`exec::finally()` shouldn't include `std::exception_ptr` in the error types if neither the source or final senders include that error type
Nobody has claimed this yet.
Assessment
- Difficulty
- 4/5
- Estimated time
- 3-5 days
- Newbie friendliness
- 35/100
Research direction
Start with the reproducer linked in the issue and inspect exec/finally.hpp together with the sender and error-type handling in stdexec/execution.hpp. Trace why let_error is instantiated with std::exception_ptr when neither sender declares it. Done means the example compiles without that extra error type while preserving finally behavior.
Written by the indexing model from the issue text.
Description
I would have expected the following code to compile, but it fails because let_error tries to instantiate a call to the lambda with an argument of type std::exception_ptr.
https://godbolt.org/z/PK8YjohW8
#include <stdexec/execution.hpp>
#include <exec/finally.hpp>
#include <cstdio>
struct X {
X() : value(0) { std::puts("X::X()"); }
X(X&& o) noexcept : value(o.value) { std::puts("X::X(X&&)"); }
X(const X& o) noexcept : value(o.value) { std::puts("X::X(const X&)"); }
~X() { std::puts("X::~X()"); value = -1; }
int value;
};
int main() {
auto result = stdexec::sync_wait(
stdexec::let_error(
exec::finally(
stdexec::just_error(X{}),
stdexec::just()),
[](const X& x) noexcept {
std::printf("caught X(value=%i)\n", x.value);
return stdexec::just();
}));
}
I suspect that this is because we don't know ahead of time whether connect() is potentially throwing.
We could potentially work around this by instead connecting the final-sender at connect-time of the finally sender. This way, we know that we will be able start the final-operation when the input operation completes regardless of whether the connect() method is throwing or not.
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- C++
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