break(e.span, ThinVec::new());
                         self.arm(hir_vec![pat_under], break_expr)
                     };
 
                     // `match <sub_expr> { ... }`
                     let arms = hir_vec![pat_arm, break_arm];
-                    let sub_expr = P(self.lower_expr(sub_expr));
                     let match_expr = self.expr(e.span,
                                                hir::ExprMatch(sub_expr,
                                                               arms,
@@ -1863,7 +1908,7 @@ impl<'a> LoweringContext<'a> {
 
                     // `::std::option::Option::Some(<pat>) => <body>`
                     let pat_arm = {
-                        let body_block = self.lower_block(body);
+                        let body_block = self.with_loop_scope(e.id, |this| this.lower_block(body));
                         let body_expr = P(self.expr_block(body_block, ThinVec::new()));
                         let pat = self.lower_pat(pat);
                         let some_pat = self.pat_some(e.span, pat);
@@ -1873,7 +1918,8 @@ impl<'a> LoweringContext<'a> {
 
                     // `::std::option::Option::None => break`
                     let break_arm = {
-                        let break_expr = self.expr_break(e.span, ThinVec::new());
+                        let break_expr = self.with_loop_scope(e.id, |this|
+                            this.expr_break(e.span, ThinVec::new()));
                         let pat = self.pat_none(e.span);
                         self.arm(hir_vec![pat], break_expr)
                     };
@@ -2151,7 +2197,8 @@ impl<'a> LoweringContext<'a> {
     }
 
     fn expr_break(&mut self, span: Span, attrs: ThinVec<Attribute>) -> P<hir::Expr> {
-        P(self.expr(span, hir::ExprBreak(None, None), attrs))
+        let expr_break = hir::ExprBreak(self.lower_label(None), None);
+        P(self.expr(span, expr_break, attrs))
     }
 
     fn expr_call(&mut self, span: Span, e: P<hir::Expr>, args: hir::HirVec<hir::Expr>)
diff --git a/src/librustc/hir/mod.rs b/src/librustc/hir/mod.rs
index 4ebe416e1bfe6..fc5282d1af2f2 100644
--- a/src/librustc/hir/mod.rs
+++ b/src/librustc/hir/mod.rs
@@ -36,7 +36,7 @@ use util::nodemap::{NodeMap, FxHashMap, FxHashSet};
 use syntax_pos::{Span, ExpnId, DUMMY_SP};
 use syntax::codemap::{self, Spanned};
 use syntax::abi::Abi;
-use syntax::ast::{Name, NodeId, DUMMY_NODE_ID, AsmDialect};
+use syntax::ast::{Ident, Name, NodeId, DUMMY_NODE_ID, AsmDialect};
 use syntax::ast::{Attribute, Lit, StrStyle, FloatTy, IntTy, UintTy, MetaItem};
 use syntax::ptr::P;
 use syntax::symbol::{Symbol, keywords};
@@ -959,9 +959,9 @@ pub enum Expr_ {
     /// A referencing operation (`&a` or `&mut a`)
     ExprAddrOf(Mutability, P<Expr>),
     /// A `break`, with an optional label to break
-    ExprBreak(Option<Label>, Option<P<Expr>>),
+    ExprBreak(Label, Option<P<Expr>>),
     /// A `continue`, with an optional label
-    ExprAgain(Option<Label>),
+    ExprAgain(Label),
     /// A `return`, with an optional value to be returned
     ExprRet(Option<P<Expr>>),
 
@@ -1033,8 +1033,7 @@ pub enum LoopSource {
 
 #[derive(Clone, PartialEq, Eq, RustcEncodable, RustcDecodable, Hash, Debug, Copy)]
 pub struct Label {
-    pub span: Span,
-    pub name: Name,
+    pub ident: Option<Spanned<Ident>>,
     pub loop_id: NodeId
 }
 
diff --git a/src/librustc/hir/print.rs b/src/librustc/hir/print.rs
index e058c48c59149..3411de9bb5df1 100644
--- a/src/librustc/hir/print.rs
+++ b/src/librustc/hir/print.rs
@@ -1354,11 +1354,11 @@ impl<'a> State<'a> {
             hir::ExprPath(ref qpath) => {
                 self.print_qpath(qpath, true)?
             }
-            hir::ExprBreak(opt_label, ref opt_expr) => {
+            hir::ExprBreak(label, ref opt_expr) => {
                 word(&mut self.s, "break")?;
                 space(&mut self.s)?;
-                if let Some(label) = opt_label {
-                    self.print_name(label.name)?;
+                if let Some(label_ident) = label.ident {
+                    self.print_name(label_ident.node.name)?;
                     space(&mut self.s)?;
                 }
                 if let Some(ref expr) = *opt_expr {
@@ -1366,11 +1366,11 @@ impl<'a> State<'a> {
                     space(&mut self.s)?;
                 }
             }
-            hir::ExprAgain(opt_label) => {
+            hir::ExprAgain(label) => {
                 word(&mut self.s, "continue")?;
                 space(&mut self.s)?;
-                if let Some(label) = opt_label {
-                    self.print_name(label.name)?;
+                if let Some(label_ident) = label.ident {
+                    self.print_name(label_ident.node.name)?;
                     space(&mut self.s)?
                 }
             }
diff --git a/src/librustc/middle/liveness.rs b/src/librustc/middle/liveness.rs
index 7fa3365694c26..60d2a213ecef6 100644
--- a/src/librustc/middle/liveness.rs
+++ b/src/librustc/middle/liveness.rs
@@ -675,23 +675,6 @@ impl<'a, 'tcx> Liveness<'a, 'tcx> {
         Ok(())
     }
 
-    fn find_loop_scope(&self,
-                       opt_label: Option<hir::Label>,
-                       sp: Span)
-                       -> NodeId {
-        match opt_label {
-            Some(label) => label.loop_id,
-            None => {
-                // Vanilla 'break' or 'continue', so use the enclosing
-                // loop scope
-                if self.loop_scope.is_empty() {
-                    span_bug!(sp, "break outside loop");
-                } else {
-                    *self.loop_scope.last().unwrap()
-                }
-            }
-        }
-    }
 
     #[allow(unused_must_use)]
     fn ln_str(&self, ln: LiveNode) -> String {
@@ -1018,9 +1001,9 @@ impl<'a, 'tcx> Liveness<'a, 'tcx> {
             self.propagate_through_opt_expr(o_e.as_ref().map(|e| &**e), exit_ln)
           }
 
-          hir::ExprBreak(opt_label, ref opt_expr) => {
+          hir::ExprBreak(label, ref opt_expr) => {
               // Find which label this break jumps to
-              let sc = self.find_loop_scope(opt_label, expr.span);
+              let sc = label.loop_id;
 
               // Now that we know the label we're going to,
               // look it up in the break loop nodes table
@@ -1031,9 +1014,9 @@ impl<'a, 'tcx> Liveness<'a, 'tcx> {
               }
           }
 
-          hir::ExprAgain(opt_label) => {
+          hir::ExprAgain(label) => {
               // Find which label this expr continues to
-              let sc = self.find_loop_scope(opt_label, expr.span);
+              let sc = label.loop_id;
 
