Rollup merge of #131702 - compiler-errors:method-lookup-trait-warning, r=jieyouxu

Suppress import errors for traits that couldve applied for method lookup error

Self-explanatory. I hit this quite often when refactoring in rustc, so even though this isn't really showing up as significant in the UI test suite, it probably will matter more for multi-module projects.

2 files changed, 10 insertions, 0 deletions

diff --git a/compiler/rustc_hir_typeck/src/method/mod.rs b/compiler/rustc_hir_typeck/src/method/mod.rs
index cb8b1df2c6e..1b65dc8214c 100644
--- a/compiler/rustc_hir_typeck/src/method/mod.rs
+++ b/compiler/rustc_hir_typeck/src/method/mod.rs
@@ -199,6 +199,8 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
             self_ty, segment, span, call_expr, self_expr, &pick, args,
         );
 
+        // NOTE: on the failure path, we also record the possibly-used trait methods
+        // since an unused import warning is kinda distracting from the method error.
         for &import_id in &pick.import_ids {
             debug!("used_trait_import: {:?}", import_id);
             self.typeck_results.borrow_mut().used_trait_imports.insert(import_id);
diff --git a/compiler/rustc_hir_typeck/src/method/suggest.rs b/compiler/rustc_hir_typeck/src/method/suggest.rs
index 4f726f3ed38..05c8912aec1 100644
--- a/compiler/rustc_hir_typeck/src/method/suggest.rs
+++ b/compiler/rustc_hir_typeck/src/method/suggest.rs
@@ -191,6 +191,14 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
         expected: Expectation<'tcx>,
         trait_missing_method: bool,
     ) -> ErrorGuaranteed {
+        // NOTE: Reporting a method error should also suppress any unused trait errors,
+        // since the method error is very possibly the reason why the trait wasn't used.
+        for &import_id in
+            self.tcx.in_scope_traits(call_id).into_iter().flatten().flat_map(|c| &c.import_ids)
+        {
+            self.typeck_results.borrow_mut().used_trait_imports.insert(import_id);
+        }
+
         let (span, sugg_span, source, item_name, args) = match self.tcx.hir_node(call_id) {
             hir::Node::Expr(&hir::Expr {
                 kind: hir::ExprKind::MethodCall(segment, rcvr, args, _),