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Introduce co- and contra-variance for Objective-C type parameters,
which allows us to express that (for example) an NSArray is covariant
in its type parameter. This means that NSArray<NSMutableString *> * is
a subtype of NSArray<NSString *> *, which is expected of the immutable
Foundation collections.
Type parameters can be annotated with __covariant or __contravariant
to make them co- or contra-variant, respectively. This feature can be
detected by __has_feature(objc_generics_variance). Implements
rdar://problem/20217490.
llvm-svn: 241549
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The __kindof type qualifier can be applied to Objective-C object
(pointer) types to indicate id-like behavior, which includes implicit
"downcasting" of __kindof types to subclasses and id-like message-send
behavior. __kindof types provide better type bounds for substitutions
into unspecified generic types, which preserves more type information.
llvm-svn: 241548
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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
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The Objective-C common-type computation had a few problems that
required a significant rework, including:
- Quadradic behavior when finding the common base type; now it's
linear.
- Keeping around type arguments when computing the common type
between a specialized and an unspecialized type
- Introducing redundant protocol qualifiers.
Part of rdar://problem/6294649. Also fixes rdar://problem/19572837 by
addressing a longstanding bug in
ASTContext::CollectInheritedProtocols().
llvm-svn: 241544
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When messaging a method that was defined in an Objective-C class (or
category or extension thereof) that has type parameters, substitute
the type arguments for those type parameters. Similarly, substitute
into property accesses, instance variables, and other references.
This includes general infrastructure for substituting the type
arguments associated with an ObjCObject(Pointer)Type into a type
referenced within a particular context, handling all of the
substitutions required to deal with (e.g.) inheritance involving
parameterized classes. In cases where no type arguments are available
(e.g., because we're messaging via some unspecialized type, id, etc.),
we substitute in the type bounds for the type parameters instead.
Example:
@interface NSSet<T : id<NSCopying>> : NSObject <NSCopying>
- (T)firstObject;
@end
void f(NSSet<NSString *> *stringSet, NSSet *anySet) {
[stringSet firstObject]; // produces NSString*
[anySet firstObject]; // produces id<NSCopying> (the bound)
}
When substituting for the type parameters given an unspecialized
context (i.e., no specific type arguments were given), substituting
the type bounds unconditionally produces type signatures that are too
strong compared to the pre-generics signatures. Instead, use the
following rule:
- In covariant positions, such as method return types, replace type
parameters with “id” or “Class” (the latter only when the type
parameter bound is “Class” or qualified class, e.g,
“Class<NSCopying>”)
- In other positions (e.g., parameter types), replace type
parameters with their type bounds.
- When a specialized Objective-C object or object pointer type
contains a type parameter in its type arguments (e.g.,
NSArray<T>*, but not NSArray<NSString *> *), replace the entire
object/object pointer type with its unspecialized version (e.g.,
NSArray *).
llvm-svn: 241543
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