export trait must operate with declared package name

[vrurg]

A simple demonstration of the problem is the following code:

unit module Foo;

class B1::C is export { }
class B2::C is export { }

then:

⇒ raku -I. -MFoo -e ''
===SORRY!=== Error while compiling /Users/vrurg/src/Raku/experiments/export/Foo.pm6 (Foo)
A symbol 'C' has already been exported
at /Users/vrurg/src/Raku/experiments/export/Foo.pm6 (Foo):4

The problem is caused by export trait using ^shortname as export name of a symbol.

[vrurg]

My point of view is that the principle of least surprise dictate that the export name must be the same as user specifies it in the declaration. I.e. the example code should be equivalent to:

sub EXPORT {
    Map.new(
        'B1::C' => B1::C,
        'B2::C' => B2::C,
    )
}

Proposed solution

There is no clean way to get these names from the information available for the trait. It could of course guess the enclosing package name and subtract it from full symbol names, but that a bit cumbersome way.

I propose to take what <longname> catches in Grammar and set a dynamic var $*DECLARED_NAME to that value for is export trait. I tested this implementation path, it takes right about three lines of code.

[vrurg]

Proposed solution is provided by rakudo/rakudo#3388.

UPD I thought that long names are imported correctly. Unfortunately, I was wrong. More work would be required to merge symbols properly. Still, it doesn't change the point that the issue has to be taken care of.

[vrurg]

The PR is ready to merge. If there're no objections for the slightly adjusted is export semantics, then it is ready for merge.