CS: optional storage key path components are read-only

[AnthonyLatsis]

...because optional storage requirements do not support mutations in Swift.

[AnthonyLatsis]

@swift-ci please smoke test

[jckarter]

Looks good, thanks!

[jckarter]

@swift-ci Please test

[AnthonyLatsis]

@swift-ci please clean test macOS

[AnthonyLatsis]

Should I bring this over to 5.7?

[jckarter]

@AnthonyLatsis If you have time, sure!

The failure on the Linux bot looks unrelated, I'll re-run the tests when #42370 is merged.

[jckarter]

@swift-ci Please test

[AnthonyLatsis]

@swift-ci please test macOS

[AnthonyLatsis]

macOS timed out on some url.

[AnthonyLatsis]

@swift-ci please test source compatibility

[jckarter]

Hi Anthony! Sorry to bother you again, but we got a report that, with this follow-up fix applied, the compiler crashes on code that looks like this:

import Foundation

@objc public protocol Test {
    @objc optional var prop: Bool { get set }
}

internal class Impl: Test {
    var prop: Bool { true }
}

It isn't obvious to my eyes how, but possibly these changes also made it so that protocol conformance checking thinks that an optional get-set property requirement can be satisfied by a read-only property implementation?

[jckarter]

Forming a key path to an optional property can still trigger a crash as well:

#import <Foundation/Foundation.h>

NS_ASSUME_NONNULL_BEGIN

@protocol ObjCProtocol
@optional
@property (nonatomic, assign) BOOL automation;
@end

NS_ASSUME_NONNULL_END

import ObjCFramework

class Object {
    var item: any ObjCProtocol
    init(item: any ObjCProtocol) { self.item = item }

    var automation: Bool { item[keyPath: \.automation] ?? false }
}

[jckarter]

From more experimentation it looks like there may be a remaining issue with properties whose types are bridged, like BOOL -> Bool or NSString * -> String.

[AnthonyLatsis]

Oof, lucky someone caught this so fast. Thanks for sharing, will start debugging all this by tomorrow!

[AnthonyLatsis]

@jckarter Do you have any tips on how to reproduce the ObjCFramework crash? I tried both -import-objc-header and importing a custom module in conjunction with %target-swift-frontend(mock-sdk: %clang-importer-sdk), but IR generation passes. SIL looks sensible too (at the very least the _convertObjCBoolToBool thunk is called).

Edit: Never mind, turns out my previous commit fixed that as well 🤦🏼‍♂️

[jckarter]

Edit: Never mind, turns out my previous commit fixed that as well 🤦🏼‍♂️

Sorry, do you mean the previous PR, or a commit not included in this PR?

[AnthonyLatsis]

Sorry, do you mean the previous PR, or a commit not included in this PR?

A local commit that I thought would only fix the conformance issue.