wip: don't make .pth files if we already have them

Author: nedbat

coverage/control.py

@@ -268,6 +268,7 @@ def __init__(                       # pylint: disable=too-many-arguments
         self._warn_preimported_source = check_preimported
         self._no_warn_slugs: set[str] = set()
         self._messages = messages
+        self._patch_pth_file = True
 
         # A record of all the warnings that have been issued.
         self._warnings: list[str] = []
@@ -678,7 +679,7 @@ def start(self) -> None:
         if self._auto_load:
             self.load()
 
-        apply_patches(self, self.config)
+        apply_patches(self, self.config, pth_file=self._patch_pth_file)
 
         self._collector.start()
         self._started = True
@@ -1432,6 +1433,7 @@ def process_startup() -> Coverage | None:
     cov._warn_unimported_source = False
     cov._warn_preimported_source = False
     cov._auto_save = True
+    cov._patch_pth_file = False
     cov.start()
 
     return cov

coverage/patch.py

@@ -19,7 +19,7 @@
     from coverage.config import CoverageConfig
 
 
-def apply_patches(cov: Coverage, config: CoverageConfig) -> None:
+def apply_patches(cov: Coverage, config: CoverageConfig, *, pth_file: bool=True) -> None:
     """Apply invasive patches requested by `[run] patch=`."""
 
     for patch in sorted(set(config.patch)):
@@ -78,9 +78,10 @@ def coverage_execv_patch(*args: Any, **kwargs: Any) -> Any:
             os.execve = make_execv_patch("execve", os.execve)
 
         elif patch == "subprocess":
-            pth_file = create_pth_file()
-            assert pth_file is not None
-            atexit.register(pth_file.unlink, missing_ok=True)
+            if pth_file:
+                pth_file = create_pth_file()
+                assert pth_file is not None
+                atexit.register(pth_file.unlink, missing_ok=True)
             assert config.config_file is not None
             os.environ["COVERAGE_PROCESS_START"] = config.config_file