Warn when an intended Objective-C specialization was actually a useless protocol qualification.

Warn in cases where one has provided redundant protocol qualification
that might be a typo for a specialization, e.g., NSArray<NSObject>,
which is pointless (NSArray declares that it conforms to NSObject) and
is likely to be a typo for NSArray<NSObject *>, i.e., an array of
NSObject pointers. This warning is very narrow, only applying when the
base type being qualified is parameterized, has the same number of
parameters as their are protocols listed, all of the names can also
refer to types (including Objective-C class types, of course), and at
least one of those types is an Objective-C class (making this a typo
for a missing '*'). The limitations are partly for performance reasons
(we don't want to do redundant name lookup unless we really need to),
and because we want the warning to apply in very limited cases to
limit false positives.

Part of rdar://problem/6294649.

llvm-svn: 241547

7 files changed, 88 insertions, 4 deletions

diff --git a/clang/include/clang/Basic/DiagnosticGroups.td b/clang/include/clang/Basic/DiagnosticGroups.td
index 85796cc0d32..4ecd5d5e184 100644
--- a/clang/include/clang/Basic/DiagnosticGroups.td
+++ b/clang/include/clang/Basic/DiagnosticGroups.td
@@ -280,6 +280,7 @@ def FunctionDefInObjCContainer : DiagGroup<"function-def-in-objc-container">;
 def BadFunctionCast : DiagGroup<"bad-function-cast">;
 def ObjCPropertyImpl : DiagGroup<"objc-property-implementation">;
 def ObjCPropertyNoAttribute : DiagGroup<"objc-property-no-attribute">;
+def ObjCProtocolQualifiers : DiagGroup<"objc-protocol-qualifiers">;
 def ObjCMissingSuperCalls : DiagGroup<"objc-missing-super-calls">;
 def ObjCDesignatedInit : DiagGroup<"objc-designated-initializers">;
 def ObjCRetainBlockProperty : DiagGroup<"objc-noncopy-retain-block-property">;
diff --git a/clang/include/clang/Basic/DiagnosticSemaKinds.td b/clang/include/clang/Basic/DiagnosticSemaKinds.td
index 8032b0b8b40..99400985d78 100644
--- a/clang/include/clang/Basic/DiagnosticSemaKinds.td
+++ b/clang/include/clang/Basic/DiagnosticSemaKinds.td
@@ -7824,4 +7824,8 @@ def err_objc_type_arg_not_id_compatible : Error<
 def err_objc_type_arg_does_not_match_bound : Error<
   "type argument %0 does not satisfy the bound (%1) of type parameter %2">;
 
+def warn_objc_redundant_qualified_class_type : Warning<
+  "parameterized class %0 already conforms to the protocols listed; did you "
+  "forget a '*'?">, InGroup<ObjCProtocolQualifiers>;
+
 } // end of sema component.
diff --git a/clang/include/clang/Parse/Parser.h b/clang/include/clang/Parse/Parser.h
index 8340739b649..fb9eb8ff5af 100644
--- a/clang/include/clang/Parse/Parser.h
+++ b/clang/include/clang/Parse/Parser.h
@@ -1274,6 +1274,7 @@ private:
   /// Objective-C object or object pointer type, which may be either
   /// type arguments or protocol qualifiers.
   void parseObjCTypeArgsOrProtocolQualifiers(
+         ParsedType baseType,
          SourceLocation &typeArgsLAngleLoc,
          SmallVectorImpl<ParsedType> &typeArgs,
          SourceLocation &typeArgsRAngleLoc,
@@ -1287,6 +1288,7 @@ private:
   /// Parse either Objective-C type arguments or protocol qualifiers; if the
   /// former, also parse protocol qualifiers afterward.
   void parseObjCTypeArgsAndProtocolQualifiers(
+         ParsedType baseType,
          SourceLocation &typeArgsLAngleLoc,
          SmallVectorImpl<ParsedType> &typeArgs,
          SourceLocation &typeArgsRAngleLoc,
diff --git a/clang/include/clang/Sema/Sema.h b/clang/include/clang/Sema/Sema.h
index a2f1197f155..edf47e233c5 100644
--- a/clang/include/clang/Sema/Sema.h
+++ b/clang/include/clang/Sema/Sema.h
@@ -7194,6 +7194,7 @@ public:
   /// arguments, as appropriate.
   void actOnObjCTypeArgsOrProtocolQualifiers(
          Scope *S,
+         ParsedType baseType,
          SourceLocation lAngleLoc,
          ArrayRef<IdentifierInfo *> identifiers,
          ArrayRef<SourceLocation> identifierLocs,
diff --git a/clang/lib/Parse/ParseObjc.cpp b/clang/lib/Parse/ParseObjc.cpp
index 3dbecd09008..0f90b684685 100644
--- a/clang/lib/Parse/ParseObjc.cpp
+++ b/clang/lib/Parse/ParseObjc.cpp
@@ -319,7 +319,8 @@ Decl *Parser::ParseObjCAtInterfaceDeclaration(SourceLocation AtLoc,
 
