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lib.callPackages(With): guard against a repeated mistake #81713

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Mar 12, 2020
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lib.callPackages(With): guard against a repeated mistake #81713

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7 changes: 6 additions & 1 deletion lib/customisation.nix
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Original file line number Diff line number Diff line change
Expand Up @@ -131,7 +131,12 @@ rec {
origArgs = auto // args;
pkgs = f origArgs;
mkAttrOverridable = name: _: makeOverridable (newArgs: (f newArgs).${name}) origArgs;
in lib.mapAttrs mkAttrOverridable pkgs;
in
if lib.isDerivation pkgs then throw
("function `callPackages` was called on a *single* derivation "
+ ''"${pkgs.name or "<unknown-name>"}";''
+ " did you mean to use `callPackage` instead?")
else lib.mapAttrs mkAttrOverridable pkgs;
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Parenthetical to this PR but doing a mapAttrs over all of pkgs seems like a really bad idea for performance. Hadn't noticed that before.

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Typically callPackages is used on tiny sets, fortunately.

Is there a faster way? Even if it's very hacky, we can at least use it to measure potential performance benefit – estimate how much human work is worth putting into this.

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A quick nix-env -qa ... trace showed only a few larger sets, all under 100

trace: 28
trace: 34
trace: 43
trace: 43
trace: 88
trace: 93

(caveat is that this quick test recurses into a bit fewer sets than Hydra)

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I'll assume it's not bad enough to invest more time (of mine).



/* Add attributes to each output of a derivation without changing
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