Add coverage export for tests.

.coveragerc

@@ -0,0 +1,17 @@
+[run]
+branch = True
+concurrency =
+    multiprocessing
+data_file = .coverage/coverage
+parallel = True
+source =
+    meson.py
+    mesonbuild/
+    mesonconf.py
+    mesonintrospect.py
+    mesonrewriter.py
+    mesontest.py
+    run_cross_test.py
+    run_project_tests.py
+    run_tests.py
+    run_unittests.py

.gitignore

@@ -5,6 +5,7 @@
 /.idea
 
 __pycache__
+.coverage
 /install dir
 /work area
 

docs/markdown/Release-notes-for-0.41.0.md

@@ -52,7 +52,12 @@ installed. This is roughly equivalent to the `distcheck` target in
 other build systems. Currently this only works for projects using Git
 and only with the Ninja backend.
 
-
 ## Support for passing arguments to Rust compiler
 
 Targets for building rust now take a `rust_args` keyword.
+
+## Code coverage export for tests
+
+Code coverage can be generated for tests by passing the `--cov` argument to
+the `run_tests.py` test runner. Note, since multiple processes are used,
+coverage must be combined before producing a report (`coverage3 combine`.)

run_tests.py

@@ -19,6 +19,7 @@ import sys
 import time
 import shutil
 import subprocess
+import tempfile
 import platform
 from mesonbuild import mesonlib
 from mesonbuild.environment import detect_ninja
@@ -125,6 +126,13 @@ class FakeEnvironment(object):
         return False
 
 if __name__ == '__main__':
+    # Enable coverage early...
+    enable_coverage = '--cov' in sys.argv
+    if enable_coverage:
+        os.makedirs('.coverage', exist_ok=True)
+        sys.argv.remove('--cov')
+        import coverage
+        coverage.process_startup()
     returncode = 0
     # Iterate over list in reverse order to find the last --backend arg
     backend = Backend.ninja
@@ -164,10 +172,19 @@ if __name__ == '__main__':
     # Can't pass arguments to unit tests, so set the backend to use in the environment
     env = os.environ.copy()
     env['MESON_UNIT_TEST_BACKEND'] = backend.name
+    with tempfile.TemporaryDirectory() as td:
+        # Enable coverage on all subsequent processes.
+        if enable_coverage:
+            with open(os.path.join(td, 'usercustomize.py'), 'w') as f:
+                f.write('import coverage\n'
+                        'coverage.process_startup()\n')
+            env['COVERAGE_PROCESS_START'] = '.coveragerc'
+            env['PYTHONPATH'] = os.pathsep.join([td] + env.get('PYTHONPATH', []))
+
         returncode += subprocess.call([sys.executable, 'run_unittests.py', '-v'] + units, env=env)
         # Ubuntu packages do not have a binary without -6 suffix.
         if should_run_linux_cross_tests():
             print('Running cross compilation tests.\n')
-        returncode += subprocess.call([sys.executable, 'run_cross_test.py', 'cross/ubuntu-armhf.txt'])
-    returncode += subprocess.call([sys.executable, 'run_project_tests.py'] + sys.argv[1:])
+            returncode += subprocess.call([sys.executable, 'run_cross_test.py', 'cross/ubuntu-armhf.txt'], env=env)
+        returncode += subprocess.call([sys.executable, 'run_project_tests.py'] + sys.argv[1:], env=env)
     sys.exit(returncode)