Bring back functionTo to prevent evalutation errors while merging #44626
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This reverts commit 4ff1ab5. We need this to type options like: services.xserver.windowManager.xmonad.extraPackages that specify functions that take an attribute set containing packages / plugins and return a list containing a selection of the values in this set. The reason we need a dedicated type for this is to have the correct merge behaviour. Without the functionTo type merging multiple function option definitions results in an evaluation error. The functionTo type merges definitions by returning a new function that applies the functions of all the definitions to the given input and merges the result.
Without this patch merging options like services.xserver.windowManager.xmonad.extraPackages results in the evaluation error: error: value is a list while a set was expected, at nixpkgs/lib/options.nix:77:23 With this patch we get the desired merging behaviour that just concatenates the resulting package lists.
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This alternative would be the last on the list of things to be added back. This was a mistake, and we have plenty of alternative before going back to such extreme. (see #44601 (comment)) Short answer: No! |
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Motivation for this change
This is an alternative for #44601 as suggested by @oxij .
This is used to type options like:
services.xserver.windowManager.xmonad.extraPackagesthat specify functions that take an attribute set containing packages / plugins and return a list containing a selection of the values in this set.The reason we need a dedicated type for this is to define the correct merge behaviour. Without the
functionTotype merging multiple function option definitions results in an evaluation error.The
functionTomerges definitions by returning a new function that applies the functions of all the definitions to the given input and merges the results.Things done
sandboxinnix.confon non-NixOS)nix-shell -p nox --run "nox-review wip"./result/bin/)nix path-info -Sbefore and after)