Revert "Prefix the entire setup.py chroot. (#12359)" (#12370)

This was causing CI to fail with:

> Exception: String("Cannot strip prefix chroot/dist from root directory (Digest with hash Fingerprint<0e3f69284c886c8b9b330122c22ed47e469e2f9020c9938fdf6d15c24471aeae>) - root directory didn't contain a directory named chroot but did contain directory named: dist")

[ci skip-rust]

[ci skip-build-wheels]

Author: Eric-Arellano

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

@@ -405,6 +405,10 @@ async def package_python_dist(
         return BuiltPackage(rel_chroot, (BuiltPackageArtifact(dirname),))
 
 
+# We write .py sources into the chroot under this dir.
+CHROOT_SOURCE_ROOT = "src"
+
+
 SETUP_BOILERPLATE = """
 # DO NOT EDIT THIS FILE -- AUTOGENERATED BY PANTS
 # Target: {target_address_spec}
@@ -429,42 +433,23 @@ async def run_setup_py(req: RunSetupPyRequest, setuptools: Setuptools) -> RunSet
             interpreter_constraints=req.interpreter_constraints,
         ),
     )
-
-    # We prefix the entire chroot, and run with this prefix as the cwd, so that we can capture any
-    # changes setup made within it (e.g., when running 'develop') without also capturing other
-    # artifacts of the pex process invocation.
-    chroot_prefix = "chroot"
-
     # The setuptools dist dir, created by it under the chroot (not to be confused with
     # pants's own dist dir, at the buildroot).
-    dist_dir = "dist"
-
-    prefixed_chroot = await Get(Digest, AddPrefix(req.chroot.digest, chroot_prefix))
-
-    # setup.py basically always expects to be run with the cwd as its own directory
-    # (e.g., paths in it are relative to that directory). This is true of the setup.py
-    # we generate and is overwhelmingly likely to be true for existing setup.py files,
-    # as there is no robust way to run them otherwise.
-    setup_script_reldir, setup_script_name = os.path.split(req.chroot.setup_script)
-    working_directory = os.path.join(chroot_prefix, setup_script_reldir)
-
+    dist_dir = "dist/"
     result = await Get(
         ProcessResult,
         VenvPexProcess(
             setuptools_pex,
-            argv=(setup_script_name, *req.args),
-            input_digest=prefixed_chroot,
-            working_directory=working_directory,
+            argv=(req.chroot.setup_script, *req.args),
+            input_digest=req.chroot.digest,
             # setuptools commands that create dists write them to the distdir.
             # TODO: Could there be other useful files to capture?
-            output_directories=(dist_dir,),  # Relative to the working_directory.
+            output_directories=(dist_dir,),
             description=f"Run setuptools for {req.exported_target.target.address}",
             level=LogLevel.DEBUG,
         ),
     )
-    output_digest = await Get(
-        Digest, RemovePrefix(result.output_digest, os.path.join(chroot_prefix, dist_dir))
-    )
+    output_digest = await Get(Digest, RemovePrefix(result.output_digest, dist_dir))
     return RunSetupPyResult(output_digest)
 
 
@@ -550,6 +535,7 @@ async def generate_chroot(request: SetupPyChrootRequest) -> SetupPyChroot:
     # specified `SetupKwargs(_allow_banned_keys=True)`.
     setup_kwargs.update(
         {
+            "package_dir": {"": CHROOT_SOURCE_ROOT, **setup_kwargs.get("package_dir", {})},
             "packages": (*sources.packages, *(setup_kwargs.get("packages", []))),
             "namespace_packages": (
                 *sources.namespace_packages,
@@ -609,8 +595,13 @@ async def generate_chroot(request: SetupPyChrootRequest) -> SetupPyChroot:
         FileContent("setup.py", setup_py_content),
         FileContent("MANIFEST.in", "include *.py".encode()),
     ]
-    extra_files_digest = await Get(Digest, CreateDigest(files_to_create))
-    chroot_digest = await Get(Digest, MergeDigests((sources.digest, extra_files_digest)))
+    extra_files_digest, src_digest = await MultiGet(
+        Get(Digest, CreateDigest(files_to_create)),
+        # Nest the sources under the src/ prefix.
+        Get(Digest, AddPrefix(sources.digest, CHROOT_SOURCE_ROOT)),
+    )
+
+    chroot_digest = await Get(Digest, MergeDigests((src_digest, extra_files_digest)))
     return SetupPyChroot(
         chroot_digest, "setup.py", FinalizedSetupKwargs(setup_kwargs, address=target.address)
     )

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

@@ -285,13 +285,13 @@ def test_generate_chroot(chroot_rule_runner: RuleRunner) -> None:
     assert_chroot(
         chroot_rule_runner,
         [
-            "files/README.txt",
-            "foo/qux/__init__.py",
-            "foo/qux/qux.py",
-            "foo/qux/qux.pyi",
-            "foo/resources/js/code.js",
-            "foo/__init__.py",
-            "foo/foo.py",
+            "src/files/README.txt",
+            "src/foo/qux/__init__.py",
+            "src/foo/qux/qux.py",
+            "src/foo/qux/qux.pyi",
+            "src/foo/resources/js/code.js",
+            "src/foo/__init__.py",
+            "src/foo/foo.py",
             "setup.py",
             "MANIFEST.in",
         ],
@@ -300,6 +300,7 @@ def test_generate_chroot(chroot_rule_runner: RuleRunner) -> None:
             "name": "foo",
             "version": "1.2.3",
             "plugin_demo": "hello world",
+            "package_dir": {"": "src"},
             "packages": ("foo", "foo.qux"),
             "namespace_packages": ("foo",),
             "package_data": {"foo": ("resources/js/code.js",)},
@@ -377,12 +378,13 @@ def test_binary_shorthand(chroot_rule_runner: RuleRunner) -> None:
     )
     assert_chroot(
         chroot_rule_runner,
-        ["project/app.py", "setup.py", "MANIFEST.in"],
+        ["src/project/app.py", "setup.py", "MANIFEST.in"],
         "setup.py",
         {
             "name": "bin",
             "version": "1.1.1",
             "plugin_demo": "hello world",
+            "package_dir": {"": "src"},
             "packages": ("project",),
             "namespace_packages": (),
             "install_requires": (),