The underlying issue is that debugger code path was
calling PosTable::operator[] in each eval method.
This has become incredibly expensive since 5d9fdab3de.
While we are it it, I've reworked the code to
not use std::shared_ptr where it really isn't necessary.
As I've documented in previous commits, this is actually
more a workaround for recursive header dependencies now
and is only necessary in `error.hh` code.
Some ad-hoc benchmarking:
After this commit:
```
Benchmark 1: nix eval nixpkgs#hello --impure --ignore-try --no-eval-cache --debugger
Time (mean ± σ): 784.2 ms ± 7.1 ms [User: 561.4 ms, System: 147.7 ms]
Range (min … max): 773.5 ms … 792.6 ms 10 runs
```
On master 3604c7c51:
```
Benchmark 1: nix eval nixpkgs#hello --impure --ignore-try --no-eval-cache --debugger
Time (mean ± σ): 22.914 s ± 0.178 s [User: 18.524 s, System: 4.151 s]
Range (min … max): 22.738 s … 23.290 s 10 runs
```
(cherry picked from commit adbd08399c)
All of this code doesn't actually depend on anything from
libexpr. Because Pos is so tigtly coupled with Error, it
makes sense to have in the same library.
(cherry picked from commit a53b184e63)
If the NIX_LOG_FILE environment variable is set, Nix will write JSON
log messages to that file in addition to the regular logger (e.g. the
progress bar).
Logging to another Logger was kind of nonsensical - it was really just
an easy way to get it to write its output to stderr, but that only
works if the underlying logger writes to stderr.
This change is needed to make it easy to log JSON output somewhere
else (like a file or socket).
This exposed a bug in FlakeHub's private toggling, where the public 3.0.0 release followed by an accidentally private 0.1.x release, managed to cause the flake to be shunted closed.
This should not be possible, so let's dig into how that came to be and make sure to create a test case against this should-be-impossible transition.
The resume call would get some non-flushed(?) data.
Extending the pause to include the newline makes the complete flush
part of the pause.
(cherry picked from commit 880489051a)