lix/tests/functional/lang/eval-fail-toJSON.err.exp
Rebecca Turner c6a89c1a16
libexpr: Support structured error classes
While preparing PRs like #9753, I've had to change error messages in
dozens of code paths. It would be nice if instead of

    EvalError("expected 'boolean' but found '%1%'", showType(v))

we could write

    TypeError(v, "boolean")

or similar. Then, changing the error message could be a mechanical
refactor with the compiler pointing out places the constructor needs to
be changed, rather than the error-prone process of grepping through the
codebase. Structured errors would also help prevent the "same" error
from having multiple slightly different messages, and could be a first
step towards error codes / an error index.

This PR reworks the exception infrastructure in `libexpr` to
support exception types with different constructor signatures than
`BaseError`. Actually refactoring the exceptions to use structured data
will come in a future PR (this one is big enough already, as it has to
touch every exception in `libexpr`).

The core design is in `eval-error.hh`. Generally, errors like this:

    state.error("'%s' is not a string", getAttrPathStr())
      .debugThrow<TypeError>()

are transformed like this:

    state.error<TypeError>("'%s' is not a string", getAttrPathStr())
      .debugThrow()

The type annotation has moved from `ErrorBuilder::debugThrow` to
`EvalState::error`.
2024-02-01 16:39:38 -08:00

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error:
… while calling the 'toJSON' builtin
at /pwd/lang/eval-fail-toJSON.nix:1:1:
1| builtins.toJSON {
| ^
2| a.b = [
… while evaluating attribute 'a'
at /pwd/lang/eval-fail-toJSON.nix:2:3:
1| builtins.toJSON {
2| a.b = [
| ^
3| true
… while evaluating attribute 'b'
at /pwd/lang/eval-fail-toJSON.nix:2:3:
1| builtins.toJSON {
2| a.b = [
| ^
3| true
… while evaluating list element at index 3
at /pwd/lang/eval-fail-toJSON.nix:2:3:
1| builtins.toJSON {
2| a.b = [
| ^
3| true
… while evaluating attribute 'c'
at /pwd/lang/eval-fail-toJSON.nix:7:7:
6| {
7| c.d = throw "hah no";
| ^
8| }
… while evaluating attribute 'd'
at /pwd/lang/eval-fail-toJSON.nix:7:7:
6| {
7| c.d = throw "hah no";
| ^
8| }
… while calling the 'throw' builtin
at /pwd/lang/eval-fail-toJSON.nix:7:13:
6| {
7| c.d = throw "hah no";
| ^
8| }
error: hah no