               // Now that we know the label we're going to,
               // look it up in the continue loop nodes table
diff --git a/src/librustc_incremental/calculate_svh/svh_visitor.rs b/src/librustc_incremental/calculate_svh/svh_visitor.rs
index c7512f2971b33..62bbb86e7dad5 100644
--- a/src/librustc_incremental/calculate_svh/svh_visitor.rs
+++ b/src/librustc_incremental/calculate_svh/svh_visitor.rs
@@ -338,8 +338,10 @@ fn saw_expr<'a>(node: &'a Expr_,
         ExprIndex(..)            => (SawExprIndex, true),
         ExprPath(_)              => (SawExprPath, false),
         ExprAddrOf(m, _)         => (SawExprAddrOf(m), false),
-        ExprBreak(label, _)      => (SawExprBreak(label.map(|l| l.name.as_str())), false),
-        ExprAgain(label)         => (SawExprAgain(label.map(|l| l.name.as_str())), false),
+        ExprBreak(label, _)      => (SawExprBreak(label.ident.map(|i|
+                                                    i.node.name.as_str())), false),
+        ExprAgain(label)         => (SawExprAgain(label.ident.map(|i|
+                                                    i.node.name.as_str())), false),
         ExprRet(..)              => (SawExprRet, false),
         ExprInlineAsm(ref a,..)  => (SawExprInlineAsm(StableInlineAsm(a)), false),
         ExprStruct(..)           => (SawExprStruct, false),
diff --git a/src/librustc_mir/build/scope.rs b/src/librustc_mir/build/scope.rs
index c702a142fab34..695564fa85bc0 100644
--- a/src/librustc_mir/build/scope.rs
+++ b/src/librustc_mir/build/scope.rs
@@ -385,22 +385,14 @@ impl<'a, 'gcx, 'tcx> Builder<'a, 'gcx, 'tcx> {
     /// resolving `break` and `continue`.
     pub fn find_loop_scope(&mut self,
                            span: Span,
-                           label: Option<CodeExtent>)
+                           label: CodeExtent)
                            -> &mut LoopScope<'tcx> {
-        let loop_scopes = &mut self.loop_scopes;
-        match label {
-            None => {
-                // no label? return the innermost loop scope
-                loop_scopes.iter_mut().rev().next()
-            }
-            Some(label) => {
-                // otherwise, find the loop-scope with the correct id
-                loop_scopes.iter_mut()
-                           .rev()
-                           .filter(|loop_scope| loop_scope.extent == label)
-                           .next()
-            }
-        }.unwrap_or_else(|| span_bug!(span, "no enclosing loop scope found?"))
+        // find the loop-scope with the correct id
+        self.loop_scopes.iter_mut()
+                   .rev()
+                   .filter(|loop_scope| loop_scope.extent == label)
+                   .next()
+            .unwrap_or_else(|| span_bug!(span, "no enclosing loop scope found?"))
     }
 
     /// Given a span and the current visibility scope, make a SourceInfo.
diff --git a/src/librustc_mir/hair/cx/expr.rs b/src/librustc_mir/hair/cx/expr.rs
index 7eaf1fe139865..80ba93f0bbfca 100644
--- a/src/librustc_mir/hair/cx/expr.rs
+++ b/src/librustc_mir/hair/cx/expr.rs
@@ -606,13 +606,13 @@ fn make_mirror_unadjusted<'a, 'gcx, 'tcx>(cx: &mut Cx<'a, 'gcx, 'tcx>,
         hir::ExprRet(ref v) => ExprKind::Return { value: v.to_ref() },
         hir::ExprBreak(label, ref value) => {
             ExprKind::Break {
-                label: label.map(|label| cx.tcx.region_maps.node_extent(label.loop_id)),
+                label: cx.tcx.region_maps.node_extent(label.loop_id),
                 value: value.to_ref(),
             }
         }
         hir::ExprAgain(label) => {
             ExprKind::Continue {
-                label: label.map(|label| cx.tcx.region_maps.node_extent(label.loop_id)),
+                label: cx.tcx.region_maps.node_extent(label.loop_id),
             }
         }
         hir::ExprMatch(ref discr, ref arms, _) => {
diff --git a/src/librustc_mir/hair/mod.rs b/src/librustc_mir/hair/mod.rs
index 4ac67cfb2fca1..3068258f6c24f 100644
--- a/src/librustc_mir/hair/mod.rs
+++ b/src/librustc_mir/hair/mod.rs
@@ -205,11 +205,11 @@ pub enum ExprKind<'tcx> {
         arg: ExprRef<'tcx>,
     },
     Break {
-        label: Option<CodeExtent>,
+        label: CodeExtent,
         value: Option<ExprRef<'tcx>>,
     },
     Continue {
-        label: Option<CodeExtent>,
+        label: CodeExtent,
     },
     Return {
         value: Option<ExprRef<'tcx>>,
diff --git a/src/librustc_passes/loops.rs b/src/librustc_passes/loops.rs
index a5bd69fff0138..5f9acc0430a81 100644
--- a/src/librustc_passes/loops.rs
+++ b/src/librustc_passes/loops.rs
@@ -88,22 +88,15 @@ impl<'a, 'hir> Visitor<'hir> for CheckLoopVisitor<'a, 'hir> {
             }
             hir::ExprBreak(label, ref opt_expr) => {
                 if opt_expr.is_some() {
-                    let loop_kind = if let Some(label) = label {
-                        if label.loop_id == ast::DUMMY_NODE_ID {
-                            None
-                        } else {
-                            Some(match self.hir_map.expect_expr(label.loop_id).node {
-                                hir::ExprWhile(..) => LoopKind::WhileLoop,
-                                hir::ExprLoop(_, _, source) => LoopKind::Loop(source),
-                                ref r => span_bug!(e.span,
-                                                   "break label resolved to a non-loop: {:?}", r),
-                            })
-                        }
-                    } else if let Loop(kind) = self.cx {
-                        Some(kind)
-                    } else {
-                        // `break` outside a loop - caught below
+                    let loop_kind = if label.loop_id == ast::DUMMY_NODE_ID {
                         None
+                    } else {
+                        Some(match self.hir_map.expect_expr(label.loop_id).node {
+                            hir::ExprWhile(..) => LoopKind::WhileLoop,
+                            hir::ExprLoop(_, _, source) => LoopKind::Loop(source),
+                            ref r => span_bug!(e.span,
+                                               "break label resolved to a non-loop: {:?}", r),
+                        })
                     };
                     match loop_kind {
                         None | Some(LoopKind::Loop(hir::LoopSource::Loop)) => (),
diff --git a/src/librustc_typeck/check/mod.rs b/src/librustc_typeck/check/mod.rs
index 4b36e682f1e82..e9c9a63d79be9 100644
--- a/src/librustc_typeck/check/mod.rs
+++ b/src/librustc_typeck/check/mod.rs
@@ -425,15 +425,11 @@ pub struct EnclosingLoops<'gcx, 'tcx> {
 }
 
 impl<'gcx, 'tcx> EnclosingLoops<'gcx, 'tcx> {
-    fn find_loop(&mut self, id: Option<ast::NodeId>) -> Option<&mut LoopCtxt<'gcx, 'tcx>> {
-        if let Some(id) = id {
-            if let Some(ix) = self.by_id.get(&id).cloned() {
-                Some(&mut self.stack[ix])
-            } else {
-                None
-            }
+    fn find_loop(&mut self, id: ast::NodeId) -> Option<&mut LoopCtxt<'gcx, 'tcx>> {
+        if let Some(ix) = self.by_id.get(&id).cloned() {
+            Some(&mut self.stack[ix])
         } else {
-            self.stack.last_mut()
+            None
         }
     }
 }
@@ -3596,7 +3592,7 @@ impl<'a, 'gcx, 'tcx> FnCtxt<'a, 'gcx, 'tcx> {
               tcx.mk_nil()
           }
           hir::ExprBreak(label, ref expr_opt) => {
-            let loop_id = label.map(|l| l.loop_id);
+            let loop_id = label.loop_id;
             let coerce_to = {
                 let mut enclosing_loops = self.enclosing_loops.borrow_mut();
                 enclosing_loops.find_loop(loop_id).map(|ctxt| ctxt.coerce_to)
diff --git a/src/test/run-pass/loop-break-value.rs b/src/test/run-pass/loop-break-value.rs
index 6a5e051c0c732..10ff8dbf18e5e 100644
--- a/src/test/run-pass/loop-break-value.rs
+++ b/src/test/run-pass/loop-break-value.rs
@@ -122,12 +122,4 @@ pub fn main() {
         panic!();
     };
     assert_eq!(nested_break_value, "hello");
-
-    let break_from_while_cond = loop {
-        while break {
-            panic!();
-        }
-        break 123;
-    };
-    assert_eq!(break_from_while_cond, 123);
 }

