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

src/extension/alterschema/CMakeLists.txt

@@ -69,6 +69,7 @@ sourcemeta_library(NAMESPACE sourcemeta PROJECT core NAME alterschema
     linter/definitions_to_defs.h
     linter/unknown_keywords_prefix.h
     linter/non_applicable_enum_validation_keywords.h
+    linter/then_false.h
 
     # Strict
     strict/required_properties_in_properties.h)

src/extension/alterschema/alterschema.cc

@@ -94,6 +94,7 @@ inline auto APPLIES_TO_POINTERS(std::vector<Pointer> &&keywords)
 #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"
@@ -130,6 +131,7 @@ 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 +1,47 @@
+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 {
+    ONLY_CONTINUE_IF(
+        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);
+                     })));
+
+    if (schema.defines("else")) {
+      return APPLIES_TO_KEYWORDS("if", "then", "else");
+    } else {
+      return APPLIES_TO_KEYWORDS("if", "then");
+    }
+  }
+
+  auto transform(JSON &schema, const Result &) 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

@@ -3275,3 +3275,179 @@ TEST(AlterSchema_lint_2019_09, unknown_keywords_prefix_11) {
 
   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);
+}