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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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68
src/libexpr/primops/fetchTree.cc
View file

@ -100,16 +100,14 @@ static void fetchTree(
if (auto aType = args[0]->attrs->get(state.sType)) {
if (type)
state.debugThrowLastTrace(EvalError({
.msg = hintfmt("unexpected attribute 'type'"),
.errPos = state.positions[pos]
}));
state.error<EvalError>(
"unexpected attribute 'type'"
).atPos(pos).debugThrow();
type = state.forceStringNoCtx(*aType->value, aType->pos, "while evaluating the `type` attribute passed to builtins.fetchTree");
} else if (!type)
state.debugThrowLastTrace(EvalError({
.msg = hintfmt("attribute 'type' is missing in call to 'fetchTree'"),
.errPos = state.positions[pos]
}));
state.error<EvalError>(
"attribute 'type' is missing in call to 'fetchTree'"
).atPos(pos).debugThrow();
attrs.emplace("type", type.value());
@ -132,8 +130,8 @@ static void fetchTree(
attrs.emplace(state.symbols[attr.name], printValueAsJSON(state, true, *attr.value, pos, context).dump());
}
else
state.debugThrowLastTrace(TypeError("fetchTree argument '%s' is %s while a string, Boolean or integer is expected",
state.symbols[attr.name], showType(*attr.value)));
state.error<TypeError>("fetchTree argument '%s' is %s while a string, Boolean or integer is expected",
state.symbols[attr.name], showType(*attr.value)).debugThrow();
}
if (params.isFetchGit && !attrs.contains("exportIgnore") && (!attrs.contains("submodules") || !*fetchers::maybeGetBoolAttr(attrs, "submodules"))) {
@ -142,10 +140,9 @@ static void fetchTree(
if (!params.allowNameArgument)
if (auto nameIter = attrs.find("name"); nameIter != attrs.end())
state.debugThrowLastTrace(EvalError({
.msg = hintfmt("attribute 'name' isn’t supported in call to 'fetchTree'"),
.errPos = state.positions[pos]
}));
state.error<EvalError>(
"attribute 'name' isn’t supported in call to 'fetchTree'"
).atPos(pos).debugThrow();
input = fetchers::Input::fromAttrs(std::move(attrs));
} else {
@ -163,10 +160,9 @@ static void fetchTree(
input = fetchers::Input::fromAttrs(std::move(attrs));
} else {
if (!experimentalFeatureSettings.isEnabled(Xp::Flakes))
state.debugThrowLastTrace(EvalError({
.msg = hintfmt("passing a string argument to 'fetchTree' requires the 'flakes' experimental feature"),
.errPos = state.positions[pos]
}));
state.error<EvalError>(
"passing a string argument to 'fetchTree' requires the 'flakes' experimental feature"
).atPos(pos).debugThrow();
input = fetchers::Input::fromURL(url);
}
}
@ -175,10 +171,14 @@ static void fetchTree(
input = lookupInRegistries(state.store, input).first;
if (evalSettings.pureEval && !input.isLocked()) {
auto fetcher = "fetchTree";
if (params.isFetchGit)
state.debugThrowLastTrace(EvalError("in pure evaluation mode, 'fetchGit' requires a locked input, at %s", state.positions[pos]));
else
state.debugThrowLastTrace(EvalError("in pure evaluation mode, 'fetchTree' requires a locked input, at %s", state.positions[pos]));
fetcher = "fetchGit";
state.error<EvalError>(
"in pure evaluation mode, %s requires a locked input",
fetcher
).atPos(pos).debugThrow();
}
state.checkURI(input.toURLString());
@ -432,17 +432,13 @@ static void fetch(EvalState & state, const PosIdx pos, Value * * args, Value & v
else if (n == "name")
name = state.forceStringNoCtx(*attr.value, attr.pos, "while evaluating the name of the content we should fetch");
else
state.debugThrowLastTrace(EvalError({
.msg = hintfmt("unsupported argument '%s' to '%s'", n, who),
.errPos = state.positions[attr.pos]
}));
state.error<EvalError>("unsupported argument '%s' to '%s'", n, who)
.atPos(pos).debugThrow();
}
if (!url)
state.debugThrowLastTrace(EvalError({
.msg = hintfmt("'url' argument required"),
.errPos = state.positions[pos]
}));
state.error<EvalError>(
"'url' argument required").atPos(pos).debugThrow();
} else
url = state.forceStringNoCtx(*args[0], pos, "while evaluating the url we should fetch");
@ -455,7 +451,7 @@ static void fetch(EvalState & state, const PosIdx pos, Value * * args, Value & v
name = baseNameOf(*url);
if (evalSettings.pureEval && !expectedHash)
state.debugThrowLastTrace(EvalError("in pure evaluation mode, '%s' requires a 'sha256' argument", who));
state.error<EvalError>("in pure evaluation mode, '%s' requires a 'sha256' argument", who).atPos(pos).debugThrow();
// early exit if pinned and already in the store
if (expectedHash && expectedHash->algo == HashAlgorithm::SHA256) {
@ -484,9 +480,15 @@ static void fetch(EvalState & state, const PosIdx pos, Value * * args, Value & v
auto hash = unpack
? state.store->queryPathInfo(storePath)->narHash
: hashFile(HashAlgorithm::SHA256, state.store->toRealPath(storePath));
if (hash != *expectedHash)
state.debugThrowLastTrace(EvalError((unsigned int) 102, "hash mismatch in file downloaded from '%s':\n specified: %s\n got: %s",
*url, expectedHash->to_string(HashFormat::Nix32, true), hash.to_string(HashFormat::Nix32, true)));
if (hash != *expectedHash) {
state.error<EvalError>(
"hash mismatch in file downloaded from '%s':\n specified: %s\n got: %s",
*url,
expectedHash->to_string(HashFormat::Nix32, true),
hash.to_string(HashFormat::Nix32, true)
).withExitStatus(102)
.debugThrow();
}
}
state.allowAndSetStorePathString(storePath, v);