[clang-tools-extra] [clang-tidy] Don't cache classes by name in `fuchsia-multiple-inheritance` (PR #171016)

[Victor Chernyakin via cfe-commits]

https://github.com/localspook updated https://github.com/llvm/llvm-project/pull/171016

>From d3bebcb6b44af2c55a83f660c9dc9034bd737be1 Mon Sep 17 00:00:00 2001
From: Victor Chernyakin <chernyakin.victor.j at outlook.com>
Date: Sat, 6 Dec 2025 22:09:40 -0800
Subject: [PATCH 1/3] [clang-tidy] Don't cache classes by name in
 `fuchsia-multiple-inheritance`

---
 .../fuchsia/MultipleInheritanceCheck.cpp          | 11 ++---------
 .../clang-tidy/fuchsia/MultipleInheritanceCheck.h |  2 +-
 .../checkers/fuchsia/multiple-inheritance.cpp     | 15 +++++++++++++++
 3 files changed, 18 insertions(+), 10 deletions(-)

diff --git a/clang-tools-extra/clang-tidy/fuchsia/MultipleInheritanceCheck.cpp b/clang-tools-extra/clang-tidy/fuchsia/MultipleInheritanceCheck.cpp
index 652dec9bcc2a9..029c482691c00 100644
--- a/clang-tools-extra/clang-tidy/fuchsia/MultipleInheritanceCheck.cpp
+++ b/clang-tools-extra/clang-tidy/fuchsia/MultipleInheritanceCheck.cpp
@@ -27,9 +27,7 @@ AST_MATCHER(CXXRecordDecl, hasBases) {
 // previously.
 void MultipleInheritanceCheck::addNodeToInterfaceMap(const CXXRecordDecl *Node,
                                                      bool IsInterface) {
-  assert(Node->getIdentifier());
-  const StringRef Name = Node->getIdentifier()->getName();
-  InterfaceMap.insert(std::make_pair(Name, IsInterface));
+  InterfaceMap.try_emplace(Node, IsInterface);
 }
 
 // Returns "true" if the boolean "isInterface" has been set to the
@@ -37,9 +35,7 @@ void MultipleInheritanceCheck::addNodeToInterfaceMap(const CXXRecordDecl *Node,
 // interface status for the current node is not yet known.
 bool MultipleInheritanceCheck::getInterfaceStatus(const CXXRecordDecl *Node,
                                                   bool &IsInterface) const {
-  assert(Node->getIdentifier());
-  const StringRef Name = Node->getIdentifier()->getName();
-  auto Pair = InterfaceMap.find(Name);
+  auto Pair = InterfaceMap.find(Node);
   if (Pair == InterfaceMap.end())
     return false;
   IsInterface = Pair->second;
@@ -59,9 +55,6 @@ bool MultipleInheritanceCheck::isCurrentClassInterface(
 }
 
 bool MultipleInheritanceCheck::isInterface(const CXXRecordDecl *Node) {
-  if (!Node->getIdentifier())
-    return false;
-
   // Short circuit the lookup if we have analyzed this record before.
   bool PreviousIsInterfaceResult = false;
   if (getInterfaceStatus(Node, PreviousIsInterfaceResult))
diff --git a/clang-tools-extra/clang-tidy/fuchsia/MultipleInheritanceCheck.h b/clang-tools-extra/clang-tidy/fuchsia/MultipleInheritanceCheck.h
index 2e268432c17cf..b9055eb58a300 100644
--- a/clang-tools-extra/clang-tidy/fuchsia/MultipleInheritanceCheck.h
+++ b/clang-tools-extra/clang-tidy/fuchsia/MultipleInheritanceCheck.h
@@ -38,7 +38,7 @@ class MultipleInheritanceCheck : public ClangTidyCheck {
   // Contains the identity of each named CXXRecord as an interface.  This is
   // used to memoize lookup speeds and improve performance from O(N^2) to O(N),
   // where N is the number of classes.
-  llvm::StringMap<bool> InterfaceMap;
+  llvm::DenseMap<const CXXRecordDecl *, bool> InterfaceMap;
 };
 
