Use abstract base class for ShellComplete

src/click/shell_completion.py

@@ -1,6 +1,8 @@
 import copy
 import os
 import re
+from abc import ABC
+from abc import abstractmethod
 from collections import abc
 from subprocess import PIPE
 from subprocess import run
@@ -125,7 +127,7 @@ def start_of_option(param_str):
     return param_str and param_str[:1] == "-"
 
 
-class ShellComplete:
+class ShellComplete(ABC):
     """The ShellComplete class acts as the minimal API contract of a
     completion class.  It is not intended to be used directly as
     :meth:`source` and :meth:`complete` must be overridden.
@@ -146,6 +148,7 @@ def __init__(self, prog_name, complete_var, cli):
         self.complete_var = complete_var
         self.cli = cli
 
+    @abstractmethod
     def source(self):
         """Returns the string to be echoed during activation, and is
         automatically invoked by :func:`shell_complete`. The string
@@ -154,8 +157,9 @@ def source(self):
 
         The default implementation is raising a not implemented error.
         """
-        raise NotImplementedError("source function needs to be overridden")
+        pass
 
+    @abstractmethod
     def complete(self):
         """This function is automatically invoked during completion by
         :func:`shell_complete`. It can be used to get completion responses
@@ -165,7 +169,7 @@ def complete(self):
 
         The default implementation is raising a not implemented error.
         """
-        raise NotImplementedError("complete function needs to be overridden")
+        pass
 
 
 class BashComplete(ShellComplete):

tests/test_imports.py

@@ -48,6 +48,7 @@ def tracking_import(module, locals=None, globals=None, fromlist=None,
     "pipes",
     "subprocess",
     "copy",
+    "abc",
 }
 
 if WIN: