Fix segfault with enumerations

When serializing map types to JSON, if it encounters an enumeration,
the rewriter goes into an infinite loop until it segfaults.  This fix
properly serializes enumerations in the same way unions and structs
are.

    enum a {
      CHOICE_A,
      CHOICE_B,
    };
    BPF_HASH(m, u32, enum a);

is serialized as:

    ["a", ["CHOICE_A","CHOICE_B"], "enum"]

src/cc/json_map_decl_visitor.cc

@@ -40,6 +40,8 @@ class BMapDeclVisitor : public clang::RecursiveASTVisitor<BMapDeclVisitor> {
   bool VisitTypedefType(const clang::TypedefType *T);
   bool VisitTagType(const clang::TagType *T);
   bool VisitPointerType(const clang::PointerType *T);
+  bool VisitEnumConstantDecl(clang::EnumConstantDecl *D);
+  bool VisitEnumDecl(clang::EnumDecl *D);
 
  private:
   clang::ASTContext &C;
@@ -55,6 +57,25 @@ bool BMapDeclVisitor::VisitFieldDecl(FieldDecl *D) {
   return true;
 }
 
+bool BMapDeclVisitor::VisitEnumConstantDecl(EnumConstantDecl *D) {
+  result_ += "\"";
+  result_ += D->getName();
+  result_ += "\",";
+  return false;
+}
+
+bool BMapDeclVisitor::VisitEnumDecl(EnumDecl *D) {
+  result_ += "[\"";
+  result_ += D->getName();
+  result_ += "\", [";
+  for (auto it = D->enumerator_begin(); it != D->enumerator_end(); ++it) {
+    TraverseDecl(*it);
+  }
+  result_.erase(result_.end() - 1);
+  result_ += "], \"enum\"]";
+  return false;
+}
+
 bool BMapDeclVisitor::TraverseRecordDecl(RecordDecl *D) {
   // skip children, handled in Visit...
   if (!WalkUpFromRecordDecl(D))

tests/python/test_clang.py

@@ -612,6 +612,18 @@ struct key_t {
         with self.assertRaises(Exception):
             b = BPF(text=text)
 
+    def test_enumerations(self):
+        text = """
+enum b {
+    CHOICE_A,
+};
+struct a {
+    enum b test;
+};
+BPF_HASH(drops, struct a);
+        """
+        b = BPF(text=text)
+
 
 if __name__ == "__main__":
     main()