[Type checker] Warn about classes conforming to AnyObject in Swift 3 mode.

Swift 3 allowed a class to explicitly conform to AnyObject, although
it was meaningless. Recent AnyObject-related changes started rejecting
such conformances as ill-formed; allow them with a warning + Fix-It in
Swift 3 compatibility mode.

Author: DougGregor

include/swift/AST/DiagnosticsSema.def

@@ -1909,7 +1909,8 @@ ERROR(inheritance_from_cf_class,none,
 ERROR(inheritance_from_objc_runtime_visible_class,none,
       "cannot inherit from class %0 because it is only visible via the "
       "Objective-C runtime", (Identifier))
-
+WARNING(class_inherits_anyobject,none,
+        "conformance of class %0 to 'AnyObject' is redundant", (Type))
 
 // Enums
 ERROR(enum_case_access,none,

lib/Sema/TypeCheckDecl.cpp

@@ -385,6 +385,55 @@ void TypeChecker::checkInheritanceClause(Decl *decl,
     }
   }
 
+  // Retrieve the location of the start of the inheritance clause.
+  auto getStartLocOfInheritanceClause = [&] {
+    if (auto genericTypeDecl = dyn_cast<GenericTypeDecl>(decl)) {
+      if (auto genericParams = genericTypeDecl->getGenericParams())
+        return genericParams->getSourceRange().End;
+
+      return genericTypeDecl->getNameLoc();
+    }
+
+    if (auto typeDecl = dyn_cast<TypeDecl>(decl))
+      return typeDecl->getNameLoc();
+
+    if (auto ext = dyn_cast<ExtensionDecl>(decl))
+      return ext->getSourceRange().End;
+
+    return SourceLoc();
+  };
+
+  // Compute the source range to be used when removing something from an
+  // inheritance clause.
+  auto getRemovalRange = [&](unsigned i) {
+    // If there is just one entry, remove the entire inheritance clause.
+    if (inheritedClause.size() == 1) {
+      SourceLoc start = getStartLocOfInheritanceClause();
+      SourceLoc end = inheritedClause[i].getSourceRange().End;
+      return SourceRange(Lexer::getLocForEndOfToken(Context.SourceMgr, start),
+                         Lexer::getLocForEndOfToken(Context.SourceMgr, end));
+    }
+
+    // If we're at the first entry, remove from the start of this entry to the
+    // start of the next entry.
+    if (i == 0) {
+      return SourceRange(inheritedClause[i].getSourceRange().Start,
+                         inheritedClause[i+1].getSourceRange().Start);
+    }
+
+    // Otherwise, remove from the end of the previous entry to the end of this
+    // entry.
+    SourceLoc afterPriorLoc =
+      Lexer::getLocForEndOfToken(Context.SourceMgr,
+                                 inheritedClause[i-1].getSourceRange().End);
+
+    SourceLoc afterMyEndLoc =
+      Lexer::getLocForEndOfToken(Context.SourceMgr,
+                                 inheritedClause[i].getSourceRange().End);
+
+    return SourceRange(afterPriorLoc, afterMyEndLoc);
+  };
+
   // Check all of the types listed in the inheritance clause.
   Type superclassTy;
   SourceRange superclassRange;
@@ -424,16 +473,10 @@ void TypeChecker::checkInheritanceClause(Decl *decl,
     CanType inheritedCanTy = inheritedTy->getCanonicalType();
     auto knownType = inheritedTypes.find(inheritedCanTy);
     if (knownType != inheritedTypes.end()) {
-      SourceLoc afterPriorLoc
-        = Lexer::getLocForEndOfToken(Context.SourceMgr,
-                                     inheritedClause[i-1].getSourceRange().End);
-      SourceLoc afterMyEndLoc
-        = Lexer::getLocForEndOfToken(Context.SourceMgr,
-                                     inherited.getSourceRange().Start);
-
+      auto removeRange = getRemovalRange(i);
       diagnose(inherited.getSourceRange().Start,
                diag::duplicate_inheritance, inheritedTy)
-        .fixItRemoveChars(afterPriorLoc, afterMyEndLoc)
+        .fixItRemoveChars(removeRange.Start, removeRange.End)
         .highlight(knownType->second);
       inherited.setInvalidType(Context);
       continue;
@@ -457,6 +500,18 @@ void TypeChecker::checkInheritanceClause(Decl *decl,
         }
         continue;
       }
+
+      // Swift 3 compatibility:
+      if (Context.LangOpts.isSwiftVersion3() && isa<ClassDecl>(decl) &&
+          inheritedTy->isAnyObject()) {
+        auto classDecl = cast<ClassDecl>(decl);
+        auto removeRange = getRemovalRange(i);
+        diagnose(inherited.getSourceRange().Start,
+                 diag::class_inherits_anyobject,
+                 classDecl->getDeclaredInterfaceType())
+          .fixItRemoveChars(removeRange.Start, removeRange.End);
+        continue;
+      }
     }
 
