Fix Go template for oneOfs with primitive types (#11826)

A recent enhancement to the template made these primitive types usable
as property names, but a small section of the template wasn't updated,
leading to compilation problems.

modules/openapi-generator/src/main/resources/go/model_oneof.mustache

@@ -55,24 +55,24 @@ func (dst *{{classname}}) UnmarshalJSON(data []byte) error {
 	{{^discriminator}}
         match := 0
         {{#oneOf}}
-        // try to unmarshal data into {{{.}}}
-        err = json.Unmarshal(data, &dst.{{{.}}})
+        // try to unmarshal data into {{#lambda.titlecase}}{{{.}}}{{/lambda.titlecase}}
+        err = json.Unmarshal(data, &dst.{{#lambda.titlecase}}{{{.}}}{{/lambda.titlecase}})
         if err == nil {
-                json{{{.}}}, _ := json.Marshal(dst.{{{.}}})
+                json{{{.}}}, _ := json.Marshal(dst.{{#lambda.titlecase}}{{{.}}}{{/lambda.titlecase}})
                 if string(json{{{.}}}) == "{}" { // empty struct
-                        dst.{{{.}}} = nil
+                        dst.{{#lambda.titlecase}}{{{.}}}{{/lambda.titlecase}} = nil
                 } else {
                         match++
                 }
         } else {
-                dst.{{{.}}} = nil
+                dst.{{#lambda.titlecase}}{{{.}}}{{/lambda.titlecase}} = nil
         }
 
         {{/oneOf}}
         if match > 1 { // more than 1 match
                 // reset to nil
                 {{#oneOf}}
-                dst.{{{.}}} = nil
+                dst.{{#lambda.titlecase}}{{{.}}}{{/lambda.titlecase}} = nil
                 {{/oneOf}}
 
                 return fmt.Errorf("Data matches more than one schema in oneOf({{classname}})")

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

@@ -19,10 +19,20 @@ package org.openapitools.codegen.go;
 
 import io.swagger.v3.oas.models.OpenAPI;
 import io.swagger.v3.oas.models.Operation;
+
+import java.io.File;
+import java.io.IOException;
+import java.nio.file.Files;
+import java.nio.file.Path;
+import java.nio.file.Paths;
+import java.util.List;
+
 import org.openapitools.codegen.CodegenConstants;
 import org.openapitools.codegen.CodegenOperation;
 import org.openapitools.codegen.CodegenParameter;
+import org.openapitools.codegen.DefaultGenerator;
 import org.openapitools.codegen.TestUtils;
+import org.openapitools.codegen.config.CodegenConfigurator;
 import org.openapitools.codegen.languages.GoClientCodegen;
 import org.testng.Assert;
 import org.testng.annotations.Test;
@@ -109,4 +119,26 @@ public class GoClientCodegenTest {
         Assert.assertEquals(codegen.toApiFilename("Animal Farm Test"), "api_animal_farm_test_");
     }
 
+    @Test
+    public void testPrimitiveTypeInOneOf() throws IOException {
+        File output = Files.createTempDirectory("test").toFile();
+        output.deleteOnExit();
+
+        final CodegenConfigurator configurator = new CodegenConfigurator()
+                .setGeneratorName("go")
+                .setInputSpec("src/test/resources/3_0/oneOf_primitive.yaml")
+                .setOutputDir(output.getAbsolutePath().replace("\\", "/"));
+
+        DefaultGenerator generator = new DefaultGenerator();
+        List<File> files = generator.opts(configurator.toClientOptInput()).generate();
+        System.out.println(files);
+        files.forEach(File::deleteOnExit);
+
+        Path modelFile = Paths.get(output + "/model_example.go");
+        TestUtils.assertFileContains(modelFile, "Child *Child");
+        TestUtils.assertFileContains(modelFile, "Int32 *int32");
+        TestUtils.assertFileContains(modelFile, "dst.Int32");
+        TestUtils.assertFileNotContains(modelFile, "int32 *int32");
+        TestUtils.assertFileNotContains(modelFile, "dst.int32");
+    }
 }

modules/openapi-generator/src/test/resources/3_0/oneOf_primitive.yaml

@@ -0,0 +1,31 @@
+openapi: 3.0.1
+info:
+  version: 1.0.0
+  title: Example
+  license:
+    name: MIT
+servers:
+  - url: http://api.example.xyz/v1
+paths:
+  /example:
+    get:
+      operationId: list
+      responses:
+        '200':
+          description: OK
+          content:
+            application/json:
+              schema:
+                $ref: "#/components/schemas/Example"
+components:
+  schemas:
+    Child:
+      type: object
+      properties:
+        name:
+          type: string
+    Example:
+      oneOf:
+      - $ref: '#/components/schemas/Child'
+      - type: integer
+        format: int32