complete/compgen fails to suggest when options contain ':' (colon)

@meuh's comment led me to https://stackoverflow.com/questions/10528695/how-to-reset-comp-wordbreaks-without-affecting-other-completion-script which led me to the answer.

Bash provides a number of macros to help in /etc/bash_completion. In debian, this sources /usr/share/bash-completion/bash_completion.

Browsing in this file there are some ways to handle the colon:

• _init_completion -n : will remove : from $COMP_WORDBREAKS. But calling only this isn't enough, or you'll find ^.*: gets repeated in your auto-complete result

  $ _foo() { local cur=${COMP_WORDS[$COMP_CWORD]} _init_completion -n : cur COMPREPLY=( $(compgen -W "h:bart h:baze" -- "$cur" ) ) } $ complete -F _foo foo $ foo <tab> $ foo h:h:ba 

• __ltrim_colon_completions will remove leading ^.*: from the completion, which fixes the previous problem a bit.

  The result is:

  $ _foo() { local cur=${COMP_WORDS[$COMP_CWORD]} _init_completion -n : cur COMPREPLY=( $(compgen -W "h:bart h:baze" -- "$cur" ) ) __ltrim_colon_completions "$cur" } $ complete -F _foo foo $ foo <tab> $ foo h:ba <-- It got the common part right! $ foo h:ba<tab> bart baze <-- It removed the prefix? $ foo h:baz<tab> $ foo h:baze <-- The final completion is correct 

The suggestions are a bit strange, especially if you were expecting http://example.com and get //example.com, but it does work.

But the documentation for __ltrim_colon_completions() says:

The preferred solution is to remove the colon (:) from COMP_WORDBREAKS in your .bashrc:

# Remove colon (:) from list of word completion separators COMP_WORDBREAKS=${COMP_WORDBREAKS//:} 

See also: Bash FAQ - E13) Why does filename completion misbehave if a colon appears in the filename? - https://tiswww.case.edu/php/chet/bash/FAQ

I'm not really a fan of imposing on /etc/bash.bashrc, especially since this completion script will be deployed in a package, and I'm not making local edits. This change could also change the behaviour of other completion scripts that actually rely on the : separator for parsing things like $PATH.

The solution I ended up with is to set this in my /usr/share/bash-completion/completions/foo script:

#!/usr/bin/env bash _foo() { COMP_WORDBREAKS=${COMP_WORDBREAKS//:} local cur=${COMP_WORDS[$COMP_CWORD]} COMPREPLY=( $(compgen -W "h:bart h:baze" -- "$cur" ) ) } complete -F _foo foo 

It's hard to tell if this has a global impact. A new shell doesn't have $COMP_WORDBREAKS defined, but I'm not sure if bash-completion reset it between completions.