Allow SchemaFlatFileResolver to take a custom reference visitor

src/core/jsonschema/include/sourcemeta/core/jsonschema_resolver.h

@@ -108,7 +108,8 @@ class SOURCEMETA_CORE_JSONSCHEMA_EXPORT SchemaFlatFileResolver {
   auto add(const std::filesystem::path &path,
            const std::optional<std::string> &default_dialect = std::nullopt,
            const std::optional<std::string> &default_id = std::nullopt,
-           const Reader &reader = sourcemeta::core::read_json)
+           const Reader &reader = read_json,
+           SchemaVisitorReference &&reference_visitor = nullptr)
       -> const std::string &;
 
   // Change the identifier of a registered schema
@@ -130,6 +131,7 @@ class SOURCEMETA_CORE_JSONSCHEMA_EXPORT SchemaFlatFileResolver {
     std::optional<std::string> default_dialect;
     std::string original_identifier;
     Reader reader;
+    SchemaVisitorReference reference_visitor;
   };
 
 private:

src/core/jsonschema/resolver.cc

@@ -92,8 +92,8 @@ static auto to_lowercase(const std::string_view input) -> std::string {
 auto SchemaFlatFileResolver::add(
     const std::filesystem::path &path,
     const std::optional<std::string> &default_dialect,
-    const std::optional<std::string> &default_id, const Reader &reader)
-    -> const std::string & {
+    const std::optional<std::string> &default_id, const Reader &reader,
+    SchemaVisitorReference &&reference_visitor) -> const std::string & {
   const auto canonical{std::filesystem::weakly_canonical(path)};
   const auto schema{reader(canonical)};
   assert(sourcemeta::core::is_schema(schema));
@@ -114,7 +114,9 @@ auto SchemaFlatFileResolver::add(
 
   const auto result{this->schemas.emplace(
       effective_identifier,
-      Entry{canonical, default_dialect, effective_identifier, reader})};
+      Entry{canonical, default_dialect, effective_identifier, reader,
+            reference_visitor ? std::move(reference_visitor)
+                              : reference_visitor_relativize})};
   if (!result.second && result.first->second.path != canonical) {
     std::ostringstream error;
     error << "Cannot register the same identifier twice: "
@@ -152,8 +154,7 @@ auto SchemaFlatFileResolver::operator()(std::string_view identifier) const
     // Because we allow re-identification, we can get into issues unless we
     // always try to relativize references
     sourcemeta::core::reference_visit(
-        schema, schema_official_walker, *this,
-        sourcemeta::core::reference_visitor_relativize,
+        schema, schema_official_walker, *this, result->second.reference_visitor,
         result->second.default_dialect, result->second.original_identifier);
     sourcemeta::core::reidentify(schema, result->first, *this,
                                  result->second.default_dialect);

test/jsonschema/jsonschema_flat_file_resolver_test.cc

@@ -344,3 +344,31 @@ TEST(JSONSchema_SchemaFlatFileResolver, with_absolute_references_reidentify) {
       resolver("https://www.example.com/2020-12-absolute-ref.json").value(),
       expected);
 }
+
+TEST(JSONSchema_SchemaFlatFileResolver, custom_reference_visitor) {
+  sourcemeta::core::SchemaFlatFileResolver resolver;
+  const auto schema_path{std::filesystem::path{SCHEMAS_PATH} /
+                         "2020-12-absolute-ref.json"};
+
+  const sourcemeta::core::JSON expected = sourcemeta::core::parse_json(R"JSON({
+    "$id": "https://www.sourcemeta.com/2020-12-absolute-ref.json",
+    "$schema": "https://json-schema.org/draft/2020-12/schema",
+    "$ref": "MUTATED"
+  })JSON");
+
+  const auto &identifier{resolver.add(
+      schema_path, std::nullopt, std::nullopt, sourcemeta::core::read_json,
+      [](sourcemeta::core::JSON &schema, const sourcemeta::core::URI &,
+         const sourcemeta::core::JSON::String &,
+         const sourcemeta::core::JSON::String &keyword,
+         sourcemeta::core::URI &) {
+        schema.assign(keyword, sourcemeta::core::JSON{"MUTATED"});
+      })};
+
+  EXPECT_EQ(identifier, "https://www.sourcemeta.com/2020-12-absolute-ref.json");
+  EXPECT_TRUE(resolver("https://www.sourcemeta.com/2020-12-absolute-ref.json")
+                  .has_value());
+  EXPECT_EQ(
+      resolver("https://www.sourcemeta.com/2020-12-absolute-ref.json").value(),
+      expected);
+}