forked from lix-project/lix
nix flake check: improve error message if overlay is not a lambda (#8582)
* nix flake check: improve error message if overlay is not a lambda Suppose you have an overlay like this { inputs = { /* ... */ }; outputs = { flake-utils, ... }: flake-utils.lib.eachDefaultSystem (system: { overlays.default = final: prev: { }; }); } then `nix flake check` (correctly) fails because `overlays` are supposed to have the structure `overlays.<name> = final: prev: exp`. However, the error-message is a little bit counter-intuitive: error: overlay does not take an argument named 'final' While one might guess where the error actually comes from because the trace above says `… while checking the overlay 'overlays.x86_64-linux'` this is still pretty confusing because it complains about an argument not being named `final` even though that's evidently the case. With this change, the error-message actually makes it clear what's wrong: [ma27@carsten:~/Projects/nix/tmp]$ nix flake check --extra-experimental-features 'nix-command flakes' path:$(pwd) error: … while checking flake output 'overlays' at /nix/store/clgblnxx003hyrq8qkz5ab6kgqkck6qc-source/flake.nix:4:5: 3| outputs = { ... }: { 4| overlays.x86_64-linux.snens = final: prev: { | ^ 5| kek = throw "snens"; … while checking the overlay 'overlays.x86_64-linux' at /nix/store/clgblnxx003hyrq8qkz5ab6kgqkck6qc-source/flake.nix:4:5: 3| outputs = { ... }: { 4| overlays.x86_64-linux.snens = final: prev: { | ^ 5| kek = throw "snens"; error: overlay is not a lambda, but a set instead
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@ -386,8 +386,10 @@ struct CmdFlakeCheck : FlakeCommand
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auto checkOverlay = [&](const std::string & attrPath, Value & v, const PosIdx pos) {
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try {
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state->forceValue(v, pos);
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if (!v.isLambda()
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|| v.lambda.fun->hasFormals()
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if (!v.isLambda()) {
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throw Error("overlay is not a function, but %s instead", showType(v));
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}
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if (v.lambda.fun->hasFormals()
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|| !argHasName(v.lambda.fun->arg, "final"))
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throw Error("overlay does not take an argument named 'final'");
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auto body = dynamic_cast<ExprLambda *>(v.lambda.fun->body);
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@ -25,6 +25,18 @@ EOF
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(! nix flake check $flakeDir)
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cat > $flakeDir/flake.nix <<EOF
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{
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outputs = { self, ... }: {
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overlays.x86_64-linux.foo = final: prev: {
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};
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};
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}
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EOF
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checkRes=$(nix flake check $flakeDir 2>&1 && fail "nix flake check --all-systems should have failed" || true)
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echo "$checkRes" | grepQuiet "error: overlay is not a function, but a set instead"
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cat > $flakeDir/flake.nix <<EOF
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{
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outputs = { self }: {
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