From 47b987eccb7c2defece8f053c197836784baf421 Mon Sep 17 00:00:00 2001
From: Samuel Tardieu <sam@rfc1149.net>
Date: Sun, 11 Jan 2026 10:15:05 +0100
Subject: [PATCH] Do not show spans from external crates in
 `missing_trait_methods`

Pointing to the missing method definition in external crates will use
paths which depend on the system, and even on the Rust compiler version
used when the iterator is defined in the standard library.

When the trait being implemented and whose method is missing is
external, point only to the trait implementation. The user will be able
to figure out, or even navigate using their IDE, to the proper
definition.

As a side-effect, this will remove a large lintcheck churn at every Rustup
for this lint.
---
 clippy_lints/src/missing_trait_methods.rs | 10 +++++++++-
 tests/ui/missing_trait_methods.rs         |  7 +++++++
 tests/ui/missing_trait_methods.stderr     | 10 +++++++++-
 3 files changed, 25 insertions(+), 2 deletions(-)

diff --git a/clippy_lints/src/missing_trait_methods.rs b/clippy_lints/src/missing_trait_methods.rs
index 8e9400e9d583..7a791f949943 100644
--- a/clippy_lints/src/missing_trait_methods.rs
+++ b/clippy_lints/src/missing_trait_methods.rs
@@ -1,6 +1,7 @@
 use clippy_utils::diagnostics::span_lint_and_then;
 use clippy_utils::is_lint_allowed;
 use clippy_utils::macros::span_is_local;
+use clippy_utils::source::snippet_opt;
 use rustc_hir::def_id::DefIdSet;
 use rustc_hir::{Impl, Item, ItemKind};
 use rustc_lint::{LateContext, LateLintPass};
@@ -84,7 +85,14 @@ impl<'tcx> LateLintPass<'tcx> for MissingTraitMethods {
                     cx.tcx.def_span(item.owner_id),
                     format!("missing trait method provided by default: `{}`", assoc.name()),
                     |diag| {
-                        diag.span_help(cx.tcx.def_span(assoc.def_id), "implement the method");
+                        if assoc.def_id.is_local() {
+                            diag.span_help(cx.tcx.def_span(assoc.def_id), "implement the method");
+                        } else if let Some(snippet) = snippet_opt(cx, of_trait.trait_ref.path.span) {
+                            diag.help(format!(
+                                "implement the missing `{}` method of the `{snippet}` trait",
+                                assoc.name(),
+                            ));
+                        }
                     },
                 );
             }
diff --git a/tests/ui/missing_trait_methods.rs b/tests/ui/missing_trait_methods.rs
index 7af186ba3322..67070a299951 100644
--- a/tests/ui/missing_trait_methods.rs
+++ b/tests/ui/missing_trait_methods.rs
@@ -62,3 +62,10 @@ impl MissingMultiple for Partial {}
 //~| missing_trait_methods
 
 fn main() {}
+
+//~v missing_trait_methods
+impl PartialEq<Partial> for Partial {
+    fn eq(&self, other: &Partial) -> bool {
+        todo!()
+    }
+}
diff --git a/tests/ui/missing_trait_methods.stderr b/tests/ui/missing_trait_methods.stderr
index d9fb8951ab3d..e5155ad587cb 100644
--- a/tests/ui/missing_trait_methods.stderr
+++ b/tests/ui/missing_trait_methods.stderr
@@ -60,5 +60,13 @@ help: implement the method
 LL |     fn three() {}
    |     ^^^^^^^^^^
 
-error: aborting due to 5 previous errors
+error: missing trait method provided by default: `ne`
+  --> tests/ui/missing_trait_methods.rs:67:1
+   |
+LL | impl PartialEq<Partial> for Partial {
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = help: implement the missing `ne` method of the `PartialEq<Partial>` trait
+
+error: aborting due to 6 previous errors