bogus "cannot implicitly convert expression" error when using vector notation to copy from immutable to mutable

[dlangBugzillaToGithub]

ag0aep6g reported this on 2016-04-20T19:27:35Z

Transferred from https://issues.dlang.org/show_bug.cgi?id=15942

Description

This is rejected, but should be accepted:
----
void main()
{
    string s = [1, 2, 3];
    auto v = new void[3];
    v[] = s[]; /* Error: cannot implicitly convert expression (s[]) of type string to void[] */
}
----

It's accepted with an intermediate step:
----
void main()
{
    string s = [1, 2, 3];
    auto v = new void[3];
    immutable(void)[] intermediate = s;
    v[] = intermediate[];
}
----