[Diagnostics] Add getRawType which allows to retrieve type associated with ASTNode

This is useful when diagnostic needs to check something about type
variables involved in a particular type e.g. whether type variable
has been defaulted.

Author: xedin

lib/Sema/CSDiagnostics.cpp

@@ -73,7 +73,11 @@ ASTNode FailureDiagnostic::getAnchor() const {
 }
 
 Type FailureDiagnostic::getType(ASTNode node, bool wantRValue) const {
-  return resolveType(S.getType(node), /*reconstituteSugar=*/false, wantRValue);
+  return resolveType(getRawType(node), /*reconstituteSugar=*/false, wantRValue);
+}
+
+Type FailureDiagnostic::getRawType(ASTNode node) const {
+  return S.getType(node);
 }
 
 template <typename... ArgTypes>
@@ -3420,7 +3424,8 @@ bool MissingMemberFailure::diagnoseInLiteralCollectionContext() const {
       return false;
   }
 
-  if (auto *defaultableVar = getType(parentExpr)->getAs<TypeVariableType>()) {
+  if (auto *defaultableVar =
+          getRawType(parentExpr)->getAs<TypeVariableType>()) {
     if (solution.DefaultedConstraints.count(
             defaultableVar->getImpl().getLocator()) != 0) {
       emitDiagnostic(diag::unresolved_member_no_inference, getName());

lib/Sema/CSDiagnostics.h

@@ -86,6 +86,10 @@ class FailureDiagnostic {
 
   Type getType(ASTNode node, bool wantRValue = true) const;
 
+  /// Get type associated with a given ASTNode without resolving it,
+  /// which means that returned type would have type variables.
+  Type getRawType(ASTNode node) const;
+
   /// Resolve type variables present in the raw type, if any.
   Type resolveType(Type rawType, bool reconstituteSugar = false,
                    bool wantRValue = true) const {
@@ -205,7 +209,7 @@ class FailureDiagnostic {
 
   bool isCollectionType(Type type) const {
     auto &cs = getConstraintSystem();
-    return bool(cs.isCollectionType(type));
+    return cs.isCollectionType(type);
   }
 
   bool isArrayType(Type type) const {