Apply show_only_unused to arguments (fixes #125)

Changelog.rst

@@ -12,6 +12,8 @@ Unreleased
 - Do not offer true/false value completions for boolean flags (``is_flag=True``,
   including ``--foo/--no-foo`` style options), which previously inserted a value
   into the positional-argument slot (#116).
+- ``show_only_unused`` now also applies to arguments, so an argument that has
+  already been given is no longer completed again (#125).
 
 
 .. _version-0.3.0:

click_repl/_completer.py

@@ -262,6 +262,29 @@ def _get_completion_for_cmd_args(
                     break
 
             elif isinstance(param, click.Argument):
+                # Show only unused arguments. A variadic argument (nargs=-1)
+                # always accepts more values, so it is never hidden.
+                already_present = False
+                get_source = getattr(autocomplete_ctx, "get_parameter_source", None)
+                source = None
+                if get_source is not None:
+                    try:
+                        source = get_source(param.name)
+                    except Exception:
+                        pass
+
+                if source is not None:
+                    already_present = getattr(source, "name", None) == "COMMANDLINE"
+                else:
+                    already_present = autocomplete_ctx.params.get(param.name) not in (
+                        None,
+                        (),
+                        [],
+                    )
+
+                if self.show_only_unused and already_present and param.nargs != -1:
+                    continue
+
                 choices.extend(
                     self._get_completion_from_params(
                         autocomplete_ctx, args, param, incomplete

tests/test_completion/test_common_tests/test_arg_completion.py

@@ -32,3 +32,37 @@ def arg_choices(handler):
 
     completions = list(c.get_completions(Document("arg-choices ")))
     assert {x.text for x in completions} == {"foo", "bar"}
+
+
+def test_only_unused_with_arg():
+    @root_command.command()
+    @click.argument("handler", type=click.Choice(("foo", "bar")))
+    def unused_arg(handler):
+        pass
+
+    c.show_only_unused = True
+
+    completions = list(c.get_completions(Document("unused-arg ")))
+    assert {x.text for x in completions} == {"foo", "bar"}
+
+    completions = list(c.get_completions(Document("unused-arg foo ")))
+    assert {x.text for x in completions} == set()
+
+    c.show_only_unused = False
+
+    completions = list(c.get_completions(Document("unused-arg foo ")))
+    assert {x.text for x in completions} == {"foo", "bar"}
+
+
+def test_only_unused_with_variadic_arg():
+    @root_command.command()
+    @click.argument("handlers", type=click.Choice(("foo", "bar")), nargs=-1)
+    def unused_variadic_arg(handlers):
+        pass
+
+    c.show_only_unused = True
+
+    completions = list(c.get_completions(Document("unused-variadic-arg foo ")))
+    assert {x.text for x in completions} == {"foo", "bar"}
+
+    c.show_only_unused = False