From 4d65622dcd3be66ec53656c499afe7bbc8aa1ae7 Mon Sep 17 00:00:00 2001
From: Taylor Cramer <cramertaylorj@gmail.com>
Date: Wed, 15 Feb 2017 23:28:59 -0800
Subject: [PATCH 2/5] Properly implement labeled breaks in while conditions

---
 src/librustc/cfg/construct.rs         | 29 ++++++++---
 src/librustc/hir/intravisit.rs        |  8 ++-
 src/librustc/hir/lowering.rs          | 71 ++++++++++++++++++++++-----
 src/librustc/hir/mod.rs               | 47 +++++++++++++++++-
 src/librustc/middle/liveness.rs       | 24 ++++++---
 src/librustc_mir/build/scope.rs       |  6 +--
 src/librustc_mir/hair/cx/expr.rs      | 17 +++++--
 src/librustc_passes/diagnostics.rs    | 16 ++++++
 src/librustc_passes/loops.rs          | 30 +++++++++--
 src/librustc_resolve/lib.rs           | 30 ++++++-----
 src/librustc_typeck/check/mod.rs      | 11 +++--
 src/test/run-pass/loop-break-value.rs | 16 ++++++
 12 files changed, 247 insertions(+), 58 deletions(-)

diff --git a/src/librustc/cfg/construct.rs b/src/librustc/cfg/construct.rs
index bc3da13ccf82d..fdb350ebaac97 100644
--- a/src/librustc/cfg/construct.rs
+++ b/src/librustc/cfg/construct.rs
@@ -220,15 +220,24 @@ impl<'a, 'tcx> CFGBuilder<'a, 'tcx> {
                 // Note that `break` and `continue` statements
                 // may cause additional edges.
 
-                // Is the condition considered part of the loop?
                 let loopback = self.add_dummy_node(&[pred]);              // 1
-                let cond_exit = self.expr(&cond, loopback);             // 2
-                let expr_exit = self.add_ast_node(expr.id, &[cond_exit]); // 3
+
+                // Create expr_exit without pred (cond_exit)
+                let expr_exit = self.add_ast_node(expr.id, &[]);         // 3
+
+                // The LoopScope needs to be on the loop_scopes stack while evaluating the
+                // condition and the body of the loop (both can break out of the loop)
                 self.loop_scopes.push(LoopScope {
                     loop_id: expr.id,
                     continue_index: loopback,
                     break_index: expr_exit
                 });
+
+                let cond_exit = self.expr(&cond, loopback);             // 2
+
+                // Add pred (cond_exit) to expr_exit
+                self.add_contained_edge(cond_exit, expr_exit);
+
                 let body_exit = self.block(&body, cond_exit);          // 4
                 self.add_contained_edge(body_exit, loopback);            // 5
                 self.loop_scopes.pop();
@@ -580,11 +589,17 @@ impl<'a, 'tcx> CFGBuilder<'a, 'tcx> {
     fn find_scope(&self,
                   expr: &hir::Expr,
                   label: hir::Label) -> LoopScope {
-        for l in &self.loop_scopes {
-            if l.loop_id == label.loop_id {
-                return *l;
+
+        match label.loop_id.into() {
+            Ok(loop_id) => {
+                for l in &self.loop_scopes {
+                    if l.loop_id == loop_id {
+                        return *l;
+                    }
+                }
+                span_bug!(expr.span, "no loop scope for id {}", loop_id);
             }
+            Err(err) => span_bug!(expr.span, "loop scope error: {}",  err)
         }
-        span_bug!(expr.span, "no loop scope for id {}", label.loop_id);
     }
 }
diff --git a/src/librustc/hir/intravisit.rs b/src/librustc/hir/intravisit.rs
index 03b59aaf319c6..fd6796ccc0bf2 100644
--- a/src/librustc/hir/intravisit.rs
+++ b/src/librustc/hir/intravisit.rs
@@ -1008,14 +1008,18 @@ pub fn walk_expr<'v, V: Visitor<'v>>(visitor: &mut V, expression: &'v Expr) {
         }
         ExprBreak(label, ref opt_expr) => {
             label.ident.map(|ident| {
-                visitor.visit_def_mention(Def::Label(label.loop_id));
+                if let Ok(loop_id) = label.loop_id.into() {
+                    visitor.visit_def_mention(Def::Label(loop_id));
+                }
                 visitor.visit_name(ident.span, ident.node.name);
             });
             walk_list!(visitor, visit_expr, opt_expr);
         }
         ExprAgain(label) => {
             label.ident.map(|ident| {
-                visitor.visit_def_mention(Def::Label(label.loop_id));
+                if let Ok(loop_id) = label.loop_id.into() {
+                    visitor.visit_def_mention(Def::Label(loop_id));
+                }
                 visitor.visit_name(ident.span, ident.node.name);
             });
         }
diff --git a/src/librustc/hir/lowering.rs b/src/librustc/hir/lowering.rs
index d6f99327d4fa2..55226fa7605d3 100644
--- a/src/librustc/hir/lowering.rs
+++ b/src/librustc/hir/lowering.rs
@@ -81,6 +81,7 @@ pub struct LoweringContext<'a> {
     bodies: FxHashMap<hir::BodyId, hir::Body>,
 
     loop_scopes: Vec<NodeId>,
+    is_in_loop_condition: bool,
 
     type_def_lifetime_params: DefIdMap<usize>,
 }
@@ -116,6 +117,7 @@ pub fn lower_crate(sess: &Session,
         impl_items: BTreeMap::new(),
         bodies: FxHashMap(),
         loop_scopes: Vec::new(),
+        is_in_loop_condition: false,
         type_def_lifetime_params: DefIdMap(),
     }.lower_crate(krate)
 }
@@ -251,21 +253,49 @@ impl<'a> LoweringContext<'a> {
     fn with_loop_scope<T, F>(&mut self, loop_id: NodeId, f: F) -> T
         where F: FnOnce(&mut LoweringContext) -> T
     {
+        // We're no longer in the base loop's condition; we're in another loop.
+        let was_in_loop_condition = self.is_in_loop_condition;
+        self.is_in_loop_condition = false;
+
         let len = self.loop_scopes.len();
         self.loop_scopes.push(loop_id);
+
         let result = f(self);
         assert_eq!(len + 1, self.loop_scopes.len(),
             "Loop scopes should be added and removed in stack order");
+
         self.loop_scopes.pop().unwrap();
+
+        self.is_in_loop_condition = was_in_loop_condition;
+
+        result
+    }
+
+    fn with_loop_condition_scope<T, F>(&mut self, f: F) -> T
+        where F: FnOnce(&mut LoweringContext) -> T
+    {
+        let was_in_loop_condition = self.is_in_loop_condition;
+        self.is_in_loop_condition = true;
+
+        let result = f(self);
+
+        self.is_in_loop_condition = was_in_loop_condition;
+
         result
     }
 
     fn with_new_loop_scopes<T, F>(&mut self, f: F) -> T
         where F: FnOnce(&mut LoweringContext) -> T
     {
+        let was_in_loop_condition = self.is_in_loop_condition;
+        self.is_in_loop_condition = false;
+
         let loop_scopes = mem::replace(&mut self.loop_scopes, Vec::new());
         let result = f(self);
         mem::replace(&mut self.loop_scopes, loop_scopes);
+
+        self.is_in_loop_condition = was_in_loop_condition;
+
         result
     }
 
