add test for enumeration conversion

tests/NewParseTest.cpp

@@ -8,7 +8,9 @@
 
 #include <complex>
 #include <cstdint>
+#include <map>
 #include <string>
+#include <unordered_map>
 #include <utility>
 #include <vector>
 
@@ -645,3 +647,69 @@ TEST_CASE_METHOD(TApp, "vectorComplex", "[newparse]") {
     CHECK(1.4 == vcomplex[1].real());
     CHECK(-4.0 == vcomplex[1].imag());
 }
+
+#if (defined(CLI11_ENABLE_EXTRA_VALIDATORS) && CLI11_ENABLE_EXTRA_VALIDATORS == 1) ||                                  \
+    (!defined(CLI11_DISABLE_EXTRA_VALIDATORS) || CLI11_DISABLE_EXTRA_VALIDATORS == 0)
+
+// enumeration with stream operator
+#define COLOR_LIST                                                                                                     \
+    X(Red)                                                                                                             \
+    X(Blue)                                                                                                            \
+    X(Green)
+
+enum class Color {
+#define X(name) name,
+    COLOR_LIST
+#undef X
+};
+
+const std::unordered_map<std::string, Color> STR_TO_COLOR_MAP{
+#define X(name) {#name, Color::name},
+    COLOR_LIST
+#undef X
+};
+
+// std::map: GCC < 6.1 has no std::hash for enums
+const std::map<Color, std::string> COLOR_TO_STR_MAP{
+#define X(name) {Color::name, #name},
+    COLOR_LIST
+#undef X
+};
+
+// this stream operator triggered the ConversionError in issue #1330
+std::ostream &operator<<(std::ostream &os, Color c) {
+    auto it = COLOR_TO_STR_MAP.find(c);
+    if(it != COLOR_TO_STR_MAP.end())
+        return os << it->second;
+
+    return os << std::string("Unknown");
+}
+
+TEST_CASE_METHOD(TApp, "enumDefaultParse", "[newparse]") {
+    Color color{Color::Blue};
+    Color other_color{Color::Red};
+    app.add_option("--color", color)
+        ->default_val(Color::Red)
+        ->transform(CLI::CheckedTransformer(STR_TO_COLOR_MAP))
+        ->force_callback();
+
+    args = {};
+    run();
+    CHECK(color == Color::Red);
+
+    args = {"--color", "Green"};
+    run();
+    CHECK(color == Color::Green);
+
+    app.add_option("--color2", other_color)
+        ->default_str("Green")
+        ->transform(CLI::CheckedTransformer(STR_TO_COLOR_MAP))
+        ->force_callback();
+
+    args = {"--color", "Blue"};
+    run();
+    CHECK(color == Color::Blue);
+    CHECK(other_color == Color::Green);
+}
+
+#endif