fix(coverage): Disable certain coverage warnings. (#3191)

These warnings appear if there are no Python source files in the
instrumented directories,
cf. #2762.

Work towards #2762

---------

Co-authored-by: Ignas Anikevicius <240938+aignas@users.noreply.github.com>

Author: phst

CHANGELOG.md

@@ -62,7 +62,8 @@ END_UNRELEASED_TEMPLATE
 
 {#v0-0-0-fixed}
 ### Fixed
-* Nothing fixed.
+* (tests) No more coverage warnings are being printed if there are no sources.
+  ([#2762](https://github.com/bazel-contrib/rules_python/issues/2762))
 
 {#v0-0-0-added}
 ### Added

python/private/py_executable.bzl

@@ -668,6 +668,7 @@ def _create_stage2_bootstrap(
         template = template,
         output = output,
         substitutions = {
+            "%coverage_instrumented%": str(int(ctx.configuration.coverage_enabled and ctx.coverage_instrumented())),
             "%coverage_tool%": _get_coverage_tool_runfiles_path(ctx, runtime),
             "%import_all%": "True" if read_possibly_native_flag(ctx, "python_import_all_repositories") else "False",
             "%imports%": ":".join(imports.to_list()),

python/private/stage2_bootstrap_template.py

@@ -41,6 +41,9 @@
 # string otherwise.
 VENV_SITE_PACKAGES = "%venv_rel_site_packages%"
 
+# Whether we should generate coverage data.
+COVERAGE_INSTRUMENTED = "%coverage_instrumented%" == "1"
+
 # ===== Template substitutions end =====
 
 
@@ -319,11 +322,14 @@ def _maybe_collect_coverage(enable):
     # We need for coveragepy to use relative paths.  This can only be configured
     # using an rc file.
     rcfile_name = os.path.join(coverage_dir, ".coveragerc_{}".format(unique_id))
+    disable_warnings = ('disable_warnings = module-not-imported, no-data-collected'
+                        if COVERAGE_INSTRUMENTED else '')
     print_verbose_coverage("coveragerc file:", rcfile_name)
     with open(rcfile_name, "w") as rcfile:
         rcfile.write(
             f"""[run]
 relative_files = True
+{disable_warnings}
 source =
 \t{source}
 """