[Frontend] Treat function with skipped body as definition

[ilya-biryukov]

Summary

This fixes an invalid warning about missing definition of a function when
parsing with SkipFunctionBodies=true

[ilya-biryukov]

• Reverted accidental whitespace change.

[sepavloff]

LGTM.

Thanks!

include/clang/AST/Decl.h

public:
   }
 
   /// Returns whether this specific declaration of the function is also a
   /// definition that does not contain uninstantiated body.
   ///
   /// This does not determine whether the function has been defined (e.g., in a
   /// previous definition); for that information, use isDefined.
   bool isThisDeclarationADefinition() const {
-    return IsDeleted || IsDefaulted || Body || IsLateTemplateParsed ||
-      WillHaveBody || hasDefiningAttr();
+    return IsDeleted || IsDefaulted || Body || HasSkippedBody ||
+           IsLateTemplateParsed || WillHaveBody || hasDefiningAttr();
   }
 
   /// doesThisDeclarationHaveABody - Returns whether this specific
   /// declaration of the function has a body - that is, if it is a non-
   /// deleted definition.
   bool doesThisDeclarationHaveABody() const {
     return Body || IsLateTemplateParsed;
   }

test/Index/skipped_function_bodies.cpp

+// RUN: env CINDEXTEST_SKIP_FUNCTION_BODIES=1 c-index-test -test-load-source all %s 2>&1 \
+// RUN: | FileCheck %s
+
+inline int with_body() { return 10; }
+inline int without_body();
+
+int x = with_body() + without_body();
+// CHECK: warning: inline function 'without_body' is not defined
+// CHECK-NOT: warning: inline function 'with_body' is not defined

tools/libclang/CIndex.cpp

if (TypeSourceInfo *TSInfo = ND->getTypeSourceInfo()) {
     // FIXME: Visit explicitly-specified template arguments!
     
     // Visit the function parameters, if we have a function type.
     if (FTL && VisitFunctionTypeLoc(FTL, true))
       return true;
     
     // FIXME: Attributes?
   }
-  
   if (ND->doesThisDeclarationHaveABody() && !ND->isLateTemplateParsed()) {
     if (CXXConstructorDecl *Constructor = dyn_cast<CXXConstructorDecl>(ND)) {
       // Find the initializers that were written in the source.
       SmallVector<CXXCtorInitializer *, 4> WrittenInits;
       for (auto *I : Constructor->inits()) {
         if (!I->isWritten())
           continue;