[clang] Fix false positive -Wmissing-field-initializer for anonymous unions (#70829)

Normally warning is not reported when a field has default initializer.
Do so for anonymous unions with default initializers as well. No release
note since it is a regression in clang 18.

Fixes #70384

Author: Fznamznon

clang/lib/Sema/SemaInit.cpp

@@ -465,7 +465,8 @@ class InitListChecker {
   void FillInEmptyInitForField(unsigned Init, FieldDecl *Field,
                                const InitializedEntity &ParentEntity,
                                InitListExpr *ILE, bool &RequiresSecondPass,
-                               bool FillWithNoInit = false);
+                               bool FillWithNoInit = false,
+                               bool WarnIfMissing = false);
   void FillInEmptyInitializations(const InitializedEntity &Entity,
                                   InitListExpr *ILE, bool &RequiresSecondPass,
                                   InitListExpr *OuterILE, unsigned OuterIndex,
@@ -654,11 +655,16 @@ void InitListChecker::FillInEmptyInitForBase(
   }
 }
 
-void InitListChecker::FillInEmptyInitForField(unsigned Init, FieldDecl *Field,
-                                        const InitializedEntity &ParentEntity,
-                                              InitListExpr *ILE,
-                                              bool &RequiresSecondPass,
-                                              bool FillWithNoInit) {
+static bool hasAnyDesignatedInits(const InitListExpr *IL) {
+  return llvm::any_of(*IL, [=](const Stmt *Init) {
+    return isa_and_nonnull<DesignatedInitExpr>(Init);
+  });
+}
+
+void InitListChecker::FillInEmptyInitForField(
+    unsigned Init, FieldDecl *Field, const InitializedEntity &ParentEntity,
+    InitListExpr *ILE, bool &RequiresSecondPass, bool FillWithNoInit,
+    bool WarnIfMissing) {
   SourceLocation Loc = ILE->getEndLoc();
   unsigned NumInits = ILE->getNumInits();
   InitializedEntity MemberEntity
@@ -726,15 +732,52 @@ void InitListChecker::FillInEmptyInitForField(unsigned Init, FieldDecl *Field,
 
