Introduce swift-xcodegen

[hamishknight]

This is a tool specifically designed to generate Xcode projects for the Swift repo (as well as a couple of adjacent repos such as LLVM and Clang). It aims to provide a much more user-friendly experience than the CMake Xcode generation (build-script --xcode). Forum post to follow.

Resolves #70604

[hamishknight]

@swift-ci please smoke test

[hamishknight]

Looks like swift-xcodegen.test is failing in CI (#77407). Passes locally, going to disable for now and will resolve tomorrow.

[jamieQ]

nit:

Suggested change

	using Xcode with with a main development snapshot (and as such is disabled
	using Xcode with a main development snapshot (and as such is disabled

[hamishknight]

Thanks, will resolve in a follow-up

[hamishknight]

Resolving in #77415

[jamieQ]

wow, this is very exciting! i expect upon merge, this will also resolve #70604?

[hamishknight]

🚢

[amritpan]

@hamishknight I'm running into this error when I attempt to generate an Xcode project using the new setup:

**error**: keyNotFound(CodingKeys(stringValue: "output", intValue: nil), Swift.DecodingError.Context(codingPath: [_JSONKey(stringValue: "Index 0", intValue: 0)], debugDescription: "No value associated with key CodingKeys(stringValue: \"output\", intValue: nil) (\"output\").", underlyingError: nil))

This is after building the toolchain for --debug-swift

The full output is:

utils/generate-xcode /Users/amritpankaur/swift-project/build/Ninja-DebugAssert
Building for production...
[1/1] Write swift-version--58304C5D6DBC2206.txt
Build complete! (0.24s)
info: Generating project for '/Users/amritpankaur/swift-project/build/Ninja-DebugAssert'...
error: keyNotFound(CodingKeys(stringValue: "output", intValue: nil), Swift.DecodingError.Context(codingPath: [_JSONKey(stringValue: "Index 0", intValue: 0)], debugDescription: "No value associated with key CodingKeys(stringValue: \"output\", intValue: nil) (\"output\").", underlyingError: nil))

[hamishknight]

@amritpan should be fixed by #77415