From 10fb062c48e6e14676a532ee5a677d8e34ba9a4a Mon Sep 17 00:00:00 2001
From: Alex Macleod <alex@macleod.io>
Date: Thu, 25 Jul 2024 20:13:55 +0000
Subject: [PATCH] missing_trait_methods: lint methods in definition order

---
 clippy_lints/src/missing_trait_methods.rs | 44 ++++++++++-------------
 tests/ui/missing_trait_methods.rs         |  8 +++++
 tests/ui/missing_trait_methods.stderr     | 38 +++++++++++++++++++-
 3 files changed, 63 insertions(+), 27 deletions(-)

diff --git a/clippy_lints/src/missing_trait_methods.rs b/clippy_lints/src/missing_trait_methods.rs
index 59c8c7f38e4..7ee746365d1 100644
--- a/clippy_lints/src/missing_trait_methods.rs
+++ b/clippy_lints/src/missing_trait_methods.rs
@@ -1,10 +1,9 @@
 use clippy_utils::diagnostics::span_lint_and_then;
 use clippy_utils::is_lint_allowed;
 use clippy_utils::macros::span_is_local;
-use rustc_hir::def_id::DefIdMap;
+use rustc_hir::def_id::DefIdSet;
 use rustc_hir::{Impl, Item, ItemKind};
 use rustc_lint::{LateContext, LateLintPass};
-use rustc_middle::ty::AssocItem;
 use rustc_session::declare_lint_pass;
 
 declare_clippy_lint! {
@@ -68,33 +67,26 @@ impl<'tcx> LateLintPass<'tcx> for MissingTraitMethods {
             }) = item.kind
             && let Some(trait_id) = trait_ref.trait_def_id()
         {
-            let mut provided: DefIdMap<&AssocItem> = cx
-                .tcx
-                .provided_trait_methods(trait_id)
-                .map(|assoc| (assoc.def_id, assoc))
+            let trait_item_ids: DefIdSet = items
+                .iter()
+                .filter_map(|impl_item| impl_item.trait_item_def_id)
                 .collect();
 
-            for impl_item in *items {
-                if let Some(def_id) = impl_item.trait_item_def_id {
-                    provided.remove(&def_id);
-                }
+            for assoc in cx
+                .tcx
+                .provided_trait_methods(trait_id)
+                .filter(|assoc| !trait_item_ids.contains(&assoc.def_id))
+            {
+                span_lint_and_then(
+                    cx,
+                    MISSING_TRAIT_METHODS,
+                    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");
+                    },
+                );
             }
-
-            cx.tcx.with_stable_hashing_context(|hcx| {
-                for assoc in provided.values_sorted(&hcx, true) {
-                    let source_map = cx.tcx.sess.source_map();
-                    span_lint_and_then(
-                        cx,
-                        MISSING_TRAIT_METHODS,
-                        source_map.guess_head_span(item.span),
-                        format!("missing trait method provided by default: `{}`", assoc.name),
-                        |diag| {
-                            let definition_span = source_map.guess_head_span(cx.tcx.def_span(assoc.def_id));
-                            diag.span_help(definition_span, "implement the method");
-                        },
-                    );
-                }
-            });
         }
     }
 }
diff --git a/tests/ui/missing_trait_methods.rs b/tests/ui/missing_trait_methods.rs
index 1b09b717ff7..55b904bde59 100644
--- a/tests/ui/missing_trait_methods.rs
+++ b/tests/ui/missing_trait_methods.rs
@@ -49,4 +49,12 @@ impl B for Complete {
     }
 }
 
+trait MissingMultiple {
+    fn one() {}
+    fn two() {}
+    fn three() {}
+}
+
+impl MissingMultiple for Partial {}
+
 fn main() {}
diff --git a/tests/ui/missing_trait_methods.stderr b/tests/ui/missing_trait_methods.stderr
index f5d5d4418b2..9c4968b022d 100644
--- a/tests/ui/missing_trait_methods.stderr
+++ b/tests/ui/missing_trait_methods.stderr
@@ -24,5 +24,41 @@ help: implement the method
 LL |     fn b<'a, T: AsRef<[u8]>>(a: &'a T) -> &'a [u8] {
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
-error: aborting due to 2 previous errors
+error: missing trait method provided by default: `one`
+  --> tests/ui/missing_trait_methods.rs:58:1
+   |
+LL | impl MissingMultiple for Partial {}
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+help: implement the method
+  --> tests/ui/missing_trait_methods.rs:53:5
+   |
+LL |     fn one() {}
+   |     ^^^^^^^^
+
+error: missing trait method provided by default: `two`
+  --> tests/ui/missing_trait_methods.rs:58:1
+   |
+LL | impl MissingMultiple for Partial {}
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+help: implement the method
+  --> tests/ui/missing_trait_methods.rs:54:5
+   |
+LL |     fn two() {}
+   |     ^^^^^^^^
+
+error: missing trait method provided by default: `three`
+  --> tests/ui/missing_trait_methods.rs:58:1
+   |
+LL | impl MissingMultiple for Partial {}
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+help: implement the method
+  --> tests/ui/missing_trait_methods.rs:55:5
+   |
+LL |     fn three() {}
+   |     ^^^^^^^^^^
+
+error: aborting due to 5 previous errors