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d9a7d03da8
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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| .. | ||
| systems | ||
| tests | ||
| asserts.nix | ||
| attrsets.nix | ||
| cli.nix | ||
| customisation.nix | ||
| debug.nix | ||
| default.nix | ||
| deprecated.nix | ||
| fetchers.nix | ||
| filesystem.nix | ||
| fixed-points.nix | ||
| generators.nix | ||
| kernel.nix | ||
| licenses.nix | ||
| lists.nix | ||
| meta.nix | ||
| minver.nix | ||
| modules.nix | ||
| options.nix | ||
| sources.nix | ||
| strings-with-deps.nix | ||
| strings.nix | ||
| trivial.nix | ||
| types.nix | ||
| versions.nix | ||
| zip-int-bits.nix | ||