lib/generators: fix toPretty throwing on (partially applied) builtins #111469
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sternenseemann
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Profpatsch
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Profpatsch
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Jan 31, 2021
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An high level example case of this problem occuring can be found below:
nix-repl> lib.generators.toPretty {} (lib.concatStringsSep "\n")
error: 'functionArgs' requires a function, at /home/lukas/src/nix/nixpkgs/lib/trivial.nix:334:42
However this does not happen on other partially applied functions:
nix-repl> lib.generators.toPretty {} (lib.concatMapStringsSep "\n")
"<function>"
The issue, as it turns out is that while builtins are functions,
builtins.functionArgs throws if is passed a builtin or a partially
applied builtin:
nix-repl> lib.generators.toPretty {} builtins.toString
error: 'functionArgs' requires a function, at /home/lukas/src/nix/nixpkgs/lib/trivial.nix:334:42
nix-repl> lib.generators.toPretty {} (builtins.foldl' (a: b: a + b))
error: 'functionArgs' requires a function, at /home/lukas/src/nix/nixpkgs/lib/trivial.nix:334:42
I'm pretty sure this qualifies as a nix bug and should be filed
accordingly, but we can work around it in lib.generators.toPretty by
using tryEval and falling back to {} which functionArgs _should_ return
for builtins.
The nix behavior is inconsistent to say the least:
nix-repl> builtins.functionArgs builtins.functionArgs
error: 'functionArgs' requires a function, at (string):1:1
nix-repl> builtins.typeOf builtins.functionArgs
"lambda"
builtins.functionArgs (a: 1 + a)
{ }
nix-repl> builtins.typeOf (a: 1 + a)
"lambda"
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Profpatsch
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Jan 31, 2021
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I’d say this looks good, but @infinisil should take a look.
infinisil
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Jan 31, 2021
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Motivation for this change
An high level example case of the issue occuring can be found below:
The issue, as it turns out is that while builtins are functions,
builtins.functionArgsthrows if is passed a builtin or a partiallyapplied builtin:
I'm pretty sure this qualifies as a nix bug and should be filedEdit: seems like this has been resolved inaccordingly,
nixUnstableandonly the latest stable version of nix is affected.
We can work around this in lib.generators.toPretty by
using
tryEvaland falling back to {} whichfunctionArgsshould returnfor builtins.
The nix behavior is inconsistent to say the least:
Things done
sandboxinnix.confon non-NixOS linux)nix-shell -p nixpkgs-review --run "nixpkgs-review wip"./result/bin/)nix path-info -Sbefore and after)