     if (hadError || VerifyOnly) {
       // Do nothing
-    } else if (Init < NumInits) {
-      ILE->setInit(Init, MemberInit.getAs<Expr>());
-    } else if (!isa<ImplicitValueInitExpr>(MemberInit.get())) {
-      // Empty initialization requires a constructor call, so
-      // extend the initializer list to include the constructor
-      // call and make a note that we'll need to take another pass
-      // through the initializer list.
-      ILE->updateInit(SemaRef.Context, Init, MemberInit.getAs<Expr>());
-      RequiresSecondPass = true;
+    } else {
+      if (WarnIfMissing) {
+        auto CheckAnonMember = [&](const FieldDecl *FD,
+                                   auto &&CheckAnonMember) -> FieldDecl * {
+          FieldDecl *Uninitialized = nullptr;
+          RecordDecl *RD = FD->getType()->getAsRecordDecl();
+          assert(RD && "Not anonymous member checked?");
+          for (auto *F : RD->fields()) {
+            FieldDecl *UninitializedFieldInF = nullptr;
+            if (F->isAnonymousStructOrUnion())
+              UninitializedFieldInF = CheckAnonMember(F, CheckAnonMember);
+            else if (!F->isUnnamedBitfield() &&
+                     !F->getType()->isIncompleteArrayType() &&
+                     !F->hasInClassInitializer())
+              UninitializedFieldInF = F;
+
+            if (RD->isUnion() && !UninitializedFieldInF)
+              return nullptr;
+            if (!Uninitialized)
+              Uninitialized = UninitializedFieldInF;
+          }
+          return Uninitialized;
+        };
+
+        FieldDecl *FieldToDiagnose = nullptr;
+        if (Field->isAnonymousStructOrUnion())
+          FieldToDiagnose = CheckAnonMember(Field, CheckAnonMember);
+        else if (!Field->isUnnamedBitfield() &&
+                 !Field->getType()->isIncompleteArrayType())
+          FieldToDiagnose = Field;
+
+        if (FieldToDiagnose)
+          SemaRef.Diag(Loc, diag::warn_missing_field_initializers)
+              << FieldToDiagnose;
+      }
+
+      if (Init < NumInits) {
+        ILE->setInit(Init, MemberInit.getAs<Expr>());
+      } else if (!isa<ImplicitValueInitExpr>(MemberInit.get())) {
+        // Empty initialization requires a constructor call, so
+        // extend the initializer list to include the constructor
+        // call and make a note that we'll need to take another pass
+        // through the initializer list.
+        ILE->updateInit(SemaRef.Context, Init, MemberInit.getAs<Expr>());
+        RequiresSecondPass = true;
+      }
     }
   } else if (InitListExpr *InnerILE
                = dyn_cast<InitListExpr>(ILE->getInit(Init))) {
@@ -802,9 +845,25 @@ InitListChecker::FillInEmptyInitializations(const InitializedEntity &Entity,
         }
       }
     } else {
+      InitListExpr *SForm =
+          ILE->isSyntacticForm() ? ILE : ILE->getSyntacticForm();
       // The fields beyond ILE->getNumInits() are default initialized, so in
       // order to leave them uninitialized, the ILE is expanded and the extra
       // fields are then filled with NoInitExpr.
+
+      // Some checks that are required for missing fields warning are bound to
+      // how many elements the initializer list originally was provided; perform
+      // them before the list is expanded.
+      bool WarnIfMissingField =
+          !SForm->isIdiomaticZeroInitializer(SemaRef.getLangOpts()) &&
+          ILE->getNumInits();
+
+      // Disable check for missing fields when designators are used in C to
+      // match gcc behaviour.
+      // FIXME: Should we emulate possible gcc warning bug?
+      WarnIfMissingField &=
+          SemaRef.getLangOpts().CPlusPlus || !hasAnyDesignatedInits(SForm);
+
       unsigned NumElems = numStructUnionElements(ILE->getType());
       if (!RDecl->isUnion() && RDecl->hasFlexibleArrayMember())
         ++NumElems;
@@ -832,7 +891,7 @@ InitListChecker::FillInEmptyInitializations(const InitializedEntity &Entity,
           return;
 
         FillInEmptyInitForField(Init, Field, Entity, ILE, RequiresSecondPass,
-                                FillWithNoInit);
+                                FillWithNoInit, WarnIfMissingField);
         if (hadError)
           return;
 
@@ -947,13 +1006,6 @@ InitListChecker::FillInEmptyInitializations(const InitializedEntity &Entity,
   }
 }
 
-static bool hasAnyDesignatedInits(const InitListExpr *IL) {
-  for (const Stmt *Init : *IL)
-    if (isa_and_nonnull<DesignatedInitExpr>(Init))
-      return true;
-  return false;
-}
-
 InitListChecker::InitListChecker(
     Sema &S, const InitializedEntity &Entity, InitListExpr *IL, QualType &T,
     bool VerifyOnly, bool TreatUnavailableAsInvalid, bool InOverloadResolution,
@@ -2225,12 +2277,8 @@ void InitListChecker::CheckStructUnionTypes(
   size_t NumRecordDecls = llvm::count_if(RD->decls(), [&](const Decl *D) {
     return isa<FieldDecl>(D) || isa<RecordDecl>(D);
   });
-  bool CheckForMissingFields =
-    !IList->isIdiomaticZeroInitializer(SemaRef.getLangOpts());
   bool HasDesignatedInit = false;
 
-  llvm::SmallPtrSet<FieldDecl *, 4> InitializedFields;
-
   while (Index < IList->getNumInits()) {
     Expr *Init = IList->getInit(Index);
     SourceLocation InitLoc = Init->getBeginLoc();
@@ -2254,24 +2302,17 @@ void InitListChecker::CheckStructUnionTypes(
 
