vector (iterator,iterator) constructor doesn't deduce second arg

[kepler-5]

Bugzilla Link	47497
Version	unspecified
OS	All
CC	@kamleshbhalui,@mclow

Extended Description

The following code is rejected by libc++ because the second iterator argument to vector(iterator, iterator) is not deduced (https://godbolt.org/z/q8f9Y7):

#include <iterator>
#include <iostream>
#include <vector>

int main() {
    std::vector<int> v({}, std::istream_iterator<int>{});
}

The following code, however, is accepted (https://godbolt.org/z/nM4Yh4):

#include <iterator>
#include <iostream>
#include <vector>

int main() {
    std::vector<int> v;
    v.assign({}, std::istream_iterator<int>{});
}

I believe this to be a conformance bug.

I stumbled on this in my own code when I noticed that a typo in the following code was being accepted:

std::vector<int> v(other.cbegin(), other.end()); // note .end(), not .cend()

Since the second argument is not deduced, and the first argument is a const iterator, the second argument is implicitly converted to a const iterator. This is a symptom of the same issue, though I think this particular case could arguably be considered a conforming extension.

[kepler-5]

assigned to @kamleshbhalui

[kepler-5]

Rereading what I wrote, I think I was unclear, so I'd like to clarify. I believe the constructor call being rejected is the conformance bug. My mention of the .assign() call was just to show that similar arguments work when passed to a different entity. It is correct that the .assign() call is accepted as written.

[mclow]

The following code compiles w/o error:
std::vector v(std::istream_iterator{}, {});

[ldionne]

There was a review open here to fix this: https://reviews.llvm.org/D88727

However, this seems to have been fixed somewhere between Clang 15 and Clang 16: https://godbolt.org/z/5EWWconno. I'll make sure we have tests for this and I'll close.