lix/src/libexpr/print-ambiguous.hh

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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`. (cherry picked from commit 0fa08b451682fb3311fe58112ff05c4fe5bee3a4, ) === Restore ambiguous value printer for `nix-instantiate` The Nix team has requested that this output format remain unchanged. I've added a warning to the man page explaining that `nix-instantiate --eval` output will not parse correctly in many situations. (cherry picked from commit df84dd4d8dd3fd6381ac2ca3064432ab31a16b79) Change-Id: I7cca6b4b53cd0642f2d49af657d5676a8554c9f8
2024-03-08 02:05:47 +00:00
#pragma once
#include "value.hh"
namespace nix {
/**
* Print a value in the deprecated format used by `nix-instantiate --eval` and
* `nix-env` (for manifests).
*
* This output can't be changed because it's part of the `nix-instantiate` API,
* but it produces ambiguous output; unevaluated thunks and lambdas (and a few
* other types) are printed as Nix path syntax like `<CODE>`.
*
* See: https://github.com/NixOS/nix/issues/9730
*/
void printAmbiguous(
Value &v,
const SymbolTable &symbols,
std::ostream &str,
std::set<const void *> *seen,
int depth);
}