Auto merge of #38552 - eddyb:bad-blocks, r=arielb1

Don't leak the compiler's internal representation of scopes in error messages.

Fixes #37884 (actually fixes #27942, which was made worse by #37412) by handling more node types.
Ideally we'd turn the unknown node type situations into ICEs and fix them as they show up in errors.
But we might want to backport this patch so I was less aggressive.

Author: bors

src/librustc/infer/error_reporting.rs

@@ -113,6 +113,22 @@ impl<'a, 'gcx, 'tcx> TyCtxt<'a, 'gcx, 'tcx> {
             }
         }
 
+        fn trait_item_scope_tag(item: &hir::TraitItem) -> &'static str {
+            match item.node {
+                hir::TraitItemKind::Method(..) => "method body",
+                hir::TraitItemKind::Const(..) |
+                hir::TraitItemKind::Type(..) => "associated item"
+            }
+        }
+
+        fn impl_item_scope_tag(item: &hir::ImplItem) -> &'static str {
+            match item.node {
+                hir::ImplItemKind::Method(..) => "method body",
+                hir::ImplItemKind::Const(..) |
+                hir::ImplItemKind::Type(_) => "associated item"
+            }
+        }
+
         fn explain_span<'a, 'gcx, 'tcx>(tcx: TyCtxt<'a, 'gcx, 'tcx>,
                                         heading: &str, span: Span)
                                         -> (String, Option<Span>) {
@@ -148,6 +164,8 @@ impl<'a, 'gcx, 'tcx> TyCtxt<'a, 'gcx, 'tcx> {
                     },
                     Some(ast_map::NodeStmt(_)) => "statement",
                     Some(ast_map::NodeItem(it)) => item_scope_tag(&it),
+                    Some(ast_map::NodeTraitItem(it)) => trait_item_scope_tag(&it),
+                    Some(ast_map::NodeImplItem(it)) => impl_item_scope_tag(&it),
                     Some(_) | None => {
                         err.span_note(span, &unknown_scope());
                         return;
@@ -186,23 +204,31 @@ impl<'a, 'gcx, 'tcx> TyCtxt<'a, 'gcx, 'tcx> {
                     }
                 };
 
-                match self.map.find(fr.scope.node_id(&self.region_maps)) {
-                    Some(ast_map::NodeBlock(ref blk)) => {
-                        let (msg, opt_span) = explain_span(self, "block", blk.span);
-                        (format!("{} {}", prefix, msg), opt_span)
-                    }
-                    Some(ast_map::NodeItem(it)) => {
-                        let tag = item_scope_tag(&it);
-                        let (msg, opt_span) = explain_span(self, tag, it.span);
-                        (format!("{} {}", prefix, msg), opt_span)
+                let node = fr.scope.node_id(&self.region_maps);
+                let unknown;
+                let tag = match self.map.find(node) {
+                    Some(ast_map::NodeBlock(_)) |
+                    Some(ast_map::NodeExpr(_)) => "body",
+                    Some(ast_map::NodeItem(it)) => item_scope_tag(&it),
+                    Some(ast_map::NodeTraitItem(it)) => trait_item_scope_tag(&it),
+                    Some(ast_map::NodeImplItem(it)) => impl_item_scope_tag(&it),
+
+                    // this really should not happen, but it does:
+                    // FIXME(#27942)
+                    Some(_) => {
+                        unknown = format!("unexpected node ({}) for scope {:?}.  \
+                                           Please report a bug.",
+                                          self.map.node_to_string(node), fr.scope);
+                        &unknown
                     }
-                    Some(_) | None => {
-                        // this really should not happen, but it does:
-                        // FIXME(#27942)
-                        (format!("{} unknown free region bounded by scope {:?}",
-                                 prefix, fr.scope), None)
+                    None => {
+                        unknown = format!("unknown node for scope {:?}.  \
+                                           Please report a bug.", fr.scope);
+                        &unknown
                     }
-                }
+                };
+                let (msg, opt_span) = explain_span(self, tag, self.map.span(node));
+                (format!("{} {}", prefix, msg), opt_span)
             }
 
             ty::ReStatic => ("the static lifetime".to_owned(), None),

src/test/compile-fail/issue-27942.rs

@@ -0,0 +1,31 @@
+// Copyright 2016 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.
+
+pub trait Resources<'a> {}
+
+pub trait Buffer<'a, R: Resources<'a>> {
+    fn select(&self) -> BufferViewHandle<R>;
+    //~^ ERROR mismatched types
+    //~| lifetime mismatch
+    //~| NOTE expected type `Resources<'_>`
+    //~| NOTE    found type `Resources<'a>`
+    //~| NOTE the lifetime 'a as defined on the method body at 14:4...
+    //~| NOTE ...does not necessarily outlive the anonymous lifetime #1 defined on the method body
+    //~| ERROR mismatched types
+    //~| lifetime mismatch
+    //~| NOTE expected type `Resources<'_>`
+    //~| NOTE    found type `Resources<'a>`
+    //~| NOTE the anonymous lifetime #1 defined on the method body at 14:4...
+    //~| NOTE ...does not necessarily outlive the lifetime 'a as defined on the method body
+}
+
+pub struct BufferViewHandle<'a, R: 'a+Resources<'a>>(&'a R);
+
+fn main() {}

src/test/compile-fail/issue-37884.rs

@@ -0,0 +1,27 @@
+// Copyright 2016 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.
+
+struct RepeatMut<'a, T>(T, &'a ());
+
+impl<'a, T: 'a> Iterator for RepeatMut<'a, T> {
+    type Item = &'a mut T;
+    fn next(&'a mut self) -> Option<Self::Item>
+    //~^ ERROR method not compatible with trait
+    //~| lifetime mismatch
+    //~| NOTE expected type `fn(&mut RepeatMut<'a, T>) -> std::option::Option<&mut T>`
+    //~| NOTE    found type `fn(&'a mut RepeatMut<'a, T>) -> std::option::Option<&mut T>`
+    {
+    //~^ NOTE the anonymous lifetime #1 defined on the body
+    //~| NOTE ...does not necessarily outlive the lifetime 'a as defined on the body
+        Some(&mut self.0)
+    }
+}
+
+fn main() {}