       // Find the field named by the designated initializer.
       DesignatedInitExpr::Designator *D = DIE->getDesignator(0);
-      if (!VerifyOnly && D->isFieldDesignator()) {
+      if (!VerifyOnly && D->isFieldDesignator() && !DesignatedInitFailed) {
         FieldDecl *F = D->getFieldDecl();
-        InitializedFields.insert(F);
-        if (!DesignatedInitFailed) {
-          QualType ET = SemaRef.Context.getBaseElementType(F->getType());
-          if (checkDestructorReference(ET, InitLoc, SemaRef)) {
-            hadError = true;
-            return;
-          }
+        QualType ET = SemaRef.Context.getBaseElementType(F->getType());
+        if (checkDestructorReference(ET, InitLoc, SemaRef)) {
+          hadError = true;
+          return;
         }
       }
 
       InitializedSomething = true;
 
-      // Disable check for missing fields when designators are used.
-      // This matches gcc behaviour.
-      if (!SemaRef.getLangOpts().CPlusPlus)
-        CheckForMissingFields = false;
       continue;
     }
 
@@ -2350,7 +2391,6 @@ void InitListChecker::CheckStructUnionTypes(
     CheckSubElementType(MemberEntity, IList, Field->getType(), Index,
                         StructuredList, StructuredIndex);
     InitializedSomething = true;
-    InitializedFields.insert(*Field);
 
     if (RD->isUnion() && StructuredList) {
       // Initialize the first field within the union.
@@ -2360,28 +2400,6 @@ void InitListChecker::CheckStructUnionTypes(
     ++Field;
   }
 
-  // Emit warnings for missing struct field initializers.
-  if (!VerifyOnly && InitializedSomething && CheckForMissingFields &&
-      !RD->isUnion()) {
-    // It is possible we have one or more unnamed bitfields remaining.
-    // Find first (if any) named field and emit warning.
-    for (RecordDecl::field_iterator it = HasDesignatedInit ? RD->field_begin()
-                                                           : Field,
-                                    end = RD->field_end();
-         it != end; ++it) {
-      if (HasDesignatedInit && InitializedFields.count(*it))
-        continue;
-
-      if (!it->isUnnamedBitfield() && !it->hasInClassInitializer() &&
-          !it->getType()->isIncompleteArrayType()) {
-        SemaRef.Diag(IList->getSourceRange().getEnd(),
-                     diag::warn_missing_field_initializers)
-            << *it;
-        break;
-      }
-    }
-  }
-
   // Check that any remaining fields can be value-initialized if we're not
   // building a structured list. (If we are, we'll check this later.)
   if (!StructuredList && Field != FieldEnd && !RD->isUnion() &&

clang/test/Sema/missing-field-initializers.c

@@ -18,7 +18,7 @@ struct Foo bar1[] = {
   1, 2,
   1, 2,
   1
-}; // expected-warning {{missing field 'b' initializer}}
+}; // expected-warning@-1 {{missing field 'b' initializer}}
 
 struct Foo bar2[] = { {}, {}, {} };
 

