Allow python protobuf codegen export to coexist with namespace/host p…

…ackage (#21665)

Before this change, if a codegen export clashes with an existing package
in the venv the export halts completely. The current change skips the
problematic exports. This is sub optimal because not all symbols are
exported but better than halting the export.

See #21659

docs/notes/2.25.x.md

@@ -17,6 +17,8 @@ established for this purpose. This non-profit's only source of revenue is
 
 ### General
 
+- [Fixed](https://github.com/pantsbuild/pants/pull/21665) bug where `pants --export-resolve=<resolve> --export-py-generated-sources-in-resolve=<resolve>` fails (see [#21659](https://github.com/pantsbuild/pants/issues/21659) for more info).
+
 ### New Options System
 
 The "legacy" options system is removed in this release. All options parsing is now handled by the new, native parser.

src/python/pants/backend/python/goals/export.py

@@ -411,6 +411,7 @@ async def python_codegen_export_setup() -> _ExportPythonCodegenSetup:
                     content=textwrap.dedent(
                         f"""\
                         import os
+                        import shutil
                         import site
                         import sys
 
@@ -424,7 +425,10 @@ async def python_codegen_export_setup() -> _ExportPythonCodegenSetup:
                         for item in os.listdir(codegen_dir):
                             if item == "{_ExportPythonCodegenSetup.SCRIPT_NAME}":
                                 continue
-                            os.rename(os.path.join(codegen_dir, item), os.path.join(site_packages_dir, item))
+                            src = os.path.join(codegen_dir, item)
+                            dest = os.path.join(site_packages_dir, item)
+                            shutil.copytree(src, dest, dirs_exist_ok=True)
+                            shutil.rmtree(src)
                         """
                     ).encode(),
                 )

src/python/pants/backend/python/goals/export_test.py

@@ -251,12 +251,32 @@ async def do_codegen(request: CodegenGenerateSourcesRequest) -> GeneratedSources
     rule_runner.write_files(
         {
             "test-resolve.lock": "",
+            # Case #1
+            # `foo`` package exports `an-input.py` file as a generated source.
             "src/python/foo/BUILD": dedent(
-                """\
-            codegen_target(name="codegen", source="an-input", resolve="test-resolve")
-            """
+                """
+                codegen_target(
+                  name="codegen",
+                  source="an-input",
+                  resolve="test-resolve"
+                )
+                """
             ),
             "src/python/foo/an-input": "print('Hello World!')\n",
+            # Case #2
+            # The local `ansicolors`` package exports `ansicolors-input.py` file as a generated source.
+            # The local `ansicolors package clashes with the 3rd party dep `ansicolors``.
+            # This is an edge case.
+            "src/python/ansicolors/BUILD": dedent(
+                """
+                codegen_target(
+                  name="codegen",
+                  source="ansicolors-input",
+                  resolve="test-resolve"
+                )
+                """
+            ),
+            "src/python/ansicolors/ansicolors-input": "print('Hello World!')\n",
         }
     )
 
@@ -267,3 +287,7 @@ async def do_codegen(request: CodegenGenerateSourcesRequest) -> GeneratedSources
     export_snapshot = rule_runner.request(Snapshot, [export_result.digest])
     assert any(p.endswith("__pants_codegen__/codegen_setup.py") for p in export_snapshot.files)
     assert any(p.endswith("__pants_codegen__/foo/an-input.py") for p in export_snapshot.files)
+    assert any(
+        p.endswith("__pants_codegen__/ansicolors/ansicolors-input.py")
+        for p in export_snapshot.files
+    )