fix: make source paths absolute where they exist. #1499

nedbat · nedbat · commit 66d69108654f · 2025-08-27T12:44:21.000-04:00
diff --git a/CHANGES.rst b/CHANGES.rst
@@ -23,7 +23,11 @@ upgrading your version of coverage.py.
 Unreleased
 ----------
 
-Nothing yet.
+- Fix: ``source`` directories were not properly communicated to subprocesses
+  that ran in different directories, as reported in `issue 1499`_.  This is now
+  fixed.
+
+.. _issue 1499: https://github.com/nedbat/coveragepy/issues/1499
 
 
 .. start-releases
diff --git a/coverage/config.py b/coverage/config.py
@@ -274,10 +274,15 @@ def __init__(self) -> None:
         "patch",
     }
 
+    # File paths to make absolute during serialization.
+    # The pairs are (config_key, must_exist).
     SERIALIZE_ABSPATH = {
-        "data_file",
-        "debug_file",
-        "source_dirs",
+        ("data_file", False),
+        ("debug_file", False),
+        # `source` can be directories or modules, so don't abspath it if it
+        # doesn't exist.
+        ("source", True),
+        ("source_dirs", False),
     }
 
     def from_args(self, **kwargs: TConfigValueIn) -> None:
@@ -569,12 +574,13 @@ def serialize(self) -> str:
         deserialized config will refer to the same files.
         """
         data = {k: v for k, v in self.__dict__.items() if not k.startswith("_")}
-        for k in self.SERIALIZE_ABSPATH:
+        for k, must_exist in self.SERIALIZE_ABSPATH:
+            abs_fn = abs_path_if_exists if must_exist else os.path.abspath
             v = data[k]
             if isinstance(v, list):
-                v = list(map(os.path.abspath, v))
+                v = list(map(abs_fn, v))
             elif isinstance(v, str):
-                v = os.path.abspath(v)
+                v = abs_fn(v)
             data[k] = v
         return base64.b64encode(json.dumps(data).encode()).decode()
 
@@ -584,6 +590,14 @@ def process_file_value(path: str) -> str:
     return os.path.expanduser(path)
 
 
+def abs_path_if_exists(path: str) -> str:
+    """os.path.abspath, but only if the path exists."""
+    if os.path.exists(path):
+        return os.path.abspath(path)
+    else:
+        return path
+
+
 def process_regexlist(name: str, option: str, values: list[str]) -> list[str]:
     """Check the values in a regex list and keep the non-blank ones."""
     value_list = []
diff --git a/tests/test_process.py b/tests/test_process.py
@@ -30,7 +30,7 @@
 
 from tests import testenv
 from tests.coveragetest import CoverageTest, TESTS_DIR
-from tests.helpers import re_line, re_lines, re_lines_text
+from tests.helpers import change_dir, re_line, re_lines, re_lines_text
 
 
 class ProcessTest(CoverageTest):
@@ -1627,6 +1627,45 @@ def f2():
         data.read()
         assert line_counts(data)["subfunctions.py"] == 11
 
+    def test_subprocess_dir_with_source(self) -> None:
+        # https://github.com/nedbat/coveragepy/issues/1499
+        self.make_file("main/d/README", "A sub-directory")
+        self.make_file(
+            "main/main.py",
+            """\
+            import os, subprocess, sys
+            orig = os.getcwd()
+            os.chdir("./d")
+            subprocess.run([sys.executable, f"{orig}/sub.py"])
+            os.chdir(orig)
+            """,
+        )
+        self.make_file("lib/other.py", "print('Other', flush=True)")
+        self.make_file(
+            "main/sub.py",
+            """
+            import other
+            print("Hello, world!", flush=True)
+            """,
+        )
+        self.make_file(
+            "main/pyproject.toml",
+            """\
+            [tool.coverage.run]
+            patch = ["subprocess"]
+            source = [".", "other"]
+            disable_warnings = ["module-not-imported"]
+            """,
+        )
+        self.set_environ("PYTHONPATH", os.path.abspath("lib"))
+        with change_dir("main"):
+            out = self.run_command("coverage run main.py")
+            assert out == "Other\nHello, world!\n"
+            self.run_command("coverage combine")
+            data = coverage.CoverageData()
+            data.read()
+            assert line_counts(data) == {"main.py": 5, "sub.py": 2, "other.py": 1}
+
 
 @pytest.fixture
 def _clean_pth_files() -> Iterable[None]:
