[Sema] FixIt for override func that should be override var and vice-versa

Resolves swiftlang#57499

This adds `override_property_not_method` and `override_method_not_property` notes by performing
a member lookup for the respective diagnostics.

Author: Rajveer100

include/swift/AST/DiagnosticsSema.def

@@ -3458,8 +3458,12 @@ ERROR(override_of_non_open,none,
 
 ERROR(method_does_not_override,none,
       "method does not override any method from its %select{parent protocol|superclass}0", (bool))
+NOTE(override_property_not_method,none,
+      "did you mean to override the property %0", (Identifier))
 ERROR(property_does_not_override,none,
       "property does not override any property from its %select{parent protocol|superclass}0", (bool))
+NOTE(override_method_not_property,none,
+      "did you mean to override the method %0", (Identifier))
 ERROR(subscript_does_not_override,none,
       "subscript does not override any subscript from its %select{parent protocol|superclass}0", (bool))
 ERROR(initializer_does_not_override,none,

lib/Sema/TypeCheckDeclPrimary.cpp

@@ -2671,6 +2671,30 @@ class DeclChecker : public DeclVisitor<DeclChecker> {
           } else {
             VD->diagnose(diag::property_does_not_override, isClassContext)
                 .highlight(OA->getLocation());
+
+            auto declName = VD->getBaseName();
+            auto declType = VD->getInterfaceType()->getRValueType();
+
+            auto inherited = DC->getSelfClassDecl()->getInherited();
+            if (!inherited.empty()) {
+              auto superClassType = inherited.getResolvedType(0);
+              auto lookupResult = TypeChecker::lookupMember(DC, superClassType,
+                                                            DeclNameRef(declName));
+              for (auto &candidate : lookupResult) {
+                auto *valueDecl = candidate.getValueDecl();
+                if (auto funcDecl = dyn_cast<FuncDecl>(valueDecl)) {
+                  if (funcDecl->getBaseName() == declName && 
+                      funcDecl->getParameters()->size() == 0) {
+                    std::string funcDeclTypeStr = " -> " +
+                                                  declType.getString();
+                    VD->diagnose(diag::override_method_not_property,
+                                 funcDecl->getBaseName().getIdentifier())
+                    .highlight(OA->getLocation())
+                    .fixItReplace(getFixItLocForVarToLet(VD), "func");
+                  }
+                }
+              }
+            }
           }
           OA->setInvalid();
         }
@@ -3717,6 +3741,34 @@ class DeclChecker : public DeclVisitor<DeclChecker> {
           } else {
             FD->diagnose(diag::method_does_not_override, isClassContext)
                 .highlight(OA->getLocation());
+
+            if (FD->getParameters()->size() == 0) {
+              auto declName = FD->getBaseName();
+              auto declRetType = FD->getResultInterfaceType()->getRValueType();
+
+              auto inherited = DC->getSelfClassDecl()->getInherited();
+              if (!inherited.empty()) {
+                auto superClassType = inherited.getResolvedType(0);
+                auto lookupResult = TypeChecker::lookupMember(DC,
+                                                              superClassType,
+                                                              DeclNameRef(declName));
+                for (auto &candidate : lookupResult) {
+                  auto *valueDecl = candidate.getValueDecl();
+                  if (auto vardecl = dyn_cast<VarDecl>(valueDecl)) {
+                    if (vardecl->getBaseName() == declName) {
+                      std::string varDeclTypeStr = ": " + declRetType.getString();
+                      FD->diagnose(diag::override_property_not_method,
+                                   vardecl->getBaseName().getIdentifier())
+                      .highlight(OA->getLocation())
+                      .fixItReplace(FD->getFuncLoc(), "var")
+                      .fixItReplaceChars(FD->getParameters()->getLParenLoc(),
+                                         FD->getBody()->getLBraceLoc().getAdvancedLoc(-1),
+                                         varDeclTypeStr);
+                    }
+                  }
+                }
+              }
+            }
           }
           OA->setInvalid();
         }

test/decl/inherit/override.swift

@@ -86,3 +86,20 @@ class ObjCSub : ObjCSuper {
 
   @objc(method3:withInt:) func method3(_ x: Sub, with y: Int) { } // expected-error{{method3(_:with:)' with Objective-C selector 'method3:withInt:' conflicts with method 'method3(_:withInt:)' from superclass 'ObjCSuper' with the same Objective-C selector}}
 }
+
+class C {
+  var v1: Bool {
+    return false
+  }
+
+  func f1() -> Int { }
+}
+
+class D: C {
+  override func v1() -> Bool { } // expected-error{{method does not override any method from its superclass}}
+  // expected-note@-1{{did you mean to override the property 'v1'}} {{12-16=var}} {{19-29=: Bool}}
+
+  override var f1: Int { // expected-error{{property does not override any property from its superclass}}
+    return 0 // expected-note@-1{{did you mean to override the method 'f1'}} {{12-15=func}}
+  }
+}