@@ -300,17 +330,16 @@ impl<'a> LoweringContext<'a> {
         match label {
             Some((id, label_ident)) => hir::Label {
                 ident: Some(label_ident),
-                loop_id: match self.expect_full_def(id) {
-                    Def::Label(loop_id) => loop_id,
-                    _ => DUMMY_NODE_ID
+                loop_id: if let Def::Label(loop_id) = self.expect_full_def(id) {
+                    hir::LoopIdResult::Ok(loop_id)
+                } else {
+                    hir::LoopIdResult::Err(hir::LoopIdError::UnresolvedLabel)
                 }
             },
             None => hir::Label {
                 ident: None,
-                loop_id: match self.loop_scopes.last() {
-                    Some(innermost_loop_id) => *innermost_loop_id,
-                    _ => DUMMY_NODE_ID
-                }
+                loop_id: self.loop_scopes.last().map(|innermost_loop_id| Ok(*innermost_loop_id))
+                            .unwrap_or(Err(hir::LoopIdError::OutsideLoopScope)).into()
             }
         }
     }
@@ -1597,7 +1626,7 @@ impl<'a> LoweringContext<'a> {
                 ExprKind::While(ref cond, ref body, opt_ident) => {
                     self.with_loop_scope(e.id, |this|
                         hir::ExprWhile(
-                            P(this.lower_expr(cond)),
+                            this.with_loop_condition_scope(|this| P(this.lower_expr(cond))),
                             this.lower_block(body),
                             this.lower_opt_sp_ident(opt_ident)))
                 }
@@ -1699,13 +1728,29 @@ impl<'a> LoweringContext<'a> {
                     hir::ExprPath(self.lower_qpath(e.id, qself, path, ParamMode::Optional))
                 }
                 ExprKind::Break(opt_ident, ref opt_expr) => {
+                    let label_result = if self.is_in_loop_condition && opt_ident.is_none() {
+                        hir::Label {
+                            ident: opt_ident,
+                            loop_id: Err(hir::LoopIdError::UnlabeledCfInWhileCondition).into(),
+                        }
+                    } else {
+                        self.lower_label(opt_ident.map(|ident| (e.id, ident)))
+                    };
                     hir::ExprBreak(
-                        self.lower_label(opt_ident.map(|ident| (e.id, ident))),
-                                   opt_expr.as_ref().map(|x| P(self.lower_expr(x))))
+                            label_result,
+                            opt_expr.as_ref().map(|x| P(self.lower_expr(x))))
                 }
                 ExprKind::Continue(opt_ident) =>
                     hir::ExprAgain(
-                        self.lower_label(opt_ident.map(|ident| (e.id, ident)))),
+                        if self.is_in_loop_condition && opt_ident.is_none() {
+                            hir::Label {
+                                ident: opt_ident,
+                                loop_id: Err(
+                                    hir::LoopIdError::UnlabeledCfInWhileCondition).into(),
+                            }
+                        } else {
+                            self.lower_label(opt_ident.map( | ident| (e.id, ident)))
+                        }),
                 ExprKind::Ret(ref e) => hir::ExprRet(e.as_ref().map(|x| P(self.lower_expr(x)))),
                 ExprKind::InlineAsm(ref asm) => {
                     let hir_asm = hir::InlineAsm {
@@ -1846,10 +1891,12 @@ impl<'a> LoweringContext<'a> {
                     //     }
                     //   }
 
+                    // Note that the block AND the condition are evaluated in the loop scope.
+                    // This is done to allow `break` from inside the condition of the loop.
                     let (body, break_expr, sub_expr) = self.with_loop_scope(e.id, |this| (
                         this.lower_block(body),
                         this.expr_break(e.span, ThinVec::new()),
-                        P(this.lower_expr(sub_expr)),
+                        this.with_loop_condition_scope(|this| P(this.lower_expr(sub_expr))),
                     ));
 
                     // `<pat> => <body>`
diff --git a/src/librustc/hir/mod.rs b/src/librustc/hir/mod.rs
index fc5282d1af2f2..4e4187cbf8905 100644
--- a/src/librustc/hir/mod.rs
+++ b/src/librustc/hir/mod.rs
@@ -1030,11 +1030,56 @@ pub enum LoopSource {
     ForLoop,
 }
 
+#[derive(Clone, PartialEq, Eq, RustcEncodable, RustcDecodable, Hash, Debug, Copy)]
+pub enum LoopIdError {
+    OutsideLoopScope,
+    UnlabeledCfInWhileCondition,
+    UnresolvedLabel,
+}
+
+impl fmt::Display for LoopIdError {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        fmt::Display::fmt(match *self {
+            LoopIdError::OutsideLoopScope => "not inside loop scope",
+            LoopIdError::UnlabeledCfInWhileCondition =>
+                "unlabeled control flow (break or continue) in while condition",
+            LoopIdError::UnresolvedLabel => "label not found",
+        }, f)
+    }
+}
+
+// FIXME(cramertj) this should use `Result` once master compiles w/ a vesion of Rust where
+// `Result` implements `Encodable`/`Decodable`
+#[derive(Clone, PartialEq, Eq, RustcEncodable, RustcDecodable, Hash, Debug, Copy)]
+pub enum LoopIdResult {
+    Ok(NodeId),
+    Err(LoopIdError),
+}
+impl Into<Result<NodeId, LoopIdError>> for LoopIdResult {
+    fn into(self) -> Result<NodeId, LoopIdError> {
+        match self {
+            LoopIdResult::Ok(ok) => Ok(ok),
+            LoopIdResult::Err(err) => Err(err),
+        }
+    }
+}
+impl From<Result<NodeId, LoopIdError>> for LoopIdResult {
+    fn from(res: Result<NodeId, LoopIdError>) -> Self {
+        match res {
+            Ok(ok) => LoopIdResult::Ok(ok),
+            Err(err) => LoopIdResult::Err(err),
+        }
+    }
+}
 
 #[derive(Clone, PartialEq, Eq, RustcEncodable, RustcDecodable, Hash, Debug, Copy)]
 pub struct Label {
+    // This is `Some(_)` iff there is an explicit user-specified `label
     pub ident: Option<Spanned<Ident>>,
-    pub loop_id: NodeId
+
+    // These errors are caught and then reported during the diagnostics pass in
+    // librustc_passes/loops.rs
+    pub loop_id: LoopIdResult,
 }
 
 #[derive(Clone, PartialEq, Eq, RustcEncodable, RustcDecodable, Hash, Debug, Copy)]
diff --git a/src/librustc/middle/liveness.rs b/src/librustc/middle/liveness.rs
index 60d2a213ecef6..b7f7c49d7b0e3 100644
--- a/src/librustc/middle/liveness.rs
+++ b/src/librustc/middle/liveness.rs
@@ -1003,7 +1003,10 @@ impl<'a, 'tcx> Liveness<'a, 'tcx> {
 
           hir::ExprBreak(label, ref opt_expr) => {
               // Find which label this break jumps to
-              let sc = label.loop_id;
+              let sc = match label.loop_id.into() {
+                  Ok(loop_id) => loop_id,
+                  Err(err) => span_bug!(expr.span, "loop scope error: {}", err),
+              };
 
