22 lines
1.2 KiB
Markdown
22 lines
1.2 KiB
Markdown
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---
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synopsis: "Build failures caused by `allowSubstitutes = false` while being the wrong system now produce a decent error"
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issues: [fj#484]
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cls: [1841]
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category: Fixes
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credits: jade
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---
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Nix allows derivations to set `allowSubstitutes = false` in order to force them to be built locally without querying substituters for them.
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This is useful for derivations that are very fast to build (especially if they produce large output).
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However, this can shoot you in the foot if the derivation *has* to be substituted such as if the derivation is for another architecture, which is what `--always-allow-substitutes` is for.
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Perhaps such derivations that are known to be impossible to build locally should ignore `allowSubstitutes` (irrespective of remote builders) in the future, but this at least reports the failure and solution directly.
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```
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$ nix build -f fail.nix
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error: a 'unicornsandrainbows-linux' with features {} is required to build '/nix/store/...-meow.drv', but I am a 'x86_64-linux' with features {...}
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Hint: the failing derivation has allowSubstitutes set to false, forcing it to be built rather than substituted.
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Passing --always-allow-substitutes to force substitution may resolve this failure if the path is available in a substituter.
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```
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