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Never update values after setting the type

Thunks are now overwritten by a helper function
`Value::finishValue(newType, payload)` (where `payload` is the
original anonymous union inside `Value`). This helps to ensure we
never update a value elsewhere, since that would be incompatible with
parallel evaluation (i.e. after a value has transitioned from being a
thunk to being a non-thunk, it should be immutable).

There were two places where this happened: `Value::mkString()` and
`ExprAttrs::eval()`.

This PR also adds a bunch of accessor functions for value contents,
like `Value::integer()` to access the integer field in the union.
This commit is contained in:
Eelco Dolstra 2024-03-25 18:20:18 +01:00
parent 6d90287f5a
commit 8c0590fa32
35 changed files with 530 additions and 556 deletions

View file

@ -121,7 +121,7 @@ static void prim_fetchClosure(EvalState & state, const PosIdx pos, Value * * arg
std::optional<StorePathOrGap> toPath;
std::optional<bool> inputAddressedMaybe;
for (auto & attr : *args[0]->attrs) {
for (auto & attr : *args[0]->attrs()) {
const auto & attrName = state.symbols[attr.name];
auto attrHint = [&]() -> std::string {
return "while evaluating the '" + attrName + "' attribute passed to builtins.fetchClosure";