Point at unknown lang item attribute

src/librustc/middle/lang_items.rs

@@ -28,6 +28,7 @@ use util::nodemap::FxHashMap;
 
 use syntax::ast;
 use syntax::symbol::Symbol;
+use syntax_pos::Span;
 use hir::itemlikevisit::ItemLikeVisitor;
 use hir;
 
@@ -104,17 +105,18 @@ struct LanguageItemCollector<'a, 'tcx: 'a> {
 
 impl<'a, 'v, 'tcx> ItemLikeVisitor<'v> for LanguageItemCollector<'a, 'tcx> {
     fn visit_item(&mut self, item: &hir::Item) {
-        if let Some(value) = extract(&item.attrs) {
+        if let Some((value, span)) = extract(&item.attrs) {
             let item_index = self.item_refs.get(&*value.as_str()).cloned();
 
             if let Some(item_index) = item_index {
                 let def_id = self.tcx.hir.local_def_id(item.id);
                 self.collect_item(item_index, def_id);
             } else {
-                let span = self.tcx.hir.span(item.id);
-                span_err!(self.tcx.sess, span, E0522,
-                          "definition of an unknown language item: `{}`.",
-                          value);
+                let mut err = struct_span_err!(self.tcx.sess, span, E0522,
+                                               "definition of an unknown language item: `{}`",
+                                               value);
+                err.span_label(span, format!("definition of unknown language item `{}`", value));
+                err.emit();
             }
         }
     }
@@ -177,11 +179,11 @@ impl<'a, 'tcx> LanguageItemCollector<'a, 'tcx> {
     }
 }
 
-pub fn extract(attrs: &[ast::Attribute]) -> Option<Symbol> {
+pub fn extract(attrs: &[ast::Attribute]) -> Option<(Symbol, Span)> {
     for attribute in attrs {
         if attribute.check_name("lang") {
             if let Some(value) = attribute.value_str() {
-                return Some(value)
+                return Some((value, attribute.span));
             }
         }
     }

src/librustc/middle/weak_lang_items.rs

@@ -55,7 +55,7 @@ pub fn check_crate<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
 }
 
 pub fn link_name(attrs: &[ast::Attribute]) -> Option<Symbol> {
-    lang_items::extract(attrs).and_then(|name| {
+    lang_items::extract(attrs).and_then(|(name, _)| {
         $(if name == stringify!($name) {
             Some(Symbol::intern(stringify!($sym)))
         } else)* {
@@ -129,7 +129,7 @@ impl<'a, 'tcx, 'v> Visitor<'v> for Context<'a, 'tcx> {
     }
 
     fn visit_foreign_item(&mut self, i: &hir::ForeignItem) {
-        if let Some(lang_item) = lang_items::extract(&i.attrs) {
+        if let Some((lang_item, _)) = lang_items::extract(&i.attrs) {
             self.register(&lang_item.as_str(), i.span);
         }
         intravisit::walk_foreign_item(self, i)

src/test/compile-fail/E0522.rs

@@ -11,6 +11,7 @@
 #![feature(lang_items)]
 
 #[lang = "cookie"]
-fn cookie() -> ! { //~ E0522
+fn cookie() -> ! {
+//~^^ ERROR definition of an unknown language item: `cookie` [E0522]
     loop {}
 }

src/test/ui/unknown-language-item.rs

@@ -0,0 +1,20 @@
+// Copyright 2018 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.
+
+#![allow(unused)]
+#![feature(lang_items)]
+
+#[lang = "foo"]
+fn bar() -> ! {
+//~^^ ERROR definition of an unknown language item: `foo`
+    loop {}
+}
+
+fn main() {}

src/test/ui/unknown-language-item.stderr

@@ -0,0 +1,8 @@
+error[E0522]: definition of an unknown language item: `foo`
+  --> $DIR/unknown-language-item.rs:14:1
+   |
+14 | #[lang = "foo"]
+   | ^^^^^^^^^^^^^^^ definition of unknown language item `foo`
+
+error: aborting due to previous error
+