pager: catch startup failures on Windows

If the user's pager settings are broken, display an error message
rather than crash to avoid confusing them.

Bug: https://crbug.com/gerrit/16173
Change-Id: Idc0891da783c68f3a96ac53a82781e34e40421fb
Reviewed-on: https://gerrit-review.googlesource.com/c/git-repo/+/343437
Reviewed-by: LaMont Jones <lamontjones@google.com>
Tested-by: Mike Frysinger <vapier@google.com>

1 files changed, 5 insertions, 2 deletions

diff --git a/pager.py b/pager.py
index 352923d9..438597ef 100644
--- a/pager.py
+++ b/pager.py
@@ -56,8 +56,11 @@ def _PipePager(pager):
   global pager_process, old_stdout, old_stderr
   assert pager_process is None, "Only one active pager process at a time"
   # Create pager process, piping stdout/err into its stdin
-  pager_process = subprocess.Popen([pager], stdin=subprocess.PIPE, stdout=sys.stdout,
-                                   stderr=sys.stderr)
+  try:
+    pager_process = subprocess.Popen([pager], stdin=subprocess.PIPE, stdout=sys.stdout,
+                                     stderr=sys.stderr)
+  except FileNotFoundError:
+    sys.exit(f'fatal: cannot start pager "{pager}"')
   old_stdout = sys.stdout
   old_stderr = sys.stderr
   sys.stdout = pager_process.stdin