Linter: create rules to add syntaxtical sugar when else is set to false

src/extension/alterschema/CMakeLists.txt

@@ -62,6 +62,7 @@ sourcemeta_library(NAMESPACE sourcemeta PROJECT core NAME alterschema
     linter/modern_official_dialect_with_empty_fragment.h
     linter/then_empty.h
     linter/else_empty.h
+    linter/else_false.h
     linter/then_without_if.h
     linter/property_names_type_default.h
     linter/property_names_default.h

src/extension/alterschema/alterschema.cc

@@ -52,6 +52,7 @@ contains_any(const Vocabularies &container,
 #include "linter/duplicate_enum_values.h"
 #include "linter/duplicate_required_values.h"
 #include "linter/else_empty.h"
+#include "linter/else_false.h"
 #include "linter/else_without_if.h"
 #include "linter/enum_to_const.h"
 #include "linter/enum_with_type.h"
@@ -106,6 +107,7 @@ auto add(SchemaTransformer &bundle, const AlterSchemaMode mode)
   bundle.add<MinContainsWithoutContains>();
   bundle.add<ThenEmpty>();
   bundle.add<ElseEmpty>();
+  bundle.add<ElseFalse>();
   bundle.add<ThenWithoutIf>();
   bundle.add<DependenciesPropertyTautology>();
   bundle.add<DependentRequiredTautology>();

src/extension/alterschema/linter/else_false.h

@@ -0,0 +1,36 @@
+class ElseFalse final : public SchemaTransformRule {
+public:
+  ElseFalse()
+      : SchemaTransformRule{"else_false",
+                            "`if: S, else: false` collapses to just `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("else") && schema.at("else").is_boolean() &&
+           !schema.at("else").to_boolean();
+  }
+
+  auto transform(JSON &schema) const -> void override {
+    const auto if_schema = schema.at("if");
+    schema.erase("if");
+    schema.erase("else");
+    if (if_schema.is_object()) {
+      for (const auto &entry : if_schema.as_object()) {
+        if (!schema.defines(entry.first)) {
+          schema.assign(entry.first, entry.second);
+        }
+      }
+    } else if (if_schema.is_boolean()) {
+      schema = if_schema;
+    }
+  }
+};

test/alterschema/alterschema_lint_2019_09_test.cc

@@ -2349,3 +2349,30 @@ TEST(AlterSchema_lint_2019_09, non_applicable_type_specific_keywords_3) {
 
   EXPECT_EQ(document, expected);
 }
+
+TEST(AlterSchema_lint_2019_09, else_false_1) {
+  sourcemeta::core::JSON document = sourcemeta::core::parse_json(R"JSON({
+    "$schema": "https://json-schema.org/draft/2019-09/schema",
+    "if": {
+      "properties": {
+        "flag": {
+          "const": true
+        }
+      }
+    },
+    "else": false
+  })JSON");
+
+  LINT_AND_FIX_FOR_READABILITY(document);
+
+  const sourcemeta::core::JSON expected = sourcemeta::core::parse_json(R"JSON({
+    "$schema": "https://json-schema.org/draft/2019-09/schema",
+    "properties": {
+      "flag": {
+        "const": true
+      }
+    }
+  })JSON");
+
+  EXPECT_EQ(document, expected);
+}

test/alterschema/alterschema_lint_2020_12_test.cc

@@ -2583,3 +2583,30 @@ TEST(AlterSchema_lint_2020_12, non_applicable_type_specific_keywords_3) {
 
   EXPECT_EQ(document, expected);
 }
+
+TEST(AlterSchema_lint_2020_12, else_false_1) {
+  sourcemeta::core::JSON document = sourcemeta::core::parse_json(R"JSON({
+    "$schema": "https://json-schema.org/draft/2020-12/schema",
+    "if": {
+      "properties": {
+        "flag": {
+          "const": true
+        }
+      }
+    },
+    "else": false
+  })JSON");
+
+  LINT_AND_FIX_FOR_READABILITY(document);
+
+  const sourcemeta::core::JSON expected = sourcemeta::core::parse_json(R"JSON({
+    "$schema": "https://json-schema.org/draft/2020-12/schema",
+    "properties": {
+      "flag": {
+        "const": true
+      }
+    }
+  })JSON");
+
+  EXPECT_EQ(document, expected);
+}

test/alterschema/alterschema_lint_draft7_test.cc

@@ -1890,3 +1890,30 @@ TEST(AlterSchema_lint_draft7, non_applicable_type_specific_keywords_3) {
 
   EXPECT_EQ(document, expected);
 }
+
+TEST(AlterSchema_lint_draft7, else_false_1) {
+  sourcemeta::core::JSON document = sourcemeta::core::parse_json(R"JSON({
+    "$schema": "http://json-schema.org/draft-07/schema#",
+    "if": {
+      "properties": {
+        "flag": {
+          "const": true
+        }
+      }
+    },
+    "else": false
+  })JSON");
+
+  LINT_AND_FIX_FOR_READABILITY(document);
+
+  const sourcemeta::core::JSON expected = sourcemeta::core::parse_json(R"JSON({
+    "$schema": "http://json-schema.org/draft-07/schema#",
+    "properties": {
+      "flag": {
+        "const": true
+      }
+    }
+  })JSON");
+
+  EXPECT_EQ(document, expected);
+}