testsuite: Don't use git status to determine whether we are inside a repo

Git status is extremely expensive for this task. We instead use `git rev-parse
HEAD` and throw away the output to ensure we don't spam the user.

2 files changed, 8 insertions, 7 deletions

diff --git a/testsuite/driver/perf_notes.py b/testsuite/driver/perf_notes.py
index c275041252..5ceede7be2 100644
--- a/testsuite/driver/perf_notes.py
+++ b/testsuite/driver/perf_notes.py
@@ -20,11 +20,12 @@ from math import ceil, trunc
 from testutil import passed, failBecause
 
 
-# Check if "git status" can be run successfully.
+# Check if "git rev-parse" can be run successfully.
 # True implies the current directory is a git repo.
-def can_git_status():
+def inside_git_repo():
     try:
-        subprocess.check_call(['git', 'status'])
+        subprocess.check_call(['git', 'rev-parse', 'HEAD'],
+                              stdout=subprocess.DEVNULL)
         return True
     except subprocess.CalledProcessError:
         return False
@@ -388,4 +389,4 @@ if __name__ == '__main__':
 
         # Printing out percentages.
         for test, metric in all_tests:
-            print("{:27}{:30}".format(test, metric) + commit_string(test,'percentages'))
\ No newline at end of file
+            print("{:27}{:30}".format(test, metric) + commit_string(test,'percentages'))
diff --git a/testsuite/driver/runtests.py b/testsuite/driver/runtests.py
index c8966b4580..c1e85744b9 100644
--- a/testsuite/driver/runtests.py
+++ b/testsuite/driver/runtests.py
@@ -25,7 +25,7 @@ import subprocess
 
 from testutil import getStdout, Watcher, str_warn, str_info
 from testglobals import getConfig, ghc_env, getTestRun, TestOptions, brokens
-from perf_notes import MetricChange, can_git_status
+from perf_notes import MetricChange, inside_git_repo
 from junit import junit
 
 # Readline sometimes spews out ANSI escapes for some values of TERM,
@@ -118,10 +118,10 @@ if args.threads:
 if args.verbose is not None:
     config.verbose = args.verbose
 
-# Note force skip perf tests: skip if this is not a git repo (estimated with can_git_status)
+# Note force skip perf tests: skip if this is not a git repo (estimated with inside_git_repo)
 # and no metrics file is given. In this case there is no way to read the previous commit's
 # perf test results, nor a way to store new perf test results.
-canGitStatus = can_git_status()
+canGitStatus = inside_git_repo()
 forceSkipPerfTests = not hasMetricsFile and not canGitStatus
 config.skip_perf_tests = args.skip_perf_tests or forceSkipPerfTests
 config.only_perf_tests = args.only_perf_tests