[crystal] Fix empty auth_settings Hash literal (#23625)

The Crystal client codegen template emits `Hash{...}` for the
`auth_settings` method. When an OpenAPI spec has no auth methods
recognized by the template (e.g. a non-standard OAuth2 flow URN like
`urn:ietf:params:oauth:grant-type:device_code`), the loop emits no
entries and the result is a bare `Hash{}` -- which Crystal rejects:

  Error: for empty hashes use '{} of KeyType => ValueType'

This wraps the populated branch in `{{#authMethods.0}}...{{/authMethods.0}}`
and adds an empty branch via `{{^authMethods}}` that emits a typed
empty hash literal `{} of String => Hash(Symbol, String)`, which
compiles cleanly.

Adds two regression tests in CrystalClientCodegenTest:
- testAuthSettingsWithNoAuthMethodsEmitsValidCrystal: asserts the
  no-auth case emits `{} of String => Hash(Symbol, String)` and not
  `Hash{}`.
- testAuthSettingsWithAuthMethodsStillEmitsHashLiteral: asserts the
  populated case still emits `Hash{` (no regression).

Co-authored-by: Jonathan Siegel <jonathan@aluminum.io>

Author: usiegj00

modules/openapi-generator/src/main/resources/crystal/configuration.mustache

@@ -209,6 +209,7 @@ module {{moduleName}}
 
     # Returns Auth Settings hash for api client.
     def auth_settings
+{{#authMethods.0}}
       Hash{
 {{#authMethods}}
 {{#isApiKey}}
@@ -250,6 +251,10 @@ module {{moduleName}}
 {{/isOAuth}}
 {{/authMethods}}
       }
+{{/authMethods.0}}
+{{^authMethods}}
+      {} of String => Hash(Symbol, String)
+{{/authMethods}}
     end
 
     # Returns an array of Server setting

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

@@ -133,6 +133,77 @@ public void testBooleanDefaultValue() throws Exception {
         }
     }
 
+    @Test
+    public void testAuthSettingsWithNoAuthMethodsEmitsValidCrystal() throws Exception {
+        // Regression test: when an OpenAPI spec has no recognized auth methods,
+        // the generated configuration.cr's auth_settings method must not emit
+        // a bare `Hash{}` literal, which is invalid Crystal. Crystal requires
+        // `{} of K => V` for empty hash literals.
+        final File output = Files.createTempDirectory("test").toFile();
+        output.mkdirs();
+        output.deleteOnExit();
+
+        final OpenAPI openAPI = TestUtils.parseFlattenSpec("src/test/resources/2_0/pathWithHtmlEntity.yaml");
+        CodegenConfig codegenConfig = new CrystalClientCodegen();
+        codegenConfig.setOutputDir(output.getAbsolutePath());
+
+        ClientOptInput clientOptInput = new ClientOptInput().openAPI(openAPI).config(codegenConfig);
+
+        DefaultGenerator generator = new DefaultGenerator();
+        List<File> files = generator.opts(clientOptInput).generate();
+        boolean configFileGenerated = false;
+        for (File file : files) {
+            if (file.getName().equals("configuration.cr")) {
+                configFileGenerated = true;
+                String content = FileUtils.readFileToString(file, StandardCharsets.UTF_8);
+                // Bug: the previous template emitted `Hash{\n      }` for empty
+                // auth methods, which Crystal rejects with:
+                //   Error: for empty hashes use '{} of KeyType => ValueType'
+                Assert.assertFalse(content.contains("Hash{\n      }"),
+                        "configuration.cr must not contain an empty `Hash{}` literal");
+                Assert.assertFalse(content.contains("Hash{}"),
+                        "configuration.cr must not contain an empty `Hash{}` literal");
+                // Fix: emit a typed empty hash literal that compiles in Crystal.
+                assertTrue(content.contains("{} of String => Hash(Symbol, String)"),
+                        "configuration.cr must emit a typed empty hash literal in auth_settings");
+            }
+        }
+        if (!configFileGenerated) {
+            fail("configuration.cr file is not generated!");
+        }
+    }
+
+    @Test
+    public void testAuthSettingsWithAuthMethodsStillEmitsHashLiteral() throws Exception {
+        // Ensure the empty-auth fix did not regress the populated case.
+        final File output = Files.createTempDirectory("test").toFile();
+        output.mkdirs();
+        output.deleteOnExit();
+
+        final OpenAPI openAPI = TestUtils.parseFlattenSpec("src/test/resources/3_0/crystal/petstore.yaml");
+        CodegenConfig codegenConfig = new CrystalClientCodegen();
+        codegenConfig.setOutputDir(output.getAbsolutePath());
+
+        ClientOptInput clientOptInput = new ClientOptInput().openAPI(openAPI).config(codegenConfig);
+
+        DefaultGenerator generator = new DefaultGenerator();
+        List<File> files = generator.opts(clientOptInput).generate();
+        boolean configFileGenerated = false;
+        for (File file : files) {
+            if (file.getName().equals("configuration.cr")) {
+                configFileGenerated = true;
+                String content = FileUtils.readFileToString(file, StandardCharsets.UTF_8);
+                assertTrue(content.contains("Hash{"),
+                        "configuration.cr should still emit `Hash{` for populated auth methods");
+                Assert.assertFalse(content.contains("{} of String => Hash(Symbol, String)"),
+                        "configuration.cr should not emit empty hash literal when auth methods exist");
+            }
+        }
+        if (!configFileGenerated) {
+            fail("configuration.cr file is not generated!");
+        }
+    }
+
     @Test
     public void testSanitizeModelName() throws Exception {
         final CrystalClientCodegen codegen = new CrystalClientCodegen();