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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
No known key found for this signature in database
40 changed files with 653 additions and 545 deletions
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6
src/libutil/error.cc
View file

@ -335,7 +335,7 @@ std::ostream & showErrorInfo(std::ostream & out, const ErrorInfo & einfo, bool s
* try {
* e->eval(*this, env, v);
* if (v.type() != nAttrs)
* throwTypeError("expected a set but found %1%", v);
* error<TypeError>("expected a set but found %1%", v);
* } catch (Error & e) {
* e.addTrace(pos, errorCtx);
* throw;
@ -349,7 +349,7 @@ std::ostream & showErrorInfo(std::ostream & out, const ErrorInfo & einfo, bool s
* e->eval(*this, env, v);
* try {
* if (v.type() != nAttrs)
* throwTypeError("expected a set but found %1%", v);
* error<TypeError>("expected a set but found %1%", v);
* } catch (Error & e) {
* e.addTrace(pos, errorCtx);
* throw;
@ -411,7 +411,7 @@ std::ostream & showErrorInfo(std::ostream & out, const ErrorInfo & einfo, bool s
oss << einfo.msg << "\n";
printPosMaybe(oss, "", einfo.errPos);
printPosMaybe(oss, "", einfo.pos);
auto suggestions = einfo.suggestions.trim();
if (!suggestions.suggestions.empty()) {