[REG-master] Fix Issue 14817 - std.algorithm.copy/std.file.copy conflict

[Poita]

#2799 introduced a regression, which prevented module that imported both std.algorithm and std.file to use unqualified calls to copy(string, string). The regression was caused by the removal of template constraints, which were preventing the std.algorithm copy from being considered for overload resolution.

std.algorithm.copy has two paths: an path for array copies, and a path for all other copies. Previously they were forked using static if inside function. Now the decision is made using template constraints.

[Poita]

I recommend viewing diff with whitespace ignored: https://github.com/D-Programming-Language/phobos/pull/3509/files?w=1

[quickfur]

Makes sense to me. Though I can't say I'm pleased with the gratuitous naming conflict between std.file.copy and std.algorithm.copy. But that's outside the scope of this PR.

[WalterBright]

You can still make it one function. Use a constraint that ORs the constraints for the two overloads.

Also needs a unit test to verify the fix.

[MartinNowak]

AFAIK this should go into stable b/c it fixes a regression.
My mistake.

[DmitryOlshansky]

@Poita - add a unittest for the fix and it should be good to go.

Personally I think splitting the function makes it simpler then following all of static if/else chains.

[WalterBright]

splitting the function makes it simpler then following all of static if/else chains.

Harder for the user reading the documentation, though.

[DmitryOlshansky]

Ping @Poita

[DmitryOlshansky]

See #3649