Objective-ARC++: infer template type arguments of

ownership-unqualified retainable object type as __strong. This allows
us to write, e.g.,

  std::vector<id>

and we'll infer that the vector's element types have __strong
ownership semantics, which is far nicer than requiring:

  std::vector<__strong id>

Note that we allow one to override the ownership qualifier of a
substituted template type parameter, e.g., given

  template<typename T>
  struct X {
    typedef __weak T type;
  };

X<id> is treated the same as X<__strong id>. At instantiation type,
the __weak in "__weak T" overrides the (inferred or specified)
__strong on the template argument type, so that we can still provide
metaprogramming transformations.

This is part of <rdar://problem/9595486>.



git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@133303 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 9 insertions, 0 deletions

diff --git a/lib/Sema/SemaTemplateDeduction.cpp b/lib/Sema/SemaTemplateDeduction.cpp
index af359316da..b5e9c25d85 100644
--- a/lib/Sema/SemaTemplateDeduction.cpp
+++ b/lib/Sema/SemaTemplateDeduction.cpp
@@ -1016,6 +1016,15 @@ DeduceTemplateArguments(Sema &S,
       DeducedQs.removeAddressSpace();
     if (ParamQs.hasObjCLifetime())
       DeducedQs.removeObjCLifetime();
+    
+    // Objective-C ARC:
+    //   If template deduction would produce an argument type with lifetime type
+    //   but no lifetime qualifier, the __strong lifetime qualifier is inferred.
+    if (S.getLangOptions().ObjCAutoRefCount &&
+        DeducedType->isObjCLifetimeType() &&
+        !DeducedQs.hasObjCLifetime())
+      DeducedQs.setObjCLifetime(Qualifiers::OCL_Strong);
+    
     DeducedType = S.Context.getQualifiedType(DeducedType.getUnqualifiedType(),
                                              DeducedQs);