Duplicate Boolean flag options "--foo/--foo" are not detected (defaults to False)

[ramses0]

I ran into an issue where I had the code:

@click.option( "--print-verbose-info/--print-verbose-info", help="...", default=False )

...and running cli.py --print-verbose-info was apparently defaulting over to the False value. Totally my mistake (it should have been --no-print-verbose-info), but it'd be nice to get a warning/error for boolean values which match exactly (ie: cannot be set to true).

It was kindof tricky to diagnose b/c I assumed that the --print-verbose-info that I was passing on the CLI was triggering the True path, not the False path, and usually Click option parsing is pretty bulletproof so it took a while to find that copy/paste problem.

This would be a good-first-issue, I'm submitting it now more as a reminder to maybe follow-up on it and figure out the appropriate P.R.

[ramses0]

untested, but probably something like this?

diff --git a/click/core.py b/click/core.py
index 36004fe..edddd9f 100644
--- a/click/core.py
+++ b/click/core.py
@@ -1731,6 +1731,8 @@ class Option(Parameter):
                     second = second.lstrip()
                     if second:
                         secondary_opts.append(second.lstrip())
+                    if first == second:
+                        raise TypeError('Boolean options cannot use the same flag for true and false.')
                 else:
                     possible_names.append(split_opt(decl))
                     opts.append(decl)

[ovezovs]

I will work on this