[ObjC] Pick a 'readwrite' property when synthesizing ambiguous

property and check for incompatible attributes

This commit changes the way ambiguous property synthesis (i.e. when synthesizing
a property that's declared in multiple protocols) is performed. Previously,
Clang synthesized the first property that was found. This lead to problems when
the property was synthesized in a class that conformed to two protocols that
declared that property and a second protocols had a 'readwrite' declaration -
the setter was not synthesized so the class didn't really conform to the second
protocol and user's code would crash at runtime when they would try to set the
property.

This commit ensures that a first readwrite property is selected. This is a
semantic change that changes users code in this manner:

```
@protocol P @property(readonly) int p; @end
@protocol P2 @property(readwrite) id p; @end
@interface I <P2> @end
@implementation I
@syntesize p; // Users previously got a warning here, and Clang synthesized
              // readonly 'int p' here. Now Clang synthesizes readwrite 'id' p..
@end
```

To ensure that this change is safe, the warning about incompatible types is
promoted to an error when this kind of readonly/readwrite ambiguity is detected
in the @implementation. This will ensure that previous code that had this subtle
bug and ignored the warning now will fail to compile with an error, and users
should not get suprises at runtime once they resolve the error.

The commit also extends the ambiguity checker, and now it can detect conflicts
among the different property attributes. An error diagnostic is used for
conflicting attributes, to ensure that the user won't get "suprises" at runtime.

ProtocolPropertyMap is removed in favour of a a set + vector because the map's
order of iteration is non-deterministic, so it couldn't be used to select the
readwrite property.

rdar://31579994

Differential Revision: https://reviews.llvm.org/D35268

llvm-svn: 307903

1 files changed, 160 insertions, 27 deletions

diff --git a/clang/lib/Sema/SemaObjCProperty.cpp b/clang/lib/Sema/SemaObjCProperty.cpp
index 62a771bcffa..e1e85dfd5e5 100644
--- a/clang/lib/Sema/SemaObjCProperty.cpp
+++ b/clang/lib/Sema/SemaObjCProperty.cpp
@@ -814,53 +814,185 @@ static void setImpliedPropertyAttributeForReadOnlyProperty(
     property->setPropertyAttributes(ObjCPropertyDecl::OBJC_PR_weak);
 }
 
