rules_r: fix exporting status vars as env vars in r_binary

This was broken by 8a4ab37 in which we
stopped exporting stable status var by default.

R/scripts/binary.sh.tpl

@@ -21,9 +21,15 @@ fatal() {
 }
 
 # Make bazel status variables available as environment variables, if available.
-if [[ -e ./stable-status.txt ]]; then
-  e="$(cat ./{stable,volatile}-status.txt | sed -e 's/\([^[:space:]]*\) \(.*\)/export \1=\"\2\"/')"
+status_to_env() {
+  local status_file="$1"
+  e="$(cat "${status_file}" | sed -e 's/\([^[:space:]]*\) \(.*\)/export \1=\"\2\"/')"
   eval "${e}"
+}
+
+status_to_env "./volatile-status.txt"
+if [[ -e ./stable-status.txt ]]; then
+  status_to_env "./stable-status.txt"
 fi
 
 # Export environment variables, if any.

tests/stamping/nostamp_test.sh

@@ -23,7 +23,13 @@ fail() {
 if ! grep "^VAR" "volatile-status.txt"; then
   fail "volatile status file expected"
 fi
+if ! [[ "${VAR:-}" ]]; then
+  fail "volatile status var expected as env var"
+fi
 
 if [[ -e stable-info.txt ]]; then
   fail "stable status file not expected"
 fi
+if [[ "${STABLE_VAR:-}" ]]; then
+  fail "stable status var not expected as env var"
+fi

tests/stamping/stamp_test.sh

@@ -23,7 +23,13 @@ fail() {
 if ! grep "^VAR" "volatile-status.txt"; then
   fail "volatile status file expected"
 fi
+if ! [[ "${VAR:-}" ]]; then
+  fail "volatile status var expected as env var"
+fi
 
 if ! grep "^STABLE_VAR" "stable-status.txt"; then
   fail "stable status file expected and not empty"
 fi
+if ! [[ "${STABLE_VAR:-}" ]]; then
+  fail "stable status var expected as env var"
+fi