Handle issue 604

src/pytest_cov/__init__.py

@@ -1,3 +1,47 @@
 """pytest-cov: avoid already-imported warning: PYTEST_DONT_REWRITE."""
 
 __version__ = '5.0.0'
+
+import pytest
+
+
+class CoverageError(Exception):
+    """Indicates that our coverage is too low"""
+
+
+class PytestCovWarning(pytest.PytestWarning):
+    """
+    The base for all pytest-cov warnings, never raised directly.
+    """
+
+
+class CovDisabledWarning(PytestCovWarning):
+    """
+    Indicates that Coverage was manually disabled.
+    """
+
+
+class CovReportWarning(PytestCovWarning):
+    """
+    Indicates that we failed to generate a report.
+    """
+
+
+class CovFailUnderWarning(PytestCovWarning):
+    """
+    Indicates that we failed to generate a report.
+    """
+
+
+class CentralCovContextWarning(PytestCovWarning):
+    """
+    Indicates that dynamic_context was set to test_function instead of using the builtin --cov-context.
+    """
+
+
+class DistCovError(Exception):
+    """
+    Raised when dynamic_context is set to test_function and xdist is also used.
+
+    See: https://github.com/pytest-dev/pytest-cov/issues/604
+    """

src/pytest_cov/engine.py

@@ -7,15 +7,23 @@
 import random
 import socket
 import sys
+import warnings
 from io import StringIO
 from pathlib import Path
 
 import coverage
 from coverage.data import CoverageData
+from coverage.sqldata import filename_suffix
 
+from . import CentralCovContextWarning
+from . import DistCovError
 from .embed import cleanup
 
 
+class BrokenCovConfigError(Exception):
+    pass
+
+
 class _NullFile:
     @staticmethod
     def write(v):
@@ -51,6 +59,10 @@ def ensure_topdir_wrapper(self, *args, **kwargs):
     return ensure_topdir_wrapper
 
 
+def _data_suffix(name):
+    return f'{filename_suffix(True)}.{name}'
+
+
 class CovController:
     """Base class for different plugin implementations."""
 
@@ -230,13 +242,20 @@ def start(self):
         self.cov = coverage.Coverage(
             source=self.cov_source,
             branch=self.cov_branch,
-            data_suffix=True,
+            data_suffix=_data_suffix('c'),
             config_file=self.cov_config,
         )
+        if self.cov.config.dynamic_context == 'test_function':
+            message = (
+                'Detected dynamic_context=test_function in coverage configuration. '
+                'This is unnecessary as this plugin provides the more complete --cov-context option.'
+            )
+            warnings.warn(CentralCovContextWarning(message), stacklevel=1)
+
         self.combining_cov = coverage.Coverage(
             source=self.cov_source,
             branch=self.cov_branch,
-            data_suffix=True,
+            data_suffix=_data_suffix('cc'),
             data_file=os.path.abspath(self.cov.config.data_file),  # noqa: PTH100
             config_file=self.cov_config,
         )
@@ -274,16 +293,22 @@ def start(self):
         self.cov = coverage.Coverage(
             source=self.cov_source,
             branch=self.cov_branch,
-            data_suffix=True,
+            data_suffix=_data_suffix('m'),
             config_file=self.cov_config,
         )
+        if self.cov.config.dynamic_context == 'test_function':
+            raise DistCovError(
+                'Detected dynamic_context=test_function in coverage configuration. '
+                'This is known to cause issues when using xdist, see: https://github.com/pytest-dev/pytest-cov/issues/604\n'
+                'It is recommended to use --cov-context instead.'
+            )
         self.cov._warn_no_data = False
         self.cov._warn_unimported_source = False
         self.cov._warn_preimported_source = False
         self.combining_cov = coverage.Coverage(
             source=self.cov_source,
             branch=self.cov_branch,
-            data_suffix=True,
+            data_suffix=_data_suffix('mc'),
             data_file=os.path.abspath(self.cov.config.data_file),  # noqa: PTH100
             config_file=self.cov_config,
         )
@@ -330,7 +355,7 @@ def testnodedown(self, node, error):
                 data.read_fileobj(StringIO(output['cov_worker_data']))
                 cov.data.update(data)
             else:
-                data = CoverageData(no_disk=True)
+                data = CoverageData(no_disk=True, suffix='should-not-exist')
                 data.loads(output['cov_worker_data'])
                 cov.get_data().update(data)
             cov.stop()
@@ -381,7 +406,7 @@ def start(self):
         self.cov = coverage.Coverage(
             source=self.cov_source,
             branch=self.cov_branch,
-            data_suffix=True,
+            data_suffix=_data_suffix(f'w{self.nodeid}'),
             config_file=self.cov_config,
         )
         self.cov.start()

src/pytest_cov/plugin.py

@@ -11,32 +11,13 @@
 from coverage.results import display_covered
 from coverage.results import should_fail_under
 
