[Issue 23300] std.array : array wrongly propagates scopeness of source

[d-bugmail at puremagic.com]

https://issues.dlang.org/show_bug.cgi?id=23300

Dennis <dkorpel at live.nl> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |dkorpel at live.nl

--- Comment #2 from Dennis <dkorpel at live.nl> ---
(In reply to RazvanN from comment #1)
> However, `array`'s
> parameter cannot be `scope` because it is copied into allocated memory.

The parameter to `array` should infer `scope` unless the range has non-scope
range primitives. It's not escaping the input array, it's dereferencing it and
copying the elements into a new GC array which is not scope. 

`scope` inference fails and it falls back on `return scope` inference from
`pure`. By making it impure, the newest DMD reports:

test_.d(12): Error: scope variable `r` assigned to non-scope parameter `r`
calling `array`
std/array.d(112):        which is not `scope` because of `__r353 = r`

https://github.com/dlang/phobos/blob/b578dfad94770574d7e522557a77276c35943daa/std/array.d#L112

So the underlying problem is that `scope` inference is defeated by `foreach` on
a struct with range primitives.

--