               // Now that we know the label we're going to,
               // look it up in the break loop nodes table
@@ -1016,7 +1019,11 @@ impl<'a, 'tcx> Liveness<'a, 'tcx> {
 
           hir::ExprAgain(label) => {
               // Find which label this expr continues to
-              let sc = label.loop_id;
+              let sc = match label.loop_id.into() {
+                  Ok(loop_id) => loop_id,
+                  Err(err) => span_bug!(expr.span, "loop scope error: {}", err),
+              };
+
 
               // Now that we know the label we're going to,
               // look it up in the continue loop nodes table
@@ -1280,12 +1287,13 @@ impl<'a, 'tcx> Liveness<'a, 'tcx> {
         debug!("propagate_through_loop: using id for loop body {} {}",
                expr.id, self.ir.tcx.hir.node_to_pretty_string(body.id));
 
-        let cond_ln = match kind {
-            LoopLoop => ln,
-            WhileLoop(ref cond) => self.propagate_through_expr(&cond, ln),
-        };
-        let body_ln = self.with_loop_nodes(expr.id, succ, ln, |this| {
-            this.propagate_through_block(body, cond_ln)
+        let (cond_ln, body_ln) = self.with_loop_nodes(expr.id, succ, ln, |this| {
+            let cond_ln = match kind {
+                LoopLoop => ln,
+                WhileLoop(ref cond) => this.propagate_through_expr(&cond, ln),
+            };
+            let body_ln = this.propagate_through_block(body, cond_ln);
+            (cond_ln, body_ln)
         });
 
         // repeat until fixed point is reached:
diff --git a/src/librustc_mir/build/scope.rs b/src/librustc_mir/build/scope.rs
index 695564fa85bc0..282361fc13e27 100644
--- a/src/librustc_mir/build/scope.rs
+++ b/src/librustc_mir/build/scope.rs
@@ -389,9 +389,9 @@ impl<'a, 'gcx, 'tcx> Builder<'a, 'gcx, 'tcx> {
                            -> &mut LoopScope<'tcx> {
         // find the loop-scope with the correct id
         self.loop_scopes.iter_mut()
-                   .rev()
-                   .filter(|loop_scope| loop_scope.extent == label)
-                   .next()
+            .rev()
+            .filter(|loop_scope| loop_scope.extent == label)
+            .next()
             .unwrap_or_else(|| span_bug!(span, "no enclosing loop scope found?"))
     }
 
