Fix #2779: Wrong error message when wrong multicharacter short opti...

src/click/parser.py

@@ -401,6 +401,18 @@ def _match_short_opt(self, arg: str, state: _ParsingState) -> None:
                 if self.ignore_unknown_options:
                     unknown_options.append(ch)
                     continue
+
+                # If a registered single-dash long option (like -dbg)
+                # is a prefix of the original argument, report the
+                # error using the full argument instead of just the
+                # single character that failed to match.
+                norm_arg = _normalize_opt(arg, self.ctx)
+                for long_opt_name in self._long_opt:
+                    if norm_arg.startswith(long_opt_name) and len(
+                        long_opt_name
+                    ) > len(opt):
+                        raise NoSuchOption(norm_arg, ctx=self.ctx)
+
                 raise NoSuchOption(opt, ctx=self.ctx)
             if option.takes_value:
                 # Any characters left in arg?  Pretend they're the

tests/test_options.py

@@ -144,6 +144,26 @@ def cli():
     assert f"No such option: {unknown_flag}" in result.output
 
 
+def test_multicharacter_short_option_wrong_option_error(runner):
+    """When a wrong multi-character short option like -dbgwrong is passed,
+    the error should reference the full argument, not just the first char."""
+
+    @click.command()
+    @click.option("-dbg", is_flag=True)
+    def cli(dbg):
+        click.echo(f"dbg={dbg}")
+
+    # Correct usage should work.
+    result = runner.invoke(cli, ["-dbg"])
+    assert not result.exception
+    assert "dbg=True" in result.output
+
+    # Wrong option should mention the full argument, not just '-d'.
+    result = runner.invoke(cli, ["-dbgwrong"])
+    assert result.exit_code != 0
+    assert "No such option: -dbgwrong" in result.output
+
+
 @pytest.mark.parametrize(
     ("value", "expect"),
     [