[WIP] Fix bugzilla 6082 - Constructors of templated types should be callabl…

[dkorpel]

…e via IFTI

https://wiki.dlang.org/DIP40

This first version works for simple cases of a struct with a regular constructor, allowing Tuple(1, 2, 3) or Pair(1, 2), but some other cases not yet, like new Pair!byte(1, 2). Specifically it fails with:

• Templated constructor functions
• new expressions
• Partial evaluation
• classes
• Structs without constructors

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Bugzilla references

Auto-close	Bugzilla	Severity	Description
✓	6082	enhancement	Constructors of templated types should be callable via IFTI

Testing this PR locally

If you don't have a local development environment setup, you can use Digger to test this PR:

dub run digger -- build "master + dmd#16910"

[dkorpel]

Interesting, there's now infinite recursion in std/container/array.d:599

this(T single) { __ctor!T(single); }

Edit: Calling a templated constructor would also trigger my new constructor rewrite, I added an extra check that it's actually an aggregate template.