Fix Issue 13732 - non-member templates can use "template this"

[ntrel]

Error if a TemplateThisParameter is declared when there's no parent aggregate type ~~or template (it could be for a mixin)~~.

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Bugzilla references

Auto-close	Bugzilla	Severity	Description
✓	13732	normal	Regular templates can use "template this", and they allow any type to be passed

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#14434"

[dkorpel]

The grammar considers this a primary expression, so it should be a semantic error instead of parser error

[ntrel]

The grammar says this is just a token:

TemplateThisParameter: this TemplateTypeParameter

I'm not sure how to make it a semantic check. In templateparametersem.d there is Scope sc available, is that enough to determine if there's a parent type or template?

[dkorpel]

The grammar says this is just a token:

You're right. What I really meant to say was: the grammar allows it outside an aggregate, so the parser should not reject it or the grammar needs to be updated as well.

I'm not sure how to make it a semantic check. In templateparametersem.d there is Scope sc available, is that enough to determine if there's a parent type or template?

I'll take a look later.

[dkorpel]

In templateparametersem.d there is Scope sc available, is that enough to determine if there's a parent type or template?

I don't know what templateparametersem.d refers to, but I think you can do the check in dsymbolsem.d in either DsymbolSemanticVisitor.visit(TemplateDeclaration) or templateInstanceSemantic().

[RazvanN7]

@ntrel Just group the error messages in the test case and we can get this in.