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libexpr: Support structured error classes

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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`.
This commit is contained in:
Rebecca Turner 2024-01-22 17:08:29 -08:00
parent c62c21e29a
commit c6a89c1a16
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40 changed files with 653 additions and 545 deletions
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10
src/libexpr/primops/fetchMercurial.cc
View file

@ -38,17 +38,11 @@ static void prim_fetchMercurial(EvalState & state, const PosIdx pos, Value * * a
else if (n == "name")
name = state.forceStringNoCtx(*attr.value, attr.pos, "while evaluating the `name` attribute passed to builtins.fetchMercurial");
else
throw EvalError({
.msg = hintfmt("unsupported argument '%s' to 'fetchMercurial'", state.symbols[attr.name]),
.errPos = state.positions[attr.pos]
});
state.error<EvalError>("unsupported argument '%s' to 'fetchMercurial'", state.symbols[attr.name]).atPos(attr.pos).debugThrow();
}
if (url.empty())
throw EvalError({
.msg = hintfmt("'url' argument required"),
.errPos = state.positions[pos]
});
state.error<EvalError>("'url' argument required").atPos(pos).debugThrow();
} else
url = state.coerceToString(pos, *args[0], context,