diff --git a/src/librustc_mir/hair/cx/expr.rs b/src/librustc_mir/hair/cx/expr.rs
index 80ba93f0bbfca..3a9ac143f783b 100644
--- a/src/librustc_mir/hair/cx/expr.rs
+++ b/src/librustc_mir/hair/cx/expr.rs
@@ -605,14 +605,21 @@ fn make_mirror_unadjusted<'a, 'gcx, 'tcx>(cx: &mut Cx<'a, 'gcx, 'tcx>,
         }
         hir::ExprRet(ref v) => ExprKind::Return { value: v.to_ref() },
         hir::ExprBreak(label, ref value) => {
-            ExprKind::Break {
-                label: cx.tcx.region_maps.node_extent(label.loop_id),
-                value: value.to_ref(),
+            match label.loop_id.into() {
+                Ok(loop_id) => ExprKind::Break {
+                    label: cx.tcx.region_maps.node_extent(loop_id),
+                    value: value.to_ref(),
+                },
+                Err(err) => bug!("invalid loop id for break: {}", err)
             }
+
         }
         hir::ExprAgain(label) => {
-            ExprKind::Continue {
-                label: cx.tcx.region_maps.node_extent(label.loop_id),
+            match label.loop_id.into() {
+                Ok(loop_id) => ExprKind::Continue {
+                    label: cx.tcx.region_maps.node_extent(loop_id),
+                },
+                Err(err) => bug!("invalid loop id for continue: {}", err)
             }
         }
         hir::ExprMatch(ref discr, ref arms, _) => {
diff --git a/src/librustc_passes/diagnostics.rs b/src/librustc_passes/diagnostics.rs
index ef871959176af..c576b35cb17b4 100644
--- a/src/librustc_passes/diagnostics.rs
+++ b/src/librustc_passes/diagnostics.rs
@@ -241,6 +241,22 @@ match 5u32 {
 }
 ```
 "##,
+
+E0583: r##"
+`break` or `continue` must include a label when used in the condition of a
+`while` loop.
+
+Example of erroneous code:
+
+```compile_fail
+while break {}
+```
+
+To fix this, add a label specifying which loop is being broken out of:
+```
+`foo: while break `foo {}
+```
+"##
 }
 
 register_diagnostics! {
diff --git a/src/librustc_passes/loops.rs b/src/librustc_passes/loops.rs
index 5f9acc0430a81..003142f349831 100644
--- a/src/librustc_passes/loops.rs
+++ b/src/librustc_passes/loops.rs
@@ -87,11 +87,21 @@ impl<'a, 'hir> Visitor<'hir> for CheckLoopVisitor<'a, 'hir> {
                 self.with_context(Closure, |v| v.visit_nested_body(b));
             }
             hir::ExprBreak(label, ref opt_expr) => {
+                let loop_id = match label.loop_id.into() {
+                    Ok(loop_id) => loop_id,
+                    Err(hir::LoopIdError::OutsideLoopScope) => ast::DUMMY_NODE_ID,
+                    Err(hir::LoopIdError::UnlabeledCfInWhileCondition) => {
+                        self.emit_unlabled_cf_in_while_condition(e.span, "break");
+                        ast::DUMMY_NODE_ID
+                    },
+                    Err(hir::LoopIdError::UnresolvedLabel) => ast::DUMMY_NODE_ID,
+                };
+
                 if opt_expr.is_some() {
-                    let loop_kind = if label.loop_id == ast::DUMMY_NODE_ID {
+                    let loop_kind = if loop_id == ast::DUMMY_NODE_ID {
                         None
                     } else {
-                        Some(match self.hir_map.expect_expr(label.loop_id).node {
+                        Some(match self.hir_map.expect_expr(loop_id).node {
                             hir::ExprWhile(..) => LoopKind::WhileLoop,
                             hir::ExprLoop(_, _, source) => LoopKind::Loop(source),
                             ref r => span_bug!(e.span,
@@ -110,9 +120,15 @@ impl<'a, 'hir> Visitor<'hir> for CheckLoopVisitor<'a, 'hir> {
                         }
                     }
                 }
+
                 self.require_loop("break", e.span);
             }
-            hir::ExprAgain(_) => self.require_loop("continue", e.span),
+            hir::ExprAgain(label) => {
+                if let Err(hir::LoopIdError::UnlabeledCfInWhileCondition) = label.loop_id.into() {
+                    self.emit_unlabled_cf_in_while_condition(e.span, "continue");
+                }
+                self.require_loop("continue", e.span)
+            },
             _ => intravisit::walk_expr(self, e),
         }
     }
@@ -143,4 +159,12 @@ impl<'a, 'hir> CheckLoopVisitor<'a, 'hir> {
             }
         }
     }
+
+    fn emit_unlabled_cf_in_while_condition(&mut self, span: Span, cf_type: &str) {
+        struct_span_err!(self.sess, span, E0583,
+                         "`break` or `continue` with no label in the condition of a `while` loop")
+            .span_label(span,
+                        &format!("unlabeled `{}` in the condition of a `while` loop", cf_type))
+            .emit();
+    }
 }
diff --git a/src/librustc_resolve/lib.rs b/src/librustc_resolve/lib.rs
index 676ff98e602d6..c254833be6472 100644
--- a/src/librustc_resolve/lib.rs
+++ b/src/librustc_resolve/lib.rs
@@ -2770,18 +2770,24 @@ impl<'a> Resolver<'a> {
         }
     }
 
-    fn resolve_labeled_block(&mut self, label: Option<SpannedIdent>, id: NodeId, block: &Block) {
+    fn with_resolved_label<F>(&mut self, label: Option<SpannedIdent>, id: NodeId, f: F)
+        where F: FnOnce(&mut Resolver)
+    {
         if let Some(label) = label {
             let def = Def::Label(id);
             self.with_label_rib(|this| {
                 this.label_ribs.last_mut().unwrap().bindings.insert(label.node, def);
-                this.visit_block(block);
+                f(this);
             });
         } else {
-            self.visit_block(block);
+            f(self);
         }
     }
 
+    fn resolve_labeled_block(&mut self, label: Option<SpannedIdent>, id: NodeId, block: &Block) {
+        self.with_resolved_label(label, id, |this| this.visit_block(block));
+    }
+
     fn resolve_expr(&mut self, expr: &Expr, parent: Option<&ExprKind>) {
         // First, record candidate traits for this expression if it could
         // result in the invocation of a method call.
@@ -2835,18 +2841,18 @@ impl<'a> Resolver<'a> {
             ExprKind::Loop(ref block, label) => self.resolve_labeled_block(label, expr.id, &block),
 
             ExprKind::While(ref subexpression, ref block, label) => {
-                self.visit_expr(subexpression);
-                self.resolve_labeled_block(label, expr.id, &block);
+                self.with_resolved_label(label, expr.id, |this| {
+                    this.visit_expr(subexpression);
+                    this.visit_block(block);
+                });
             }
 
             ExprKind::WhileLet(ref pattern, ref subexpression, ref block, label) => {
-                self.visit_expr(subexpression);
-                self.ribs[ValueNS].push(Rib::new(NormalRibKind));
-                self.resolve_pattern(pattern, PatternSource::WhileLet, &mut FxHashMap());
-
-                self.resolve_labeled_block(label, expr.id, block);
-
-                self.ribs[ValueNS].pop();
+                self.with_resolved_label(label, expr.id, |this| {
+                    this.visit_expr(subexpression);
+                    this.resolve_pattern(pattern, PatternSource::WhileLet, &mut FxHashMap());
+                    this.visit_block(block);
+                });
             }
 
             ExprKind::ForLoop(ref pattern, ref subexpression, ref block, label) => {
diff --git a/src/librustc_typeck/check/mod.rs b/src/librustc_typeck/check/mod.rs
index e9c9a63d79be9..f2c256ed7b158 100644
--- a/src/librustc_typeck/check/mod.rs
+++ b/src/librustc_typeck/check/mod.rs
@@ -425,8 +425,9 @@ pub struct EnclosingLoops<'gcx, 'tcx> {
 }
 
 impl<'gcx, 'tcx> EnclosingLoops<'gcx, 'tcx> {
-    fn find_loop(&mut self, id: ast::NodeId) -> Option<&mut LoopCtxt<'gcx, 'tcx>> {
-        if let Some(ix) = self.by_id.get(&id).cloned() {
+    fn find_loop(&mut self, id: hir::LoopIdResult) -> Option<&mut LoopCtxt<'gcx, 'tcx>> {
+        let id_res: Result<_,_> = id.into();
+        if let Some(ix) = id_res.ok().and_then(|id| self.by_id.get(&id).cloned()) {
             Some(&mut self.stack[ix])
         } else {
             None
@@ -3592,10 +3593,9 @@ impl<'a, 'gcx, 'tcx> FnCtxt<'a, 'gcx, 'tcx> {
               tcx.mk_nil()
           }
