Merge pull request #40660 from etcwilde/ewilde/abstract-closures-are-…

…alright-now

Diagnose unavailable closures without types

lib/Sema/TypeCheckAvailability.cpp

@@ -3586,34 +3586,6 @@ bool ExprAvailabilityWalker::diagnoseDeclRefAvailability(
 static bool
 diagnoseDeclAsyncAvailability(const ValueDecl *D, SourceRange R,
  const Expr *call, const ExportContext &Where) {
- // FIXME: I don't think this is right, but I don't understand the issue well
- // enough to fix it properly. If the decl context is an abstract
- // closure, we need it to have a type assigned to it before we can
- // determine whether it is an asynchronous context. It will crash
- // when we go to check without one. In TypeChecker::typeCheckExpression
- // (TypeCheckConstraints.cpp:403), we apply a solution before calling
- // `performSyntacticDiagnosticsForTarget`, which eventually calls
- // down to this function. Under most circumstances, the context that
- // we're in is typechecked at that point and has a type assigned.
- // When working with specific result builders, the solution applied
- // results in an expression with an unset type. In these cases, the
- // application makes its way into `ConstraintSystem::applySolution` for
- // closures (CSClosure.cpp:1356). The type is computed, but is
- // squirreled away in the constrain system to be applied once the
- // checks (including this one) approve of the decls within the decl
- // context before applying the type to the expression. It might be
- // possible to drive the constraint solver through the availability
- // checker and into us so that we can ask for it, but that feels wrong
- // too.
- // This behavior is demonstrated by the first use of the `tuplify`
- // function in `testExistingPatternsInCaseStatements` in
- // `test/Constraints/result_builder.swift`.
- const AbstractClosureExpr *declCtxAsExpr =
- dyn_cast<AbstractClosureExpr>(Where.getDeclContext());
- if (declCtxAsExpr && !declCtxAsExpr->getType()) {
- return false;
- }
-
  // If we are in a synchronous context, don't check it
  if (!Where.getDeclContext()->isAsyncContext())
  return false;