fix(core): single value enums (const) are not generated correctly in 3.1 specs (#19696)

* fix(core): single value enums (`const`) are not generated correctly in `3.1` specs

* fix: const enums

* chore: update samples

* chore: update samples

Author: joscha

bin/configs/typescript-consolidated-single-value-enum.yaml

@@ -0,0 +1,4 @@
+generatorName: typescript
+outputDir: samples/client/others/typescript/builds/enum-single-value
+inputSpec: modules/openapi-generator/src/test/resources/3_1/enum-single-value.yaml
+templateDir: modules/openapi-generator/src/main/resources/typescript

modules/openapi-generator/src/main/java/org/openapitools/codegen/OpenAPINormalizer.java

@@ -1281,6 +1281,12 @@ private Schema processNormalize31Spec(Schema schema, Set<Schema> visitedSchemas)
             schema.getTypes().remove("null");
         }
 
+        // process const
+        if (schema.getConst() != null) {
+            schema.setEnum(Arrays.asList(schema.getConst()));
+            schema.setConst(null);
+        }
+
         // only one item (type) left
         if (schema.getTypes().size() == 1) {
             String type = String.valueOf(schema.getTypes().iterator().next());

modules/openapi-generator/src/test/java/org/openapitools/codegen/OpenAPINormalizerTest.java

@@ -758,4 +758,29 @@ public void testOpenAPINormalizerSimplifyOneOfAnyOf31Spec() {
         assertEquals(schema18.getOneOf(), null);
         assertEquals(schema18.get$ref(), "#/components/schemas/Parent");
     }
+
+    @Test
+    public void testOpenAPINormalizerSingleConstEnum31Spec() {
+        OpenAPI openAPI = TestUtils.parseSpec("src/test/resources/3_1/enum-single-value.yaml");
+
+        Schema reference_3_0 = openAPI.getComponents().getSchemas().get("SingleValueEnum_3_0");
+        assertEquals(((Schema) reference_3_0.getProperties().get("type")).getEnum().size(), 1);
+
+        Schema schema = openAPI.getComponents().getSchemas().get("SingleValueEnum_3_1");
+        Schema originalTypeSchema = (Schema) schema.getProperties().get("type");
+        assertFalse(ModelUtils.isEnumSchema(originalTypeSchema));
+        var originalConst = originalTypeSchema.getConst();
+        assertNotNull(originalConst);
+
+        Map<String, String> inputRules = Map.of("NORMALIZE_31SPEC", "true");
+        OpenAPINormalizer openAPINormalizer = new OpenAPINormalizer(openAPI, inputRules);
+        openAPINormalizer.normalize();
+
+        Schema schema2 = openAPI.getComponents().getSchemas().get("SingleValueEnum_3_1");
+        Schema normalizedTypeSchema = (Schema) schema2.getProperties().get("type");
+        assertTrue(ModelUtils.isEnumSchema(normalizedTypeSchema));
+        assertNull(normalizedTypeSchema.getConst());
+        assertEquals(normalizedTypeSchema.getEnum().size(), 1);
+        assertEquals(Arrays.asList(originalConst), normalizedTypeSchema.getEnum());
+    }
 }

modules/openapi-generator/src/test/resources/3_1/enum-single-value.yaml

@@ -0,0 +1,20 @@
+openapi: 3.1.0
+info:
+  title: ""
+  version: 1.0.0
+components:
+  schemas:
+      SingleValueEnum_3_1:
+        required:
+          - type      
+        properties:
+          type:
+            const: this-is-my-only-value
+            type: string
+      SingleValueEnum_3_0:
+        required:
+          - type
+        properties:
+          type:
+            enum:
+              - this-is-my-only-value