[Modules] Detect ODR mismatches for enums in non-C++ like in C++. (#90298)

There is no reason for C and Objective-C to differ from C++ in this
matter.

rdar://85531830

Author: vsapsai

clang/lib/Serialization/ASTReaderDecl.cpp

@@ -805,9 +805,7 @@ void ASTDeclReader::VisitEnumDecl(EnumDecl *ED) {
 
   // If this is a definition subject to the ODR, and we already have a
   // definition, merge this one into it.
-  if (ED->isCompleteDefinition() &&
-      Reader.getContext().getLangOpts().Modules &&
-      Reader.getContext().getLangOpts().CPlusPlus) {
+  if (ED->isCompleteDefinition() && Reader.getContext().getLangOpts().Modules) {
     EnumDecl *&OldDef = Reader.EnumDefinitions[ED->getCanonicalDecl()];
     if (!OldDef) {
       // This is the first time we've seen an imported definition. Look for a
@@ -3304,8 +3302,7 @@ DeclContext *ASTDeclReader::getPrimaryContextForMerging(ASTReader &Reader,
     return RD->getDefinition();
 
   if (auto *ED = dyn_cast<EnumDecl>(DC))
-    return ED->getASTContext().getLangOpts().CPlusPlus? ED->getDefinition()
-                                                      : nullptr;
+    return ED->getDefinition();
 
   if (auto *OID = dyn_cast<ObjCInterfaceDecl>(DC))
     return OID->getDefinition();

clang/test/Modules/odr_hash-enum.c

@@ -0,0 +1,75 @@
+// Clear and create directories
+// RUN: rm -rf %t
+// RUN: mkdir %t
+// RUN: mkdir %t/cache
+// RUN: mkdir %t/Inputs
+
+// Build first header file
+// RUN: echo "#define FIRST" >> %t/Inputs/first.h
+// RUN: cat %s               >> %t/Inputs/first.h
+
+// Build second header file
+// RUN: echo "#define SECOND" >> %t/Inputs/second.h
+// RUN: cat %s                >> %t/Inputs/second.h
+
+// Test that each header can compile
+// RUN: %clang_cc1 -fsyntax-only -x c %t/Inputs/first.h
+// RUN: %clang_cc1 -fsyntax-only -x c %t/Inputs/second.h
+
+// Build module map file
+// RUN: echo "module FirstModule {"     >> %t/Inputs/module.modulemap
+// RUN: echo "    header \"first.h\""   >> %t/Inputs/module.modulemap
+// RUN: echo "}"                        >> %t/Inputs/module.modulemap
+// RUN: echo "module SecondModule {"    >> %t/Inputs/module.modulemap
+// RUN: echo "    header \"second.h\""  >> %t/Inputs/module.modulemap
+// RUN: echo "}"                        >> %t/Inputs/module.modulemap
+
+// Run test
+// RUN: %clang_cc1 -fmodules -fimplicit-module-maps -fmodules-cache-path=%t/cache -x c -I%t/Inputs -verify %s
+
+#if !defined(FIRST) && !defined(SECOND)
+#include "first.h"
+#include "second.h"
+#endif
+
+#if defined(FIRST)
+enum DifferentEnumConstants { kDifferentEnumConstantsValueFirst };
+#elif defined(SECOND)
+enum DifferentEnumConstants { kDifferentEnumConstantsValueSecond };
+#else
+enum DifferentEnumConstants differentEnumConstants;
+// [email protected]:* {{'kDifferentEnumConstantsValueSecond' from module 'SecondModule' is not present in definition of 'enum DifferentEnumConstants' in module 'FirstModule'}}
+// [email protected]:* {{definition has no member 'kDifferentEnumConstantsValueSecond'}}
+#endif
+
+#if defined(FIRST)
+enum DifferentEnumValues { kDifferentEnumValue = 0 };
+#elif defined(SECOND)
+enum DifferentEnumValues { kDifferentEnumValue = 1 };
+#else
+enum DifferentEnumValues differentEnumValue;
+// [email protected]:* {{'DifferentEnumValues' has different definitions in different modules; definition in module 'FirstModule' first difference is 1st element 'kDifferentEnumValue' has an initializer}}
+// [email protected]:* {{but in 'SecondModule' found 1st element 'kDifferentEnumValue' has different initializer}}
+#endif
+
+#if defined(FIRST)
+enum {
+    kAnonymousEnumValueFirst = 1,
+};
+#elif defined(SECOND)
+enum {
+    kAnonymousEnumValueSecond = 2,
+};
+#else
+// Anonymous enums don't have to match, no errors expected.
+int anonymousEnumValue = kAnonymousEnumValueFirst + kAnonymousEnumValueSecond;
+#endif
+
+// Keep macros contained to one file.
+#ifdef FIRST
+#undef FIRST
+#endif
+
+#ifdef SECOND
+#undef SECOND
+#endif