I have no idea why `apt-cache --no-generate show` is so slow since it basically
dumps the contents of the cache file located at `/var/lib/dpkg/status`. We are
technically bypassing any waits on the cache lock file so this may produce
incorrect results if the cache is being regenerated in the moment, but that's a
small price to pay and the results are likely confined to simply not generating
comprehensive results.
With this change, we no longer need to truncate results to the first n matches
and we no longer only print packages beginning with the commandline argument
enabling fish's partial completions logic to offer less-perfect suggestions when
no better options are available.
Even though we are generating more usable completions, we still trounce the old
performance by leaps and bounds:
```
Benchmark #1: fish -c "complete -C\"apt install ac\""
Time (mean ± σ): 2.165 s ± 0.033 s [User: 267.0 ms, System: 1932.2 ms]
Range (min … max): 2.136 s … 2.256 s 10 runs
Benchmark #2: build/fish -c "complete -C\"apt install ac\""
Time (mean ± σ): 111.1 ms ± 1.8 ms [User: 38.9 ms, System: 72.9 ms]
Range (min … max): 108.2 ms … 114.9 ms 26 runs
Summary
'build/fish -c "complete -C\"apt install ac\""' ran
19.49 ± 0.44 times faster than 'fish -c "complete -C\"apt install ac\""'
```
I think this should be preferred for all subcommand completions because it
handles typos or subcommands we don't recognize better (`apt foo <TAB>` no
longer suggests subcommands since the subcommand position has been taken).
Simple way to make the apt completions spew:
function apt; end
on a system without an apt command installed. (even if it isn't
Darwin, because this uses test combiners!)
This is a thing some people do to avoid learning other package managers.
(of course our completions would probably be *wrong* still, but at least they
won't spew a `test` error)
The same hack that is used for `pkg remove <foo>` is required here, too.
Due to the massive number of results, we use `head -n 250` to prevent
the completion from hanging or the shell from being overencumbered by
too many possibe completions. However, this would only generate matches
for any of the first 250 packages, rather than printing the first 250
packages that match.
[ci skip]
Of note: The rpm/yum thing seems to be coupled, so I put it into one
function that tries the yum helper and uses the rpm path otherwise.
Zypper is already its own thing, so this should only be used for yum
and probably dnf (does that still have the helper?)
Zypper can be dropped, as that already used a separate function in the file.
Apk can just be inlined - it's literally one line for installed and another for all packages.
Fixes some potentially unsafe uses of direct substitution into regex
expressions and also switches some completions to regex-based now that
there is a safe way of using it.
Use `apt-cache show` instead of `apt-cache packagenames` to efficiently
print package names and a brief description instead of the placeholder
(localized) "Package" text that was previously printed. This applies to
both available and installed packages (for inistall and remove operations,
respectively).
TODO: update `__fish_print_packages` for non-debian platforms to do the
same.
Added a new flag `--installed` via `argparse` to `__fish_print_packages`
which indicates that only installed packages should be listed.
TODO: Other non-debian/apt platforms should take advantage of this flag/
behavior as well.