clang/test/SemaCXX/cxx2a-initializer-aggregates.cpp

@@ -1,6 +1,6 @@
 // RUN: %clang_cc1 -std=c++20 %s -verify=cxx20,expected,pedantic,override,reorder -pedantic-errors
 // RUN: %clang_cc1 -std=c++17 %s -verify=expected,pedantic,override,reorder -Wno-c++20-designator -pedantic-errors
-// RUN: %clang_cc1 -std=c++20 %s -verify=cxx20,expected,pedantic -Werror=c99-designator -Wno-reorder-init-list -Wno-initializer-overrides
+// RUN: %clang_cc1 -std=c++20 %s -verify=cxx20,expected,pedantic -Werror=c99-designator -Wno-reorder-init-list -Wno-initializer-overrides -Werror=nested-anon-types -Werror=gnu-anonymous-struct
 // RUN: %clang_cc1 -std=c++20 %s -verify=cxx20,expected,reorder -Wno-c99-designator -Werror=reorder-init-list -Wno-initializer-overrides
 // RUN: %clang_cc1 -std=c++20 %s -verify=cxx20,expected,override -Wno-c99-designator -Wno-reorder-init-list -Werror=initializer-overrides
 // RUN: %clang_cc1 -std=c++20 %s -verify=cxx20,expected -Wno-c99-designator -Wno-reorder-init-list -Wno-initializer-overrides
@@ -39,6 +39,7 @@ A a1 = {
 };
 int arr[3] = {[1] = 5}; // pedantic-error {{array designators are a C99 extension}}
 B b = {.a.x = 0}; // pedantic-error {{nested designators are a C99 extension}}
+                  // wmissing-warning@-1 {{missing field 'y' initializer}}
 A a2 = {
   .x = 1, // pedantic-error {{mixture of designated and non-designated initializers in the same initializer list is a C99 extension}}
   2 // pedantic-note {{first non-designated initializer is here}}
@@ -60,7 +61,6 @@ B b2 = {.a = 1}; // pedantic-error {{brace elision for designated initializer is
 B b3 = {.a = 1, 2}; // pedantic-error {{mixture of designated and non-designated}} pedantic-note {{first non-designated}} pedantic-error {{brace elision}}
 B b4 = {.a = 1, 2, 3}; // pedantic-error {{mixture of designated and non-designated}} pedantic-note {{first non-designated}} pedantic-error {{brace elision}} expected-error {{excess elements}}
 B b5 = {.a = nullptr}; // expected-error {{cannot initialize}}
-                       // wmissing-warning@-1 {{missing field 'y' initializer}}
 struct C { int :0, x, :0, y, :0; };
 C c = {
   .x = 1, // override-note {{previous}}
@@ -247,3 +247,87 @@ void foo() {
                            //
 }
 }
+
+namespace GH70384 {
+
+struct A {
+  int m;
+  union { int a; float n = 0; };
+};
+
+struct B {
+  int m;
+  int b;
+  union { int a ; };
+};
+
+union CU {
+  int a = 1;
+  double b;
+};
+
+struct C {
+  int a;
+  union { int b; CU c;};
+};
+
+struct CC {
+  int a;
+  CU c;
+};
+
+void foo() {
+  A a = A{.m = 0};
+  A aa = {0};
+  A aaa = {.a = 7}; // wmissing-warning {{missing field 'm' initializer}}
+  B b = {.m = 1, .b = 3 }; //wmissing-warning {{missing field 'a' initializer}}
+  B bb = {1}; // wmissing-warning {{missing field 'b' initializer}}
+              // wmissing-warning@-1 {{missing field 'a' initializer}}
+  C c = {.a = 1}; // wmissing-warning {{missing field 'b' initializer}}
+  CC cc = {.a = 1}; // wmissing-warning {{missing field 'c' initializer}}
+}
+
+struct C1 {
+  int m;
+  union { float b; union {int n = 1; }; };
+  // pedantic-error@-1 {{anonymous types declared in an anonymous union are an extension}}
+};
+
+struct C2 {
+  int m;
+  struct { float b; int n = 1; }; // pedantic-error {{anonymous structs are a GNU extension}}
+};
+
+struct C3 {
+  int m;
+  struct { float b = 1; union {int a;}; int n = 1; };
+  // pedantic-error@-1 {{anonymous structs are a GNU extension}}
+  // pedantic-error@-2 {{anonymous types declared in an anonymous struct are an extension}}
+};
+
+C1 c = C1{.m = 1};
+C1 cc = C1{.b = 1}; // wmissing-warning {{missing field 'm' initializer}}
+C2 c1 = C2{.m = 1}; // wmissing-warning {{missing field 'b' initializer}}
+C2 c22 = C2{.m = 1, .b = 1};
+C3 c2 = C3{.b = 1}; // wmissing-warning {{missing field 'a' initializer}}
+                    // wmissing-warning@-1 {{missing field 'm' initializer}}
+
+struct C4 {
+  union {
+    struct { int n; }; // pedantic-error {{anonymous structs are a GNU extension}}
+    // pedantic-error@-1 {{anonymous types declared in an anonymous union are an extension}}
+    int m = 0; };
+  int z;
+};
+C4 a = {.z = 1};
+
+struct C5 {
+  int a;
+  struct { // pedantic-error {{anonymous structs are a GNU extension}}
+    int x;
+    struct { int y = 0; };  // pedantic-error {{anonymous types declared in an anonymous struct are an extension}}
+                            // pedantic-error@-1 {{anonymous structs are a GNU extension}}
+  };
+};
+C5 c5 = C5{.a = 0}; //wmissing-warning {{missing field 'x' initializer}}
+}