Linter: create rule to to add syntactical sugar when then is set to false

src/extension/alterschema/CMakeLists.txt

@@ -65,7 +65,8 @@ sourcemeta_library(NAMESPACE sourcemeta PROJECT core NAME alterschema
     linter/then_without_if.h
     linter/property_names_type_default.h
     linter/property_names_default.h
-    linter/draft_ref_siblings.h)
+    linter/draft_ref_siblings.h
+    linter/then_false.h)
 
 if(SOURCEMETA_CORE_INSTALL)
   sourcemeta_library_install(NAMESPACE sourcemeta PROJECT core NAME alterschema)

src/extension/alterschema/alterschema.cc

@@ -75,6 +75,7 @@ contains_any(const Vocabularies &container,
 #include "linter/property_names_type_default.h"
 #include "linter/single_type_array.h"
 #include "linter/then_empty.h"
+#include "linter/then_false.h"
 #include "linter/then_without_if.h"
 #include "linter/unevaluated_items_default.h"
 #include "linter/unevaluated_properties_default.h"
@@ -106,6 +107,7 @@ auto add(SchemaTransformer &bundle, const AlterSchemaMode mode)
   bundle.add<MinContainsWithoutContains>();
   bundle.add<ThenEmpty>();
   bundle.add<ElseEmpty>();
+  bundle.add<ThenFalse>();
   bundle.add<ThenWithoutIf>();
   bundle.add<DependenciesPropertyTautology>();
   bundle.add<DependentRequiredTautology>();

src/extension/alterschema/linter/then_false.h

@@ -0,0 +1,29 @@
+class ThenFalse final : public SchemaTransformRule {
+public:
+  ThenFalse()
+      : SchemaTransformRule{
+            "then_false",
+            "`if: S, then: false` is logically equivalent to `not: S`"} {};
+
+  [[nodiscard]] auto
+  condition(const JSON &schema, const JSON &, const Vocabularies &vocabularies,
+            const SchemaFrame &, const SchemaFrame::Location &,
+            const SchemaWalker &, const SchemaResolver &) const
+      -> SchemaTransformRule::Result override {
+    return contains_any(
+               vocabularies,
+               {"https://json-schema.org/draft/2020-12/vocab/applicator",
+                "https://json-schema.org/draft/2019-09/vocab/applicator",
+                "http://json-schema.org/draft-07/schema#"}) &&
+           schema.is_object() && schema.defines("if") &&
+           schema.defines("then") && schema.at("then").is_boolean() &&
+           !schema.at("then").to_boolean();
+  }
+
+  auto transform(JSON &schema) const -> void override {
+    const auto if_schema = schema.at("if");
+    schema.erase("if");
+    schema.erase("then");
+    schema.assign("not", if_schema);
+  }
+};

test/alterschema/alterschema_lint_2019_09_test.cc

@@ -2349,3 +2349,32 @@ TEST(AlterSchema_lint_2019_09, non_applicable_type_specific_keywords_3) {
 
   EXPECT_EQ(document, expected);
 }
+
+TEST(AlterSchema_lint_2019_09, then_false_1) {
+  sourcemeta::core::JSON document = sourcemeta::core::parse_json(R"JSON({
+    "$schema": "https://json-schema.org/draft/2019-09/schema",
+    "if": {
+      "properties": {
+        "flag": {
+          "const": true
+        }
+      }
+    },
+    "then": false
+  })JSON");
+
+  LINT_AND_FIX_FOR_READABILITY(document);
+
+  const sourcemeta::core::JSON expected = sourcemeta::core::parse_json(R"JSON({
+    "$schema": "https://json-schema.org/draft/2019-09/schema",
+    "not": {
+      "properties": {
+        "flag": {
+          "const": true
+        }
+      }
+    }
+  })JSON");
+
+  EXPECT_EQ(document, expected);
+}

test/alterschema/alterschema_lint_2020_12_test.cc

@@ -2583,3 +2583,32 @@ TEST(AlterSchema_lint_2020_12, non_applicable_type_specific_keywords_3) {
 
   EXPECT_EQ(document, expected);
 }
+
+TEST(AlterSchema_lint_2020_12, then_false_1) {
+  sourcemeta::core::JSON document = sourcemeta::core::parse_json(R"JSON({
+    "$schema": "https://json-schema.org/draft/2020-12/schema",
+    "if": {
+      "properties": {
+        "flag": {
+          "const": true
+        }
+      }
+    },
+    "then": false
+  })JSON");
+
+  LINT_AND_FIX_FOR_READABILITY(document);
+
+  const sourcemeta::core::JSON expected = sourcemeta::core::parse_json(R"JSON({
+    "$schema": "https://json-schema.org/draft/2020-12/schema",
+    "not": {
+      "properties": {
+        "flag": {
+          "const": true
+        }
+      }
+    }
+  })JSON");
+
+  EXPECT_EQ(document, expected);
+}

test/alterschema/alterschema_lint_draft7_test.cc

@@ -1890,3 +1890,32 @@ TEST(AlterSchema_lint_draft7, non_applicable_type_specific_keywords_3) {
 
   EXPECT_EQ(document, expected);
 }
+
+TEST(AlterSchema_lint_draft7, then_false_1) {
+  sourcemeta::core::JSON document = sourcemeta::core::parse_json(R"JSON({
+    "$schema": "http://json-schema.org/draft-07/schema#",
+    "if": {
+      "properties": {
+        "flag": {
+          "const": true
+        }
+      }
+    },
+    "then": false
+  })JSON");
+
+  LINT_AND_FIX_FOR_READABILITY(document);
+
+  const sourcemeta::core::JSON expected = sourcemeta::core::parse_json(R"JSON({
+    "$schema": "http://json-schema.org/draft-07/schema#",
+    "not": {
+      "properties": {
+        "flag": {
+          "const": true
+        }
+      }
+    }
+  })JSON");
+
+  EXPECT_EQ(document, expected);
+}