[WIP] feat(alterschema): [linter] create rule to remove empty fragment

src/extension/alterschema/CMakeLists.txt

@@ -55,6 +55,7 @@ sourcemeta_library(NAMESPACE sourcemeta PROJECT core NAME alterschema
     linter/if_without_then_else.h
     linter/max_contains_without_contains.h
     linter/min_contains_without_contains.h
+    linter/modern_official_dialect_with_empty_fragment.h
     linter/then_without_if.h)
 
 if(SOURCEMETA_CORE_INSTALL)

src/extension/alterschema/alterschema.cc

@@ -73,6 +73,7 @@ static auto every_item_is_boolean(const T &container) -> bool {
 #include "linter/maximum_real_for_integer.h"
 #include "linter/min_contains_without_contains.h"
 #include "linter/minimum_real_for_integer.h"
+#include "linter/modern_official_dialect_with_empty_fragment.h"
 #include "linter/multiple_of_default.h"
 #include "linter/non_applicable_type_specific_keywords.h"
 #include "linter/pattern_properties_default.h"
@@ -113,6 +114,7 @@ auto add(SchemaTransformer &bundle, const AlterSchemaMode mode)
   bundle.add<DuplicateEnumValues>();
   bundle.add<DuplicateRequiredValues>();
   bundle.add<ConstWithType>();
+  bundle.add<ModernOfficialDialectWithEmptyFragment>();
   bundle.add<ExclusiveMaximumNumberAndMaximum>();
   bundle.add<ExclusiveMinimumNumberAndMinimum>();
 

src/extension/alterschema/linter/modern_official_dialect_with_empty_fragment.h

@@ -0,0 +1,36 @@
+class ModernOfficialDialectWithEmptyFragment final
+    : public SchemaTransformRule {
+public:
+  ModernOfficialDialectWithEmptyFragment()
+      : SchemaTransformRule{
+            "modern_official_dialect_with_empty_fragment",
+            "The official dialect URI of Draft 2019-09 and newer versions must "
+            "not contain the empty fragment"} {};
+
+  [[nodiscard]] auto condition(const sourcemeta::core::JSON &schema,
+                               const sourcemeta::core::JSON &,
+                               const sourcemeta::core::Vocabularies &,
+                               const sourcemeta::core::SchemaFrame &,
+                               const sourcemeta::core::SchemaFrame::Location &,
+                               const sourcemeta::core::SchemaWalker &,
+                               const sourcemeta::core::SchemaResolver &) const
+      -> sourcemeta::core::SchemaTransformRule::Result override {
+    if (!schema.is_object() || !schema.defines("$schema") ||
+        !schema.at("$schema").is_string()) {
+      return false;
+    }
+
+    const auto &schema_value = schema.at("$schema").to_string();
+    return (
+        schema_value == "https://json-schema.org/draft/2019-09/schema#" ||
+        schema_value == "https://json-schema.org/draft/2019-09/hyper-schema#" ||
+        schema_value == "https://json-schema.org/draft/2020-12/schema#" ||
+        schema_value == "https://json-schema.org/draft/2020-12/hyper-schema#");
+  }
+
+  auto transform(sourcemeta::core::JSON &schema) const -> void override {
+    auto schema_value = schema.at("$schema").to_string();
+    schema_value.pop_back();
+    schema.at("$schema").into(sourcemeta::core::JSON{std::move(schema_value)});
+  }
+};