nix repl `:p` is not interruptible

[tejing1]

Describe the bug

The lazy evaluation and traversal of a large datastructure through the repl's :p command cannot be interrupted via ctrl-c.

Steps To Reproduce

• nix-repl> pkgs = import <nixpkgs> {}
  nix-repl> :p pkgs
  

• Try to stop it with ctrl-c
• Be ready to send a TERM signal from another terminal or wait... quite a while.

Expected behavior

Ctrl-c should stop the current evaluation and return to the repl prompt in a timely manner.

Metadata

$ nix-env --version
nix-env (Nix) 2.28.3

Additional context

I'm writing some flake-parts modules that handle and name nixpkgs instantiations for memoization purposes... I triggered this quite a few times in debugging even after I already knew not to in theory.

Checklist

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

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[roberth]

Printer::printAttrs makes recursive calls to Printer::print while iterating over the attributes, and Printer::print has a checkInterrupt() call, so it should have bailed out.
That leads me to believe the problem is either in the interrupt mechanism, or the way nix repl uses it differently.

[xokdvium]

Yeah the issue is more like interrupting the second time doesn't work. The simple fix is #14687