Fix completions for quoted/escaped parameters in Fish (#3013)

Author: HansLehnert

src/click/shell_completion.py

@@ -405,6 +405,8 @@ class FishComplete(ShellComplete):
     def get_completion_args(self) -> tuple[list[str], str]:
         cwords = split_arg_string(os.environ["COMP_WORDS"])
         incomplete = os.environ["COMP_CWORD"]
+        if incomplete:
+            incomplete = split_arg_string(incomplete)[0]
         args = cwords[1:]
 
         # Fish stores the partial word in both COMP_WORDS and

tests/test_shell_completion.py

@@ -359,6 +359,7 @@ def test_full_source(runner, shell):
         ("zsh", {"COMP_WORDS": "a b", "COMP_CWORD": "1"}, "plain\nb\nbee\n"),
         ("fish", {"COMP_WORDS": "", "COMP_CWORD": ""}, "plain,a\nplain,b\tbee\n"),
         ("fish", {"COMP_WORDS": "a b", "COMP_CWORD": "b"}, "plain,b\tbee\n"),
+        ("fish", {"COMP_WORDS": 'a "b', "COMP_CWORD": '"b'}, "plain,b\tbee\n"),
     ],
 )
 @pytest.mark.usefixtures("_patch_for_completion")