Fix forward declarations interfering with USR generation of external source symbols

[nathawes]

Summary

ObjC interfaces marked with an ExternalSourceSymbolAttr have the name of the external module they were defined in included in their USR. During USR generation we were looking for this attribute only on the canonical decl. In the case of ObjC interfaces and Tag decls however, the canonical declaration is simply the first one, which may be a forward declaration, rather than the definition that has the the attribute. This patch changes the logic to look for the attribute on the definitions for these cases.

[akyrtzi]

I recommend to add a Decl::getExternalSourceSymbolAttr() to reuse this and avoid code duplication.

[nathawes]

Ah sorry, missed the "Decl::" part of your recommendation. I'll move it.

[akyrtzi]

Also used the new Decl:: function in a place in libclang/CIndex.cpp and committed in r303484

include/clang/AST/DeclBase.h

 class DependentDiagnostic;
 class EnumDecl;
 class ExportDecl;
+class ExternalSourceSymbolAttr;
 class FunctionDecl;
 class FunctionType;
 enum Linkage : unsigned char;

     NextInContextAndBits.setInt(Bits);
   }
 
+  /// \brief Looks on this and related declarations for an applicable
+  /// external source symbol attribute.
+  ExternalSourceSymbolAttr *getExternalSourceSymbolAttr() const;
+
   /// \brief Whether this declaration was marked as being private to the
   /// module in which it was defined.
   bool isModulePrivate() const {

lib/AST/DeclBase.cpp

   return false;
 }
 
+ExternalSourceSymbolAttr *Decl::getExternalSourceSymbolAttr() const {
+  const Decl *Definition = nullptr;
+  if (auto ID = dyn_cast<ObjCInterfaceDecl>(this)) {
+    Definition = ID->getDefinition();
+  } else if (auto PD = dyn_cast<ObjCProtocolDecl>(this)) {
+    Definition = PD->getDefinition();
+  } else if (auto TD = dyn_cast<TagDecl>(this)) {
+    Definition = TD->getDefinition();
+  }
+  if (!Definition)
+    Definition = this;
+
+  if (auto *attr = Definition->getAttr<ExternalSourceSymbolAttr>())
+    return attr;
+  if (auto *dcd = dyn_cast<Decl>(getDeclContext())) {
+    return dcd->getAttr<ExternalSourceSymbolAttr>();
+  }
+
+  return nullptr;
+}
+
 bool Decl::hasDefiningAttr() const {
   return hasAttr<AliasAttr>() || hasAttr<IFuncAttr>();
 }

lib/Index/IndexSymbol.cpp

   if (Info.Properties & (unsigned)SymbolProperty::Generic)
     Info.Lang = SymbolLanguage::CXX;
 
-  auto getExternalSymAttr = [](const Decl *D) -> ExternalSourceSymbolAttr* {
-    if (auto *attr = D->getAttr<ExternalSourceSymbolAttr>())
-      return attr;
-    if (auto *dcd = dyn_cast<Decl>(D->getDeclContext())) {
-      if (auto *attr = dcd->getAttr<ExternalSourceSymbolAttr>())
-        return attr;
-    }
-    return nullptr;
-  };
-  if (auto *attr = getExternalSymAttr(D)) {
+  if (auto *attr = D->getExternalSourceSymbolAttr()) {
     if (attr->getLanguage() == "Swift")
       Info.Lang = SymbolLanguage::Swift;
   }

lib/Index/USRGeneration.cpp

 static StringRef GetExternalSourceContainer(const NamedDecl *D) {
   if (!D)
     return StringRef();
-  if (auto *attr = D->getAttr<ExternalSourceSymbolAttr>()) {
+  if (auto *attr = D->getExternalSourceSymbolAttr()) {
     return attr->getDefinedIn();
   }
   return StringRef();

test/Index/Core/external-source-symbol-attr.m

 #define GEN_DECL(mod_name) __attribute__((external_source_symbol(language="Swift", defined_in=mod_name, generated_declaration)))
 #define PUSH_GEN_DECL(mod_name) push(GEN_DECL(mod_name), apply_to=any(enum, objc_interface, objc_category, objc_protocol))
 
+// Forward declarations should not affect module namespacing below
+@class I1;
+@class I2;
+
 // This should not be indexed.
 GEN_DECL("some_module")
 @interface I1