Exact command name matches are unambiguous

When the user provides a StGit command name on the command line that
is a valid prefix for several commands, do not report that command as
ambiguous if it is an exact match for a command (or alias).

Fixes #110

Signed-off-by: Peter Grayson <pete@jpgrayson.net>

stgit/main.py

@@ -69,15 +69,17 @@ def canonical_cmd(self, key):
                 'Try "%s help" for a list of supported commands' % prog,
             )
             sys.exit(utils.STGIT_GENERAL_ERROR)
-        elif len(candidates) > 1:
+        elif len(candidates) == 1:
+            return candidates[0]
+        elif key in candidates:
+            return key
+        else:
             out.error(
                 'Ambiguous command: %s' % key,
                 'Candidates are: %s' % ', '.join(candidates),
             )
             sys.exit(utils.STGIT_GENERAL_ERROR)
 
-        return candidates[0]
-
     def __getitem__(self, key):
         cmd_mod = self.get(key) or self.get(self.canonical_cmd(key))
         if is_cmd_alias(cmd_mod):

t/t0004-main.sh

@@ -37,6 +37,14 @@ test_expect_success 'Test help on ambiguous command' '
     grep -e "Ambiguous command: pu"
 '
 
+test_expect_success 'Test ambiguous alias' '
+    test_config stgit.alias.show-stat "git show --stat" &&
+    stg show-stat &&
+    stg init &&
+    stg show &&
+    general_error stg sho 2>&1 | grep -e "Ambiguous command: sho"
+'
+
 test_expect_success 'Test version/--version equivalence' '
     stg version > v0.txt &&
     stg --version > v1.txt &&