fix: complete subcommands after a flag that needs no value on the root command - #2501

What type of PR is this?

• bug

What this PR does / why we need it:

The shell scripts send the word under the cursor only when it starts with -, so for app --verbose <TAB> the program gets app --verbose --generate-shell-completion. A subcommand completes its parsed arguments, where --verbose has already been consumed, so app deploy --verbose <TAB> lists deploy's subcommands. The root command completes its raw arguments instead, so its last argument is --verbose, DefaultCompleteWithFlags prints flag suggestions for it, and since printFlagSuggestions skips the flag that was typed in full, it prints nothing. The same thing happens after a value given with =:

app --verbose <TAB>       # nothing (bash falls back to file names, zsh to _files)
app --verbose d<TAB>      # nothing
app --config=x <TAB>      # nothing
app -c x <TAB>            # build deploy help
app deploy --verbose <TAB>  # staging prod help

DefaultCompleteWithFlags now treats the last argument as a complete flag, and lists the subcommands, when it names a flag that takes no value (including a BoolWithInverseFlag's --no- names) or has its value after =, and no longer flag starts with it. So --debug still suggests --debug-level, --format with no value still prints nothing, and partial flags such as --verb work as before. Subcommands do not reach the new branch for a known flag, since their parsed arguments no longer hold it.

This is separate from #2489, which changes where the root command's arguments come from and not how the last one is read. It is rebased on #2489, so the new test passes its arguments to Run instead of setting os.Args.

Which issue(s) this PR fixes:

None, found while testing the generated scripts in bash and fish.

Testing

• New TestCompletionAfterCompleteRootFlag: a bool flag, an inverse bool flag and --format=json list the subcommands (these three fail on main); --format with no value, --debug next to --debug-level, and a partial --verb keep their current output.
• Checked in bash 5.3 with bash-completion 2, fish 4.9.3, and the zsh script's function: app --verbose <TAB>, app --verbose d<TAB> and app --config=x <TAB> now complete the subcommands. The other cases are unchanged.
• make (generate, vet, tests, binary size, gfmrun), make lint and make v3diff pass. go test -race passes, as do the tests with urfave_cli_no_template, urfave_cli_no_docs and urfave_cli_no_suggest.

The change and the test were written with Claude Code (AI).

Release Notes

Shell completion on the root command now lists subcommands after a flag that takes no value or has its value after "=".

🤖 Generated with Claude Code