tree cfe779cbb1b405106e47a5159a9228fa7b5dd3a0
parent 6fcf7cec353bacaa62c675ad1149abc6217fead2
author Jordan Rose <jordan_rose@apple.com> 1506364397 -0700
committer GitHub <noreply@github.com> 1506364397 -0700

[ClangImporter] Handle inheritance from a class/protocol composition (#12067)

This is legal Objective-C code:

    typedef NSBar <NSFooing> BarAndFoo
    @interface MyBaz : BarAndFoo
    @end

    // Equivalent
    @interface MyBaz : NSBar <NSFooing>
    @end

In Swift 3, we usually handled these by just dropping the protocol
part, making everything appear to work. (The protocols get added to
the class later, without looking at sugar.) However, in Swift 4, we
started supporting these compositions directly* and suddenly
inheriting from them didn't work (read: crashed the compiler). As an
extra twist, even Swift 3 can hit the problem case when the base type
is NSObject, because we figured 'id <NSObject, NSFooing>' was a better
approximation of 'NSObject <NSFooing> *' than 'NSObject *' was.

Fix this by just ignoring protocols when looking for a superclass. As
mentioned, we attach those separately anyway, so we aren't losing any
information.

* This isn't exactly true; there's still a difference between
'NSBar <NSFooing>' and 'NSBar <NSFooing> *'. Jacopo Andrea Giola fixed
a previous issue with this in a598277ad. But Swift doesn't do anything
meaningful with the first form, so it usually just pretends it's the
second.

rdar://problem/34586035