forked from lix-project/lix
65 lines
3 KiB
Markdown
65 lines
3 KiB
Markdown
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---
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synopsis: "Trace when the `foo` part of a `foo.bar.baz` expression errors"
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cls: 1505
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credits: Qyriad
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category: Improvements
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---
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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.
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The previous error looks like this:
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```
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let
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inherit (pkgs.linuxKernel.kernels) linux_4_9;
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in linux_4_9.meta.description
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error:
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… while evaluating the attribute 'linux_4_9'
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at /nix/store/dk2rpyb6ndvfbf19bkb2plcz5y3k8i5v-source/pkgs/top-level/linux-kernels.nix:278:5:
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277| } // lib.optionalAttrs config.allowAliases {
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278| linux_4_9 = throw "linux 4.9 was removed because it will reach its end of life within 22.11";
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| ^
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279| linux_4_14 = throw "linux 4.14 was removed because it will reach its end of life within 23.11";
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… while calling the 'throw' builtin
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at /nix/store/dk2rpyb6ndvfbf19bkb2plcz5y3k8i5v-source/pkgs/top-level/linux-kernels.nix:278:17:
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277| } // lib.optionalAttrs config.allowAliases {
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278| linux_4_9 = throw "linux 4.9 was removed because it will reach its end of life within 22.11";
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| ^
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279| linux_4_14 = throw "linux 4.14 was removed because it will reach its end of life within 23.11";
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error: linux 4.9 was removed because it will reach its end of life within 22.11
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```
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Now, the error will look like this:
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```
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let
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inherit (pkgs.linuxKernel.kernels) linux_4_9;
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in linux_4_9.meta.description
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error:
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… while evaluating 'linux_4_9' to select 'meta.description' on it
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at «string»:3:4:
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2| inherit (pkgs.linuxKernel.kernels) linux_4_9;
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3| in linux_4_9.meta.description
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| ^
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… while evaluating the attribute 'linux_4_9'
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at /nix/store/dk2rpyb6ndvfbf19bkb2plcz5y3k8i5v-source/pkgs/top-level/linux-kernels.nix:278:5:
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277| } // lib.optionalAttrs config.allowAliases {
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278| linux_4_9 = throw "linux 4.9 was removed because it will reach its end of life within 22.11";
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| ^
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279| linux_4_14 = throw "linux 4.14 was removed because it will reach its end of life within 23.11";
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… caused by explicit throw
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at /nix/store/dk2rpyb6ndvfbf19bkb2plcz5y3k8i5v-source/pkgs/top-level/linux-kernels.nix:278:17:
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277| } // lib.optionalAttrs config.allowAliases {
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278| linux_4_9 = throw "linux 4.9 was removed because it will reach its end of life within 22.11";
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| ^
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279| linux_4_14 = throw "linux 4.14 was removed because it will reach its end of life within 23.11";
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error: linux 4.9 was removed because it will reach its end of life within 22.11
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```
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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.
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