fix: make coverage work with bootstrap=script

Author: rickeylev

python/private/py_executable.bzl

@@ -557,13 +557,25 @@ def _create_venv(ctx, output_prefix, imports, runtime_details):
     site_init = ctx.actions.declare_file("{}/_bazel_site_init.py".format(site_packages))
     computed_subs = ctx.actions.template_dict()
     computed_subs.add_joined("%imports%", imports, join_with = ":", map_each = _map_each_identity)
+
+    if (ctx.configuration.coverage_enabled and
+        runtime and
+        runtime.coverage_tool):
+        coverage_tool_runfiles_path = "{}/{}".format(
+            ctx.workspace_name,
+            runtime.coverage_tool.short_path,
+        )
+    else:
+        coverage_tool_runfiles_path = ""
+
     ctx.actions.expand_template(
         template = runtime.site_init_template,
         output = site_init,
         substitutions = {
             "%import_all%": "True" if ctx.fragments.bazel_py.python_import_all_repositories else "False",
             "%site_init_runfiles_path%": "{}/{}".format(ctx.workspace_name, site_init.short_path),
             "%workspace_name%": ctx.workspace_name,
+            "%coverage_tool%": coverage_tool_runfiles_path,
         },
         computed_substitutions = computed_subs,
     )

python/private/site_init_template.py

@@ -185,7 +185,7 @@ def _maybe_add_path(path):
             coverage_setup = True
         else:
             _print_verbose_coverage(
-                "Coverage was enabled, but python coverage tool was not configured."
+                "Coverage was enabled, but python coverage tool was not configured. "
                 + "To enable coverage, consult the docs at "
                 + "https://rules-python.readthedocs.io/en/latest/coverage.html"
             )

python/private/stage2_bootstrap_template.py

@@ -106,8 +106,8 @@ def print_verbose(*args, mapping=None, values=None):
 
 def print_verbose_coverage(*args):
     """Print output if VERBOSE_COVERAGE is non-empty in the environment."""
-    if os.environ.get("VERBOSE_COVERAGE"):
-        print(*args, file=sys.stderr, flush=True)
+    if is_verbose_coverage():
+        print("bootstrap: coverage:", *args, file=sys.stderr, flush=True)
 
 
 def is_verbose_coverage():
@@ -398,6 +398,8 @@ def main():
     else:
         coverage_enabled = False
 
+    print_verbose_coverage("coverage_enabled:", coverage_enabled)
+
     with _maybe_collect_coverage(enable=coverage_enabled):
         # The first arg is this bootstrap, so drop that for the re-invocation.
         _run_py(main_filename, args=sys.argv[1:])