+from . import CovDisabledWarning
+from . import CovFailUnderWarning
+from . import CovReportWarning
 from . import compat
 from . import embed
 
 
-class CoverageError(Exception):
-    """Indicates that our coverage is too low"""
-
-
-class PytestCovWarning(pytest.PytestWarning):
-    """
-    The base for all pytest-cov warnings, never raised directly
-    """
-
-
-class CovDisabledWarning(PytestCovWarning):
-    """Indicates that Coverage was manually disabled"""
-
-
-class CovReportWarning(PytestCovWarning):
-    """Indicates that we failed to generate a report"""
-
-
-class CovFailUnderWarning(PytestCovWarning):
-    """Indicates that we failed to generate a report"""
-
-
 def validate_report(arg):
     file_choices = ['annotate', 'html', 'xml', 'json', 'lcov']
     term_choices = ['term', 'term-missing']

tests/test_pytest_cov.py

@@ -48,7 +48,6 @@ def test_bar():
 
 """
 
-
 COVERAGERC_SOURCE = """\
 [run]
 source = .
@@ -153,8 +152,13 @@ def test_foo(cov):
 
 xdist_params = pytest.mark.parametrize(
     'opts',
-    ['', pytest.param('-n 1', marks=pytest.mark.skipif('sys.platform == "win32" and platform.python_implementation() == "PyPy"'))],
-    ids=['nodist', 'xdist'],
+    [
+        '',
+        pytest.param('-n 1', marks=pytest.mark.skipif('sys.platform == "win32" and platform.python_implementation() == "PyPy"')),
+        pytest.param('-n 2', marks=pytest.mark.skipif('sys.platform == "win32" and platform.python_implementation() == "PyPy"')),
+        pytest.param('-n 3', marks=pytest.mark.skipif('sys.platform == "win32" and platform.python_implementation() == "PyPy"')),
+    ],
+    ids=['nodist', '1xdist', '2xdist', '3xdist'],
 )
 
 
@@ -1631,6 +1635,71 @@ def test_append_coverage(pytester, testdir, opts, prop):
     )
 
 
+@xdist_params
+def test_coverage_plugin(pytester, testdir, opts, prop):
+    script = testdir.makepyfile(test_1=prop.code)
+    testdir.makepyfile(
+        coverageplugin="""
+import coverage
+
+class ExamplePlugin(coverage.CoveragePlugin):
+    pass
+
+def coverage_init(reg, options):
+    reg.add_file_tracer(ExamplePlugin())
+"""
+    )
+    testdir.makepyprojecttoml(f"""
+[tool.coverage.run]
+plugins = ["coverageplugin"]
+concurrency = ["thread", "multiprocessing"]
+{prop.conf}
+""")
+    result = testdir.runpytest('-v', f'--cov={script.dirpath()}', script, *opts.split() + prop.args)
+    result.stdout.fnmatch_lines(
+        [
+            f'test_1* {prop.result}*',
+        ]
+    )
+
+
+@xdist_params
+def test_dynamic_context(pytester, testdir, opts, prop):
+    script = testdir.makepyfile(test_1=prop.code)
+    testdir.makepyprojecttoml(f"""
+[tool.coverage.run]
+dynamic_context = "test_function"
+parallel = true
+{prop.conf}
+""")
+    result = testdir.runpytest('-v', f'--cov={script.dirpath()}', script, *opts.split() + prop.args)
+    if opts:
+        result.stderr.fnmatch_lines(['pytest_cov.DistCovError: Detected dynamic_context=test_function*'])
+    else:
+        result.stdout.fnmatch_lines(
+            [
+                '* CentralCovContextWarning: Detected dynamic_context=test_function*',
+                f'test_1* {prop.result}*',
+            ]
+        )
+
+
+@xdist_params
+def test_simple(pytester, testdir, opts, prop):
+    script = testdir.makepyfile(test_1=prop.code)
+    testdir.makepyprojecttoml(f"""
+[tool.coverage.run]
+parallel = true
+{prop.conf}
+""")
+    result = testdir.runpytest('-v', f'--cov={script.dirpath()}', script, *opts.split() + prop.args)
+    result.stdout.fnmatch_lines(
+        [
+            f'test_1* {prop.result}*',
+        ]
+    )
+
+
 @xdist_params
 def test_do_not_append_coverage(pytester, testdir, opts, prop):
     script = testdir.makepyfile(test_1=prop.code)