[Modules] Implement ODR-like semantics for tag types in C/ObjC

Allow ODR for ObjC/C in the sense that we won't keep more that
one definition around (merge them). However, ensure the decl
pass the structural compatibility check in C11 6.2.7/1, for that,
reuse the structural equivalence checks used by the ASTImporter.

Few other considerations:
- Create error diagnostics for tag types mismatches and thread
them into the structural equivalence checks.
- Note that by doing this we only support redefinition between types
that are considered "compatible types" by C.

This is mixed approach of the suggestions discussed in
http://lists.llvm.org/pipermail/cfe-dev/2017-March/053257.html

Differential Revision: https://reviews.llvm.org/D31778

rdar://problem/31909368

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@306918 91177308-0d34-0410-b5e6-96231b3b80d8

3 files changed, 34 insertions, 15 deletions

diff --git a/include/clang/AST/ASTStructuralEquivalence.h b/include/clang/AST/ASTStructuralEquivalence.h
index 770bb5763f..23674c65f3 100644
--- a/include/clang/AST/ASTStructuralEquivalence.h
+++ b/include/clang/AST/ASTStructuralEquivalence.h
@@ -62,9 +62,11 @@ struct StructuralEquivalenceContext {
   StructuralEquivalenceContext(
       ASTContext &FromCtx, ASTContext &ToCtx,
       llvm::DenseSet<std::pair<Decl *, Decl *>> &NonEquivalentDecls,
-      bool StrictTypeSpelling = false, bool Complain = true)
+      bool StrictTypeSpelling = false, bool Complain = true,
+      bool ErrorOnTagTypeMismatch = false)
       : FromCtx(FromCtx), ToCtx(ToCtx), NonEquivalentDecls(NonEquivalentDecls),
-        StrictTypeSpelling(StrictTypeSpelling), Complain(Complain),
+        StrictTypeSpelling(StrictTypeSpelling),
+        ErrorOnTagTypeMismatch(ErrorOnTagTypeMismatch), Complain(Complain),
         LastDiagFromC2(false) {}
 
   DiagnosticBuilder Diag1(SourceLocation Loc, unsigned DiagID);
diff --git a/include/clang/Basic/DiagnosticASTKinds.td b/include/clang/Basic/DiagnosticASTKinds.td
index 652d062785..b3cba2066e 100644
--- a/include/clang/Basic/DiagnosticASTKinds.td
+++ b/include/clang/Basic/DiagnosticASTKinds.td
@@ -200,12 +200,17 @@ def note_odr_defined_here : Note<"also defined here">;
 def err_odr_function_type_inconsistent : Error<
   "external function %0 declared with incompatible types in different "
   "translation units (%1 vs. %2)">;
-def warn_odr_tag_type_inconsistent : Warning<
-  "type %0 has incompatible definitions in different translation units">,
-  InGroup<DiagGroup<"odr">>;
+def warn_odr_tag_type_inconsistent
+    : Warning<"type %0 has incompatible definitions in different translation "
+              "units">,
+      InGroup<DiagGroup<"odr">>;
+def err_odr_tag_type_inconsistent
+    : Error<"type %0 has incompatible definitions in different translation "
+            "units">;
 def note_odr_tag_kind_here: Note<
   "%0 is a %select{struct|interface|union|class|enum}1 here">;
 def note_odr_field : Note<"field %0 has type %1 here">;
+def note_odr_field_name : Note<"field has name %0 here">;
 def note_odr_missing_field : Note<"no corresponding field here">;
 def note_odr_bit_field : Note<"bit-field %0 with type %1 and length %2 here">;
 def note_odr_not_bit_field : Note<"field %0 is not a bit-field">;
diff --git a/include/clang/Sema/Sema.h b/include/clang/Sema/Sema.h
index 75ff5fdb37..95134d52f8 100644
--- a/include/clang/Sema/Sema.h
+++ b/include/clang/Sema/Sema.h
@@ -1542,6 +1542,10 @@ public:
 
   bool hasVisibleMergedDefinition(NamedDecl *Def);
 
+  /// Determine if \p D and \p Suggested have a structurally compatible
+  /// layout as described in C11 6.2.7/1.
+  bool hasStructuralCompatLayout(Decl *D, Decl *Suggested);
+
   /// Determine if \p D has a visible definition. If not, suggest a declaration
   /// that should be made visible to expose the definition.
   bool hasVisibleDefinition(NamedDecl *D, NamedDecl **Suggested,
@@ -1629,9 +1633,13 @@ public:
   //
 
   struct SkipBodyInfo {
-    SkipBodyInfo() : ShouldSkip(false), Previous(nullptr) {}
+    SkipBodyInfo()
+        : ShouldSkip(false), CheckSameAsPrevious(false), Previous(nullptr),
+          New(nullptr) {}
     bool ShouldSkip;
+    bool CheckSameAsPrevious;
     NamedDecl *Previous;
+    NamedDecl *New;
   };
 
   DeclGroupPtrTy ConvertDeclToDeclGroup(Decl *Ptr, Decl *OwnedType = nullptr);
@@ -2145,13 +2153,11 @@ public:
   };
 
   Decl *ActOnTag(Scope *S, unsigned TagSpec, TagUseKind TUK,
-                 SourceLocation KWLoc, CXXScopeSpec &SS,
-                 IdentifierInfo *Name, SourceLocation NameLoc,
-                 AttributeList *Attr, AccessSpecifier AS,
-                 SourceLocation ModulePrivateLoc,
-                 MultiTemplateParamsArg TemplateParameterLists,
-                 bool &OwnedDecl, bool &IsDependent,
-                 SourceLocation ScopedEnumKWLoc,
+                 SourceLocation KWLoc, CXXScopeSpec &SS, IdentifierInfo *Name,
+                 SourceLocation NameLoc, AttributeList *Attr,
+                 AccessSpecifier AS, SourceLocation ModulePrivateLoc,
+                 MultiTemplateParamsArg TemplateParameterLists, bool &OwnedDecl,
+                 bool &IsDependent, SourceLocation ScopedEnumKWLoc,
                  bool ScopedEnumUsesClassTag, TypeResult UnderlyingType,
                  bool IsTypeSpecifier, bool IsTemplateParamOrArg,
                  SkipBodyInfo *SkipBody = nullptr);
@@ -2219,6 +2225,12 @@ public:
   /// struct, or union).
   void ActOnTagStartDefinition(Scope *S, Decl *TagDecl);
 
+  /// Perform ODR-like check for C/ObjC when merging tag types from modules.
+  /// Differently from C++, actually parse the body and reject / error out
+  /// in case of a structural mismatch.
+  bool ActOnDuplicateDefinition(DeclSpec &DS, Decl *Prev,
+                                SkipBodyInfo &SkipBody);
+
   typedef void *SkippedDefinitionContext;
 
   /// \brief Invoked when we enter a tag definition that we're skipping.
@@ -2272,8 +2284,8 @@ public:
 
   Decl *ActOnEnumConstant(Scope *S, Decl *EnumDecl, Decl *LastEnumConstant,
                           SourceLocation IdLoc, IdentifierInfo *Id,
-                          AttributeList *Attrs,
-                          SourceLocation EqualLoc, Expr *Val);
+                          AttributeList *Attrs, SourceLocation EqualLoc,
+                          Expr *Val);
   void ActOnEnumBody(SourceLocation EnumLoc, SourceRange BraceRange,
                      Decl *EnumDecl,
                      ArrayRef<Decl *> Elements,