-/// DiagnosePropertyMismatchDeclInProtocols - diagnose properties declared
-/// in inherited protocols with mismatched types. Since any of them can
-/// be candidate for synthesis.
-static void
-DiagnosePropertyMismatchDeclInProtocols(Sema &S, SourceLocation AtLoc,
+static bool
+isIncompatiblePropertyAttribute(unsigned Attr1, unsigned Attr2,
+                                ObjCPropertyDecl::PropertyAttributeKind Kind) {
+  return (Attr1 & Kind) != (Attr2 & Kind);
+}
+
+static bool areIncompatiblePropertyAttributes(unsigned Attr1, unsigned Attr2,
+                                              unsigned Kinds) {
+  return ((Attr1 & Kinds) != 0) != ((Attr2 & Kinds) != 0);
+}
+
+/// SelectPropertyForSynthesisFromProtocols - Finds the most appropriate
+/// property declaration that should be synthesised in all of the inherited
+/// protocols. It also diagnoses properties declared in inherited protocols with
+/// mismatched types or attributes, since any of them can be candidate for
+/// synthesis.
+static ObjCPropertyDecl *
+SelectPropertyForSynthesisFromProtocols(Sema &S, SourceLocation AtLoc,
                                         ObjCInterfaceDecl *ClassDecl,
                                         ObjCPropertyDecl *Property) {
-  ObjCInterfaceDecl::ProtocolPropertyMap PropMap;
+  assert(isa<ObjCProtocolDecl>(Property->getDeclContext()) &&
+         "Expected a property from a protocol");
+  ObjCInterfaceDecl::ProtocolPropertySet ProtocolSet;
+  ObjCInterfaceDecl::PropertyDeclOrder Properties;
   for (const auto *PI : ClassDecl->all_referenced_protocols()) {
     if (const ObjCProtocolDecl *PDecl = PI->getDefinition())
-      PDecl->collectInheritedProtocolProperties(Property, PropMap);
+      PDecl->collectInheritedProtocolProperties(Property, ProtocolSet,
+                                                Properties);
   }
-  if (ObjCInterfaceDecl *SDecl = ClassDecl->getSuperClass())
+  if (ObjCInterfaceDecl *SDecl = ClassDecl->getSuperClass()) {
     while (SDecl) {
       for (const auto *PI : SDecl->all_referenced_protocols()) {
         if (const ObjCProtocolDecl *PDecl = PI->getDefinition())
-          PDecl->collectInheritedProtocolProperties(Property, PropMap);
+          PDecl->collectInheritedProtocolProperties(Property, ProtocolSet,
+                                                    Properties);
       }
       SDecl = SDecl->getSuperClass();
     }
-  
-  if (PropMap.empty())
-    return;
-  
+  }
+
+  if (Properties.empty())
+    return Property;
+
+  ObjCPropertyDecl *OriginalProperty = Property;
+  size_t SelectedIndex = 0;
+  for (const auto &Prop : llvm::enumerate(Properties)) {
+    // Select the 'readwrite' property if such property exists.
+    if (Property->isReadOnly() && !Prop.value()->isReadOnly()) {
+      Property = Prop.value();
+      SelectedIndex = Prop.index();
+    }
+  }
+  if (Property != OriginalProperty) {
+    // Check that the old property is compatible with the new one.
+    Properties[SelectedIndex] = OriginalProperty;
+  }
+
   QualType RHSType = S.Context.getCanonicalType(Property->getType());
-  bool FirsTime = true;
-  for (ObjCInterfaceDecl::ProtocolPropertyMap::iterator
-       I = PropMap.begin(), E = PropMap.end(); I != E; I++) {
-    ObjCPropertyDecl *Prop = I->second;
+  unsigned OriginalAttributes = Property->getPropertyAttributes();
+  enum MismatchKind {
+    IncompatibleType = 0,
+    HasNoExpectedAttribute,
+    HasUnexpectedAttribute,
+    DifferentGetter,
+    DifferentSetter
+  };
+  // Represents a property from another protocol that conflicts with the
+  // selected declaration.
+  struct MismatchingProperty {
+    const ObjCPropertyDecl *Prop;
+    MismatchKind Kind;
+    StringRef AttributeName;
+  };
+  SmallVector<MismatchingProperty, 4> Mismatches;
+  for (ObjCPropertyDecl *Prop : Properties) {
+    // Verify the property attributes.
+    unsigned Attr = Prop->getPropertyAttributes();
+    if (Attr != OriginalAttributes) {
+      auto Diag = [&](bool OriginalHasAttribute, StringRef AttributeName) {
+        MismatchKind Kind = OriginalHasAttribute ? HasNoExpectedAttribute
+                                                 : HasUnexpectedAttribute;
+        Mismatches.push_back({Prop, Kind, AttributeName});
+      };
+      if (isIncompatiblePropertyAttribute(OriginalAttributes, Attr,
+                                          ObjCPropertyDecl::OBJC_PR_copy)) {
