Revert "Has generators set default template engine (#11245)" (#11316)

This reverts commit dd3bba8c9442f2ee40d6ea8f0872ab0be43714b9.
Because it broke peoples builds per this issue https://github.com/OpenAPITools/openapi-generator/issues/11276

bin/configs/python-experimental.yaml

@@ -2,6 +2,7 @@ generatorName: python-experimental
 outputDir: samples/openapi3/client/petstore/python-experimental
 inputSpec: modules/openapi-generator/src/test/resources/3_0/python-experimental/petstore-with-fake-endpoints-models-for-testing-with-http-signature.yaml
 templateDir: modules/openapi-generator/src/main/resources/python-experimental
+templatingEngineName: handlebars
 additionalProperties:
   packageName: petstore_api
   recursionLimit: "1234"

modules/openapi-generator-core/src/main/java/org/openapitools/codegen/config/WorkflowSettings.java

@@ -46,7 +46,7 @@ public class WorkflowSettings {
     public static final boolean DEFAULT_ENABLE_MINIMAL_UPDATE = false;
     public static final boolean DEFAULT_STRICT_SPEC_BEHAVIOR = true;
     public static final boolean DEFAULT_GENERATE_ALIAS_AS_MODEL = false;
-    public static final String DEFAULT_TEMPLATING_ENGINE_NAME = null; // this is set by the generator
+    public static final String DEFAULT_TEMPLATING_ENGINE_NAME = "mustache";
     public static final Map<String, String> DEFAULT_GLOBAL_PROPERTIES = Collections.unmodifiableMap(new HashMap<>());
 
     private String inputSpec;

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

@@ -305,8 +305,6 @@ public interface CodegenConfig {
 
     Schema unaliasSchema(Schema schema, Map<String, String> usedImportMappings);
 
-    public String defaultTemplatingEngine();
-
     public GeneratorLanguage generatorLanguage();
 
     /*

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

@@ -7357,11 +7357,6 @@ public class DefaultCodegen implements CodegenConfig {
         return xOf;
     }
 
-    @Override
-    public String defaultTemplatingEngine() {
-        return "mustache";
-    }
-
     @Override
     public GeneratorLanguage generatorLanguage() { return GeneratorLanguage.JAVA; }
 

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

@@ -91,18 +91,11 @@ public class CodegenConfigurator {
             WorkflowSettings workflowSettings = settings.getWorkflowSettings();
             List<TemplateDefinition> userDefinedTemplateSettings = settings.getFiles();
 
-            CodegenConfig config = CodegenConfigLoader.forName(generatorSettings.getGeneratorName());
-            String templatingEngineName = workflowSettings.getTemplatingEngineName();
-            if (isEmpty(templatingEngineName)) {
-                // if templatingEngineName is empty check the config for a default
-                templatingEngineName = config.defaultTemplatingEngine();
-            }
-
             // We copy "cached" properties into configurator so it is appropriately configured with all settings in external files.
             // FIXME: target is to eventually move away from CodegenConfigurator properties except gen/workflow settings.
             configurator.generatorName = generatorSettings.getGeneratorName();
             configurator.inputSpec = workflowSettings.getInputSpec();
-            configurator.templatingEngineName = templatingEngineName;
+            configurator.templatingEngineName = workflowSettings.getTemplatingEngineName();
             if (workflowSettings.getGlobalProperties() != null) {
                 configurator.globalProperties.putAll(workflowSettings.getGlobalProperties());
             }
@@ -489,17 +482,15 @@ public class CodegenConfigurator {
         Validate.notEmpty(generatorName, "generator name must be specified");
         Validate.notEmpty(inputSpec, "input spec must be specified");
 
-        GeneratorSettings generatorSettings = generatorSettingsBuilder.build();
-        CodegenConfig config = CodegenConfigLoader.forName(generatorSettings.getGeneratorName());
         if (isEmpty(templatingEngineName)) {
-            // if templatingEngineName is empty check the config for a default
+            // Built-in templates are mustache, but allow users to use a simplified handlebars engine for their custom templates.
-            String defaultTemplatingEngine = config.defaultTemplatingEngine();
+            workflowSettingsBuilder.withTemplatingEngineName("mustache");
-            workflowSettingsBuilder.withTemplatingEngineName(defaultTemplatingEngine);
         } else {
             workflowSettingsBuilder.withTemplatingEngineName(templatingEngineName);
         }
 
         // at this point, all "additionalProperties" are set, and are now immutable per GeneratorSettings instance.
+        GeneratorSettings generatorSettings = generatorSettingsBuilder.build();
         WorkflowSettings workflowSettings = workflowSettingsBuilder.build();
 
         if (workflowSettings.isVerbose()) {

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

@@ -2086,11 +2086,6 @@ public class PythonExperimentalClientCodegen extends AbstractPythonCodegen {
         return co;
     }
 
-    @Override
-    public String defaultTemplatingEngine() {
-        return "handlebars";
-    }
-
     @Override
     public String generatorLanguageVersion() { return ">=3.9"; };
 }