[AST] Introduce TypedPattern::createPropagated

Author: hamishknight

include/swift/AST/Pattern.h

@@ -447,6 +447,13 @@ class TypedPattern : public Pattern {
     return tp;
   }
 
+  static TypedPattern *createPropagated(ASTContext &ctx, Pattern *pattern,
+                                        TypeRepr *typeRepr) {
+    auto *TP = new (ctx) TypedPattern(pattern, typeRepr);
+    TP->setPropagatedType();
+    return TP;
+  }
+
   /// True if the type in this \c TypedPattern was propagated from a different
   /// \c TypedPattern.
   ///

lib/Parse/ParseDecl.cpp

@@ -8536,9 +8536,8 @@ Parser::parseDeclVar(ParseDeclOptions Flags,
             Status.setIsParseError();
           }
 
-          TypedPattern *NewTP = new (Context) TypedPattern(PrevPat,
-                                                           TP->getTypeRepr());
-          NewTP->setPropagatedType();
+          auto *NewTP = TypedPattern::createPropagated(Context, PrevPat,
+                                                       TP->getTypeRepr());
           PBDEntries[i-1].setPattern(NewTP);
         }
       }