Couple of diagnostics improvements for EII

compiler/rustc_passes/src/eii.rs

@@ -141,6 +141,7 @@ pub(crate) fn check_externally_implementable_items<'tcx>(tcx: TyCtxt<'tcx>, ():
                         decl_crate_name: tcx.crate_name(decl_crate),
                         // FIXME: shouldn't call `item_name`
                         name: decl.name.name,
+                        kind: tcx.def_kind(decl.foreign_item).descr(decl.foreign_item),
                         span: decl.name.span,
                         help: (),
                     });

compiler/rustc_passes/src/errors.rs

@@ -1209,12 +1209,13 @@ pub(crate) struct EiiWithTrackCaller {
 }
 
 #[derive(Diagnostic)]
-#[diag("`#[{$name}]` required, but not found")]
+#[diag("`#[{$name}]` {$kind} required, but not found")]
 pub(crate) struct EiiWithoutImpl {
     #[primary_span]
     #[label("expected because `#[{$name}]` was declared here in crate `{$decl_crate_name}`")]
     pub span: Span,
     pub name: Symbol,
+    pub kind: &'static str,
 
     pub current_crate_name: Symbol,
     pub decl_crate_name: Symbol,

compiler/rustc_resolve/src/check_unused.rs

@@ -438,7 +438,10 @@ impl Resolver<'_, '_> {
                             && !tcx.is_panic_runtime(cnum)
                             && !tcx.has_global_allocator(cnum)
                             && !tcx.has_panic_handler(cnum)
-                            && tcx.externally_implementable_items(cnum).is_empty()
+                            && tcx
+                                .externally_implementable_items(cnum)
+                                .values()
+                                .all(|(_, defs)| defs.is_empty())
                     }) {
                         maybe_unused_extern_crates.insert(id, import.span);
                     }

tests/ui/eii/auxiliary/unused_extern_crate_decl.rs

@@ -0,0 +1,6 @@
+//@ no-prefer-dynamic
+#![crate_type = "rlib"]
+#![feature(extern_item_impls)]
+
+#[eii(eii1)]
+pub fn decl1(x: u64);

tests/ui/eii/auxiliary/unused_extern_crate_impl.rs

@@ -0,0 +1,9 @@
+//@ no-prefer-dynamic
+//@ aux-build:unused_extern_crate_decl.rs
+#![crate_type = "rlib"]
+#![feature(extern_item_impls)]
+
+extern crate unused_extern_crate_decl;
+
+#[unused_extern_crate_decl::eii1]
+fn impl1(x: u64) {}

tests/ui/eii/dylib_needs_impl.rs

@@ -3,5 +3,5 @@
 #![crate_type = "dylib"]
 #![feature(extern_item_impls)]
 
-#[eii(eii1)] //~ ERROR `#[eii1]` required, but not found
+#[eii(eii1)] //~ ERROR `#[eii1]` function required, but not found
 fn decl1(x: u64);

tests/ui/eii/dylib_needs_impl.stderr

@@ -1,4 +1,4 @@
-error: `#[eii1]` required, but not found
+error: `#[eii1]` function required, but not found
   --> $DIR/dylib_needs_impl.rs:6:7
    |
 LL | #[eii(eii1)]

tests/ui/eii/privacy2.rs

@@ -5,8 +5,8 @@
 extern crate other_crate_privacy2 as codegen;
 
 // has a span but in the other crate
-//~? ERROR `#[eii2]` required, but not found
-//~? ERROR `#[eii3]` required, but not found
+//~? ERROR `#[eii2]` function required, but not found
+//~? ERROR `#[eii3]` function required, but not found
 
 #[codegen::eii1]
 fn eii1_impl(x: u64) {

tests/ui/eii/privacy2.stderr

@@ -16,15 +16,15 @@ note: the function `decl1` is defined here
 LL | fn decl1(x: u64);
    | ^^^^^^^^^^^^^^^^^
 
-error: `#[eii2]` required, but not found
+error: `#[eii2]` function required, but not found
   --> $DIR/auxiliary/other_crate_privacy2.rs:9:7
    |
 LL | #[eii(eii2)]
    |       ^^^^ expected because `#[eii2]` was declared here in crate `other_crate_privacy2`
    |
    = help: expected at least one implementation in crate `privacy2` or any of its dependencies
 
-error: `#[eii3]` required, but not found
+error: `#[eii3]` function required, but not found
   --> $DIR/auxiliary/other_crate_privacy2.rs:13:11
    |
 LL |     #[eii(eii3)]

tests/ui/eii/shadow_builtin.rs

@@ -5,7 +5,7 @@
 #![feature(extern_item_impls)]
 
 #[eii(inline)]
-//~^ ERROR `#[inline]` required, but not found
+//~^ ERROR `#[inline]` function required, but not found
 fn test(x: u64);
 
 #[inline]
@@ -14,4 +14,4 @@ fn test_impl(x: u64) {
     println!("{x:?}")
 }
 
-fn main() { }
+fn main() {}

tests/ui/eii/shadow_builtin.stderr

@@ -13,7 +13,7 @@ LL | #[eii(inline)]
    | ^^^^^^^^^^^^^^
    = help: use `crate::inline` to refer to this attribute macro unambiguously
 
-error: `#[inline]` required, but not found
+error: `#[inline]` function required, but not found
   --> $DIR/shadow_builtin.rs:7:7
    |
 LL | #[eii(inline)]

tests/ui/eii/unused_extern_crate.rs

@@ -0,0 +1,11 @@
+//@ aux-build:unused_extern_crate_decl.rs
+//@ aux-build:unused_extern_crate_impl.rs
+// Tests that dependencies that contain an EII decl without any EII impl are
+// still considered unused.
+#![feature(extern_item_impls)]
+#![deny(unused_extern_crates)]
+
+extern crate unused_extern_crate_decl; //~ ERROR unused extern crate
+extern crate unused_extern_crate_impl;
+
+fn main() {}

tests/ui/eii/unused_extern_crate.stderr

@@ -0,0 +1,19 @@
+error: unused extern crate
+  --> $DIR/unused_extern_crate.rs:8:1
+   |
+LL | extern crate unused_extern_crate_decl;
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ unused
+   |
+note: the lint level is defined here
+  --> $DIR/unused_extern_crate.rs:6:9
+   |
+LL | #![deny(unused_extern_crates)]
+   |         ^^^^^^^^^^^^^^^^^^^^
+help: remove the unused `extern crate`
+   |
+LL - extern crate unused_extern_crate_decl;
+LL +
+   |
+
+error: aborting due to 1 previous error
+