trace when the foo part of foo.bar.baz errors

Turns errors like:

let
  errpkg = throw "invalid foobar";
in errpkg.meta

error:
       … while calling the 'throw' builtin
         at «string»:2:12:
            1| let
            2|   errpkg = throw "invalid foobar";
             |            ^
            3| in errpkg.meta

       error: invalid foobar

into errors like:

let
  errpkg = throw "invalid foobar";
in errpkg.meta

error:
       … while evaluating 'errpkg' to select 'meta' on it
         at «string»:3:4:
            2|   errpkg = throw "invalid foobar";
            3| in errpkg.meta
             |    ^

       … while calling the 'throw' builtin
         at «string»:2:12:
            1| let
            2|   errpkg = throw "invalid foobar";
             |            ^
            3| in errpkg.meta

       error: invalid foobar

For the low price of one try/catch, you too can have the incorrect line
of code actually show up in the trace!

Change-Id: If8d6200ec1567706669d405c34adcd7e2d2cd29d
This commit is contained in:
Qyriad 2024-06-22 21:22:29 -06:00
parent 139cfdfb53
commit d00edfb28d
3 changed files with 84 additions and 1 deletions

View file

@ -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.

View file

@ -1432,7 +1432,20 @@ void ExprSelect::eval(EvalState & state, Env & env, Value & v)
Value * vCurrent = &vFirst;
// Position for the current attrset Value in this select chain.
PosIdx posCurrent;
try {
e->eval(state, env, vFirst);
} catch (Error & e) {
assert(this->e != nullptr);
state.addErrorTrace(
e,
getPos(),
"while evaluating '%s' to select '%s' on it",
ExprPrinter(state, *this->e),
showAttrPath(state.symbols, this->attrPath)
);
throw;
}
try {
auto dts = state.debugRepl

View file

@ -1,4 +1,10 @@
error:
… while evaluating 'a' to select 'foo' on it
at /pwd/lang/eval-fail-recursion.nix:1:21:
1| let a = {} // a; in a.foo
| ^
2|
… in the right operand of the update (//) operator
at /pwd/lang/eval-fail-recursion.nix:1:12:
1| let a = {} // a; in a.foo