completeFlakeRefWithFragment: handle names with dots

[ylh]

Motivation

remedies a FIXME:

nix build /etc/nixos#nixosConfigurations.w
# may now tab-complete to e.g.:
nix build /etc/nixos#nixosConfigurations.\"www.example.com\"

& subsequent completions into deeper attrpaths will preserve escaped quotes.

Context

{un,}escaping done in this PR errs on the side of simplicity to the point of being naïve (pretty easy to demonstrate that they are not strict inverses of each other), expectation being that tab completion is used interactively.

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[nixos-discourse]

This pull request has been mentioned on NixOS Discourse. There might be relevant details there:

https://discourse.nixos.org/t/2024-08-26-nix-team-meeting-minutes-172/51300/1

[roberth]

Reviewed in meeting today:
We think before we support this feature we should clean up the code a bit.

• We should strive to have separate functions for quoting and unquoting (and ideally unit test that they round-trip). There might be something in libutil already to help with this (quoteStrings)
  • Maybe it needs to be a variation of what we have because of the potentially missing start/end quotes
  • Even if it's a variation, centralizing it makes sure that we don't duplicate code unnecessarily

[nixos-discourse]

This pull request has been mentioned on NixOS Discourse. There might be relevant details there:

https://discourse.nixos.org/t/2024-08-28-nix-team-meeting-minutes-173/51302/1

[ylh]

fair point as to the goto and tests in general; pushed accordingly—a bit confused as to what you mean by this, though:

We should strive to have separate functions for quoting and unquoting

as there already are, and they are in use here. namely, parseAttrPath and SymbolStr::operator<<. if you mean the backslash trickery alongside those calls, that is exclusive to the problem of shell completion, as is the function being patched here. emitting \" is about the most that can be done for the intersection of shells for which nix publishes completion hooks. the alternative would be to rewrite those hooks to communicate with nix in some canonical representation and escape/unescape on their end.

if you just mean the bit for detecting when a completion is taking place inside a quoted string, it would be possible, though of dubious utility, to add a variant of parseAttrPath with a special side-channel return to indicate EOF inside a quoted segment.