[CSBindings] Prefer key path type over a disjunction if key path is resolved

If key path type has bindings and is no longer delayed it means
that it's fully resolved and ready to be bound (even though value
type might not be resolved yet).

Author: xedin

lib/Sema/CSBindings.cpp

@@ -1257,6 +1257,11 @@ bool BindingSet::favoredOverDisjunction(Constraint *disjunction) const {
   if (Bindings.empty())
     return false;
 
+  // Always prefer key path type if it has bindings and is not delayed
+  // because that means that it was possible to infer its capability.
+  if (TypeVar->getImpl().isKeyPathType())
+    return true;
+
   return !involvesTypeVariables();
 }
 

validation-test/Sema/type_checker_perf/fast/rdar118993030.swift.gyb

@@ -0,0 +1,14 @@
+// RUN: %scale-test --begin 2 --end 10 --step 1 --select NumConstraintScopes %s
+// REQUIRES: asserts,no_asan
+
+struct Test {
+  var id: String
+}
+
+func test(data: [Test]) -> Set<String> {
+  Set(data.map(\.id) +
+%for i in range(0, N):
+      data.map(\.id) +
+%end
+    data.map(\.id))
+}