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doc: Explain why tryEval does not return the message

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Robert Hensing 2024-10-20 19:31:16 +02:00
parent 694c378d14
commit 90d257b771
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src/libexpr/primops.cc
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@ -944,6 +944,9 @@ static RegisterPrimOp primop_tryEval({
`let e = { x = throw ""; }; in `let e = { x = throw ""; }; in
(builtins.tryEval (builtins.deepSeq e e)).success` will be (builtins.tryEval (builtins.deepSeq e e)).success` will be
`false`. `false`.
`tryEval` intentionally does not return the error message, because that risks bringing non-determinism into the evaluation result, and it would become very difficult to improve error reporting without breaking existing expressions.
Instead, use [`builtins.addErrorContext`](@docroot@/language/builtins.md#builtins-addErrorContext) to add context to the error message, and use a Nix unit testing tool for testing.
)", )",
.fun = prim_tryEval, .fun = prim_tryEval,
}); });