[ConstraintSystem] NFC: Extract opening of individual generic parameters into a method

Author: xedin

include/swift/Sema/ConstraintSystem.h

@@ -4173,6 +4173,13 @@ class ConstraintSystem {
                              OpenedTypeMap &replacements,
                              ConstraintLocatorBuilder locator);
 
+  /// Open a generic parameter into a type variable and record
+  /// it in \c replacements.
+  TypeVariableType *openGenericParameter(DeclContext *outerDC,
+                                         GenericTypeParamType *parameter,
+                                         OpenedTypeMap &replacements,
+                                         ConstraintLocatorBuilder locator);
+
   /// Given generic signature open its generic requirements,
   /// using substitution function, and record them in the
   /// constraint system for further processing.

lib/Sema/ConstraintSystem.cpp

@@ -1591,16 +1591,7 @@ void ConstraintSystem::openGenericParameters(DeclContext *outerDC,
 
   // Create the type variables for the generic parameters.
   for (auto gp : sig.getGenericParams()) {
-    auto *paramLocator = getConstraintLocator(
-        locator.withPathElement(LocatorPathElt::GenericParameter(gp)));
-
-    auto typeVar = createTypeVariable(paramLocator, TVO_PrefersSubtypeBinding |
-                                                    TVO_CanBindToHole);
-    auto result = replacements.insert(std::make_pair(
-        cast<GenericTypeParamType>(gp->getCanonicalType()), typeVar));
-
-    assert(result.second);
-    (void)result;
+    (void)openGenericParameter(outerDC, gp, replacements, locator);
   }
 
   auto *baseLocator = getConstraintLocator(
@@ -1609,6 +1600,23 @@ void ConstraintSystem::openGenericParameters(DeclContext *outerDC,
   bindArchetypesFromContext(*this, outerDC, baseLocator, replacements);
 }
 
+TypeVariableType *ConstraintSystem::openGenericParameter(
+    DeclContext *outerDC, GenericTypeParamType *parameter,
+    OpenedTypeMap &replacements, ConstraintLocatorBuilder locator) {
+  auto *paramLocator = getConstraintLocator(
+      locator.withPathElement(LocatorPathElt::GenericParameter(parameter)));
+
+  auto typeVar = createTypeVariable(paramLocator, TVO_PrefersSubtypeBinding |
+                                                      TVO_CanBindToHole);
+  auto result = replacements.insert(std::make_pair(
+      cast<GenericTypeParamType>(parameter->getCanonicalType()), typeVar));
+
+  assert(result.second);
+  (void)result;
+
+  return typeVar;
+}
+
 void ConstraintSystem::openGenericRequirements(
     DeclContext *outerDC, GenericSignature signature,
     bool skipProtocolSelfConstraint, ConstraintLocatorBuilder locator,