Make Checkstyle integration test macOS-compatible (#867)

integration-tests/checkstyle.sh

@@ -2,7 +2,7 @@
 
 set -e -u -o pipefail
 
-integration_test_root="$(readlink -f "$(dirname "${0}")")"
+integration_test_root="$(cd "$(dirname -- "${0}")" && pwd)"
 error_prone_support_root="${integration_test_root}/.."
 repos_root="${integration_test_root}/.repos"
 
@@ -25,6 +25,21 @@ else
   trap 'rm -rf -- "${report_directory}"' INT TERM HUP EXIT
 fi
 
+case "$(uname -s)" in
+  Linux*)
+    grep_command=grep
+    sed_command=sed
+    ;;
+  Darwin*)
+    grep_command=ggrep
+    sed_command=gsed
+    ;;
+  *)
+    echo "Unsupported distribution $(uname -s) for this script."
+    exit 1
+    ;;
+esac
+
 # XXX: Configure Renovate to manage the AssertJ version declared here.
 shared_build_flags="
   -Perror-prone-compile,error-prone-test-compile
@@ -50,19 +65,19 @@ error_prone_shared_flags='-XepExcludedPaths:(\Q${project.basedir}${file.separato
 # in a separate Maven module.
 error_prone_patch_flags="${error_prone_shared_flags} -XepPatchLocation:IN_PLACE -XepPatchChecks:$(
   find "${error_prone_support_root}" -path "*/META-INF/services/com.google.errorprone.bugpatterns.BugChecker" -print0 \
-    | xargs -0 grep -hoP '[^.]+$' \
-    | grep -v ErrorProneRuntimeClasspath \
-    | paste -s -d ','
+    | xargs -0 "${grep_command}" -hoP '[^.]+$' \
+    | "${grep_command}" -v ErrorProneRuntimeClasspath \
+    | paste -s -d ',' -
 )"
 
 # XXX: Drop the `ErrorProneRuntimeClasspath` exclusion once that check resides
 # in a separate Maven module.
 error_prone_validation_flags="${error_prone_shared_flags} -XepDisableAllChecks $(
   find "${error_prone_support_root}" -path "*/META-INF/services/com.google.errorprone.bugpatterns.BugChecker" -print0 \
-    | xargs -0 grep -hoP '[^.]+$' \
-    | sed -r 's,(.*),-Xep:\1:WARN,' \
-    | grep -v ErrorProneRuntimeClasspath \
-    | paste -s -d ' '
+    | xargs -0 "${grep_command}" -hoP '[^.]+$' \
+    | "${sed_command}" -r 's,(.*),-Xep:\1:WARN,' \
+    | "${grep_command}" -v ErrorProneRuntimeClasspath \
+    | paste -s -d ' ' -
 )"
 
 echo "Shared build flags: ${shared_build_flags}"
@@ -157,12 +172,12 @@ mvn ${shared_build_flags} \
 # Collect the applied changes.
 expected_changes="${integration_test_root}/${test_name}-expected-changes.patch"
 actual_changes="${report_directory}/${test_name}-changes.patch"
-(git diff "${diff_base}"..HEAD | grep -vP '^(diff|index)' || true) > "${actual_changes}"
+(git diff "${diff_base}"..HEAD | "${grep_command}" -vP '^(diff|index)' || true) > "${actual_changes}"
 
 # Collect the warnings reported by Error Prone Support checks.
 expected_warnings="${integration_test_root}/${test_name}-expected-warnings.txt"
 actual_warnings="${report_directory}/${test_name}-validation-build-warnings.txt"
-(grep -oP "(?<=^\\Q[WARNING] ${PWD}/\\E).*" "${validation_build_log}" | grep -P '\] \[' || true) | LC_ALL=C sort > "${actual_warnings}"
+("${grep_command}" -oP "(?<=^\\Q[WARNING] ${PWD}/\\E).*" "${validation_build_log}" | "${grep_command}" -P '\] \[' || true) | LC_ALL=C sort > "${actual_warnings}"
 
 # Persist or validate the applied changes and reported warnings.
 if [ -n "${do_sync}" ]; then
@@ -174,12 +189,12 @@ else
   # XXX: This "diff of diffs" also contains vacuous sections, introduced due to
   # line offset differences. Try to omit those from the final output.
   if ! diff -u "${expected_changes}" "${actual_changes}"; then
-    echo 'There are unexpected changes.'
+    echo 'There are unexpected changes. Inspect the preceding output for details.'
     failure=1
   fi
   echo 'Inspecting emitted warnings...'
   if ! diff -u "${expected_warnings}" "${actual_warnings}"; then
-    echo 'Diagnostics output changed.'
+    echo 'Diagnostics output changed. Inspect the preceding output for details.'
     failure=1
   fi
 fi