     // Type arguments for the superclass or protocol conformances.
     if (Tok.is(tok::less)) {
-      parseObjCTypeArgsOrProtocolQualifiers(typeArgsLAngleLoc,
+      parseObjCTypeArgsOrProtocolQualifiers(ParsedType(),
+                                            typeArgsLAngleLoc,
                                             typeArgs,
                                             typeArgsRAngleLoc,
                                             LAngleLoc,
@@ -1589,6 +1590,7 @@ TypeResult Parser::parseObjCProtocolQualifierType(SourceLocation &rAngleLoc) {
 ///     '<' type-name '...'[opt] (',' type-name '...'[opt])* '>'
 ///
 void Parser::parseObjCTypeArgsOrProtocolQualifiers(
+       ParsedType baseType,
        SourceLocation &typeArgsLAngleLoc,
        SmallVectorImpl<ParsedType> &typeArgs,
        SourceLocation &typeArgsRAngleLoc,
@@ -1648,6 +1650,7 @@ void Parser::parseObjCTypeArgsOrProtocolQualifiers(
 
     // Let Sema figure out what we parsed.
     Actions.actOnObjCTypeArgsOrProtocolQualifiers(getCurScope(),
+                                                  baseType,
                                                   lAngleLoc,
                                                   identifiers,
                                                   identifierLocs,
@@ -1723,6 +1726,7 @@ void Parser::parseObjCTypeArgsOrProtocolQualifiers(
 }
 
 void Parser::parseObjCTypeArgsAndProtocolQualifiers(
+       ParsedType baseType,
        SourceLocation &typeArgsLAngleLoc,
        SmallVectorImpl<ParsedType> &typeArgs,
        SourceLocation &typeArgsRAngleLoc,
@@ -1734,7 +1738,8 @@ void Parser::parseObjCTypeArgsAndProtocolQualifiers(
   assert(Tok.is(tok::less));
 
   // Parse the first angle-bracket-delimited clause.
-  parseObjCTypeArgsOrProtocolQualifiers(typeArgsLAngleLoc,
+  parseObjCTypeArgsOrProtocolQualifiers(baseType,
+                                        typeArgsLAngleLoc,
                                         typeArgs,
                                         typeArgsRAngleLoc,
                                         protocolLAngleLoc,
@@ -1786,7 +1791,7 @@ TypeResult Parser::parseObjCTypeArgsAndProtocolQualifiers(
   SourceLocation protocolRAngleLoc;
 
   // Parse type arguments and protocol qualifiers.
-  parseObjCTypeArgsAndProtocolQualifiers(typeArgsLAngleLoc, typeArgs,
+  parseObjCTypeArgsAndProtocolQualifiers(type, typeArgsLAngleLoc, typeArgs,
                                          typeArgsRAngleLoc, protocolLAngleLoc,
                                          protocols, protocolLocs,
                                          protocolRAngleLoc, consumeLastToken);
diff --git a/clang/lib/Sema/SemaDeclObjC.cpp b/clang/lib/Sema/SemaDeclObjC.cpp
index 48aa2467d24..74fbec23545 100644
--- a/clang/lib/Sema/SemaDeclObjC.cpp
+++ b/clang/lib/Sema/SemaDeclObjC.cpp
@@ -1220,6 +1220,7 @@ class ObjCTypeArgOrProtocolValidatorCCC : public CorrectionCandidateCallback {
 
 void Sema::actOnObjCTypeArgsOrProtocolQualifiers(
        Scope *S,
+       ParsedType baseType,
        SourceLocation lAngleLoc,
        ArrayRef<IdentifierInfo *> identifiers,
        ArrayRef<SourceLocation> identifierLocs,
@@ -1237,6 +1238,27 @@ void Sema::actOnObjCTypeArgsOrProtocolQualifiers(
   auto resolvedAsProtocols = [&] {
     assert(numProtocolsResolved == identifiers.size() && "Unresolved protocols");
     
