[CS] Some more NFC changes

[hamishknight]

Split a couple more changes off #63963

[hamishknight]

@swift-ci please test

[AnthonyLatsis]

@hamishknight Why is SyntacticElementTarget a better name than SolutionApplicationTarget?

[xedin]

Mostly consistency, we have SyntacticElement{ConstraintGenerator, SolutionApplication} and it makes sense to move away from "solution application" because it's a solver target as well.

[AnthonyLatsis]

it makes sense to move away from "solution application" because it's a solver target as well

I still find SyntacticElementTarget far less idiomatic than the old name. I can’t imagine a lot of people getting even a rough idea of what this currency type exists for by reading the name alone. Both SyntacticElementConstraintGenerator and SyntacticElementSolutionApplication at least express an action by which the purpose of the class can be inferred. Also, isn’t SyntacticElementConstraintGenerator used for stuff inside closures only, unlike SyntacticElementTarget? What do you think of TypeCheckTarget or SyntacticElementTypeCheckTarget?

[xedin]

Also, isn’t SyntacticElementConstraintGenerator used for stuff inside closures only, unlike SyntacticElementTarget?

No, it's not only for closures, it could be used in any supported context which includes function/accessor declarations and if/switch expressions and soon string interpolations.

I personally don't like TypeCheck in the name because I think it's important to maintain distinction that this type is part of the constraint solver.

[AnthonyLatsis]

Maybe ConstraintSystemTarget then?

[xedin]

I suggested ConstraintSolverTarget before but it seems kind of tautological...

[AnthonyLatsis]

I suggested ConstraintSolverTarget before but it seems kind of tautological...

Totally works for me as well. There is no ConstraintSolver type but I don’t think that hurts clarity of purpose. I’m not sure I catch on to the tautology though: I see a clear separation between stuff that does the solving (action) and the thing + context data acted upon.