Make nix output completions in the form `completion\tdescription`.
This can't be used by bash (afaik), but other shells like zsh or fish
can display it along the completion choices
When running `nix build -L` it can be fairly hard to read the output if
the build program intentionally renders whitespace on the left. A
typical example is `g++` displaying compilation errors.
With this patch, the whitespace on the left is retained to make the log
more readable:
```
foo> no configure script, doing nothing
foo> building
foo> foobar.cc: In function 'int main()':
foo> foobar.cc:5:5: error: 'wrong_func' was not declared in this scope
foo> 5 | wrong_func(1);
foo> | ^~~~~~~~~~
error: --- Error ------------------------------------------------------------------------------------- nix
error: --- Error --- nix-daemon
builder for '/nix/store/i1q76cw6cyh91raaqg5p5isd1l2x6rx2-foo-1.0.drv' failed with exit code 1
```
When having a message like `waiting for a machine to build X` and
building with `nix build -L`, the log-prefix is always colored yellow[1]
on a small terminal-width as everything (including the ANSI color-reset) is
stripped away.
To work around that problem, this patch explicitly adds an `ANSI_NORMAL`
to the end of the line.
[1] https://imgur.com/a/FjtJOk3
Needed so that we can include it as a logger in loggers.cc without
adding a dependency on nix
This also requires moving names.hh to libutil to prevent a circular
dependency between libmain and libexpr
Make the printing of the build logs systematically go through the
logger, and replicate the behavior of `no-build-output` by having two
different loggers (one that prints the build logs and one that doesn't)
Add a new `--log-format` cli argument to change the format of the logs.
The possible values are
- raw (the default one for old-style commands)
- bar (the default one for new-style commands)
- bar-with-logs (equivalent to `--print-build-logs`)
- internal-json (the internal machine-readable json format)