+    // Determine whether the base type is a parameterized class, in
+    // which case we want to warn about typos such as
+    // "NSArray<NSObject>" (that should be NSArray<NSObject *>).
+    ObjCInterfaceDecl *baseClass = nullptr;
+    QualType base = GetTypeFromParser(baseType, nullptr);
+    bool allAreTypeNames = false;
+    SourceLocation firstClassNameLoc;
+    if (!base.isNull()) {
+      if (const auto *objcObjectType = base->getAs<ObjCObjectType>()) {
+        baseClass = objcObjectType->getInterface();
+        if (baseClass) {
+          if (auto typeParams = baseClass->getTypeParamList()) {
+            if (typeParams->size() == numProtocolsResolved) {
+              // Note that we should be looking for type names, too.
+              allAreTypeNames = true;
+            }
+          }
+        }
+      }
+    }
+
     for (unsigned i = 0, n = protocols.size(); i != n; ++i) {
       ObjCProtocolDecl *&proto 
         = reinterpret_cast<ObjCProtocolDecl *&>(protocols[i]);
@@ -1261,6 +1283,47 @@ void Sema::actOnObjCTypeArgsOrProtocolQualifiers(
         Diag(forwardDecl->getLocation(), diag::note_protocol_decl_undefined)
           << forwardDecl;
       }
+
+      // If everything this far has been a type name (and we care
+      // about such things), check whether this name refers to a type
+      // as well.
+      if (allAreTypeNames) {
+        if (auto *decl = LookupSingleName(S, identifiers[i], identifierLocs[i],
+                                          LookupOrdinaryName)) {
+          if (isa<ObjCInterfaceDecl>(decl)) {
+            if (firstClassNameLoc.isInvalid())
+              firstClassNameLoc = identifierLocs[i];
+          } else if (!isa<TypeDecl>(decl)) {
+            // Not a type.
+            allAreTypeNames = false;
+          }
+        } else {
+          allAreTypeNames = false;
+        }
+      }
+    }
+    
+    // All of the protocols listed also have type names, and at least
+    // one is an Objective-C class name. Check whether all of the
+    // protocol conformances are declared by the base class itself, in
+    // which case we warn.
+    if (allAreTypeNames && firstClassNameLoc.isValid()) {
+      llvm::SmallPtrSet<ObjCProtocolDecl*, 8> knownProtocols;
+      Context.CollectInheritedProtocols(baseClass, knownProtocols);
+      bool allProtocolsDeclared = true;
+      for (auto proto : protocols) {
+        if (knownProtocols.count(static_cast<ObjCProtocolDecl *>(proto)) == 0) {
+          allProtocolsDeclared = false;
+          break;
+        }
+      }
+
+      if (allProtocolsDeclared) {
+        Diag(firstClassNameLoc, diag::warn_objc_redundant_qualified_class_type)
+          << baseClass->getDeclName() << SourceRange(lAngleLoc, rAngleLoc)
+          << FixItHint::CreateInsertion(
+               PP.getLocForEndOfToken(firstClassNameLoc), " *");
+      }
     }
 
     protocolLAngleLoc = lAngleLoc;
diff --git a/clang/test/SemaObjC/parameterized_classes_subst.m b/clang/test/SemaObjC/parameterized_classes_subst.m
index 979053bfa78..6804bdc7955 100644
--- a/clang/test/SemaObjC/parameterized_classes_subst.m
+++ b/clang/test/SemaObjC/parameterized_classes_subst.m
@@ -3,8 +3,11 @@
 // Test the substitution of type arguments for type parameters when
 // using parameterized classes in Objective-C.
 
+@protocol NSObject
+@end
+
 __attribute__((objc_root_class))
-@interface NSObject
+@interface NSObject <NSObject>
 + (instancetype)alloc;
 - (instancetype)init;
 @end
@@ -376,3 +379,8 @@ void test_ternary_operator(NSArray<NSString *> *stringArray,
   ip = [super array]; // expected-warning{{from 'NSArray<NSString *> *'}}
 }
 @end
+
+// --------------------------------------------------------------------------
+// warning about likely protocol/class name typos.
+// --------------------------------------------------------------------------
+typedef NSArray<NSObject> ArrayOfNSObjectWarning; // expected-warning{{parameterized class 'NSArray' already conforms to the protocols listed; did you forget a '*'?}}