[GSoC 2023] Key Path inference and diagnostic improvements

amritpan · 2023-05-30T20:46:56.963Z

Hi everyone!

I will be working on improving key path inference and diagnostics this summer as part of GSoC 2023 with my mentor, @xedin. Perhaps you've encountered key path errors that show type inference failures or do not provide actionable information like the infamous "type of expression is ambiguous without more context". We hope to fix many of these by the end of the summer.

If anyone comes across any other odd key path behavior, feel free to share here!

mtsrodrigues · 2023-05-30T20:51:26.213Z

Does solving this bug Key Path Expressions as Functions and Identity Key Path is on the scope?

amritpan · 2023-05-30T22:32:15.301Z

Hopefully, yes! We expect to change how key path expressions are type checked so that certain type information that currently goes missing during constraint solving and is causing many of these errors is not handled until much later in the type-checking process.

StevenSorial · 2023-05-31T00:02:45.313Z

This also may be related to your work

github.com/apple/swift

KeyPath causes a compiler crash on an existential root

opened 07:04PM - 24 Jul 22 UTC

StevenSorial

bug compiler SILGen key paths crash

**Describe the bug** KeyPath causes a compiler crash on an array of existential…s while a normal closure doesn't **Steps To Reproduce** Steps to reproduce the behavior: ```swift import Foundation protocol Brand { var name: String { get } } protocol Car { associatedtype BrandType: Brand var brand: BrandType { get } } func test() { let cars: [any Car] = [] let brandsByClosure: [any Brand] = cars.map { $0.brand } // Works let brandsByKey: [any Brand] = cars.map(\.brand) // Compiler failure let sortedByClosure: [any Car] = cars.sorted { $0.brand.name < $1.brand.name } // Works let sortedByKey: [any Car] = cars.sorted(using: KeyPathComparator(\.brand.name)) // Compiler failure } ``` **Expected behavior** Both forms of `map` and `sorted` should work **Environment (please fill out the following information)** - OS: macOS 12.5 - Xcode Version/Tag/Branch: Xcode 14.0 beta 3

mgriebling · 2023-05-31T03:08:10.739Z

Excellent! These are some of the more frustrating errors from the compiler.

sjavora · 2023-05-31T18:43:38.489Z

Not sure if this is in scope, but since I came across it today: Using key path literals as functions defeats @MainActor checks · Issue #63189 · apple/swift · GitHub

dkz · 2023-06-01T03:14:24.381Z

This is a pretty cool project, cant wait to follow along the progress!