Support Python codegen for the OpenAPI backend (#21316)

docs/notes/2.25.x.md

@@ -70,6 +70,11 @@ Reverence to Python Build Standalone not refer to the [GitHub organization](http
 
 The default version of the [Pex](https://docs.pex-tool.org/) tool has been updated from 2.20.3 to [2.27.1](https://github.com/pex-tool/pex/releases/tag/v2.24.3).  Among many improvements and bug fixes, this unlocks support for pip [24.3.1](https://pip.pypa.io/en/stable/news/#v24-3-1).
 
+##### NEW: Python for OpenAPI
+
+A new experimental `pants.backend.experimental.openapi.codegen.python` backend
+was added to support python codegen for OpenAPI documents.
+
 #### Shell
 
 The previously deprecated `[shell-setup].tailor` option has now been removed. See [`[shell-setup].tailor_sources`](https://www.pantsbuild.org/2.25/reference/subsystems/shell-setup#tailor_sources) and [`[shell-setup].tailor_shunit2_tests`](https://www.pantsbuild.org/2.25/reference/subsystems/shell#tailor_shunit2_tests) to update.

src/python/pants/backend/experimental/openapi/codegen/python/BUILD

@@ -0,0 +1,4 @@
+# Copyright 2024 Pants project contributors (see CONTRIBUTORS.md).
+# Licensed under the Apache License, Version 2.0 (see LICENSE).
+
+python_sources()

src/python/pants/backend/experimental/openapi/codegen/python/register.py

@@ -0,0 +1,18 @@
+# Copyright 2024 Pants project contributors (see CONTRIBUTORS.md).
+# Licensed under the Apache License, Version 2.0 (see LICENSE).
+
+from __future__ import annotations
+
+from pants.backend.experimental.openapi.register import rules as openapi_rules
+from pants.backend.experimental.openapi.register import target_types as openapi_target_types
+from pants.backend.experimental.python.register import rules as python_rules
+from pants.backend.experimental.python.register import target_types as python_target_types
+from pants.backend.openapi.codegen.python.rules import rules as openapi_python_codegen_rules
+
+
+def target_types():
+    return [*python_target_types(), *openapi_target_types()]
+
+
+def rules():
+    return [*python_rules(), *openapi_rules(), *openapi_python_codegen_rules()]

src/python/pants/backend/openapi/codegen/java/rules.py

@@ -21,10 +21,7 @@
     OpenApiSourceField,
 )
 from pants.backend.openapi.util_rules import generator_process, pom_parser
-from pants.backend.openapi.util_rules.generator_process import (
-    OpenAPIGeneratorProcess,
-    OpenAPIGeneratorType,
-)
+from pants.backend.openapi.util_rules.generator_process import OpenAPIGeneratorProcess
 from pants.backend.openapi.util_rules.pom_parser import AnalysePomRequest, PomReport
 from pants.engine.fs import (
     EMPTY_SNAPSHOT,
@@ -106,7 +103,7 @@ async def compile_openapi_into_java(
     merged_digests = await Get(Digest, MergeDigests([request.input_digest, output_digest]))
 
     process = OpenAPIGeneratorProcess(
-        generator_type=OpenAPIGeneratorType.JAVA,
+        generator_name="java",
         argv=[
             *(
                 ("--additional-properties", f"apiPackage={request.api_package}")

src/python/pants/backend/openapi/codegen/python/BUILD

@@ -0,0 +1,8 @@
+# Copyright 2024 Pants project contributors (see CONTRIBUTORS.md).
+# Licensed under the Apache License, Version 2.0 (see LICENSE).
+
+python_sources()
+
+python_tests(name="tests", dependencies=[":lockfiles"])
+
+resources(name="lockfiles", sources=["*.test.lock"])

src/python/pants/backend/openapi/codegen/python/extra_fields.py

@@ -0,0 +1,42 @@
+# Copyright 2024 Pants project contributors (see CONTRIBUTORS.md).
+# Licensed under the Apache License, Version 2.0 (see LICENSE).
+import itertools
+
+from pants.backend.openapi.target_types import OpenApiDocumentGeneratorTarget, OpenApiDocumentTarget
+from pants.backend.python.target_types import PrefixedPythonResolveField
+from pants.engine.target import BoolField, DictStringToStringField, StringField
+
+
+class OpenApiPythonGeneratorNameField(StringField):
+    alias = "python_generator_name"
+    required = False
+    help = "Python generator name"
+
+
+class OpenApiPythonAdditionalPropertiesField(DictStringToStringField):
+    alias = "python_additional_properties"
+    help = "Additional properties for python generator"
+
+
+class OpenApiPythonSkipField(BoolField):
+    alias = "skip_python"
+    default = False
+    help = "If true, skips generation of Python sources from this target"
+
+
+def rules():
+    return [
+        target.register_plugin_field(field)
+        for target, field in itertools.product(
+            (
+                OpenApiDocumentTarget,
+                OpenApiDocumentGeneratorTarget,
+            ),
+            (
+                OpenApiPythonSkipField,
+                OpenApiPythonGeneratorNameField,
+                OpenApiPythonAdditionalPropertiesField,
+                PrefixedPythonResolveField,
+            ),
+        )
+    ]