Merge pull request #785 from pre-commit/better_trace

Improve not found error with script paths (`./exe`)

pre_commit/parse_shebang.py

@@ -42,16 +42,21 @@ def find_executable(exe, _environ=None):
         return None
 
 
-def normexe(orig_exe):
-    if os.sep not in orig_exe:
-        exe = find_executable(orig_exe)
+def normexe(orig):
+    def _error(msg):
+        raise ExecutableNotFoundError('Executable `{}` {}'.format(orig, msg))
+
+    if os.sep not in orig and (not os.altsep or os.altsep not in orig):
+        exe = find_executable(orig)
         if exe is None:
-            raise ExecutableNotFoundError(
-                'Executable `{}` not found'.format(orig_exe),
-            )
+            _error('not found')
         return exe
+    elif not os.access(orig, os.X_OK):
+        _error('not found')
+    elif os.path.isdir(orig):
+        _error('is a directory')
     else:
-        return orig_exe
+        return orig
 
 
 def normalize_cmd(cmd):