Implement a Conditional token for PointerTemplate (#1567)

Signed-off-by: Juan Cruz Viotti <[email protected]>

src/core/jsonpointer/include/sourcemeta/core/jsonpointer_template.h

@@ -15,12 +15,15 @@ namespace sourcemeta::core {
 /// @ingroup jsonpointer
 template <typename PointerT> class GenericPointerTemplate {
 public:
-  /// The type of wildcard
   enum class Wildcard { Property, Item, Key };
-
+  struct Conditional {
+    auto operator==(const Conditional &) const noexcept -> bool = default;
+    auto operator<(const Conditional &) const noexcept -> bool { return false; }
+  };
   using Regex = typename PointerT::Value::String;
   using Token = typename PointerT::Token;
-  using Container = std::vector<std::variant<Token, Wildcard, Regex>>;
+  using Container =
+      std::vector<std::variant<Wildcard, Conditional, Regex, Token>>;
 
   /// This constructor creates an empty JSON Pointer template. For example:
   ///

src/core/jsonpointer/stringify.h

@@ -469,6 +469,12 @@ auto stringify(const PointerT &pointer,
         const auto &value{std::get<typename PointerT::Regex>(token)};
         stream.write(value.c_str(), static_cast<std::streamsize>(value.size()));
         stream.put(internal::token_pointer_tilde<CharT>);
+      } else if (std::holds_alternative<typename PointerT::Conditional>(
+                     token)) {
+        stream.put(internal::token_pointer_slash<CharT>);
+        stream.put(internal::token_pointer_tilde<CharT>);
+        stream.put('?');
+        stream.put(internal::token_pointer_tilde<CharT>);
       } else {
         stringify_token<CharT, Traits, Allocator, typename PointerT::Token>(
             std::get<typename PointerT::Token>(token), stream,

test/jsonpointer/jsonpointer_template_test.cc

@@ -134,6 +134,36 @@ TEST(JSONPointer_template, equality_with_key_wildcard_false) {
   EXPECT_NE(left, right);
 }
 
+TEST(JSONPointer_template, equality_with_conditional_wildcard_true) {
+  const sourcemeta::core::Pointer prefix{"foo", "bar"};
+  const sourcemeta::core::Pointer suffix{"baz"};
+
+  sourcemeta::core::PointerTemplate left{prefix};
+  left.emplace_back(sourcemeta::core::PointerTemplate::Conditional{});
+  left.push_back(suffix);
+
+  sourcemeta::core::PointerTemplate right{prefix};
+  right.emplace_back(sourcemeta::core::PointerTemplate::Conditional{});
+  right.push_back(suffix);
+
+  EXPECT_EQ(left, right);
+}
+
+TEST(JSONPointer_template, equality_with_conditional_wildcard_false) {
+  const sourcemeta::core::Pointer prefix{"foo", "bar"};
+  const sourcemeta::core::Pointer suffix{"baz"};
+
+  sourcemeta::core::PointerTemplate left{prefix};
+  left.emplace_back(sourcemeta::core::PointerTemplate::Conditional{});
+  left.push_back(suffix);
+
+  sourcemeta::core::PointerTemplate right{prefix};
+  right.push_back(suffix);
+  right.emplace_back(sourcemeta::core::PointerTemplate::Conditional{});
+
+  EXPECT_NE(left, right);
+}
+
 TEST(JSONPointer_template, pop_back) {
   const sourcemeta::core::Pointer base{"foo", "bar"};
   sourcemeta::core::PointerTemplate pointer{base};
@@ -202,6 +232,18 @@ TEST(JSONPointer_template, stringify_key_wildcard) {
   EXPECT_EQ(stream.str(), "/foo/bar/~K~");
 }
 
+TEST(JSONPointer_template, stringify_conditional) {
+  const sourcemeta::core::Pointer prefix{"foo", "bar"};
+
+  sourcemeta::core::PointerTemplate pointer{prefix};
+  pointer.emplace_back(sourcemeta::core::PointerTemplate::Conditional{});
+
+  std::ostringstream stream;
+  sourcemeta::core::stringify(pointer, stream);
+
+  EXPECT_EQ(stream.str(), "/foo/bar/~?~");
+}
+
 TEST(JSONPointer_template, concat_move) {
   const sourcemeta::core::Pointer pointer_left{"foo"};
   const sourcemeta::core::Pointer pointer_right{"bar", "baz"};