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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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50
src/libexpr/primops/context.cc
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@ -98,30 +98,30 @@ static void prim_addDrvOutputDependencies(EvalState & state, const PosIdx pos, V
auto contextSize = context.size();
if (contextSize != 1) {
throw EvalError({
.msg = hintfmt("context of string '%s' must have exactly one element, but has %d", *s, contextSize),
.errPos = state.positions[pos]
});
state.error<EvalError>(
"context of string '%s' must have exactly one element, but has %d",
*s,
contextSize
).atPos(pos).debugThrow();
}
NixStringContext context2 {
(NixStringContextElem { std::visit(overloaded {
[&](const NixStringContextElem::Opaque & c) -> NixStringContextElem::DrvDeep {
if (!c.path.isDerivation()) {
throw EvalError({
.msg = hintfmt("path '%s' is not a derivation",
state.store->printStorePath(c.path)),
.errPos = state.positions[pos],
});
state.error<EvalError>(
"path '%s' is not a derivation",
state.store->printStorePath(c.path)
).atPos(pos).debugThrow();
}
return NixStringContextElem::DrvDeep {
.drvPath = c.path,
};
},
[&](const NixStringContextElem::Built & c) -> NixStringContextElem::DrvDeep {
throw EvalError({
.msg = hintfmt("`addDrvOutputDependencies` can only act on derivations, not on a derivation output such as '%1%'", c.output),
.errPos = state.positions[pos],
});
state.error<EvalError>(
"`addDrvOutputDependencies` can only act on derivations, not on a derivation output such as '%1%'",
c.output
).atPos(pos).debugThrow();
},
[&](const NixStringContextElem::DrvDeep & c) -> NixStringContextElem::DrvDeep {
/* Reuse original item because we want this to be idempotent. */
@ -261,10 +261,10 @@ static void prim_appendContext(EvalState & state, const PosIdx pos, Value * * ar
for (auto & i : *args[1]->attrs) {
const auto & name = state.symbols[i.name];
if (!state.store->isStorePath(name))
throw EvalError({
.msg = hintfmt("context key '%s' is not a store path", name),
.errPos = state.positions[i.pos]
});
state.error<EvalError>(
"context key '%s' is not a store path",
name
).atPos(i.pos).debugThrow();
auto namePath = state.store->parseStorePath(name);
if (!settings.readOnlyMode)
state.store->ensurePath(namePath);
@ -281,10 +281,10 @@ static void prim_appendContext(EvalState & state, const PosIdx pos, Value * * ar
if (iter != i.value->attrs->end()) {
if (state.forceBool(*iter->value, iter->pos, "while evaluating the `allOutputs` attribute of a string context")) {
if (!isDerivation(name)) {
throw EvalError({
.msg = hintfmt("tried to add all-outputs context of %s, which is not a derivation, to a string", name),
.errPos = state.positions[i.pos]
});
state.error<EvalError>(
"tried to add all-outputs context of %s, which is not a derivation, to a string",
name
).atPos(i.pos).debugThrow();
}
context.emplace(NixStringContextElem::DrvDeep {
.drvPath = namePath,
@ -296,10 +296,10 @@ static void prim_appendContext(EvalState & state, const PosIdx pos, Value * * ar
if (iter != i.value->attrs->end()) {
state.forceList(*iter->value, iter->pos, "while evaluating the `outputs` attribute of a string context");
if (iter->value->listSize() && !isDerivation(name)) {
throw EvalError({
.msg = hintfmt("tried to add derivation output context of %s, which is not a derivation, to a string", name),
.errPos = state.positions[i.pos]
});
state.error<EvalError>(
"tried to add derivation output context of %s, which is not a derivation, to a string",
name
).atPos(i.pos).debugThrow();
}
for (auto elem : iter->value->listItems()) {
auto outputName = state.forceStringNoCtx(*elem, iter->pos, "while evaluating an output name within a string context");