build_py: Allow get_outputs() to work without re-running egg-info

2 files changed, 132 insertions, 65 deletions

diff --git a/setuptools/command/build_py.py b/setuptools/command/build_py.py
index 9575cdf8..dab81327 100644
--- a/setuptools/command/build_py.py
+++ b/setuptools/command/build_py.py
@@ -29,6 +29,8 @@ class build_py(orig.build_py):
     'py_modules' and 'packages' in the same setup operation.
     """
 
+    existing_egg_info_dir = None  #: Private API, setuptools internal use only.
+
     def finalize_options(self):
         orig.build_py.finalize_options(self)
         self.package_data = self.distribution.package_data
@@ -143,10 +145,19 @@ class build_py(orig.build_py):
             # Locate package source directory
             src_dirs[assert_relative(self.get_package_dir(package))] = package
 
-        self.run_command('egg_info')
+        if (
+            getattr(self, 'existing_egg_info_dir', None)
+            and Path(self.existing_egg_info_dir, "SOURCES.txt").exists()
+        ):
+            manifest = Path(self.existing_egg_info_dir, "SOURCES.txt")
+            files = manifest.read_text(encoding="utf-8").splitlines()
+        else:
+            self.run_command('egg_info')
+            ei_cmd = self.get_finalized_command('egg_info')
+            files = ei_cmd.filelist.files
+
         check = _IncludePackageDataAbuse()
-        ei_cmd = self.get_finalized_command('egg_info')
-        for path in ei_cmd.filelist.files:
+        for path in files:
             d, f = os.path.split(assert_relative(path))
             prev = None
             oldf = f
diff --git a/setuptools/tests/test_build_py.py b/setuptools/tests/test_build_py.py
index 13fa64de..87d4bcfe 100644
--- a/setuptools/tests/test_build_py.py
+++ b/setuptools/tests/test_build_py.py
@@ -1,10 +1,11 @@
 import os
 import stat
 import shutil
+from pathlib import Path
+from unittest.mock import Mock
 
 import pytest
 import jaraco.path
-from path import Path
 
 from setuptools import SetuptoolsDeprecationWarning
 from setuptools.dist import Distribution
@@ -109,67 +110,122 @@ def test_executable_data(tmpdir_cwd):
         "Script is not executable"
 
 
-def test_excluded_subpackages(tmp_path):
-    files = {
-        "setup.cfg": DALS("""
-            [metadata]
-            name = mypkg
-            version = 42
+EXAMPLE_WITH_MANIFEST = {
+    "setup.cfg": DALS("""
+        [metadata]
+        name = mypkg
+        version = 42
 
-            [options]
-            include_package_data = True
-            packages = find:
+        [options]
+        include_package_data = True
+        packages = find:
 