           hir::ExprBreak(label, ref expr_opt) => {
-            let loop_id = label.loop_id;
             let coerce_to = {
                 let mut enclosing_loops = self.enclosing_loops.borrow_mut();
-                enclosing_loops.find_loop(loop_id).map(|ctxt| ctxt.coerce_to)
+                enclosing_loops.find_loop(label.loop_id).map(|ctxt| ctxt.coerce_to)
             };
             if let Some(coerce_to) = coerce_to {
                 let e_ty;
@@ -3610,8 +3610,9 @@ impl<'a, 'gcx, 'tcx> FnCtxt<'a, 'gcx, 'tcx> {
                     e_ty = tcx.mk_nil();
                     cause = self.misc(expr.span);
                 }
+
                 let mut enclosing_loops = self.enclosing_loops.borrow_mut();
-                let ctxt = enclosing_loops.find_loop(loop_id).unwrap();
+                let ctxt = enclosing_loops.find_loop(label.loop_id).unwrap();
 
                 let result = if let Some(ref e) = *expr_opt {
                     // Special-case the first element, as it has no "previous expressions".
diff --git a/src/test/run-pass/loop-break-value.rs b/src/test/run-pass/loop-break-value.rs
index 10ff8dbf18e5e..4906a8e71d7a4 100644
--- a/src/test/run-pass/loop-break-value.rs
+++ b/src/test/run-pass/loop-break-value.rs
@@ -122,4 +122,20 @@ pub fn main() {
         panic!();
     };
     assert_eq!(nested_break_value, "hello");
+
+    let break_from_while_cond = loop {
+        'inner_loop: while break 'inner_loop {
+            panic!();
+        }
+        break 123;
+    };
+    assert_eq!(break_from_while_cond, 123);
+
+    let break_from_while_to_outer = 'outer_loop: loop {
+        while break 'outer_loop 567 {
+            panic!("from_inner");
+        }
+        panic!("from outer");
+    };
+    assert_eq!(break_from_while_to_outer, 567);
 }

From 56e519dd5c8df832dfb78a180ac771de3649b12f Mon Sep 17 00:00:00 2001
From: Taylor Cramer <cramertaylorj@gmail.com>
Date: Thu, 16 Feb 2017 20:24:18 -0800
Subject: [PATCH 3/5] Add tests for control flow in while condition

---
 src/test/compile-fail/issue-37576.rs          | 55 +++++++++++++++++++
 src/test/compile-fail/resolve-label.rs        |  3 +-
 .../graphviz-flowgraph/f10.dot-expected.dot   | 16 +++---
 .../graphviz-flowgraph/f23.dot-expected.dot   | 48 ++++++++--------
 4 files changed, 88 insertions(+), 34 deletions(-)
 create mode 100644 src/test/compile-fail/issue-37576.rs

diff --git a/src/test/compile-fail/issue-37576.rs b/src/test/compile-fail/issue-37576.rs
new file mode 100644
index 0000000000000..e3c1ada878df5
--- /dev/null
+++ b/src/test/compile-fail/issue-37576.rs
@@ -0,0 +1,55 @@
+// Copyright 2012 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+fn main() {
+    'test_1: while break 'test_1 {}
+    while break {}
+    //~^ ERROR `break` or `continue` with no label
+
+    'test_2: while let true = break 'test_2 {}
+    while let true = break {}
+    //~^ ERROR `break` or `continue` with no label
+
+    loop { 'test_3: while break 'test_3 {} }
+    loop { while break {} }
+    //~^ ERROR `break` or `continue` with no label
+
+    loop {
+        'test_4: while break 'test_4 {}
+        break;
+    }
+    loop {
+        while break {}
+        //~^ ERROR `break` or `continue` with no label
+        break;
+    }
+
+    'test_5: while continue 'test_5 {}
+    while continue {}
+    //~^ ERROR `break` or `continue` with no label
+
+    'test_6: while let true = continue 'test_6 {}
+    while let true = continue {}
+    //~^ ERROR `break` or `continue` with no label
+
+    loop { 'test_7: while continue 'test_7 {} }
+    loop { while continue {} }
+    //~^ ERROR `break` or `continue` with no label
+
+    loop {
+        'test_8: while continue 'test_8 {}
+        continue;
+    }
+    loop {
+        while continue {}
+        //~^ ERROR `break` or `continue` with no label
+        continue;
+    }
+}
diff --git a/src/test/compile-fail/resolve-label.rs b/src/test/compile-fail/resolve-label.rs
index ed2c3e0e9b860..6695e972f3337 100644
--- a/src/test/compile-fail/resolve-label.rs
+++ b/src/test/compile-fail/resolve-label.rs
@@ -17,8 +17,7 @@ fn f() {
         }
     }
 
-    // issue #37353
-    loop { 'w: while break 'w { } } //~ ERROR use of undeclared label
+    loop { 'w: while break 'w { } }
 }
 
 fn main() {}
diff --git a/src/test/run-make/graphviz-flowgraph/f10.dot-expected.dot b/src/test/run-make/graphviz-flowgraph/f10.dot-expected.dot
index a3b531b1e2f41..07b9c744a7171 100644
--- a/src/test/run-make/graphviz-flowgraph/f10.dot-expected.dot
+++ b/src/test/run-make/graphviz-flowgraph/f10.dot-expected.dot
@@ -5,10 +5,10 @@ digraph block {
     N3[label="local mut x"];
     N4[label="stmt let mut x = 10;"];
     N5[label="(dummy_node)"];
-    N6[label="expr x"];
-    N7[label="expr 0"];
-    N8[label="expr x > 0"];
-    N9[label="expr while x > 0 { x -= 1; }"];
+    N6[label="expr while x > 0 { x -= 1; }"];
+    N7[label="expr x"];
+    N8[label="expr 0"];
+    N9[label="expr x > 0"];
     N10[label="expr 1"];
     N11[label="expr x"];
     N12[label="expr x -= 1"];
@@ -20,17 +20,17 @@ digraph block {
     N2 -> N3;
     N3 -> N4;
     N4 -> N5;
-    N5 -> N6;
-    N6 -> N7;
+    N5 -> N7;
     N7 -> N8;
     N8 -> N9;
-    N8 -> N10;
+    N9 -> N6;
+    N9 -> N10;
     N10 -> N11;
     N11 -> N12;
     N12 -> N13;
     N13 -> N14;
     N14 -> N5;
-    N9 -> N15;
+    N6 -> N15;
     N15 -> N16;
     N16 -> N1;
 }
diff --git a/src/test/run-make/graphviz-flowgraph/f23.dot-expected.dot b/src/test/run-make/graphviz-flowgraph/f23.dot-expected.dot
index f152977438c50..c8bfcd6510b30 100644
--- a/src/test/run-make/graphviz-flowgraph/f23.dot-expected.dot
+++ b/src/test/run-make/graphviz-flowgraph/f23.dot-expected.dot
@@ -11,28 +11,28 @@ digraph block {
     N9[label="local mut z"];
     N10[label="stmt let mut z = 23;"];
     N11[label="(dummy_node)"];
-    N12[label="expr x"];
-    N13[label="expr 0"];
-    N14[label="expr x > 0"];
-    N15[label="expr while x > 0 {\l    x -= 1;\l    while y > 0 {\l        y -= 1;\l        while z > 0 { z -= 1; }\l        if x > 10 { return; \"unreachable\"; }\l    }\l}\l"];
+    N12[label="expr while x > 0 {\l    x -= 1;\l    while y > 0 {\l        y -= 1;\l        while z > 0 { z -= 1; }\l        if x > 10 { return; \"unreachable\"; }\l    }\l}\l"];
+    N13[label="expr x"];
+    N14[label="expr 0"];
+    N15[label="expr x > 0"];
     N16[label="expr 1"];
     N17[label="expr x"];
     N18[label="expr x -= 1"];
     N19[label="stmt x -= 1;"];
     N20[label="(dummy_node)"];
-    N21[label="expr y"];
-    N22[label="expr 0"];
-    N23[label="expr y > 0"];
-    N24[label="expr while y > 0 {\l    y -= 1;\l    while z > 0 { z -= 1; }\l    if x > 10 { return; \"unreachable\"; }\l}\l"];
+    N21[label="expr while y > 0 {\l    y -= 1;\l    while z > 0 { z -= 1; }\l    if x > 10 { return; \"unreachable\"; }\l}\l"];
+    N22[label="expr y"];
+    N23[label="expr 0"];
+    N24[label="expr y > 0"];
     N25[label="expr 1"];
     N26[label="expr y"];
     N27[label="expr y -= 1"];
     N28[label="stmt y -= 1;"];
     N29[label="(dummy_node)"];
-    N30[label="expr z"];
-    N31[label="expr 0"];
-    N32[label="expr z > 0"];
-    N33[label="expr while z > 0 { z -= 1; }"];
+    N30[label="expr while z > 0 { z -= 1; }"];
+    N31[label="expr z"];
+    N32[label="expr 0"];
+    N33[label="expr z > 0"];
     N34[label="expr 1"];
     N35[label="expr z"];
     N36[label="expr z -= 1"];
@@ -63,35 +63,35 @@ digraph block {
     N8 -> N9;
     N9 -> N10;
     N10 -> N11;
-    N11 -> N12;
-    N12 -> N13;
+    N11 -> N13;
     N13 -> N14;
     N14 -> N15;
-    N14 -> N16;
+    N15 -> N12;
+    N15 -> N16;
     N16 -> N17;
     N17 -> N18;
     N18 -> N19;
     N19 -> N20;
-    N20 -> N21;
-    N21 -> N22;
+    N20 -> N22;
     N22 -> N23;
     N23 -> N24;
-    N23 -> N25;
+    N24 -> N21;
+    N24 -> N25;
     N25 -> N26;
     N26 -> N27;
     N27 -> N28;
     N28 -> N29;
-    N29 -> N30;
-    N30 -> N31;
+    N29 -> N31;
     N31 -> N32;
     N32 -> N33;
-    N32 -> N34;
+    N33 -> N30;
+    N33 -> N34;
     N34 -> N35;
     N35 -> N36;
     N36 -> N37;
     N37 -> N38;
     N38 -> N29;
-    N33 -> N39;
