CF_RETURNS_* issues when naming Core Foundation functions

[zhongwuzw]

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Issue Info

Info	Value
SDWebImage Version	5.x`

Issue Description and Steps

// Marks functions which return a CF type that needs to be released by the caller but whose names are not consistent with CoreFoundation naming rules. The recommended fix to this is to rename the functions, but this macro can be used to let the clang static analyzer know of any exceptions that cannot be fixed.
// This macro is ONLY to be used in exceptional circumstances, not to annotate functions which conform to the CoreFoundation naming rules.
#ifndef CF_RETURNS_RETAINED
#if __has_feature(attribute_cf_returns_retained)
#define CF_RETURNS_RETAINED __attribute__((cf_returns_retained))
#else
#define CF_RETURNS_RETAINED
#endif
#endif

// Marks functions which return a CF type that may need to be retained by the caller but whose names are not consistent with CoreFoundation naming rules. The recommended fix to this is to rename the functions, but this macro can be used to let the clang static analyzer know of any exceptions that cannot be fixed. 
// This macro is ONLY to be used in exceptional circumstances, not to annotate functions which conform to the CoreFoundation naming rules.
#ifndef CF_RETURNS_NOT_RETAINED
#if __has_feature(attribute_cf_returns_not_retained)
#define CF_RETURNS_NOT_RETAINED __attribute__((cf_returns_not_retained))
#else
#define CF_RETURNS_NOT_RETAINED
#endif
#endif

CF_RETURNS_RETAINED and CF_RETURNS_NOT_RETAINED can only used in exceptional circumstances, which is to say, if function name conforms the naming rules, we should not annotate it. But currently, we don't conform this rule, like :

+ (CGColorSpaceRef _Nonnull)colorSpaceGetDeviceRGB CF_RETURNS_NOT_RETAINED;
+ (CGImageRef _Nullable)CGImageCreateDecoded:(_Nonnull CGImageRef)cgImage CF_RETURNS_RETAINED;
and so on.....

From the git log, seems it try to optimize Swift Unmanaged type.

Two options we can solve issues:

1. Remove all CF_RETURNS_* annotate if it already satisfy naming rules. Let Unmanaged type exist.
2. Remove all CF_RETURNS_* annotate if it already satisfy naming rules. Refactor SDImageCoderHelper, make all class methods to be C functions, use CF_IMPLICIT_BRIDGING_ENABLED to fix swift Unmanaged type issues.

[dreampiggy]

Objective-C method return any CF data type, does not follow CF rules. You must annotation it with either CF_RETURNS_RETAINED (caller call CFRelease) or CF_RETURNS_NOT_RETAINED (caller don't need call CFRelease).

The CF Create / Get Rule of naming, is for C function, but not for Objective-C method.

[dreampiggy]

See all the Objective-C API with CF data type inside all the Apple's framework, like UIImage.CGImage.

[zhongwuzw]

@dreampiggy Oh, it's true, I always think compiler can do memory management the same as C function based on method return type, unfortunately clang don't do it, the reason is compiler may cannot figure out returned C type.