Use abspath to rc file so that chdir doesn't bork us. #890

CHANGES.rst

@@ -21,10 +21,16 @@ want to know what's different in 5.0 since 4.5.x, see :ref:`whatsnew5x`.
     ..  Version 7.8.1 --- 2021-07-27
     ..  ----------------------------
 
+
 Unreleased
 ----------
 
-Nothing yet.
+- Programs that used multiprocessing and changed directories would fail under
+  coverage.  This is now fixed (`issue 890`_).  A side effect is that debug
+  information about the config files read now shows absolute paths to the
+  files.
+
+.. _issue 890: https://github.com/nedbat/coveragepy/issues/890
 
 
 .. _changes_501:

coverage/config.py

@@ -6,6 +6,7 @@
 import collections
 import copy
 import os
+import os.path
 import re
 
 from coverage import env
@@ -275,7 +276,7 @@ def from_file(self, filename, our_file):
         if not files_read:
             return False
 
-        self.config_files_read.extend(files_read)
+        self.config_files_read.extend(map(os.path.abspath, files_read))
 
         any_set = False
         try:
@@ -323,7 +324,7 @@ def from_file(self, filename, our_file):
             used = any_set
 
         if used:
-            self.config_file = filename
+            self.config_file = os.path.abspath(filename)
             with open(filename) as f:
                 self._config_contents = f.read()
 

coverage/multiproc.py

@@ -6,6 +6,7 @@
 import multiprocessing
 import multiprocessing.process
 import os
+import os.path
 import sys
 import traceback
 
@@ -85,7 +86,7 @@ def patch_multiprocessing(rcfile):
 
     # Set the value in ProcessWithCoverage that will be pickled into the child
     # process.
-    os.environ["COVERAGE_RCFILE"] = rcfile
+    os.environ["COVERAGE_RCFILE"] = os.path.abspath(rcfile)
 
     # When spawning processes rather than forking them, we have no state in the
     # new process.  We sneak in there with a Stowaway: we stuff one of our own

tests/test_concurrency.py

@@ -493,6 +493,25 @@ def test_multiprocessing_bootstrap_error_handling(self):
         self.assertIn("Exception during multiprocessing bootstrap init", out)
         self.assertIn("Exception: Crashing because called by _bootstrap", out)
 
+    def test_bug890(self):
+        # chdir in multiprocessing shouldn't keep us from finding the
+        # .coveragerc file.
+        self.make_file("multi.py", """\
+            import multiprocessing, os, os.path
+            if __name__ == "__main__":
+                if not os.path.exists("./tmp"): os.mkdir("./tmp")
+                os.chdir("./tmp")
+                with multiprocessing.Manager():
+                    pass
+                print("ok")
+            """)
+        self.make_file(".coveragerc", """\
+            [run]
+            concurrency = multiprocessing
+            """)
+        out = self.run_command("coverage run multi.py")
+        self.assertEqual(out.splitlines()[-1], "ok")
+
 
 def test_coverage_stop_in_threads():
     has_started_coverage = []