-            [options.packages.find]
-            exclude = *.tests*
-            """),
-        "mypkg": {
+        [options.packages.find]
+        exclude = *.tests*
+        """),
+    "mypkg": {
+        "__init__.py": "",
+        "resource_file.txt": "",
+        "tests": {
             "__init__.py": "",
-            "resource_file.txt": "",
-            "tests": {
-                "__init__.py": "",
-                "test_mypkg.py": "",
-                "test_file.txt": "",
-            }
-        },
-        "MANIFEST.in": DALS("""
-            global-include *.py *.txt
-            global-exclude *.py[cod]
-            prune dist
-            prune build
-            prune *.egg-info
-            """)
-    }
-
-    with Path(tmp_path):
-        jaraco.path.build(files)
-        dist = Distribution({"script_name": "%PEP 517%"})
-        dist.parse_config_files()
-
-        build_py = dist.get_command_obj("build_py")
-        msg = r"Python recognizes 'mypkg\.tests' as an importable package"
-        with pytest.warns(SetuptoolsDeprecationWarning, match=msg):
-            # TODO: To fix #3260 we need some transition period to deprecate the
-            # existing behavior of `include_package_data`. After the transition, we
-            # should remove the warning and fix the behaviour.
-            build_py.finalize_options()
-            build_py.run()
-
-        build_dir = Path(dist.get_command_obj("build_py").build_lib)
-        assert (build_dir / "mypkg/__init__.py").exists()
-        assert (build_dir / "mypkg/resource_file.txt").exists()
-
-        # Setuptools is configured to ignore `mypkg.tests`, therefore the following
-        # files/dirs should not be included in the distribution.
-        for f in [
-            "mypkg/tests/__init__.py",
-            "mypkg/tests/test_mypkg.py",
-            "mypkg/tests/test_file.txt",
-            "mypkg/tests",
-        ]:
-            with pytest.raises(AssertionError):
-                # TODO: Enforce the following assertion once #3260 is fixed
-                # (remove context manager and the following xfail).
-                assert not (build_dir / f).exists()
-
-        pytest.xfail("#3260")
+            "test_mypkg.py": "",
+            "test_file.txt": "",
+        }
+    },
+    "MANIFEST.in": DALS("""
+        global-include *.py *.txt
+        global-exclude *.py[cod]
+        prune dist
+        prune build
+        prune *.egg-info
+        """)
+}
+
+
+def test_excluded_subpackages(tmpdir_cwd):
+    jaraco.path.build(EXAMPLE_WITH_MANIFEST)
+    dist = Distribution({"script_name": "%PEP 517%"})
+    dist.parse_config_files()
+
+    build_py = dist.get_command_obj("build_py")
+    msg = r"Python recognizes 'mypkg\.tests' as an importable package"
+    with pytest.warns(SetuptoolsDeprecationWarning, match=msg):
+        # TODO: To fix #3260 we need some transition period to deprecate the
+        # existing behavior of `include_package_data`. After the transition, we
+        # should remove the warning and fix the behaviour.
+        build_py.finalize_options()
+        build_py.run()
+
+    build_dir = Path(dist.get_command_obj("build_py").build_lib)
+    assert (build_dir / "mypkg/__init__.py").exists()
+    assert (build_dir / "mypkg/resource_file.txt").exists()
+
+    # Setuptools is configured to ignore `mypkg.tests`, therefore the following
+    # files/dirs should not be included in the distribution.
+    for f in [
+        "mypkg/tests/__init__.py",
+        "mypkg/tests/test_mypkg.py",
+        "mypkg/tests/test_file.txt",
+        "mypkg/tests",
+    ]:
+        with pytest.raises(AssertionError):
+            # TODO: Enforce the following assertion once #3260 is fixed
+            # (remove context manager and the following xfail).
+            assert not (build_dir / f).exists()
+
+    pytest.xfail("#3260")
+
+
+@pytest.mark.filterwarnings("ignore::setuptools.SetuptoolsDeprecationWarning")
+def test_existing_egg_info(tmpdir_cwd, monkeypatch):
+    """When provided with the ``existing_egg_info_dir`` attribute, build_py should not
+    attempt to run egg_info again.
+    """
+    # == Pre-condition ==
+    # Generate an egg-info dir
+    jaraco.path.build(EXAMPLE_WITH_MANIFEST)
+    dist = Distribution({"script_name": "%PEP 517%"})
+    dist.parse_config_files()
+    assert dist.include_package_data
+
+    egg_info = dist.get_command_obj("egg_info")
+    dist.run_command("egg_info")
+    egg_info_dir = next(Path(egg_info.egg_base).glob("*.egg-info"))
+    assert egg_info_dir.is_dir()
+
+    # == Setup ==
+    build_py = dist.get_command_obj("build_py")
+    build_py.finalize_options()
+    egg_info = dist.get_command_obj("egg_info")
+    egg_info_run = Mock(side_effect=egg_info.run)
+    monkeypatch.setattr(egg_info, "run", egg_info_run)
+
+    # == Remove caches ==
+    # egg_info is called when build_py looks for data_files, which gets cached.
+    # We need to ensure it is not cached yet, otherwise it may impact on the tests
+    build_py.__dict__.pop('data_files', None)
+    dist.reinitialize_command(egg_info)
+
+    # == Sanity check ==
+    # Ensure that if existing_egg_info is not given, build_py attempts to run egg_info
+    build_py.existing_egg_info_dir = None
+    build_py.run()
+    egg_info_run.assert_called()
+
+    # == Remove caches ==
+    egg_info_run.reset_mock()
+    build_py.__dict__.pop('data_files', None)
+    dist.reinitialize_command(egg_info)
+
+    # == Actual test ==
+    # Ensure that if existing_egg_info_dir is given, egg_info doesn't run
+    build_py.existing_egg_info_dir = egg_info_dir
+    build_py.run()
+    egg_info_run.assert_not_called()
+    assert build_py.data_files
+
+    # Make sure the list of outputs is actually OK
+    outputs = map(lambda x: x.replace(os.sep, "/"), build_py.get_outputs())
+    assert outputs
+    example = str(Path(build_py.build_lib, "mypkg/__init__.py")).replace(os.sep, "/")
+    assert example in outputs