Emit dropped unemitted errors to aid in ICE debugging

src/librustc_errors/diagnostic_builder.rs

@@ -380,10 +380,13 @@ impl<'a> Debug for DiagnosticBuilder<'a> {
 impl<'a> Drop for DiagnosticBuilder<'a> {
     fn drop(&mut self) {
         if !panicking() && !self.cancelled() {
-            let mut db = DiagnosticBuilder::new(self.handler,
+            let mut db = DiagnosticBuilder::new(
-                                                Level::Bug,
+                self.handler,
-                                                "Error constructed but not emitted");
+                Level::Bug,
+                "the following error was constructed but not emitted",
+            );
             db.emit();
+            self.emit();
             panic!();
         }
     }

src/libsyntax/parse/parser.rs

@@ -6666,12 +6666,13 @@ impl<'a> Parser<'a> {
     }
 
     /// Reads a module from a source file.
-    fn eval_src_mod(&mut self,
+    fn eval_src_mod(
-                    path: PathBuf,
+        &mut self,
-                    directory_ownership: DirectoryOwnership,
+        path: PathBuf,
-                    name: String,
+        directory_ownership: DirectoryOwnership,
-                    id_sp: Span)
+        name: String,
-                    -> PResult<'a, (ast::Mod, Vec<Attribute> )> {
+        id_sp: Span,
+    ) -> PResult<'a, (ast::Mod, Vec<Attribute>)> {
         let mut included_mod_stack = self.sess.included_mod_stack.borrow_mut();
         if let Some(i) = included_mod_stack.iter().position(|p| *p == path) {
             let mut err = String::from("circular modules: ");

src/libsyntax/util/parser_testing.rs

@@ -34,7 +34,7 @@ fn with_error_checking_parse<'a, T, F>(s: String, ps: &'a ParseSess, f: F) -> T
 }
 
 /// Parse a string, return a crate.
-pub fn string_to_crate (source_str : String) -> ast::Crate {
+pub fn string_to_crate(source_str : String) -> ast::Crate {
     let ps = ParseSess::new(FilePathMapping::empty());
     with_error_checking_parse(source_str, &ps, |p| {
         p.parse_crate_mod()
@@ -42,7 +42,7 @@ pub fn string_to_crate (source_str : String) -> ast::Crate {
 }
 
 /// Parse a string, return an expr
-pub fn string_to_expr (source_str : String) -> P<ast::Expr> {
+pub fn string_to_expr(source_str : String) -> P<ast::Expr> {
     let ps = ParseSess::new(FilePathMapping::empty());
     with_error_checking_parse(source_str, &ps, |p| {
         p.parse_expr()
@@ -50,7 +50,7 @@ pub fn string_to_expr (source_str : String) -> P<ast::Expr> {
 }
 
 /// Parse a string, return an item
-pub fn string_to_item (source_str : String) -> Option<P<ast::Item>> {
+pub fn string_to_item(source_str : String) -> Option<P<ast::Item>> {
     let ps = ParseSess::new(FilePathMapping::empty());
     with_error_checking_parse(source_str, &ps, |p| {
         p.parse_item()