Fix coverage runfiles directory issue

As discovered in bazelbuild#15030 there
was another bug with the short circuiting coverage logic where tests
were not run from the correct directory. In that PR this issue is fixed
directly, with this change we instead make missing LCOV_MERGER be
deferred until after all test setup and run, which I think is more
future proof to other changes here, and also allows users to know their
tests are being run with coverage, and output the correct files, even in
the case they don't setup the coverage merger infrastructure.

Closes bazelbuild#15031.

PiperOrigin-RevId: 434715347

src/test/shell/bazel/bazel_coverage_starlark_test.sh

@@ -40,8 +40,22 @@ function test_starlark_rule_without_lcov_merger() {
     cat <<EOF > rules.bzl
 def _impl(ctx):
     output = ctx.actions.declare_file(ctx.attr.name)
-    ctx.actions.write(output, "", is_executable = True)
-    return [DefaultInfo(executable=output)]
+    ctx.actions.write(output, """\
+#!/bin/bash
+
+if [[ ! -r extra ]]; then
+  echo "extra file not found" >&2
+  exit 1
+fi
+
+if [[ -z \$COVERAGE ]]; then
+  echo "COVERAGE environment variable not set, coverage not run."
+  exit 1
+fi
+""", is_executable = True)
+    extra_file = ctx.actions.declare_file("extra")
+    ctx.actions.write(extra_file, "extra")
+    return [DefaultInfo(executable=output, runfiles=ctx.runfiles(files=[extra_file]))]
 
 custom_test = rule(
     implementation = _impl,

tools/test/collect_coverage.sh

@@ -30,21 +30,6 @@ if [[ -n "$VERBOSE_COVERAGE" ]]; then
   set -x
 fi
 
-if [[ -z "$LCOV_MERGER" ]]; then
-  # this can happen if a rule returns an InstrumentedFilesInfo (which all do
-  # following 5b216b2) but does not define an _lcov_merger attribute.
-  # Unfortunately, we cannot simply stop this script being called in this case
-  # due to conflicts with how things work within Google.
-  # The file creation is required because TestActionBuilder has already declared
-  # it.
-  # TODO(cmita): Improve this situation so this early-exit isn't required.
-  touch $COVERAGE_OUTPUT_FILE
-  # Execute the test.
-  "$@"
-  TEST_STATUS=$?
-  exit "$TEST_STATUS"
-fi
-
 function resolve_links() {
   local name="$1"
 
@@ -101,15 +86,6 @@ export JAVA_COVERAGE_FILE=$COVERAGE_DIR/jvcov.dat
 export COVERAGE=1
 export BULK_COVERAGE_RUN=1
 
-
-for name in "$LCOV_MERGER"; do
-  if [[ ! -e $name ]]; then
-    echo --
-    echo Coverage runner: cannot locate file $name
-    exit 1
-  fi
-done
-
 # Setting up the environment for executing the C++ tests.
 if [[ -z "$GCOV_PREFIX_STRIP" ]]; then
   # TODO: GCOV_PREFIX_STRIP=3 is incorrect on MacOS in the default setup
@@ -202,6 +178,24 @@ if [[ "$CC_CODE_COVERAGE_SCRIPT" ]]; then
     eval "${CC_CODE_COVERAGE_SCRIPT}"
 fi
 
+if [[ -z "$LCOV_MERGER" ]]; then
+  # this can happen if a rule returns an InstrumentedFilesInfo (which all do
+  # following 5b216b2) but does not define an _lcov_merger attribute.
+  # Unfortunately, we cannot simply stop this script being called in this case
+  # due to conflicts with how things work within Google.
+  # The file creation is required because TestActionBuilder has already declared
+  # it.
+  exit 0
+fi
+
+for name in "$LCOV_MERGER"; do
+  if [[ ! -e $name ]]; then
+    echo --
+    echo Coverage runner: cannot locate file $name
+    exit 1
+  fi
+done
+
 # Export the command line that invokes LcovMerger with the flags:
 # --coverage_dir          The absolute path of the directory where the
 #                         intermediate coverage reports are located.