[ruby] fix: enumUnknownDefaultCase declares the unknown-default member but never deserializes to it (#24879)

* fix: [ruby] enumUnknownDefaultCase must reach build_from_hash, not just declare the member

With enumUnknownDefaultCase=true the generator adds UNKNOWN_DEFAULT_OPEN_API to
every enum class's constants and all_vars, but the enum's build_from_hash still
raised 'Invalid ENUM value' for any wire value outside the list — the flag
changed nothing observable, and one new enum value from the server still
destroyed the whole response.

build_from_hash now falls back to the enum's own unknown-default member — the
last declared enum var, which under the flag is always the appended
UNKNOWN_DEFAULT_OPEN_API. The tolerance lives in each generated enum class;
without the flag the generated code is byte-identical to before and still
raises. Java's fromValue behavior under the same flag is the reference.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01CxDNCjqJycKTfzVWg2SeTJ

* test: [ruby] drop enumUnknownDefaultCase assertions the build_from_hash checks imply

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

* test: [ruby] keep the enumUnknownDefaultCase member value assertions

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

---------

Co-authored-by: Claude Fable 5 <noreply@anthropic.com>
Co-authored-by: William Cheng <wing328hk@gmail.com>

Author: 3 people

modules/openapi-generator/src/main/resources/ruby-client/partial_model_enum_class.mustache

@@ -18,6 +18,11 @@
     # @return [String] The enum value
     def build_from_hash(value)
       return value if {{classname}}.all_vars.include?(value)
+      {{#enumUnknownDefaultCase}}
+      {{#allowableValues}}{{#enumVars}}{{#-last}}{{{name}}}{{/-last}}{{/enumVars}}{{/allowableValues}}
+      {{/enumUnknownDefaultCase}}
+      {{^enumUnknownDefaultCase}}
       raise "Invalid ENUM value #{value} for class #{{{classname}}}"
+      {{/enumUnknownDefaultCase}}
     end
   end

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

@@ -858,4 +858,58 @@ public void testAliasModelDoesNotDelegateToItsBuiltInSuperclass() throws Excepti
                 "def self.acceptable_openapi_nullable\n      openapi_nullable\n    end");
         TestUtils.assertFileNotContains(arrayAlias, "superclass.", "super(attributes)");
     }
+
+    @Test(description = "enumUnknownDefaultCase=true makes build_from_hash fall back to the unknown default member")
+    public void testEnumUnknownDefaultCaseBuildFromHashFallback() throws Exception {
+        final File output = Files.createTempDirectory("test").toFile();
+        output.deleteOnExit();
+
+        final OpenAPI openAPI = TestUtils.parseFlattenSpec("src/test/resources/3_0/enum.yaml");
+        CodegenConfig codegenConfig = new RubyClientCodegen();
+        codegenConfig.additionalProperties().put(CodegenConstants.ENUM_UNKNOWN_DEFAULT_CASE, "true");
+        codegenConfig.setOutputDir(output.getAbsolutePath());
+
+        ClientOptInput clientOptInput = new ClientOptInput().openAPI(openAPI).config(codegenConfig);
+        new DefaultGenerator().opts(clientOptInput).generate();
+
+        Path stringEnum = new File(output, "lib/openapi_client/models/type.rb").toPath(); 
+        TestUtils.assertFileContains(stringEnum, "UNKNOWN_DEFAULT_OPEN_API = \"unknown_default_open_api\".freeze");
+        TestUtils.assertFileContains(stringEnum,
+                "def build_from_hash(value)\n" +
+                "      return value if Type.all_vars.include?(value)\n" +
+                "      UNKNOWN_DEFAULT_OPEN_API\n" +
+                "    end");
+        TestUtils.assertFileNotContains(stringEnum, "raise \"Invalid ENUM value");
+
+        // the integer enum's unknown-default member keeps its (pre-existing) numeric-prefixed name
+        Path integerEnum = new File(output, "lib/openapi_client/models/integer_enum.rb").toPath();
+        TestUtils.assertFileContains(integerEnum, "Nunknown_default_open_api = 11184809.freeze");
+        TestUtils.assertFileContains(integerEnum,
+                "def build_from_hash(value)\n" +
+                "      return value if IntegerEnum.all_vars.include?(value)\n" +
+                "      Nunknown_default_open_api\n" +
+                "    end");
+        TestUtils.assertFileNotContains(integerEnum, "raise \"Invalid ENUM value");
+    }
+
+    @Test(description = "without enumUnknownDefaultCase build_from_hash still raises on unknown values")
+    public void testEnumBuildFromHashRaisesByDefault() throws Exception {
+        final File output = Files.createTempDirectory("test").toFile();
+        output.deleteOnExit();
+
+        final OpenAPI openAPI = TestUtils.parseFlattenSpec("src/test/resources/3_0/enum.yaml");
+        CodegenConfig codegenConfig = new RubyClientCodegen();
+        codegenConfig.setOutputDir(output.getAbsolutePath());
+
+        ClientOptInput clientOptInput = new ClientOptInput().openAPI(openAPI).config(codegenConfig);
+        new DefaultGenerator().opts(clientOptInput).generate();
+
+        Path stringEnum = new File(output, "lib/openapi_client/models/type.rb").toPath();
+        TestUtils.assertFileNotContains(stringEnum, "UNKNOWN_DEFAULT_OPEN_API");
+        TestUtils.assertFileContains(stringEnum,
+                "def build_from_hash(value)\n" +
+                "      return value if Type.all_vars.include?(value)\n" +
+                "      raise \"Invalid ENUM value #{value} for class #Type\"\n" +
+                "    end");
+    }
 }