[python] Add buildSystem option to support hatchling as build backend

Allow users to choose between setuptools (default) and hatchling as the build system in generated pyproject.toml files. The buildSystem option can be set to 'hatchling' to generate projects using hatchling instead of setuptools.

- Add BUILD_SYSTEM constant and CLI option to PythonClientCodegen
- Update pyproject.mustache template to conditionally use hatchling or setuptools
- Add tests to verify both buildSystem configurations work correctly
- Update python generator documentation with buildSystem option

Co-Authored-By: Claude Haiku 4.5 <noreply@anthropic.com>

Author: tughril

docs/generators/python.md

@@ -19,6 +19,7 @@ These options may be applied as additional-properties (cli) or configOptions (pl
 
 | Option | Description | Values | Default |
 | ------ | ----------- | ------ | ------- |
+|buildSystem|Build system to use in pyproject.toml (setuptools, hatchling).| |setuptools|
 |dateFormat|date format for query parameters| |%Y-%m-%d|
 |datetimeFormat|datetime format for query parameters| |%Y-%m-%dT%H:%M:%S%z|
 |disallowAdditionalPropertiesIfNotPresent|If false, the 'additionalProperties' implementation (set to true by default) is compliant with the OAS and JSON schema specifications. If true (default), keep the old (incorrect) behaviour that 'additionalProperties' is set to false by default.|<dl><dt>**false**</dt><dd>The 'additionalProperties' implementation is compliant with the OAS and JSON schema specifications.</dd><dt>**true**</dt><dd>Keep the old (incorrect) behaviour that 'additionalProperties' is set to false by default.</dd></dl>|true|

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

@@ -49,6 +49,7 @@ public class PythonClientCodegen extends AbstractPythonCodegen implements Codege
     public static final String SET_ENSURE_ASCII_TO_FALSE = "setEnsureAsciiToFalse";
     public static final String POETRY1_FALLBACK = "poetry1";
     public static final String LAZY_IMPORTS = "lazyImports";
+    public static final String BUILD_SYSTEM = "buildSystem";
 
     @Setter protected String packageUrl;
     protected String apiDocPath = "docs/";
@@ -153,6 +154,7 @@ public PythonClientCodegen() {
         cliOptions.add(new CliOption(CodegenConstants.USE_ONEOF_DISCRIMINATOR_LOOKUP, CodegenConstants.USE_ONEOF_DISCRIMINATOR_LOOKUP_DESC).defaultValue("false"));
         cliOptions.add(new CliOption(POETRY1_FALLBACK, "Fallback to formatting pyproject.toml to Poetry 1.x format."));
         cliOptions.add(new CliOption(LAZY_IMPORTS, "Enable lazy imports.").defaultValue(Boolean.FALSE.toString()));
+        cliOptions.add(new CliOption(BUILD_SYSTEM, "Build system to use in pyproject.toml (setuptools, hatchling).").defaultValue("setuptools"));
 
         supportedLibraries.put("urllib3", "urllib3-based client");
         supportedLibraries.put("asyncio", "asyncio-based client");
@@ -271,6 +273,13 @@ public void processOpts() {
             additionalProperties.put(LAZY_IMPORTS, Boolean.valueOf(additionalProperties.get(LAZY_IMPORTS).toString()));
         }
 
+        if (additionalProperties.containsKey(BUILD_SYSTEM)) {
+            String buildSystem = (String) additionalProperties.get(BUILD_SYSTEM);
+            if ("hatchling".equals(buildSystem)) {
+                additionalProperties.put("hatchling", true);
+            }
+        }
+
         String modelPath = packagePath() + File.separatorChar + modelPackage.replace('.', File.separatorChar);
         String apiPath = packagePath() + File.separatorChar + apiPackage.replace('.', File.separatorChar);
 

modules/openapi-generator/src/main/resources/python/pyproject.mustache

@@ -108,10 +108,15 @@ flake8 = ">= 4.0.0"
 types-python-dateutil = ">= 2.8.19.14"
 mypy = ">= 1.5"
 
-
 [build-system]
+{{#hatchling}}
+requires = ["hatchling"]
+build-backend = "hatchling.build"
+{{/hatchling}}
+{{^hatchling}}
 requires = ["setuptools"]
 build-backend = "setuptools.build_meta"
+{{/hatchling}}
 
 [tool.pylint.'MESSAGES CONTROL']
 extension-pkg-whitelist = "pydantic"

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

@@ -670,6 +670,47 @@ public void testUuidWithPatternImportsFieldValidator() throws IOException {
         assertFileContains(p, "from pydantic import BaseModel, ConfigDict, field_validator");
     }
 
+    @Test(description = "Verify default buildSystem uses setuptools")
+    public void testDefaultBuildSystemSetuptools() throws IOException {
+        File output = Files.createTempDirectory("test").toFile().getCanonicalFile();
+        output.deleteOnExit();
+
+        final CodegenConfigurator configurator = new CodegenConfigurator()
+            .setGeneratorName("python")
+            .setInputSpec("src/test/resources/bugs/issue_21619.yaml")
+            .setOutputDir(output.getAbsolutePath());
+
+        DefaultGenerator generator = new DefaultGenerator();
+        List<File> files = generator.opts(configurator.toClientOptInput()).generate();
+        files.forEach(File::deleteOnExit);
+
+        Path pyprojectPath = Paths.get(output.getAbsolutePath(), "pyproject.toml");
+        TestUtils.assertFileExists(pyprojectPath);
+        TestUtils.assertFileContains(pyprojectPath, "requires = [\"setuptools\"]");
+        TestUtils.assertFileContains(pyprojectPath, "build-backend = \"setuptools.build_meta\"");
+    }
+
+    @Test(description = "Verify buildSystem=hatchling uses hatchling")
+    public void testBuildSystemHatchling() throws IOException {
+        File output = Files.createTempDirectory("test").toFile().getCanonicalFile();
+        output.deleteOnExit();
+
+        final CodegenConfigurator configurator = new CodegenConfigurator()
+            .setGeneratorName("python")
+            .setInputSpec("src/test/resources/bugs/issue_21619.yaml")
+            .setOutputDir(output.getAbsolutePath())
+            .addAdditionalProperty("buildSystem", "hatchling");
+
+        DefaultGenerator generator = new DefaultGenerator();
+        List<File> files = generator.opts(configurator.toClientOptInput()).generate();
+        files.forEach(File::deleteOnExit);
+
+        Path pyprojectPath = Paths.get(output.getAbsolutePath(), "pyproject.toml");
+        TestUtils.assertFileExists(pyprojectPath);
+        TestUtils.assertFileContains(pyprojectPath, "requires = [\"hatchling\"]");
+        TestUtils.assertFileContains(pyprojectPath, "build-backend = \"hatchling.build\"");
+    }
+
     @Test(description = "Verify non-poetry1 mode uses object notation for license")
     public void testNonPoetry1LicenseFormat() throws IOException {
         File output = Files.createTempDirectory("test").toFile().getCanonicalFile();