[frontend] Initialize the diagnostic client before loading an ast file.

Issue reported by Tom Honermann!
http://llvm.org/bugs/show_bug.cgi?id=15377

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@177336 91177308-0d34-0410-b5e6-96231b3b80d8

lib/Frontend/FrontendAction.cpp

@@ -188,6 +188,10 @@ bool FrontendAction::BeginSourceFile(CompilerInstance &CI,
 
     setCurrentInput(Input, AST);
 
+    // Inform the diagnostic client we are processing a source file.
+    CI.getDiagnosticClient().BeginSourceFile(CI.getLangOpts(), 0);
+    HasBegunSourceFile = true;
+
     // Set the shared objects, these are reset when we finish processing the
     // file, otherwise the CompilerInstance will happily destroy them.
     CI.setFileManager(&AST->getFileManager());

test/Frontend/ast-main.cpp

+// RUN: %clang -emit-llvm -S -o %t1.ll -x c++ - < %s
+// RUN: %clang -emit-ast -o %t.ast %s
+// RUN: %clang -emit-llvm -S -o %t2.ll -x ast - < %t.ast
+// RUN: diff %t1.ll %t2.ll
+
+// http://llvm.org/bugs/show_bug.cgi?id=15377
+template<typename T>
+struct S {
+    T *mf();
+};
+template<typename T>
+T *S<T>::mf() {
+    // warning: control reaches end of non-void function [-Wreturn-type]
+}
+
+void f() {
+    S<int>().mf();
+}
+
+int main() {
+  return 0;
+}