Verify the git revision before launching UI.

This has the added benefit of checking that we're in a Git repo.

Author: georgebrock

git-browse

@@ -4,6 +4,7 @@ import argparse
 import textwrap
 
 from gitbrowse.browser import GitBrowser
+from gitbrowse import git
 
 
 parser = argparse.ArgumentParser(
@@ -54,5 +55,6 @@ parser.add_argument('file',
                     help='the path to the file you want to examine')
 args = parser.parse_args()
 
-browser = GitBrowser(args.file, args.rev)
-browser.run()
+if git.verify_revision(args.rev):
+    browser = GitBrowser(args.file, args.rev)
+    browser.run()

gitbrowse/git.py

@@ -273,3 +273,17 @@ def _build_line_mappings(self, start, finish):
             finish_ln += 1
 
         return forward, backward
+
+
+def verify_revision(rev):
+    """
+    Verifies that a revision is valid in the current working directory,
+    and returns True or False accordingly.
+
+    Errors are not supressed, so if the revision is bad or the CWD isn't
+    a Git repository then Git's error message will be output.
+    """
+    status = os.system('git rev-parse --verify --no-revs %s' % (
+        rev
+    ))
+    return status == 0