How to add VSCode editor completions for iOS frameworks on linux

Question

I would still like to be able to use VSCode to draft Swift code on my Linux machine while I'm away from my Mac. But I can't get the sourcekit-lsp to recognize the modules from the iOS SDK.

I have occasional access to a Mac but mostly use my Linux machine. As such, I can build apps on my Mac, but I would still like to be able to use VSCode to draft Swift code on my Linux machine ahead of time.

But I can't get the sourcekit-lsp to recognize the modules from the iOS SDK. Similar to references.d.ts for TypeScript devs, but with swift, and only VSCode/sourcekit-lsp cares about it.

I've dug around Xcode.app and found various .modulemap and .swiftinterface files that, after looking in a text editor, look like they provide what I want, but I don't know how to get sourcekit-lsp to look at them.

To emphasize, I do not expect or want to be able to compile iOS code on a Linux machine. In my troubleshooting, I have used swift build only to find more meaningful errors. I don't expect actual builds to happen - that's what the Mac is for. I simply want to be able to use autocompletions from native modules, like UIKit, in VSCode, so I can later copy it over to the Mac to test it.

I know, it's a weird workflow but it's what I have access to right now.

Setup

I've downloaded the Xcode 11 beta and extracted it so I can access the frameworks/SDKs. However, I can't seem to find a way to get sourcekit-lsp to understand the headers for the various frameworks.

Also, swift is installed under /usr/local/bin/swift-5.1-DEVELOPMENT-SNAPSHOT-2019-06-21-a-ubuntu18.04.

Since sourcekit-lsp doesn't log many errors, I decided to try swift build over and over again, getting as close to "working" as possible until hopefully sourcekit-lsp would pick something up.

Trial and error

So far I have tried many different commands. But I'll follow the best line of progress I have gotten.

I started by pointing swiftc to my SDK and iOS target using -sdk Xcode-beta.app/Contents/Developer/Platforms/iPhoneOS.platform/Developer/SDKs/iPhoneOS.sdk -target arm64-apple-ios13.0

This fixed the module not found errors (when I ran swift build)

<unknown>:0: error: unable to load standard library for target 'arm64-apple-ios13.0'

I guessed that this was the swift libraries not being included, so I copied Xcode-beta.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/lib/swift/iphoneos to /usr/local/bin/swift-5.1-DEVELOPMENT-SNAPSHOT-2019-06-21-a-ubuntu18.04/usr/lib/swift/iphoneos, which does indeed fix the above error.

Where I'm stuck

Now, swift build gives me a new error:

<unknown>:0: error: compiled module was created by an older version of the compiler; rebuild 'Swift' and try again: /usr/local/bin/swift-5.1-DEVELOPMENT-SNAPSHOT-2019-06-21-a-ubuntu18.04/usr/lib/swift/iphoneos/Swift.swiftmodule/arm64.swiftmodule

Additionally, going back to VSCode, hovering over a module import (like Foundation) yields a different error:

error response (Request Failed): did not find primary SourceFile

I've tried without success to fix these errors. I don't need swift build to work but I just want sourcekit-lsp to let me write code that uses UIKit/etc.

Package.swift

// swift-tools-version:5.0
// The swift-tools-version declares the minimum version of Swift required to build this package.
import PackageDescription

let package = Package(
    name: "Example",
    platforms: [
        .iOS("13.0")
    ],
    products: [
        // Products define the executables and libraries produced by a package, and make them visible to other packages.
        .library(
            name: "Example",
            targets: ["Example"]),
    ],
    dependencies: [
        // Dependencies declare other packages that this package depends on.
        // .package(url: /* package url */, from: "1.0.0"),
    ],
    targets: [
        // Targets are the basic building blocks of a package. A target can define a module or a test suite.
        // Targets can depend on other targets in this package, and on products in packages which this package depends on.
        .target(
            name: "Example",
            dependencies: [], swiftSettings: [SwiftSetting.unsafeFlags(["-sdk", "/why/doesnt/this/work/Xcode-beta.app/Contents/Developer/Platforms/iPhoneOS.platform/Developer/SDKs/iPhoneOS.sdk", "-target", "arm64-apple-ios13.0"])])
    ]

)