+        Diag(OriginalAttributes & ObjCPropertyDecl::OBJC_PR_copy, "copy");
+        continue;
+      }
+      if (areIncompatiblePropertyAttributes(
+              OriginalAttributes, Attr, ObjCPropertyDecl::OBJC_PR_retain |
+                                            ObjCPropertyDecl::OBJC_PR_strong)) {
+        Diag(OriginalAttributes & (ObjCPropertyDecl::OBJC_PR_retain |
+                                   ObjCPropertyDecl::OBJC_PR_strong),
+             "retain (or strong)");
+        continue;
+      }
+      if (isIncompatiblePropertyAttribute(OriginalAttributes, Attr,
+                                          ObjCPropertyDecl::OBJC_PR_atomic)) {
+        Diag(OriginalAttributes & ObjCPropertyDecl::OBJC_PR_atomic, "atomic");
+        continue;
+      }
+    }
+    if (Property->getGetterName() != Prop->getGetterName()) {
+      Mismatches.push_back({Prop, DifferentGetter, ""});
+      continue;
+    }
+    if (!Property->isReadOnly() && !Prop->isReadOnly() &&
+        Property->getSetterName() != Prop->getSetterName()) {
+      Mismatches.push_back({Prop, DifferentSetter, ""});
+      continue;
+    }
     QualType LHSType = S.Context.getCanonicalType(Prop->getType());
     if (!S.Context.propertyTypesAreCompatible(LHSType, RHSType)) {
       bool IncompatibleObjC = false;
       QualType ConvertedType;
       if (!S.isObjCPointerConversion(RHSType, LHSType, ConvertedType, IncompatibleObjC)
           || IncompatibleObjC) {
-        if (FirsTime) {
-          S.Diag(Property->getLocation(), diag::warn_protocol_property_mismatch)
-            << Property->getType();
-          FirsTime = false;
-        }
-        S.Diag(Prop->getLocation(), diag::note_protocol_property_declare)
-          << Prop->getType();
+        Mismatches.push_back({Prop, IncompatibleType, ""});
+        continue;
       }
     }
   }
-  if (!FirsTime && AtLoc.isValid())
+
+  if (Mismatches.empty())
+    return Property;
+
+  // Diagnose incompability.
+  {
+    bool HasIncompatibleAttributes = false;
+    for (const auto &Note : Mismatches)
+      HasIncompatibleAttributes =
+          Note.Kind != IncompatibleType ? true : HasIncompatibleAttributes;
+    // Promote the warning to an error if there are incompatible attributes or
+    // incompatible types together with readwrite/readonly incompatibility.
+    auto Diag = S.Diag(Property->getLocation(),
+                       Property != OriginalProperty || HasIncompatibleAttributes
+                           ? diag::err_protocol_property_mismatch
+                           : diag::warn_protocol_property_mismatch);
+    Diag << Mismatches[0].Kind;
+    switch (Mismatches[0].Kind) {
+    case IncompatibleType:
+      Diag << Property->getType();
+      break;
+    case HasNoExpectedAttribute:
+    case HasUnexpectedAttribute:
+      Diag << Mismatches[0].AttributeName;
+      break;
+    case DifferentGetter:
+      Diag << Property->getGetterName();
+      break;
+    case DifferentSetter:
+      Diag << Property->getSetterName();
+      break;
+    }
+  }
+  for (const auto &Note : Mismatches) {
+    auto Diag =
+        S.Diag(Note.Prop->getLocation(), diag::note_protocol_property_declare)
+        << Note.Kind;
+    switch (Note.Kind) {
+    case IncompatibleType:
+      Diag << Note.Prop->getType();
+      break;
+    case HasNoExpectedAttribute:
+    case HasUnexpectedAttribute:
+      Diag << Note.AttributeName;
+      break;
+    case DifferentGetter:
+      Diag << Note.Prop->getGetterName();
+      break;
+    case DifferentSetter:
+      Diag << Note.Prop->getSetterName();
+      break;
+    }
+  }
+  if (AtLoc.isValid())
     S.Diag(AtLoc, diag::note_property_synthesize);
+
+  return Property;
 }
 
 /// Determine whether any storage attributes were written on the property.
@@ -996,8 +1128,9 @@ Decl *Sema::ActOnPropertyImplDecl(Scope *S,
       }
     }
     if (Synthesize && isa<ObjCProtocolDecl>(property->getDeclContext()))
-      DiagnosePropertyMismatchDeclInProtocols(*this, AtLoc, IDecl, property);
-        
+      property = SelectPropertyForSynthesisFromProtocols(*this, AtLoc, IDecl,
+                                                         property);
+
   } else if ((CatImplClass = dyn_cast<ObjCCategoryImplDecl>(ClassImpDecl))) {
     if (Synthesize) {
       Diag(AtLoc, diag::err_synthesize_category_decl);