Auto merge of #31957 - GuillaumeGomez:error_display, r=brson

Add error file for E0152

It completes #31818.

However it is not complete yet:
 * test will need to be updated
 * the file name displayed is a bit too unclear.

I'm not sure yet what's the "correct" file name to display. If anyone has an idea on this, it'd be very appreciated.

r? @brson

src/librustc/middle/lang_items.rs

@@ -32,7 +32,6 @@ use util::nodemap::FnvHashMap;
 
 use syntax::ast;
 use syntax::attr::AttrMetaMethods;
-use syntax::codemap::{DUMMY_SP, Span};
 use syntax::parse::token::InternedString;
 use rustc_front::intravisit::Visitor;
 use rustc_front::hir;
@@ -158,7 +157,7 @@ impl<'a, 'v, 'tcx> Visitor<'v> for LanguageItemCollector<'a, 'tcx> {
             let item_index = self.item_refs.get(&value[..]).cloned();
 
             if let Some(item_index) = item_index {
-                self.collect_item(item_index, self.ast_map.local_def_id(item.id), item.span)
+                self.collect_item(item_index, self.ast_map.local_def_id(item.id))
             }
         }
     }
@@ -180,15 +179,26 @@ impl<'a, 'tcx> LanguageItemCollector<'a, 'tcx> {
     }
 
     pub fn collect_item(&mut self, item_index: usize,
-                        item_def_id: DefId, span: Span) {
+                        item_def_id: DefId) {
         // Check for duplicates.
         match self.items.items[item_index] {
             Some(original_def_id) if original_def_id != item_def_id => {
                 let cstore = &self.session.cstore;
-                span_err!(self.session, span, E0152,
-                          "duplicate entry for `{}`, first definition found in `{}`",
-                          LanguageItems::item_name(item_index),
-                          cstore.crate_name(item_def_id.krate));
+                let span = self.ast_map.span_if_local(item_def_id)
+                                       .expect("we should have found local duplicate earlier");
+                let mut err = struct_span_err!(self.session,
+                                               span,
+                                               E0152,
+                                               "duplicate lang item found: `{}`.",
+                                               LanguageItems::item_name(item_index));
+                if let Some(span) = self.ast_map.span_if_local(original_def_id) {
+                    span_note!(&mut err, span,
+                               "first defined here.");
+                } else {
+                    err.note(&format!("first defined in crate `{}`.",
+                                      cstore.crate_name(original_def_id.krate)));
+                }
+                err.emit();
             }
             _ => {
                 // OK.
@@ -205,17 +215,18 @@ impl<'a, 'tcx> LanguageItemCollector<'a, 'tcx> {
 
     pub fn collect_external_language_items(&mut self) {
         let cstore = &self.session.cstore;
+
         for cnum in cstore.crates() {
             for (index, item_index) in cstore.lang_items(cnum) {
                 let def_id = DefId { krate: cnum, index: index };
-                self.collect_item(item_index, def_id, DUMMY_SP);
+                self.collect_item(item_index, def_id);
             }
         }
     }
 
     pub fn collect(&mut self, krate: &hir::Crate) {
-        self.collect_local_language_items(krate);
         self.collect_external_language_items();
+        self.collect_local_language_items(krate);
     }
 }
 

src/test/compile-fail/duplicate_entry_error.rs

@@ -8,14 +8,15 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
-// Test for issue #31788
+// note-pattern: first defined in crate `std`.
 
-// error-pattern: duplicate entry for `panic_fmt`, first definition found in `std`
+// Test for issue #31788 and E0152
 
 #![feature(lang_items)]
 
 #[lang = "panic_fmt"]
 fn panic_fmt() -> ! {
+//~^ ERROR: duplicate lang item found: `panic_fmt`.
     loop {}
 }