Recurse into build / dist directories

See #12625 for context

changelog/12625.improvement.rst

@@ -0,0 +1,2 @@
+Conditionally ignore collection of setuptools artifacts dirnames only if the
+directories reside inside a setuptools project, i.e. `setup.cfg`, is present, etc.

src/_pytest/main.py

@@ -63,9 +63,7 @@ def pytest_addoption(parser: Parser) -> None:
             "*.egg",
             ".*",
             "_darcs",
-            "build",
             "CVS",
-            "dist",
             "node_modules",
             "venv",
             "{arch}",
@@ -367,6 +365,22 @@ def pytest_runtestloop(session: Session) -> bool:
     return True
 
 
+def _in_build(path: Path) -> bool:
+    """Attempt to detect if ``path`` is the root of a buildsystem's artifacts
+    by checking known dirnames patterns, and the presence of configuration in
+    the parent dir by checking for a setup.py, setup.cfg, or pyproject.toml.
+    """
+    if not path.is_dir():
+        return False
+
+    if any(fnmatch_ex(pat, path) for pat in ("build", "dist")):
+        indicators = ("setup.py", "setup.cfg", "pyproject.toml")
+        if any((path.parent / f).is_file() for f in indicators):
+            return True
+
+    return False
+
+
 def _in_venv(path: Path) -> bool:
     """Attempt to detect if ``path`` is the root of a Virtual Environment by
     checking for the existence of the pyvenv.cfg file.
@@ -418,6 +432,10 @@ def pytest_ignore_collect(collection_path: Path, config: Config) -> bool | None:
     if not allow_in_venv and _in_venv(collection_path):
         return True
 
+    allow_in_build = False  # config.getoption("collect_in_build")
+    if not allow_in_build and _in_build(collection_path):
+        return True
+
     if collection_path.is_dir():
         norecursepatterns = config.getini("norecursedirs")
         if any(fnmatch_ex(pat, collection_path) for pat in norecursepatterns):

testing/test_collection.py

@@ -137,8 +137,6 @@ def test_foo():
 class TestCollectFS:
     def test_ignored_certain_directories(self, pytester: Pytester) -> None:
         tmp_path = pytester.path
-        ensure_file(tmp_path / "build" / "test_notfound.py")
-        ensure_file(tmp_path / "dist" / "test_notfound.py")
         ensure_file(tmp_path / "_darcs" / "test_notfound.py")
         ensure_file(tmp_path / "CVS" / "test_notfound.py")
         ensure_file(tmp_path / "{arch}" / "test_notfound.py")
@@ -276,6 +274,29 @@ def test_missing_permissions_on_unselected_directory_doesnt_crash(
         assert result.ret == ExitCode.OK
         result.assert_outcomes(passed=1)
 
+    known_build_dirs = pytest.mark.parametrize("build_dir", ["build", "dist"])
+    known_buildsystem_env = pytest.mark.parametrize(
+        "buildsystem_indicator_file", ["setup.py", "setup.cfg", "pyproject.toml"]
+    )
+
+    @known_build_dirs
+    @known_buildsystem_env
+    def test_build_dirs_collected(
+        self, pytester: Pytester, build_dir: str, buildsystem_indicator_file: str
+    ) -> None:
+        tmp_path = pytester.path
+        ensure_file(tmp_path / build_dir / "test_module.py").write_text(
+            "def test_hello(): pass", encoding="utf-8"
+        )
+
+        result = pytester.runpytest("--collect-only").stdout.str()
+        assert "test_module" in result
+
+        ensure_file(tmp_path / buildsystem_indicator_file)
+
+        result = pytester.runpytest("--collect-only").stdout.str()
+        assert "test_module" not in result
+
 
 class TestCollectPluginHookRelay:
     def test_pytest_collect_file(self, pytester: Pytester) -> None: