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Diffstat (limited to 'doc/manual')
| -rw-r--r-- | doc/manual/rl-next/better-attrpath-errors.md | 64 |
1 files changed, 64 insertions, 0 deletions
diff --git a/doc/manual/rl-next/better-attrpath-errors.md b/doc/manual/rl-next/better-attrpath-errors.md new file mode 100644 index 000000000..d06bfc43b --- /dev/null +++ b/doc/manual/rl-next/better-attrpath-errors.md @@ -0,0 +1,64 @@ +--- +synopsis: "Trace when the `foo` part of a `foo.bar.baz` expression errors" +cls: 1505 +credits: Qyriad +category: Improvements +--- + +Previously, if an expression like `linux_4_9.meta.description` errored in the `linux_4_9` part, it wouldn't show you that that's the part of the expression that failed to evaluate, or even that that line of code is what caused evaluation of the failing expression. +The previous error looks like this: + +``` +let + inherit (pkgs.linuxKernel.kernels) linux_4_9; +in linux_4_9.meta.description + +error: + … while evaluating the attribute 'linux_4_9' + at /nix/store/dk2rpyb6ndvfbf19bkb2plcz5y3k8i5v-source/pkgs/top-level/linux-kernels.nix:278:5: + 277| } // lib.optionalAttrs config.allowAliases { + 278| linux_4_9 = throw "linux 4.9 was removed because it will reach its end of life within 22.11"; + | ^ + 279| linux_4_14 = throw "linux 4.14 was removed because it will reach its end of life within 23.11"; + + … while calling the 'throw' builtin + at /nix/store/dk2rpyb6ndvfbf19bkb2plcz5y3k8i5v-source/pkgs/top-level/linux-kernels.nix:278:17: + 277| } // lib.optionalAttrs config.allowAliases { + 278| linux_4_9 = throw "linux 4.9 was removed because it will reach its end of life within 22.11"; + | ^ + 279| linux_4_14 = throw "linux 4.14 was removed because it will reach its end of life within 23.11"; + + error: linux 4.9 was removed because it will reach its end of life within 22.11 +``` + +Now, the error will look like this: + +``` +let + inherit (pkgs.linuxKernel.kernels) linux_4_9; +in linux_4_9.meta.description +error: + … while evaluating 'linux_4_9' to select 'meta.description' on it + at «string»:3:4: + 2| inherit (pkgs.linuxKernel.kernels) linux_4_9; + 3| in linux_4_9.meta.description + | ^ + + … while evaluating the attribute 'linux_4_9' + at /nix/store/dk2rpyb6ndvfbf19bkb2plcz5y3k8i5v-source/pkgs/top-level/linux-kernels.nix:278:5: + 277| } // lib.optionalAttrs config.allowAliases { + 278| linux_4_9 = throw "linux 4.9 was removed because it will reach its end of life within 22.11"; + | ^ + 279| linux_4_14 = throw "linux 4.14 was removed because it will reach its end of life within 23.11"; + + … caused by explicit throw + at /nix/store/dk2rpyb6ndvfbf19bkb2plcz5y3k8i5v-source/pkgs/top-level/linux-kernels.nix:278:17: + 277| } // lib.optionalAttrs config.allowAliases { + 278| linux_4_9 = throw "linux 4.9 was removed because it will reach its end of life within 22.11"; + | ^ + 279| linux_4_14 = throw "linux 4.14 was removed because it will reach its end of life within 23.11"; + + error: linux 4.9 was removed because it will reach its end of life within 22.11 +``` + +Not only does the line of code that referenced the failing binding show up in the trace, it also tells you that it was specifically the `linux_4_9` part that failed. |