[clang-tidy] Skip union-like classes in use-equals-default

Skip unions/union-like classes since in this case constructors
with empty bodies behave differently in comparison with regular
structs/classes.

Test plan: ninja check-clang-tools

Differential revision: https://reviews.llvm.org/D132713

clang-tools-extra/clang-tidy/modernize/UseEqualsDefaultCheck.cpp

@@ -218,17 +218,20 @@ void UseEqualsDefaultCheck::storeOptions(ClangTidyOptions::OptionMap &Opts) {
 }
 
 void UseEqualsDefaultCheck::registerMatchers(MatchFinder *Finder) {
-  // Skip unions since constructors with empty bodies behave differently
-  // in comparison with structs/classes.
+  // Skip unions/union-like classes since their constructors behave differently
+  // when defaulted vs. empty.
+  auto IsUnionLikeClass = recordDecl(
+      anyOf(isUnion(),
+            has(fieldDecl(isImplicit(), hasType(cxxRecordDecl(isUnion()))))));
 
   // Destructor.
-  Finder->addMatcher(cxxDestructorDecl(unless(hasParent(recordDecl(isUnion()))),
-                                       isDefinition())
-                         .bind(SpecialFunction),
-                     this);
+  Finder->addMatcher(
+      cxxDestructorDecl(unless(hasParent(IsUnionLikeClass)), isDefinition())
+          .bind(SpecialFunction),
+      this);
   Finder->addMatcher(
       cxxConstructorDecl(
-          unless(hasParent(recordDecl(isUnion()))), isDefinition(),
+          unless(hasParent(IsUnionLikeClass)), isDefinition(),
           anyOf(
               // Default constructor.
               allOf(unless(hasAnyConstructorInitializer(isWritten())),
@@ -243,7 +246,7 @@ void UseEqualsDefaultCheck::registerMatchers(MatchFinder *Finder) {
       this);
   // Copy-assignment operator.
   Finder->addMatcher(
-      cxxMethodDecl(unless(hasParent(recordDecl(isUnion()))), isDefinition(),
+      cxxMethodDecl(unless(hasParent(IsUnionLikeClass)), isDefinition(),
                     isCopyAssignmentOperator(),
                     // isCopyAssignmentOperator() allows the parameter to be
                     // passed by value, and in this case it cannot be

clang-tools-extra/docs/ReleaseNotes.rst

@@ -144,9 +144,10 @@ Changes in existing checks
 - Improved :doc:`modernize-use-equals-default <clang-tidy/checks/modernize/use-equals-default>`
   check.
 
-  The check now skips unions since in this case a default constructor with empty body
-  is not equivalent to the explicitly defaulted one. The check also skips copy assignment
-  operators with nonstandard return types. The check is restricted to c++11-or-later.
+  The check now skips unions/union-like classes since in this case a default constructor
+  with empty body is not equivalent to the explicitly defaulted one. The check also skips
+  copy assignment operators with nonstandard return types. The check is restricted to
+  c++11-or-later.
 
 Removed checks
 ^^^^^^^^^^^^^^

clang-tools-extra/test/clang-tidy/checkers/modernize/use-equals-default-copy.cpp

@@ -44,6 +44,20 @@ union NU {
   IL Field;
 };
 
+// Skip structs/classes containing anonymous unions.
+struct SU {
+  SU(const SU &Other) : Field(Other.Field) {}
+  // CHECK-FIXES: SU(const SU &Other) :
+  SU &operator=(const SU &Other) {
+    Field = Other.Field;
+    return *this;
+  }
+  // CHECK-FIXES: SU &operator=(const SU &Other) {
+  union {
+    IL Field;
+  };
+};
+
 // Wrong type.
 struct WT {
   WT(const IL &Other) {}

clang-tools-extra/test/clang-tidy/checkers/modernize/use-equals-default.cpp

@@ -42,6 +42,17 @@ union NU {
   NE Field;
 };
 
+// Skip structs/classes containing anonymous unions.
+struct SU {
+  SU() {}
+  // CHECK-FIXES: SU() {}
+  ~SU() {}
+  // CHECK-FIXES: ~SU() {}
+  union {
+    NE Field;
+  };
+};
+
 // Initializer or arguments.
 class IA {
 public: