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Unify and refactor value printing Previously, there were two mostly-identical value printers -- one in `libexpr/eval.cc` (which didn't force values) and one in `libcmd/repl.cc` (which did force values and also printed ANSI color codes). This PR unifies both of these printers into `print.cc` and provides a `PrintOptions` struct for controlling the output, which allows for toggling whether values are forced, whether repeated values are tracked, and whether ANSI color codes are displayed. Additionally, `PrintOptions` allows tuning the maximum number of attributes, list items, and bytes in a string that will be displayed; this makes it ideal for contexts where printing too much output (e.g. all of Nixpkgs) is distracting. (As requested by @roberth in https://github.com/NixOS/nix/pull/9554#issuecomment-1845095735) Please read the tests for example output. Future work: - It would be nice to provide this function as a builtin, perhaps `builtins.toStringDebug` -- a printing function that never fails would be useful when debugging Nix code. - It would be nice to support customizing `PrintOptions` members on the command line, e.g. `--option to-string-max-attrs 1000`.

2023-12-12 21:57:36 +00:00

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