[RecursiveASTVisitor] Visit the implicit expression of a CXXDefaultArgExpr

[malcolm.parsons]

Summary

The matcher
varDecl(hasDescendant(

callExpr(hasDeclaration(functionDecl(unless(isNoThrow()))))))

didn't match calls from default arguments because the expression
for a CXXDefaultArgExpr was not visited.

[aaron.ballman]

LGTM!

include/clang/AST/RecursiveASTVisitor.h

DEF_TRAVERSE_STMT(BlockExpr, {
   return true; // no child statements to loop through.
 })
 DEF_TRAVERSE_STMT(ChooseExpr, {})
 DEF_TRAVERSE_STMT(CompoundLiteralExpr, {
   TRY_TO(TraverseTypeLoc(S->getTypeSourceInfo()->getTypeLoc()));
 })
 DEF_TRAVERSE_STMT(CXXBindTemporaryExpr, {})
 DEF_TRAVERSE_STMT(CXXBoolLiteralExpr, {})
-DEF_TRAVERSE_STMT(CXXDefaultArgExpr, {})
+DEF_TRAVERSE_STMT(CXXDefaultArgExpr, {
+  if (getDerived().shouldVisitImplicitCode())
+    TRY_TO(TraverseStmt(S->getExpr()));
+})
 DEF_TRAVERSE_STMT(CXXDefaultInitExpr, {})
 DEF_TRAVERSE_STMT(CXXDeleteExpr, {})
 DEF_TRAVERSE_STMT(ExprWithCleanups, {})
 DEF_TRAVERSE_STMT(CXXInheritedCtorInitExpr, {})
 DEF_TRAVERSE_STMT(CXXNullPtrLiteralExpr, {})
 DEF_TRAVERSE_STMT(CXXStdInitializerListExpr, {})
 DEF_TRAVERSE_STMT(CXXPseudoDestructorExpr, {
   TRY_TO(TraverseNestedNameSpecifierLoc(S->getQualifierLoc()));

unittests/Tooling/RecursiveASTVisitorTest.cpp

TEST(RecursiveASTVisitor, ArrayInitializersAreVisited) {
   Visitor.ExpectMatch("__i0", 1, 8);
   EXPECT_TRUE(
       Visitor.runOver("struct MyClass {\n"
                       "  int c[1];\n"
                       "  static MyClass Create() { return MyClass(); }\n"
                       "};\n"));
 }
 
+// Check to ensure that implicit default argument expressions are visited.
+class IntegerLiteralVisitor
+    : public ExpectedLocationVisitor<IntegerLiteralVisitor> {
+public:
+  bool VisitIntegerLiteral(const IntegerLiteral *IL) {
+    Match("literal", IL->getLocation());
+    return true;
+  }
+};
+
+TEST(RecursiveASTVisitor, DefaultArgumentsAreVisited) {
+  IntegerLiteralVisitor Visitor;
+  Visitor.ExpectMatch("literal", 1, 15, 2);
+  EXPECT_TRUE(Visitor.runOver("int f(int i = 1);\n"
+                              "static int k = f();\n"));
+}
+
 } // end anonymous namespace