[SR-7471] Need to diagnose @usableFromInline stored property with inferred non-@usableFromInline type

[phausler]

Previous ID	SR-7471
Radar	rdar://problem/39532028
Original Reporter	@phausler
Type	Bug
Status	Resolved
Resolution	Done

Additional Detail from JIRA

Votes	0
Component/s	Compiler
Labels	Bug
Assignee	@slavapestov
Priority	Medium

md5: 54ba0b5368cafb49e35e02f8c2858087

Issue Description:

internal final class _Bar {
    func foo() {
        
    }
    
    @usableFromInline
    func fooCalledFromInline() {
        
    }
}

public struct Bar {
    @usableFromInline
    internal var bar = _Bar()
    public func foo() {
        bar.foo()
    }
    
    @inlinable
    public func inlineFoo() {
        bar.fooCalledFromInline()
    }
}

inlineFoo reports an error (which seems incorrect)

/tmp/inlines/inlines/main.swift:31:13: error: instance method 'fooCalledFromInline()' is internal and cannot be referenced from an '@inlinable' function
        bar.fooCalledFromInline()
            ^
/tmp/inlines/inlines/main.swift:17:10: note: instance method 'fooCalledFromInline()' is not '@usableFromInline' or public
    func fooCalledFromInline() {

[phausler]

This is blocking [rdar://problem/33678210]

[phausler]

@belkadan do you know who I can talk to about this? I need to either figure out a way around this or we may loose all inlines in Data.

[belkadan]

Me or @slavapestov, I guess. It looks like the answer is that _Bar has to be @usableFromInline too, and in fact there should be an error about that where the property bar is declared, and not the nonsense error you're getting.

[belkadan]

That gets you unblocked, at least. One of us'll add the correct error.

@swift-ci create

[phausler]

that does it! yea that error is a bit misleading to say the least.

[slavapestov]

What should actually happen here is we need to diagnose the declaration of 'bar'. 'bar' cannot be @usableFromInline because the struct _Bar is internal.

[slavapestov]

Slavas-iMac-Pro:swift spestov$ ../build/Ninja-RelWithDebInfoAssert/swift-macosx-x86_64/bin/swiftc x.swift -swift-version 5
x.swift:14:18: error: type referenced from a '@usableFromInline' property with inferred type '_Bar' must be '@usableFromInline' or public
 internal var bar = _Bar()
              ^

[slavapestov]

#16586