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

src/extension/alterschema/CMakeLists.txt

@@ -69,7 +69,8 @@ sourcemeta_library(NAMESPACE sourcemeta PROJECT core NAME alterschema
     linter/definitions_to_defs.h
 
     # Strict
-    strict/required_properties_in_properties.h)
+    strict/required_properties_in_properties.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"
@@ -108,6 +109,7 @@ auto add(SchemaTransformer &bundle, const AlterSchemaMode mode) -> void {
   bundle.add<NotFalse>();
   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 +1,42 @@
+class ThenFalse final : public SchemaTransformRule {
+public:
+  ThenFalse()
+      : SchemaTransformRule{
+            "then_false",
+            "`Setting the `then` keyword to the false schema is a convoluted "
+            "way of negating the `if` subschema, which you can more cleanly "
+            "represent using the `not` keyword"} {};
+
+  [[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") && is_schema(schema.at("then")) &&
+           schema.at("then").is_boolean() && !schema.at("then").to_boolean() &&
+           is_schema(schema.at("if")) &&
+           !(schema.at("if").is_boolean() && schema.at("if").to_boolean()) &&
+           (!schema.defines("else") || (schema.at("else").is_boolean() &&
+                                        schema.at("else").to_boolean())) &&
+           (!schema.at("if").is_object() ||
+            std::all_of(schema.at("if").as_object().begin(),
+                        schema.at("if").as_object().end(),
+                        [&schema](const auto &entry) {
+                          return !schema.defines(entry.first);
+                        }));
+  }
+
+  auto transform(JSON &schema) const -> void override {
+    auto if_schema = schema.at("if");
+    schema.erase("if");
+    schema.erase("then");
+    schema.erase("else");
+    schema.assign("not", std::move(if_schema));
+  }
+};

test/alterschema/alterschema_lint_2019_09_test.cc

@@ -2831,3 +2831,179 @@ TEST(AlterSchema_lint_2019_09, required_properties_in_properties_5) {
 
   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_lint_2019_09, then_false_2) {
+  sourcemeta::core::JSON document = sourcemeta::core::parse_json(R"JSON({
+    "$schema": "https://json-schema.org/draft/2019-09/schema",
+    "if": {
+      "properties": {
+        "flag": {
+          "const": true
+        }
+      }
+    },
+    "then": false,
+    "else": true
+  })JSON");
+
+  LINT_AND_FIX_FOR_READABILITY(document);
+
+  const sourcemeta::core::JSON expected = sourcemeta::core::parse_json(R"JSON({
+    "$schema": "https://json-schema.org/draft/2019-09/schema",
+    "not": {
+      "properties": {
+        "flag": {
+          "const": true
+        }
+      }
+    }
+  })JSON");
+
+  EXPECT_EQ(document, expected);
+}
+
+TEST(AlterSchema_lint_2019_09, then_false_3) {
+  sourcemeta::core::JSON document = sourcemeta::core::parse_json(R"JSON({
+    "$schema": "https://json-schema.org/draft/2019-09/schema",
+    "if": true,
+    "then": false
+  })JSON");
+
+  LINT_AND_FIX_FOR_READABILITY(document);
+
+  const sourcemeta::core::JSON expected = sourcemeta::core::parse_json(R"JSON({
+    "$schema": "https://json-schema.org/draft/2019-09/schema",
+    "if": true,
+    "then": false
+  })JSON");
+
+  EXPECT_EQ(document, expected);
+}
+
+TEST(AlterSchema_lint_2019_09, then_false_4) {
+  sourcemeta::core::JSON document = sourcemeta::core::parse_json(R"JSON({
+    "$schema": "https://json-schema.org/draft/2019-09/schema",
+    "if": false,
+    "then": false
+  })JSON");
+
+  LINT_AND_FIX_FOR_READABILITY(document);
+
+  const sourcemeta::core::JSON expected = sourcemeta::core::parse_json(R"JSON({
+    "$schema": "https://json-schema.org/draft/2019-09/schema"
+  })JSON");
+
+  EXPECT_EQ(document, expected);
+}
+
+TEST(AlterSchema_lint_2019_09, then_false_5) {
+  sourcemeta::core::JSON document = sourcemeta::core::parse_json(R"JSON({
+    "$schema": "https://json-schema.org/draft/2019-09/schema",
+    "type": "object",
+    "properties": {
+      "name": { "type": "string" }
+    },
+    "if": {
+      "properties": {
+        "name": { "type": "number" }
+      }
+    },
+    "then": false
+  })JSON");
+
+  LINT_AND_FIX_FOR_READABILITY(document);
+
+  const sourcemeta::core::JSON expected = sourcemeta::core::parse_json(R"JSON({
+    "$schema": "https://json-schema.org/draft/2019-09/schema",
+    "type": "object",
+    "properties": {
+      "name": { "type": "string" }
+    },
+    "if": {
+      "properties": {
+        "name": { "type": "number" }
+      }
+    },
+    "then": false
+  })JSON");
+
+  EXPECT_EQ(document, expected);
+}
+
+TEST(AlterSchema_lint_2019_09, then_false_6) {
+  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_lint_2019_09, then_false_7) {
+  sourcemeta::core::JSON document = sourcemeta::core::parse_json(R"JSON({
+    "$schema": "https://json-schema.org/draft/2019-09/schema",
+    "if": {
+      "type": "object"
+    },
+    "then": false,
+    "else": false
+  })JSON");
+
+  LINT_AND_FIX_FOR_READABILITY(document);
+
+  const sourcemeta::core::JSON expected = sourcemeta::core::parse_json(R"JSON({
+    "$schema": "https://json-schema.org/draft/2019-09/schema",
+    "if": {
+      "type": "object"
+    },
+    "then": false,
+    "else": false
+  })JSON");
+
+  EXPECT_EQ(document, expected);
+}