fix(coverage): generating lcov was causing issues (bazel-contrib#1734)

* examples/bzlmod - bazel coverage
//tests:version_3_10_takes_3_9_subprocess_test was always failing due to
.coveragerc generated file not being unique
* generating the locv report resulted in messages going to stdout/stderr
that resulted in test failures. To fix this, we run with --quiet. If
VERBOSE_COVERAGE is defined we will output to stderr.


Reproduction steps:
```bash
git co main
cd examples/bzlmod
bazel coverage //tests/...
# failures occur
```

Author: trentontrees

.bazelci/presubmit.yml

@@ -59,7 +59,7 @@ buildifier:
   build_targets: ["..."]
   test_targets: ["..."]
 .coverage_targets_example_bzlmod: &coverage_targets_example_bzlmod
-  coverage_targets: ["//:test"]
+  coverage_targets: ["..."]
 .coverage_targets_example_bzlmod_build_file_generation: &coverage_targets_example_bzlmod_build_file_generation
   coverage_targets: ["//:bzlmod_build_file_generation_test"]
 .coverage_targets_example_multi_python: &coverage_targets_example_multi_python
@@ -218,7 +218,7 @@ tasks:
   integration_test_bzlmod_ubuntu_min:
     <<: *minimum_supported_version
     <<: *reusable_build_test_all
-    <<: *coverage_targets_example_bzlmod
+    coverage_targets: ["//:test"]
     name: "examples/bzlmod: Ubuntu, minimum Bazel"
     working_directory: examples/bzlmod
     platform: ubuntu2004

CHANGELOG.md

@@ -38,6 +38,10 @@ A brief description of the categories of changes:
 * (bzlmod) pip.parse now does not fail with an empty `requirements.txt`.
 * (py_wheel) Wheels generated by `py_wheel` now preserve executable bits when
   being extracted by `installer` and/or `pip`.
+* (coverage) During the running of lcov, the stdout/stderr was causing test
+  failures.  By default, suppress output when generating lcov.  This can be
+  overridden by setting 'VERBOSE_COVERAGE'.  This change only affect bazel
+  7.x.x and above.
 
 ### Added
 

python/private/python_bootstrap_template.txt

@@ -20,6 +20,7 @@ del sys.path[0]
 
 import os
 import subprocess
+import uuid
 
 def IsRunningFromZip():
   return %is_zipfile%
@@ -93,6 +94,10 @@ def PrintVerboseCoverage(*args):
   if os.environ.get("VERBOSE_COVERAGE"):
     print(*args, file=sys.stderr)
 
+def IsVerboseCoverage():
+  """Returns True if VERBOSE_COVERAGE is non-empty in the environment."""
+  return os.environ.get("VERBOSE_COVERAGE")
+
 def FindCoverageEntryPoint(module_space):
   cov_tool = '%coverage_tool%'
   if cov_tool:
@@ -389,8 +394,8 @@ def _RunForCoverage(python_program, main_filename, args, env,
         runfiles directory if set.
   """
   # We need for coveragepy to use relative paths.  This can only be configured
-  # via an rc file, so we need to make one.
-  rcfile_name = os.path.join(os.environ['COVERAGE_DIR'], '.coveragerc')
+  unique_id = uuid.uuid4()
+  rcfile_name = os.path.join(os.environ['COVERAGE_DIR'], ".coveragerc_{}".format(unique_id))
   with open(rcfile_name, "w") as rcfile:
     rcfile.write('''[run]
 relative_files = True
@@ -415,18 +420,20 @@ relative_files = True
 
   PrintVerboseCoverage('Converting coveragepy database to lcov:', output_filename)
   # Run coveragepy again to convert its .coverage database file into lcov.
+  # Under normal conditions running lcov outputs to stdout/stderr, which causes problems for `coverage`.
+  params = [python_program, coverage_entrypoint, "lcov", "--rcfile=" + rcfile_name, "-o", output_filename, "--quiet"]
+  kparams = {"env": env, "cwd": workspace, "stdout": subprocess.DEVNULL, "stderr": subprocess.DEVNULL}
+  if IsVerboseCoverage():
+    # reconnect stdout/stderr to lcov generation.  Should be useful for debugging `coverage` issues.
+    params.remove("--quiet")
+    kparams['stdout'] = sys.stderr
+    kparams['stderr'] = sys.stderr
+
   ret_code = subprocess.call(
-    [
-      python_program,
-      coverage_entrypoint,
-      "lcov",
-      "--rcfile=" + rcfile_name,
-      "-o",
-      output_filename
-    ],
-    env=env,
-    cwd=workspace
+    params,
+    **kparams
   ) or ret_code
+
   try:
     os.unlink(rcfile_name)
   except OSError as err: