Prefer operator<< to range-based stringification

Fixes #1172

projects/SelfTest/UsageTests/ToStringWhich.tests.cpp

@@ -71,3 +71,76 @@ TEST_CASE( "toString( vectors<has_maker_and_operator> )", "[toString]" ) {
     std::vector<has_maker_and_operator> v(1);
     REQUIRE( ::Catch::Detail::stringify( v ) == "{ StringMaker<has_maker_and_operator> }" );
 }
+
+// Conversion should go
+// StringMaker specialization, operator<<, range/enum detection, unprintable
+struct int_iterator {
+    using iterator_category = std::input_iterator_tag;
+    using difference_type = std::ptrdiff_t;
+    using value_type = int;
+    using reference = int&;
+    using pointer = int*;
+
+    int_iterator() = default;
+    int_iterator(int i) :val(i) {}
+
+    value_type operator*() const { return val; }
+    bool operator==(int_iterator rhs) const { return val == rhs.val; }
+    bool operator!=(int_iterator rhs) const { return val != rhs.val; }
+    int_iterator operator++() { ++val; return *this; }
+    int_iterator operator++(int) {
+        auto temp(*this);
+        ++val;
+        return temp;
+    }
+private:
+    int val = 5;
+};
+
+struct streamable_range {
+    int_iterator begin() const { return int_iterator{ 1 }; }
+    int_iterator end() const { return {}; }
+};
+
+std::ostream& operator<<(std::ostream& os, const streamable_range&) {
+    os << "op<<(streamable_range)";
+    return os;
+}
+
+struct stringmaker_range {
+    int_iterator begin() const { return int_iterator{ 1 }; }
+    int_iterator end() const { return {}; }
+};
+
+namespace Catch {
+template <>
+struct StringMaker<stringmaker_range> {
+    static std::string convert(stringmaker_range const&) {
+        return "stringmaker(streamable_range)";
+    }
+};
+}
+
+struct just_range {
+    int_iterator begin() const { return int_iterator{ 1 }; }
+    int_iterator end() const { return {}; }
+};
+
+struct disabled_range {
+    int_iterator begin() const { return int_iterator{ 1 }; }
+    int_iterator end() const { return {}; }
+};
+
+namespace Catch {
+template <>
+struct is_range<disabled_range> {
+    static const bool value = false;
+};
+}
+
+TEST_CASE("toString streamable range", "[toString]") {
+    REQUIRE(::Catch::Detail::stringify(streamable_range{}) == "op<<(streamable_range)");
+    REQUIRE(::Catch::Detail::stringify(stringmaker_range{}) == "stringmaker(streamable_range)");
+    REQUIRE(::Catch::Detail::stringify(just_range{}) == "{ 1, 2, 3, 4 }");
+    REQUIRE(::Catch::Detail::stringify(disabled_range{}) == "{?}");
+}