 } // namespace clang::tidy::fuchsia
diff --git a/clang-tools-extra/test/clang-tidy/checkers/fuchsia/multiple-inheritance.cpp b/clang-tools-extra/test/clang-tidy/checkers/fuchsia/multiple-inheritance.cpp
index d53b3fde7736b..c60649f52cb94 100644
--- a/clang-tools-extra/test/clang-tidy/checkers/fuchsia/multiple-inheritance.cpp
+++ b/clang-tools-extra/test/clang-tidy/checkers/fuchsia/multiple-inheritance.cpp
@@ -148,3 +148,18 @@ void test_no_crash() {
   auto foo = []() {};
   WithTemplBase<decltype(foo)>();
 }
+
+struct S1 {};
+struct S2 {};
+
+struct S3 : S1, S2 {};
+
+namespace N {
+
+struct S1 { int i; };
+struct S2 { int i; };
+
+// CHECK-MESSAGES: [[@LINE+1]]:1: warning: inheriting multiple classes that aren't pure virtual is discouraged [fuchsia-multiple-inheritance]
+struct S3 : S1, S2 {};
+
+} // namespace N

>From 11522aacfa117ff748907c21c74f16dec032abdb Mon Sep 17 00:00:00 2001
From: Victor Chernyakin <chernyakin.victor.j at outlook.com>
Date: Sun, 7 Dec 2025 00:05:28 -0800
Subject: [PATCH 2/3] Update comment

---
 .../clang-tidy/fuchsia/MultipleInheritanceCheck.cpp             | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/clang-tools-extra/clang-tidy/fuchsia/MultipleInheritanceCheck.cpp b/clang-tools-extra/clang-tidy/fuchsia/MultipleInheritanceCheck.cpp
index 029c482691c00..df40d166bd404 100644
--- a/clang-tools-extra/clang-tidy/fuchsia/MultipleInheritanceCheck.cpp
+++ b/clang-tools-extra/clang-tidy/fuchsia/MultipleInheritanceCheck.cpp
@@ -23,7 +23,7 @@ AST_MATCHER(CXXRecordDecl, hasBases) {
 }
 } // namespace
 
-// Adds a node (by name) to the interface map, if it was not present in the map
+// Adds a node to the interface map, if it was not present in the map
 // previously.
 void MultipleInheritanceCheck::addNodeToInterfaceMap(const CXXRecordDecl *Node,
                                                      bool IsInterface) {

>From 362275a62cecdc151b6c49e29315e0225aec501e Mon Sep 17 00:00:00 2001
From: Victor Chernyakin <chernyakin.victor.j at outlook.com>
Date: Sun, 7 Dec 2025 00:35:30 -0800
Subject: [PATCH 3/3] Release notes

---
 clang-tools-extra/docs/ReleaseNotes.rst | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/clang-tools-extra/docs/ReleaseNotes.rst b/clang-tools-extra/docs/ReleaseNotes.rst
index 42160fa9cb51c..7457ffb3f4d1e 100644
--- a/clang-tools-extra/docs/ReleaseNotes.rst
+++ b/clang-tools-extra/docs/ReleaseNotes.rst
@@ -441,6 +441,12 @@ Changes in existing checks
   correctly ignore ``std::array`` and other array-like containers when
   `IgnoreArrays` option is set to `true`.
 
+- Improved :doc:`fuchsia-multiple-inheritance
+  <clang-tidy/checks/fuchsia/multiple-inheritance>`
+  by fixing an issue where the check would only analyze the first class with a
+  given name in the program, even if there were multiple classes with that
+  name in different scopes.
+
 - Improved :doc:`google-readability-casting
   <clang-tidy/checks/google/readability-casting>` check by adding fix-it
   notes for downcasts and casts to void pointer.