From a23e4fc5116f6d7ec5e045533e89c0c14ac868e2 Mon Sep 17 00:00:00 2001
From: ggomez <guillaume1.gomez@gmail.com>
Date: Mon, 22 Feb 2016 14:05:01 +0100
Subject: [PATCH 1/2] Add crate_name in E0152 error display

---
 src/librustc/middle/lang_items.rs | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/src/librustc/middle/lang_items.rs b/src/librustc/middle/lang_items.rs
index a22ad7a0707c2..6cbb90627eab5 100644
--- a/src/librustc/middle/lang_items.rs
+++ b/src/librustc/middle/lang_items.rs
@@ -184,10 +184,13 @@ impl<'a, 'tcx> LanguageItemCollector<'a, 'tcx> {
         // 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 `{}`", LanguageItems::item_name(item_index));
+                          "duplicate entry for `{}`, first definition found in `{}`",
+                          LanguageItems::item_name(item_index),
+                          cstore.crate_name(item_def_id.krate));
             }
-            Some(_) | None => {
+            _ => {
                 // OK.
             }
         }

From dfe72fa4ce2c31be3ee941f6df216e3a463cf68a Mon Sep 17 00:00:00 2001
From: Guillaume Gomez <guillaume1.gomez@gmail.com>
Date: Sat, 20 Feb 2016 22:53:29 +0100
Subject: [PATCH 2/2] Add test for E0152 error message improvement

---
 .../compile-fail/duplicate_entry_error.rs     | 22 +++++++++++++++++++
 1 file changed, 22 insertions(+)
 create mode 100644 src/test/compile-fail/duplicate_entry_error.rs

diff --git a/src/test/compile-fail/duplicate_entry_error.rs b/src/test/compile-fail/duplicate_entry_error.rs
new file mode 100644
index 0000000000000..d39553a7267e0
--- /dev/null
+++ b/src/test/compile-fail/duplicate_entry_error.rs
@@ -0,0 +1,22 @@
+// Copyright 2015 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.
+
+// Test for issue #31788
+
+// error-pattern: duplicate entry for `panic_fmt`, first definition found in `std`
+
+#![feature(lang_items)]
+
+#[lang = "panic_fmt"]
+fn panic_fmt() -> ! {
+    loop {}
+}
+
+fn main() {}
\ No newline at end of file