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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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4
src/libstore/build/entry-points.cc
View file

@ -33,7 +33,7 @@ void Store::buildPaths(const std::vector<DerivedPath> & reqs, BuildMode buildMod
}
if (failed.size() == 1 && ex) {
ex->status = worker.failingExitStatus();
ex->withExitStatus(worker.failingExitStatus());
throw std::move(*ex);
} else if (!failed.empty()) {
if (ex) logError(ex->info());
@ -104,7 +104,7 @@ void Store::ensurePath(const StorePath & path)
if (goal->exitCode != Goal::ecSuccess) {
if (goal->ex) {
goal->ex->status = worker.failingExitStatus();
goal->ex->withExitStatus(worker.failingExitStatus());
throw std::move(*goal->ex);
} else
throw Error(worker.failingExitStatus(), "path '%s' does not exist and cannot be created", printStorePath(path));