Add an AST matcher for external formal linkage.

Patch by Visoiu Mistrih

llvm-svn: 278926
diff --git a/clang/unittests/ASTMatchers/ASTMatchersNarrowingTest.cpp b/clang/unittests/ASTMatchers/ASTMatchersNarrowingTest.cpp
index 108fd43..1527eac 100644
--- a/clang/unittests/ASTMatchers/ASTMatchersNarrowingTest.cpp
+++ b/clang/unittests/ASTMatchers/ASTMatchersNarrowingTest.cpp
@@ -1937,5 +1937,21 @@
   EXPECT_TRUE(notMatches("int i = 0;", expr(nullPointerConstant())));
 }
 
+TEST(HasExternalFormalLinkage, Basic) {
+  EXPECT_TRUE(matches("int a = 0;", namedDecl(hasExternalFormalLinkage())));
+  EXPECT_TRUE(
+      notMatches("static int a = 0;", namedDecl(hasExternalFormalLinkage())));
+  EXPECT_TRUE(notMatches("static void f(void) { int a = 0; }",
+                         namedDecl(hasExternalFormalLinkage())));
+  EXPECT_TRUE(matches("void f(void) { int a = 0; }",
+                      namedDecl(hasExternalFormalLinkage())));
+
+  // Despite having internal semantic linkage, the anonymous namespace member
+  // has external linkage because the member has a unique name in all
+  // translation units.
+  EXPECT_TRUE(matches("namespace { int a = 0; }",
+                      namedDecl(hasExternalFormalLinkage())));
+}
+
 } // namespace ast_matchers
 } // namespace clang