[Issue 12359] implicit overload merging with selective imports should be removed

[d-bugmail at puremagic.com]

https://d.puremagic.com/issues/show_bug.cgi?id=12359



--- Comment #10 from Kenji Hara <k.hara.pg at gmail.com> 2014-04-06 21:40:13 PDT ---
The negative effect of the implicit alias is that it makes selective imports
and basic imports unexchangeable. For example:

module a;
auto foo(int[] ) { return 2; }

module b;
import a;  // [A]
auto foo(long[] ) { return 1; }
void main()
{
    assert(foo([1,2]) == 1);
}

At the line [A], the basic import makes b.foo visible, but it is hidden by
b.foo. Therefore foo([1,2]) in main will call b.foo properly.

Next, what's will occur if you replace `import a;` to `import a : foo`?

import a : foo;  // [A2]
auto foo(long[] ) { return 1; }

The selected a.foo is *implicitly* added in the overload set of b.foo, then
foo([1,2]) will match a.foo(int[] ) more better than b.foo(long[] ), and the
assertion in main will fail in runtime.

I think this is much non-intuitive behavior. No one would expect the silent
code breaking in module b.

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