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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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16
src/libexpr/flake/flake.cc
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@ -147,8 +147,8 @@ static FlakeInput parseFlakeInput(EvalState & state,
NixStringContext emptyContext = {};
attrs.emplace(state.symbols[attr.name], printValueAsJSON(state, true, *attr.value, pos, emptyContext).dump());
} else
throw TypeError("flake input attribute '%s' is %s while a string, Boolean, or integer is expected",
state.symbols[attr.name], showType(*attr.value));
state.error<TypeError>("flake input attribute '%s' is %s while a string, Boolean, or integer is expected",
state.symbols[attr.name], showType(*attr.value)).debugThrow();
}
#pragma GCC diagnostic pop
}
@ -295,15 +295,15 @@ static Flake getFlake(
std::vector<std::string> ss;
for (auto elem : setting.value->listItems()) {
if (elem->type() != nString)
throw TypeError("list element in flake configuration setting '%s' is %s while a string is expected",
state.symbols[setting.name], showType(*setting.value));
state.error<TypeError>("list element in flake configuration setting '%s' is %s while a string is expected",
state.symbols[setting.name], showType(*setting.value)).debugThrow();
ss.emplace_back(state.forceStringNoCtx(*elem, setting.pos, ""));
}
flake.config.settings.emplace(state.symbols[setting.name], ss);
}
else
throw TypeError("flake configuration setting '%s' is %s",
state.symbols[setting.name], showType(*setting.value));
state.error<TypeError>("flake configuration setting '%s' is %s",
state.symbols[setting.name], showType(*setting.value)).debugThrow();
}
}
@ -865,11 +865,11 @@ static void prim_flakeRefToString(
attrs.emplace(state.symbols[attr.name],
std::string(attr.value->string_view()));
} else {
state.error(
state.error<EvalError>(
"flake reference attribute sets may only contain integers, Booleans, "
"and strings, but attribute '%s' is %s",
state.symbols[attr.name],
showType(*attr.value)).debugThrow<EvalError>();
showType(*attr.value)).debugThrow();
}
}
auto flakeRef = FlakeRef::fromAttrs(attrs);