+    N30 -> N39;
     N39 -> N40;
     N40 -> N41;
     N41 -> N42;
@@ -105,9 +105,9 @@ digraph block {
     N48 -> N49;
     N49 -> N50;
     N50 -> N20;
-    N24 -> N51;
+    N21 -> N51;
     N51 -> N11;
-    N15 -> N52;
+    N12 -> N52;
     N52 -> N53;
     N53 -> N1;
 }

From a611bbcceb15ca6d191dbbb2436da92677d0ca99 Mon Sep 17 00:00:00 2001
From: Taylor Cramer <cramertaylorj@gmail.com>
Date: Fri, 17 Feb 2017 18:55:28 -0800
Subject: [PATCH 4/5] Rename hir::Label to hir::Destination

---
 src/librustc/cfg/construct.rs | 12 ++++++------
 src/librustc/hir/lowering.rs  | 20 +++++++++++---------
 src/librustc/hir/mod.rs       |  6 +++---
 3 files changed, 20 insertions(+), 18 deletions(-)

diff --git a/src/librustc/cfg/construct.rs b/src/librustc/cfg/construct.rs
index fdb350ebaac97..122543aee40ec 100644
--- a/src/librustc/cfg/construct.rs
+++ b/src/librustc/cfg/construct.rs
@@ -303,17 +303,17 @@ impl<'a, 'tcx> CFGBuilder<'a, 'tcx> {
                 self.add_unreachable_node()
             }
 
-            hir::ExprBreak(label, ref opt_expr) => {
+            hir::ExprBreak(destination, ref opt_expr) => {
                 let v = self.opt_expr(opt_expr, pred);
-                let loop_scope = self.find_scope(expr, label);
+                let loop_scope = self.find_scope(expr, destination);
                 let b = self.add_ast_node(expr.id, &[v]);
                 self.add_exiting_edge(expr, b,
                                       loop_scope, loop_scope.break_index);
                 self.add_unreachable_node()
             }
 
-            hir::ExprAgain(label) => {
-                let loop_scope = self.find_scope(expr, label);
+            hir::ExprAgain(destination) => {
+                let loop_scope = self.find_scope(expr, destination);
                 let a = self.add_ast_node(expr.id, &[pred]);
                 self.add_exiting_edge(expr, a,
                                       loop_scope, loop_scope.continue_index);
@@ -588,9 +588,9 @@ impl<'a, 'tcx> CFGBuilder<'a, 'tcx> {
 
     fn find_scope(&self,
                   expr: &hir::Expr,
-                  label: hir::Label) -> LoopScope {
+                  destination: hir::Destination) -> LoopScope {
 
-        match label.loop_id.into() {
+        match destination.loop_id.into() {
             Ok(loop_id) => {
                 for l in &self.loop_scopes {
                     if l.loop_id == loop_id {
diff --git a/src/librustc/hir/lowering.rs b/src/librustc/hir/lowering.rs
index 55226fa7605d3..efb351e032557 100644
--- a/src/librustc/hir/lowering.rs
+++ b/src/librustc/hir/lowering.rs
@@ -326,9 +326,11 @@ impl<'a> LoweringContext<'a> {
         o_id.map(|sp_ident| respan(sp_ident.span, sp_ident.node.name))
     }
 
-    fn lower_label(&mut self, label: Option<(NodeId, Spanned<Ident>)>) -> hir::Label {
-        match label {
-            Some((id, label_ident)) => hir::Label {
+    fn lower_destination(&mut self, destination: Option<(NodeId, Spanned<Ident>)>)
+        -> hir::Destination
+    {
+        match destination {
+            Some((id, label_ident)) => hir::Destination {
                 ident: Some(label_ident),
                 loop_id: if let Def::Label(loop_id) = self.expect_full_def(id) {
                     hir::LoopIdResult::Ok(loop_id)
@@ -336,7 +338,7 @@ impl<'a> LoweringContext<'a> {
                     hir::LoopIdResult::Err(hir::LoopIdError::UnresolvedLabel)
                 }
             },
-            None => hir::Label {
+            None => hir::Destination {
                 ident: None,
                 loop_id: self.loop_scopes.last().map(|innermost_loop_id| Ok(*innermost_loop_id))
                             .unwrap_or(Err(hir::LoopIdError::OutsideLoopScope)).into()
@@ -1729,12 +1731,12 @@ impl<'a> LoweringContext<'a> {
                 }
                 ExprKind::Break(opt_ident, ref opt_expr) => {
                     let label_result = if self.is_in_loop_condition && opt_ident.is_none() {
-                        hir::Label {
+                        hir::Destination {
                             ident: opt_ident,
                             loop_id: Err(hir::LoopIdError::UnlabeledCfInWhileCondition).into(),
                         }
                     } else {
-                        self.lower_label(opt_ident.map(|ident| (e.id, ident)))
+                        self.lower_destination(opt_ident.map(|ident| (e.id, ident)))
                     };
                     hir::ExprBreak(
                             label_result,
@@ -1743,13 +1745,13 @@ impl<'a> LoweringContext<'a> {
                 ExprKind::Continue(opt_ident) =>
                     hir::ExprAgain(
                         if self.is_in_loop_condition && opt_ident.is_none() {
-                            hir::Label {
+                            hir::Destination {
                                 ident: opt_ident,
                                 loop_id: Err(
                                     hir::LoopIdError::UnlabeledCfInWhileCondition).into(),
                             }
                         } else {
-                            self.lower_label(opt_ident.map( | ident| (e.id, ident)))
+                            self.lower_destination(opt_ident.map( |ident| (e.id, ident)))
                         }),
                 ExprKind::Ret(ref e) => hir::ExprRet(e.as_ref().map(|x| P(self.lower_expr(x)))),
                 ExprKind::InlineAsm(ref asm) => {
@@ -2244,7 +2246,7 @@ impl<'a> LoweringContext<'a> {
     }
 
     fn expr_break(&mut self, span: Span, attrs: ThinVec<Attribute>) -> P<hir::Expr> {
-        let expr_break = hir::ExprBreak(self.lower_label(None), None);
+        let expr_break = hir::ExprBreak(self.lower_destination(None), None);
         P(self.expr(span, expr_break, attrs))
     }
 
diff --git a/src/librustc/hir/mod.rs b/src/librustc/hir/mod.rs
index 4e4187cbf8905..e8c5f2447cd6f 100644
--- a/src/librustc/hir/mod.rs
+++ b/src/librustc/hir/mod.rs
@@ -959,9 +959,9 @@ pub enum Expr_ {
     /// A referencing operation (`&a` or `&mut a`)
     ExprAddrOf(Mutability, P<Expr>),
     /// A `break`, with an optional label to break
-    ExprBreak(Label, Option<P<Expr>>),
+    ExprBreak(Destination, Option<P<Expr>>),
     /// A `continue`, with an optional label
-    ExprAgain(Label),
+    ExprAgain(Destination),
     /// A `return`, with an optional value to be returned
     ExprRet(Option<P<Expr>>),
 
@@ -1073,7 +1073,7 @@ impl From<Result<NodeId, LoopIdError>> for LoopIdResult {
 }
 
 #[derive(Clone, PartialEq, Eq, RustcEncodable, RustcDecodable, Hash, Debug, Copy)]
-pub struct Label {
+pub struct Destination {
     // This is `Some(_)` iff there is an explicit user-specified `label
     pub ident: Option<Spanned<Ident>>,
 

From 6f0447b52bdbe1bc54902816078f3dbef4426515 Mon Sep 17 00:00:00 2001
From: Taylor Cramer <cramertaylorj@gmail.com>
Date: Wed, 22 Feb 2017 18:10:37 -0800
Subject: [PATCH 5/5] Change break or continue with no label to error nmbr 590

---
 src/librustc_passes/diagnostics.rs | 2 +-
 src/librustc_passes/loops.rs       | 2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/src/librustc_passes/diagnostics.rs b/src/librustc_passes/diagnostics.rs
index c576b35cb17b4..5f06eadb84a92 100644
--- a/src/librustc_passes/diagnostics.rs
+++ b/src/librustc_passes/diagnostics.rs
@@ -242,7 +242,7 @@ match 5u32 {
 ```
 "##,
 
-E0583: r##"
+E0590: r##"
 `break` or `continue` must include a label when used in the condition of a
 `while` loop.
 
diff --git a/src/librustc_passes/loops.rs b/src/librustc_passes/loops.rs
index 003142f349831..b2d51be5bf720 100644
--- a/src/librustc_passes/loops.rs
+++ b/src/librustc_passes/loops.rs
@@ -161,7 +161,7 @@ impl<'a, 'hir> CheckLoopVisitor<'a, 'hir> {
     }
 
     fn emit_unlabled_cf_in_while_condition(&mut self, span: Span, cf_type: &str) {
-        struct_span_err!(self.sess, span, E0583,
+        struct_span_err!(self.sess, span, E0590,
                          "`break` or `continue` with no label in the condition of a `while` loop")
             .span_label(span,
                         &format!("unlabeled `{}` in the condition of a `while` loop", cf_type))