Merge pull request #19203 from xedin/iterative-solver

[ConstraintSystem] Implementation of the iterative constraint solver

Author: xedin

lib/Sema/CMakeLists.txt

@@ -11,6 +11,7 @@ add_swift_library(swiftSema STATIC
   CSRanking.cpp
   CSSimplify.cpp
   CSSolver.cpp
+  CSStep.cpp
   CSFix.cpp
   CSDiagnostics.cpp
   CalleeCandidateInfo.cpp

lib/Sema/CSBindings.cpp

@@ -849,7 +849,7 @@ bool TypeVarBindingProducer::computeNext() {
   return true;
 }
 
-void TypeVariableBinding::attempt(ConstraintSystem &cs) const {
+bool TypeVariableBinding::attempt(ConstraintSystem &cs) const {
   auto type = Binding.BindingType;
   auto *locator = TypeVar->getImpl().getLocator();
 
@@ -878,4 +878,6 @@ void TypeVariableBinding::attempt(ConstraintSystem &cs) const {
   // If this was from a defaultable binding note that.
   if (Binding.isDefaultableBinding())
     cs.DefaultedConstraints.push_back(Binding.DefaultableBinding);
+
+  return !cs.failedConstraint && !cs.simplify();
 }