[Constraint system] Sink optional “some” pattern handling into constraint gen

Author: DougGregor

lib/Sema/CSGen.cpp

@@ -3903,6 +3903,18 @@ bool ConstraintSystem::generateConstraints(
     shrink(expr);
     target.setExpr(expr);
 
+    // If the target requires an optional of some type, form a new appropriate
+    // type variable and update the target's type with an optional of that
+    // type variable.
+    if (target.isOptionalSomePatternInit()) {
+      assert(!target.getExprContextualType() &&
+             "some pattern cannot have contextual type pre-configured");
+      auto *convertTypeLocator =
+          getConstraintLocator(expr, LocatorPathElt::ContextualType());
+      Type var = createTypeVariable(convertTypeLocator, TVO_CanBindToNoEscape);
+      target.setExprConversionType(TypeChecker::getOptionalType(expr->getLoc(), var));
+    }
+
     // Generate constraints for the main system.
     expr = generateConstraints(expr, target.getDeclContext());
     if (!expr)

lib/Sema/TypeCheckConstraints.cpp

@@ -2085,18 +2085,6 @@ TypeChecker::typeCheckExpression(
   if (options.contains(TypeCheckExprFlags::AllowUnresolvedTypeVariables))
     allowFreeTypeVariables = FreeTypeVariableBinding::UnresolvedType;
 
-  // If the target requires an optional of some type, form a new appropriate
-  // type variable and update the target's type with an optional of that
-  // type variable.
-  if (target.isOptionalSomePatternInit()) {
-    assert(!target.getExprContextualType() &&
-           "some pattern cannot have contextual type pre-configured");
-    auto *convertTypeLocator =
-        cs.getConstraintLocator(expr, LocatorPathElt::ContextualType());
-    Type var = cs.createTypeVariable(convertTypeLocator, TVO_CanBindToNoEscape);
-    target.setExprConversionType(getOptionalType(expr->getLoc(), var));
-  }
-
   // Attempt to solve the constraint system.
   auto viable = cs.solve(target, listener, allowFreeTypeVariables);
   if (!viable) {