zsh completion with nested control functions

Question

I'm writing completion function for zsh. I took cargo completion function as a basis for mine. For the most part it works fine except for -h and --help options. Completion ouput for these functions is unaligned and repeated multiple times (presented below). This only happens when control functions (_describe, _arguments etc) are present in case structure. Why this is happening and how can I fix this behavior?

Completion function:

#compdef test
_test() {
    local context state state_descr line
    typeset -A opt_args
    _arguments \
        "(- 1 *)"{-h,--help}"[Help]" \
        "1: :->command" \
        "*:: :->args"

    case $state in
        command)
            _alternative 'arguments:custom arg:(a b c)'
            ;;
        args)
            _arguments \
              "-a[All]" \
              "-n[None]"
    esac
}
_test

Shell output:

> test -[TAB]
--help
-h
-- Help
--help
-h
-- Help
--help
-h
-- Help

Answer 1

I've just encountered the same issue. The solution is to return zero from your completion function:

#compdef test

_test() {
    ...

    return 0
}

_test

All completion scripts that I've seen use ret variable which is initially 1 and then set to 0 if any completion function succeeded:

#compdef test
_test() {
    local context state state_descr line
    local ret=1

    typeset -A opt_args
    _arguments \
        "(- 1 *)"{-h,--help}"[Help]" \
        "1: :->command" \
        "*:: :->args" && ret=0

    case $state in
        command)
            _alternative 'arguments:custom arg:(a b c)' && ret=0
            ;;
        args)
            _arguments \
              "-a[All]" \
              "-n[None]" && ret=0
    esac

    return ret
}

_test

I'm not sure why they do it, though.