From 2094909df35db45ca7a409cc37f38d49c3191d2a Mon Sep 17 00:00:00 2001
From: Ned Batchelder <ned@nedbatchelder.com>
Date: Thu, 18 Nov 2021 06:16:55 -0500
Subject: [PATCH] fix: suffix=False will suppress the suffix even with
 multiprocessing. #989

---
 CHANGES.rst         |  5 +++++
 coverage/control.py |  7 ++++++-
 tests/test_api.py   | 20 ++++++++++++++++++++
 3 files changed, 31 insertions(+), 1 deletion(-)

diff --git a/CHANGES.rst b/CHANGES.rst
index 1d9ec9225..0c48b706a 100644
--- a/CHANGES.rst
+++ b/CHANGES.rst
@@ -37,6 +37,10 @@ Unreleased
 - API: The exceptions raised by Coverage.py have been specialized, to provide
   finer-grained catching of exceptions by third-party code.
 
+- API: Using ``suffix=False`` when constructing a Coverage object with
+  multiprocessing wouldn't suppress the data file suffix (`issue 989`_).  This
+  is now fixed.
+
 - Debug: The `coverage debug data` command will now sniff out combinable data
   files, and report on all of them.
 
@@ -44,6 +48,7 @@ Unreleased
   time, and show all of them, though this was never documented.  This no longer
   works, to allow for command-line options in the future.
 
+.. _issue 989: https://github.com/nedbat/coveragepy/issues/989
 .. _issue 1203: https://github.com/nedbat/coveragepy/issues/1203
 
 
diff --git a/coverage/control.py b/coverage/control.py
index ce8ce153f..00836b3cc 100644
--- a/coverage/control.py
+++ b/coverage/control.py
@@ -482,10 +482,15 @@ def _init_for_start(self):
             )
 
         suffix = self._data_suffix_specified
-        if suffix or self.config.parallel:
+        if suffix:
             if not isinstance(suffix, str):
                 # if data_suffix=True, use .machinename.pid.random
                 suffix = True
+        elif self.config.parallel:
+            if suffix is None:
+                suffix = True
+            elif not isinstance(suffix, str):
+                suffix = bool(suffix)
         else:
             suffix = None
 
diff --git a/tests/test_api.py b/tests/test_api.py
index 6b0657096..a76fe3b9c 100644
--- a/tests/test_api.py
+++ b/tests/test_api.py
@@ -1199,3 +1199,23 @@ def test_combine_relative(self):
         assert files == {'foo.py', 'bar.py', os_sep('modsrc/__init__.py')}
         res = cov.report()
         assert res == 100
+
+    def test_combine_no_suffix_multiprocessing(self):
+        self.make_file(".coveragerc", """\
+            [run]
+            branch = True
+            """)
+        cov = coverage.Coverage(
+            config_file=".coveragerc",
+            concurrency="multiprocessing",
+            data_suffix=False,
+            )
+        cov.start()
+        cov.stop()
+        # The warning isn't the point of this test, but suppress it.
+        with pytest.warns(Warning) as warns:
+            cov.combine()
+        assert_coverage_warnings(warns, "No data was collected. (no-data-collected)")
+        cov.save()
+        self.assert_file_count(".coverage.*", 0)
+        self.assert_exists(".coverage")