[FixCode] Add a fixit to help users migrate to Swift 3 name convention. (#4058)

* [FixCode] Add a fixit to help users migrate to Swift 3 name convention of enum cases. rdar://26887735

When users' referring to a enum case with a wrong name and we can find a correct enum case whose name
differs from the wrong name only in capitalization, we replace the wrong name with the correct one.

* Addressing Argyrios' code review comments. NFC

* [test] Update existing test.

* Grammatical polish suggested by @CodaFi.

Author: nkcsgexi

include/swift/AST/DiagnosticsSema.def

@@ -72,6 +72,9 @@ ERROR(could_not_find_value_member,none,
 ERROR(could_not_find_type_member,none,
       "type %0 has no member %1", (Type, DeclName))
 
+ERROR(could_not_find_enum_case,none,
+      "enum type %0 has no case %1; did you mean %2", (Type, DeclName, DeclName))
+
 NOTE(did_you_mean_raw_type,none,
      "did you mean to specify a raw type on the enum declaration?", ())
 

lib/Sema/CSDiag.cpp

@@ -2448,6 +2448,32 @@ diagnoseTypeMemberOnInstanceLookup(Type baseObjTy,
   return;
 }
 
+/// When a user refers a enum case with a wrong member name, we try to find a enum
+/// element whose name differs from the wrong name only in convention; meaning their
+/// lower case counterparts are identical.
+///   - DeclName is valid when such a correct case is found; invalid otherwise.
+static DeclName
+findCorrectEnumCaseName(MetatypeType *MetaTy, LookupResult &Result,
+                        DeclName memberName) {
+  if (!memberName.isSimpleName())
+    return DeclName();
+  if (!MetaTy->getInstanceType()->is<EnumType>())
+    return DeclName();
+  std::vector<DeclName> candidates;
+  for (auto &correction : Result) {
+    DeclName correctName = correction.Decl->getFullName();
+    if (!correctName.isSimpleName())
+      continue;
+    if (!isa<EnumElementDecl>(correction.Decl))
+      continue;
+    if (correctName.getBaseName().str().
+          compare_lower(memberName.getBaseName().str()) == 0)
+      candidates.push_back(correctName);
+  }
+  if (candidates.size() == 1)
+    return candidates.front();
+  return DeclName();
+}
 
 /// Given a result of name lookup that had no viable results, diagnose the
 /// unviable ones.
@@ -2473,10 +2499,17 @@ diagnoseUnviableLookupResults(MemberLookupResult &result, Type baseObjTy,
       diagnose(loc, diag::type_not_subscriptable, baseObjTy)
         .highlight(baseRange);
     } else if (auto MTT = baseObjTy->getAs<MetatypeType>()) {
+      tryTypoCorrection();
+      if (DeclName rightName = findCorrectEnumCaseName(MTT, correctionResults,
+                                                       memberName)) {
+        diagnose(loc, diag::could_not_find_enum_case, MTT->getInstanceType(),
+          memberName, rightName).fixItReplace(nameLoc.getBaseNameLoc(),
+                                              rightName.getBaseName().str());
+        return;
+      }
       diagnose(loc, diag::could_not_find_type_member,
                MTT->getInstanceType(), memberName)
         .highlight(baseRange).highlight(nameLoc.getSourceRange());
-      tryTypoCorrection();
     } else {
       diagnose(loc, diag::could_not_find_value_member,
                baseObjTy, memberName)

test/Constraints/diagnostics.swift

@@ -412,7 +412,7 @@ CurriedClass.m2(12)  // expected-error {{use of instance member 'm2' on type 'Cu
 
 // <rdar://problem/20491794> Error message does not tell me what the problem is
 enum Color {
-  case Red // expected-note 2 {{did you mean 'Red'?}}
+  case Red
   case Unknown(description: String)
 
   static func rainbow() -> Color {}
@@ -446,8 +446,8 @@ let _: Color = .frob(1, i)  // expected-error {{passing value of type 'Int' to a
 let _: Color = .frob(1, b: i)  // expected-error {{passing value of type 'Int' to an inout parameter requires explicit '&'}}
 let _: Color = .frob(1, &d) // expected-error {{cannot convert value of type 'Double' to expected argument type 'Int'}}
 let _: Color = .frob(1, b: &d) // expected-error {{cannot convert value of type 'Double' to expected argument type 'Int'}}
-var someColor : Color = .red // expected-error {{type 'Color' has no member 'red'}}
-someColor = .red  // expected-error {{type 'Color' has no member 'red'}}
+var someColor : Color = .red // expected-error {{enum type 'Color' has no case 'red'; did you mean 'Red'}}
+someColor = .red  // expected-error {{enum type 'Color' has no case 'red'; did you mean 'Red'}}
 
 func testTypeSugar(_ a : Int) {
   typealias Stride = Int

test/NameBinding/name_lookup.swift

@@ -522,7 +522,8 @@ class r16954496 {
 enum MyEnum {
   case one
   case two
-  
+  case oneTwoThree
+
   static let kMyConstant = "myConstant"
 }
 
@@ -535,3 +536,8 @@ default:
   break
 }
 
+func foo() {
+  _ = MyEnum.One // expected-error {{enum type 'MyEnum' has no case 'One'; did you mean 'one'}}{{14-17=one}}
+  _ = MyEnum.Two // expected-error {{enum type 'MyEnum' has no case 'Two'; did you mean 'two'}}{{14-17=two}}
+  _ = MyEnum.OneTwoThree // expected-error {{enum type 'MyEnum' has no case 'OneTwoThree'; did you mean 'oneTwoThree'}}{{14-25=oneTwoThree}}
+}