     // If this is an enum inheritance clause, check for a raw type.
@@ -472,17 +527,11 @@ void TypeChecker::checkInheritanceClause(Decl *decl,
 
       // If this is not the first entry in the inheritance clause, complain.
       if (i > 0) {
-        SourceLoc afterPriorLoc
-          = Lexer::getLocForEndOfToken(
-              Context.SourceMgr,
-              inheritedClause[i-1].getSourceRange().End);
-        SourceLoc afterMyEndLoc
-          = Lexer::getLocForEndOfToken(Context.SourceMgr,
-                                       inherited.getSourceRange().End);
+        auto removeRange = getRemovalRange(i);
 
         diagnose(inherited.getSourceRange().Start,
                  diag::raw_type_not_first, inheritedTy)
-          .fixItRemoveChars(afterPriorLoc, afterMyEndLoc)
+          .fixItRemoveChars(removeRange.Start, removeRange.End)
           .fixItInsert(inheritedClause[0].getSourceRange().Start,
                        inheritedTy.getString() + ", ");
 
@@ -532,17 +581,10 @@ void TypeChecker::checkInheritanceClause(Decl *decl,
 
       // If this is not the first entry in the inheritance clause, complain.
       if (i > 0) {
-        SourceLoc afterPriorLoc
-          = Lexer::getLocForEndOfToken(
-              Context.SourceMgr,
-              inheritedClause[i-1].getSourceRange().End);
-        SourceLoc afterMyEndLoc
-          = Lexer::getLocForEndOfToken(Context.SourceMgr,
-                                       inherited.getSourceRange().End);
-
+        auto removeRange = getRemovalRange(i);
         diagnose(inherited.getSourceRange().Start,
                  diag::superclass_not_first, inheritedTy)
-          .fixItRemoveChars(afterPriorLoc, afterMyEndLoc)
+          .fixItRemoveChars(removeRange.Start, removeRange.End)
           .fixItInsert(inheritedClause[0].getSourceRange().Start,
                        inheritedTy.getString() + ", ");
 

test/Compatibility/anyobject.swift

@@ -0,0 +1,10 @@
+// RUN: %target-typecheck-verify-swift -swift-version 3
+
+protocol P { }
+protocol Q { }
+
+class Foo: AnyObject { } // expected-warning{{conformance of class 'Foo' to 'AnyObject' is redundant}}{{10-21=}}
+
+class Bar: AnyObject, P { } // expected-warning{{conformance of class 'Bar' to 'AnyObject' is redundant}}{{12-23=}}
+
+class Wibble: Bar, AnyObject, Q { } // expected-warning{{conformance of class 'Wibble' to 'AnyObject' is redundant}}{{18-29=}}

test/decl/protocol/conforms/placement.swift

@@ -106,7 +106,7 @@ extension ExplicitSub1 : P1 { } // expected-error{{redundant conformance of 'Exp
 // ---------------------------------------------------------------------------
 // Suppression of synthesized conformances
 // ---------------------------------------------------------------------------
-class SynthesizedClass1 : AnyObject { } // expected-error{{inheritance from non-protocol, non-class type 'AnyObject'}}
+class SynthesizedClass1 : AnyObject { } // expected-warning{{conformance of class 'SynthesizedClass1' to 'AnyObject' is redundant}}
 
 class SynthesizedClass2 { }
 extension SynthesizedClass2 : AnyObject { } // expected-error{{inheritance from non-protocol type 'AnyObject'}}
@@ -116,7 +116,7 @@ class SynthesizedClass3 : AnyObjectRefinement { }
 class SynthesizedClass4 { }
 extension SynthesizedClass4 : AnyObjectRefinement { }
 
-class SynthesizedSubClass1 : SynthesizedClass1, AnyObject { } // expected-error{{inheritance from non-protocol, non-class type 'AnyObject'}}
+class SynthesizedSubClass1 : SynthesizedClass1, AnyObject { } // expected-warning{{conformance of class 'SynthesizedSubClass1' to 'AnyObject' is redundant}}
 
 class SynthesizedSubClass2 : SynthesizedClass2 { }
 extension SynthesizedSubClass2 : AnyObject { } // expected-error{{inheritance from non-protocol type 'AnyObject'}}