fix: only offer language names in zsh tab completion for -l

[truffle-dev]

Closes #3735.

bat --list-languages prints <name>:<file-matchers>, where the matcher
column is a comma-separated mix of plain extensions (rs), globs
(*.rs), absolute paths (/etc/profile), and full filenames
(Containerfile). The zsh completion's awk script split each line on
: or , and emitted every field as a completion value, so tab
completion offered candidates that -l cannot parse:

$ bat -l '*.bash_login' /dev/null
[bat error]: unknown syntax: '*.bash_login'

Switch to splitting on : only, emit the language name as the
completion value, and use the matcher list as its description. This
matches the bash completion's behavior, which already keeps only the
first column (assets/completions/bat.bash.in:80-89).

After the change, the completion menu shows just language names with
their extensions as descriptive context:

ASP                            -- (asa)
ActionScript                   -- (as)
Ada                            -- (adb,ads)
...

Verified locally with cargo build and cargo test --test integration_tests -- --test-threads=1 (232 passed). Unit tests (cargo test --lib) also pass (124).

The fish completion has a similar but partially-mitigated bug; out of scope here.

[LangLangBart]

The patch works for me.

I initially thought the right fix would be not pulling in the built-in mappings,
but the benefit of the status quo is the informative value on what files a given
syntax will be auto applied.

I particularly like the reduced number of items to choose from, less duplicated
values for a given syntax.

Bad thing, a value like bat -l zsh is supported and would no longer be listed
in the completion as a value, but hopefully in the future syntect will get an
upgrade and Zsh.sublime-syntax can finally be used.

So I am ok with it.

Verified locally with cargo build and cargo test --test integration_tests -- --test-threads=1 (232 passed). Unit tests (cargo test --lib) also pass (124).

There are no zsh completion tests.

EDIT1: syntect note updated

[LangLangBart]

wouldn't the awk part become redundant ?

[truffle-dev]

Yes, you're right. bat --list-languages already emits each entry in name:matchers form, which is exactly what _describe consumes, so the awk pipeline is byte-identical to the input.

I verified against the current syntax set:

$ diff <(bat --list-languages) \
       <(bat --list-languages | awk -F: '{ printf("%s:%s\n", $1, $2) }')
$ echo $?
0

Dropped the awk and refreshed the comment in 138d70f.