Rollup merge of rust-lang#73449 - ehuss:duplicate-lang-item, r=matthe…

…wjasper

Provide more information on duplicate lang item error.

This gives some notes on the location of the files where the lang items were loaded from. Some duplicate lang item errors can be a little confusing, and this might help in diagnosing what has happened.

Here's an example when hitting a bug with Cargo's build-std:

```
error: duplicate lang item in crate `core` (which `rustc_std_workspace_core` depends on): `try`.
  |
  = note: the lang item is first defined in crate `core` (which `z10` depends on)
  = note: first definition in `core` loaded from /Users/eric/Proj/rust/cargo/scratch/z10/target/target/debug/deps/libcore-a764da499c7385f4.rmeta
  = note: second definition in `core` loaded from /Users/eric/Proj/rust/cargo/scratch/z10/target/target/debug/deps/libcore-5b082675aea34986.rmeta
```

src/librustc_metadata/rmeta/decoder/cstore_impl.rs

@@ -239,6 +239,8 @@ provide! { <'tcx> tcx, def_id, other, cdata,
 
         syms
     }
+
+    crate_extern_paths => { cdata.source().paths().cloned().collect() }
 }
 
 pub fn provide(providers: &mut Providers<'_>) {

src/librustc_middle/query/mod.rs

@@ -1042,6 +1042,10 @@ rustc_queries! {
             eval_always
             desc { "looking up the extra filename for a crate" }
         }
+        query crate_extern_paths(_: CrateNum) -> Vec<PathBuf> {
+            eval_always
+            desc { "looking up the paths for extern crates" }
+        }
     }
 
     TypeChecking {

src/librustc_middle/ty/query/mod.rs

@@ -57,6 +57,7 @@ use rustc_span::{Span, DUMMY_SP};
 use std::borrow::Cow;
 use std::collections::BTreeMap;
 use std::ops::Deref;
+use std::path::PathBuf;
 use std::sync::Arc;
 
 #[macro_use]

src/librustc_passes/lang_items.rs

@@ -146,6 +146,28 @@ impl LanguageItemCollector<'tcx> {
                             ));
                         }
                     }
+                    let mut note_def = |which, def_id: DefId| {
+                        let crate_name = self.tcx.crate_name(def_id.krate);
+                        let note = if def_id.is_local() {
+                            format!("{} definition in the local crate (`{}`)", which, crate_name)
+                        } else {
+                            let paths: Vec<_> = self
+                                .tcx
+                                .crate_extern_paths(def_id.krate)
+                                .iter()
+                                .map(|p| p.display().to_string())
+                                .collect();
+                            format!(
+                                "{} definition in `{}` loaded from {}",
+                                which,
+                                crate_name,
+                                paths.join(", ")
+                            )
+                        };
+                        err.note(&note);
+                    };
+                    note_def("first", original_def_id);
+                    note_def("second", item_def_id);
                 }
                 err.emit();
             }

src/test/ui/duplicate_entry_error.rs

@@ -1,3 +1,4 @@
+// normalize-stderr-test "loaded from .*libstd-.*.rlib" -> "loaded from SYSROOT/libstd-*.rlib"
 // note-pattern: first defined in crate `std`.
 
 // Test for issue #31788 and E0152

src/test/ui/duplicate_entry_error.stderr

@@ -1,5 +1,5 @@
 error[E0152]: found duplicate lang item `panic_impl`
-  --> $DIR/duplicate_entry_error.rs:10:1
+  --> $DIR/duplicate_entry_error.rs:11:1
    |
 LL | / fn panic_impl(info: &PanicInfo) -> ! {
 LL | |
@@ -8,6 +8,8 @@ LL | | }
    | |_^
    |
    = note: the lang item is first defined in crate `std` (which `duplicate_entry_error` depends on)
+   = note: first definition in `std` loaded from SYSROOT/libstd-*.rlib
+   = note: second definition in the local crate (`duplicate_entry_error`)
 
 error: aborting due to previous error
 

src/test/ui/error-codes/E0152.rs

@@ -1,3 +1,4 @@
+// normalize-stderr-test "loaded from .*liballoc-.*.rlib" -> "loaded from SYSROOT/liballoc-*.rlib"
 #![feature(lang_items)]
 
 #[lang = "owned_box"]

src/test/ui/error-codes/E0152.stderr

@@ -1,10 +1,12 @@
 error[E0152]: found duplicate lang item `owned_box`
-  --> $DIR/E0152.rs:4:1
+  --> $DIR/E0152.rs:5:1
    |
 LL | struct Foo;
    | ^^^^^^^^^^^
    |
    = note: the lang item is first defined in crate `alloc` (which `std` depends on)
+   = note: first definition in `alloc` loaded from SYSROOT/liballoc-*.rlib
+   = note: second definition in the local crate (`E0152`)
 
 error: aborting due to previous error
 

src/test/ui/panic-handler/panic-handler-std.rs

@@ -1,3 +1,4 @@
+// normalize-stderr-test "loaded from .*libstd-.*.rlib" -> "loaded from SYSROOT/libstd-*.rlib"
 // error-pattern: found duplicate lang item `panic_impl`
 
 

src/test/ui/panic-handler/panic-handler-std.stderr

@@ -1,15 +1,17 @@
 error[E0152]: found duplicate lang item `panic_impl`
-  --> $DIR/panic-handler-std.rs:7:1
+  --> $DIR/panic-handler-std.rs:8:1
    |
 LL | / fn panic(info: PanicInfo) -> ! {
 LL | |     loop {}
 LL | | }
    | |_^
    |
    = note: the lang item is first defined in crate `std` (which `panic_handler_std` depends on)
+   = note: first definition in `std` loaded from SYSROOT/libstd-*.rlib
+   = note: second definition in the local crate (`panic_handler_std`)
 
 error: argument should be `&PanicInfo`
-  --> $DIR/panic-handler-std.rs:7:16
+  --> $DIR/panic-handler-std.rs:8:16
    |
 LL | fn panic(info: PanicInfo) -> ! {
    |                ^^^^^^^^^