[SR-5688] Unhelpful diagnostic when missing a ? in a KeyPath expression

[mdiep]

Previous ID	SR-5688
Radar	None
Original Reporter	@mdiep
Type	Bug
Status	Resolved
Resolution	Done

Attachment: Download

Environment

Xcode 9.0.0 ß5

Apple Swift version 4.0 (swiftlang-900.0.59 clang-900.0.34.2)

Target: x86_64-apple-macosx10.9

Additional Detail from JIRA

Votes	0
Component/s	Compiler
Labels	Bug, DiagnosticsQoI
Assignee	@LucianoPAlmeida
Priority	Medium

md5: c71e85e71edfd0319c05a4dfe3d8443e

Issue Description:

This code:

struct A {
    var b: B?
}

struct B {
    var c: Int
}

let ab1 = \A.b.c
dump(ab1)

gives this diagnostic:

error: MyPlayground.playground:3:11: error: expression type 'WritableKeyPath<A, Int>' is ambiguous without more context
let ab1 = \A.b.c

That's really unhelpful. The issue here is that a ? is missing. It should be \A.b?.c.

[mdiep]

It's not clear to me that \A.b.c means anything, so I'm left wondering if KeyPaths should even use ?.

[belkadan]

cc @jckarter, @xedin

[LucianoPAlmeida]

On 2020-06-13 master snapshot I'm seeing


[gregomni]

@LucianoPAlmeida - Sorry, I started looking at this because I hadn't noticed that you'd assigned it to yourself. The fix needs to deal with key path expressions specially to get the particular component involved. Something like this: <gregomni@b164ae8c7a30656d7b986aa1edfaf1f08b7c2f1c\>

[LucianoPAlmeida]

Ahh thank you, I had the PR opened right after the post, very similar except for the SourceLoc part, which I believe is an improvement. I'll adjust that and add you as a reviewer as well 🙂

[LucianoPAlmeida]

@mdiep This is fixed on master, can you please verify on the next available master snapshot and close? Thanks