From Vassil Vassilev:

Like in r126648, provide (empty) default implementation for pure virtual getMemoryBufferSizes(). Not all use cases have meaningful implementations.

llvm-svn: 130838

clang/include/clang/AST/ExternalASTSource.h

@@ -211,7 +211,7 @@ public:
     return sizes;
   }
 
-  virtual void getMemoryBufferSizes(MemoryBufferSizes &sizes) const = 0;
+  virtual void getMemoryBufferSizes(MemoryBufferSizes &sizes) const;
 
 protected:
   static DeclContextLookupResult

clang/lib/AST/ExternalASTSource.cpp

@@ -57,3 +57,5 @@ ExternalASTSource::FindExternalLexicalDecls(const DeclContext *DC,
                                          llvm::SmallVectorImpl<Decl*> &Result) {
   return true;
 }
+
+void ExternalASTSource::getMemoryBufferSizes(MemoryBufferSizes &sizes) const { }