Highlight current flake source paths in stack trace

[roberth]

Is your feature request related to a problem?

Stack traces can be long, and involve many library frames, like those from callPackage or evalModules.

While these are occassionally somewhat useful, more often the mistake is in the current flake's source.

Proposed solution

Make it quick to visually identify trace frames that originate from the current project, e.g. the current flake's source, or subpaths of the cwd.

I think we have options for how to do this, but I'd try to make this a libcmd responsibility.
The trace printing can still live in libutil, but we could give it an isCurrentSource callback (assuming we preserve that info in a structured way...).
Alternatively, we could make the formatting of the path an EvalState responsibility, and put the isCurrentSource callback there.
libcmd can then configure the EvalState according to what kind of installable(s) are passed.

Alternative solutions

Additional context

Checklist

• checked latest Nix manual (source)
• checked open feature issues and pull requests for possible duplicates

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[xokdvium]

Could it be the responsibility of the SourcePath to implement something like this and hide that behind some stateful logic in Inputs (or something like that)? I can see some cross-over with #14424 that we want to have more hooks for rendering paths in error messages/profiler traces.

[roberth]

I don't think it needs to be very stateful at all. One of the CLI mixins in libcmd can just have that info in a immutable or set-once way and render accordingly.
#14424 seems related by topic, but I don't see much interaction with my proposal here.

[xokdvium]

Yeah, by interaction I meant that both these issues would benefit from common infrastructure for setting up custom handlers for rendering SourcePaths.