AI spam

src/click/core.py

@@ -2674,10 +2674,21 @@ def handle_parse_result(
             and existing_default_explicit
             and not self._default_explicit
         )
+        unprocessed_would_downgrade_callback = (
+            same_source
+            and source == ParameterSource.COMMANDLINE
+            and self.callback is None
+            and existing_value is not UNSET
+            and existing_value != value
+        )
         is_winner = (
             slot_empty
             or more_explicit
-            or (same_source and not auto_would_downgrade_explicit)
+            or (
+                same_source
+                and not auto_would_downgrade_explicit
+                and not unprocessed_would_downgrade_callback
+            )
         )
 
         if is_winner:

tests/test_options.py

@@ -1626,6 +1626,32 @@ def main(fmt):
     assert result.exit_code == 0
 
 
+def test_shared_option_callback_value_is_preserved(runner):
+    marker = "$_fetch"
+
+    def fetch_value(ctx, param, value):
+        if value == marker:
+            return "fetched"
+
+        return value
+
+    @click.command()
+    @click.option("--custom", "custom")
+    @click.option("--fetch", "custom", flag_value=marker, callback=fetch_value)
+    def cli(custom):
+        click.echo(custom)
+
+    for args, expected in (
+        (["--fetch"], "fetched"),
+        (["--custom", "typed", "--fetch"], "fetched"),
+        (["--fetch", "--custom", "typed"], "typed"),
+    ):
+        result = runner.invoke(cli, args)
+
+        assert result.output == f"{expected}\n"
+        assert result.exit_code == 0
+
+
 @pytest.mark.parametrize(
     ("flag_value", "envvar_value", "expected"),
     [