[clang-tools-extra] [clang-tidy] Fix `cppcoreguidelines-prefer-member-initializer` false positive for inherited members (PR #153941)

[via cfe-commits]

https://github.com/v1nh1shungry updated https://github.com/llvm/llvm-project/pull/153941

>From 05f32d9dfe70e08c9a72f972a7c48116575081f8 Mon Sep 17 00:00:00 2001
From: Yuanjing Hong <v1nh1shungry at outlook.com>
Date: Fri, 15 Aug 2025 15:59:35 +0800
Subject: [PATCH] [clang-tidy] Fix
 `cppcoreguidelines-prefer-member-initializer` false positive for inherited
 members in class templates

```cpp
struct Base {
  int m;
};

template <class T>
struct Derived : Base {
  Derived() { m = 0; }
};
```

would previously generate the following output:

```
<source>:7:15: warning: 'm' should be initialized in a member initializer of the constructor [cppcoreguidelines-prefer-member-initializer]
    7 |   Derived() { m = 0; }
      |               ^~~~~~
      |             : m(0)
```

This patch fixes this false positive.
---
 .../PreferMemberInitializerCheck.cpp            |  3 +++
 clang-tools-extra/docs/ReleaseNotes.rst         |  4 ++++
 .../prefer-member-initializer.cpp               | 17 +++++++++++++++++
 3 files changed, 24 insertions(+)

diff --git a/clang-tools-extra/clang-tidy/cppcoreguidelines/PreferMemberInitializerCheck.cpp b/clang-tools-extra/clang-tidy/cppcoreguidelines/PreferMemberInitializerCheck.cpp
index 593a4f85d1309..79cd4bbcc9a60 100644
--- a/clang-tools-extra/clang-tidy/cppcoreguidelines/PreferMemberInitializerCheck.cpp
+++ b/clang-tools-extra/clang-tidy/cppcoreguidelines/PreferMemberInitializerCheck.cpp
@@ -191,6 +191,9 @@ void PreferMemberInitializerCheck::check(
     if (!AssignmentToMember)
       continue;
     const FieldDecl *Field = AssignmentToMember->Field;
+    // Skip if the field is inherited from a base class.
+    if (Field->getParent() != Class)
+      continue;
     const Expr *InitValue = AssignmentToMember->Init;
     updateAssignmentLevel(Field, InitValue, Ctor, AssignedFields);
     if (!canAdvanceAssignment(AssignedFields[Field]))
diff --git a/clang-tools-extra/docs/ReleaseNotes.rst b/clang-tools-extra/docs/ReleaseNotes.rst
index 1553f461634d0..c8374ce33dc7a 100644
--- a/clang-tools-extra/docs/ReleaseNotes.rst
+++ b/clang-tools-extra/docs/ReleaseNotes.rst
@@ -163,6 +163,10 @@ Changes in existing checks
   an additional matcher that generalizes the copy-and-swap idiom pattern
   detection.
 
+- Improved :doc:`cppcoreguidelines-prefer-member-initializer
+  <clang-tidy/checks/cppcoreguidelines/prefer-member-initializer>` check to
+  avoid false positives on inherited members in class templates.
+
 - Improved :doc:`misc-header-include-cycle
   <clang-tidy/checks/misc/header-include-cycle>` check performance.
 
diff --git a/clang-tools-extra/test/clang-tidy/checkers/cppcoreguidelines/prefer-member-initializer.cpp b/clang-tools-extra/test/clang-tidy/checkers/cppcoreguidelines/prefer-member-initializer.cpp
index 7d6164946fc3d..faff4882142f1 100644
--- a/clang-tools-extra/test/clang-tidy/checkers/cppcoreguidelines/prefer-member-initializer.cpp
+++ b/clang-tools-extra/test/clang-tidy/checkers/cppcoreguidelines/prefer-member-initializer.cpp
@@ -650,3 +650,20 @@ struct InitFromBindingDecl {
   }
 };
 } // namespace GH82970
+
+namespace inherited_members {
+
+struct A {
+  int m;
+};
+
+struct B : A {
+  B() { m = 0; }
+};
+
+template <class T>
+struct C : A {
+  C() { m = 0; }
+};
+
+} // namespace inherited_members