Index data (SourceKit and Indexstore) for an `extension` of a `typealias` does not reference the `typealias`

[dylansturg]

Description
When Swift code extends a typealias, the index data (either from SourceKit using its index request or the indexstore from index while building) contains no reference to the typealias. Instead it only references the real type that the typealias is alias-ing.

Consider this code:

Module Foo:

typealias ExtendableFoo = Foo

Module Bar:

extension ExtendableFoo { ... }

The index for Bar contains a reference to the type Foo, with no reference to the typealias ExtendableFoo.

Steps to reproduce

Create 2 Swift files, to be built as 2 separate Swift modules:

File Typealias.swift

public struct MyType {}
public typealias AliasType = MyType

File Extension.swift

import Typealias
extension AliasType {
	func foo() {}
}

Build a swiftmodule for Typealias.swift:

$ swiftc \
  -sdk /var/db/xcode_select_link//Platforms/iPhoneSimulator.platform/Developer/SDKs/iPhoneSimulator.sdk \
  -target x86_64-apple-ios15.0-simulator \
  -emit-module-path .build/Typealias.swiftmodule \
  Typealias.swift

Run sourcekitd-test to index Extension.swift:

$ sourcekitd-test -req index Extension.swift -- \
  -target x86_64-apple-ios15.0-simulator \
  -sdk /var/db/xcode_select_link/Platforms/iPhoneSimulator.platform/Developer/SDKs/iPhoneSimulator.sdk \
  -F/var/db/xcode_select_link/Platforms/iPhoneSimulator.platform/Developer/Library/Frameworks \
  -F/var/db/xcode_select_link/Platforms/iPhoneSimulator.platform/Developer/SDKs/iPhoneSimulator.sdk/Developer/Library/Frameworks \
  -I/var/db/xcode_select_link/Platforms/iPhoneSimulator.platform/Developer/usr/lib \
  -I$(pwd)/.build -module-name Extension \
  Extension.swift 

Observe the entities results in the index data:

key.entities: [
    {
      key.kind: source.lang.swift.ref.module,
      key.name: "Typealias",
      key.usr: "c:@M@Typealias",
      key.line: 1,
      key.column: 8
    },
    {
      key.kind: source.lang.swift.decl.extension.struct,
      key.name: "MyType",
      key.usr: "s:e:s:9Typealias6MyTypeV9ExtensionE3fooyyF",
      key.line: 2,
      key.column: 11,
      key.entities: [
        {
          key.kind: source.lang.swift.ref.struct,
          key.name: "MyType",
          key.usr: "s:9Typealias6MyTypeV",
          key.line: 2,
          key.column: 11
        },
        {
          key.kind: source.lang.swift.decl.function.method.instance,
          key.name: "foo()",
          key.usr: "s:9Typealias6MyTypeV9ExtensionE3fooyyF",
          key.line: 3,
          key.column: 7,
          key.effective_access: source.decl.effective_access.internal
        }
      ]
    }
  ]

Expected behavior

I expect to see a reference to the typealias that is being extend, e.g. AliasType in this case.

Environment

• Swift compiler version info Apple Swift version 5.8 (swiftlang-5.8.0.124.2 clang-1403.0.22.11.100)
• Xcode version info Xcode 14.3 Build version 14E222b
• Deployment target: iOS 15.0

[keith]

Can you verify with the 5.9 toolchain, I might have fixed this one (in the index data, maybe not sourcekit)

[dylansturg]

Using the 5.9 toolchain from Xcode 15 beta 4, I see the typealias now! 🎉

I have a couple follow up questions:

1. The index data also has a reference to the "aliased" type. The source.lang.swift.ref.struct for MyType remains and the source.lang.swift.decl.extension.struct still uses MyType for its name:

{
      key.kind: source.lang.swift.decl.extension.struct,
      key.name: "MyType",
      key.usr: "s:e:s:9Typealias6MyTypeV9ExtensionE3fooyyF",
      key.line: 2,
      key.column: 11,
      key.entities: [
        {
          key.kind: source.lang.swift.ref.typealias,
          key.name: "AliasType",
          key.usr: "s:9Typealias9AliasTypea",
          key.line: 2,
          key.column: 11
        },
        {
          key.kind: source.lang.swift.ref.struct,
          key.usr: "s:9Typealias6MyTypeV",
          key.line: 2,
          key.column: 11,
          key.is_implicit: 1
        },

Is this the desired/correct behavior? The code really only uses the typealias. I'm wondering if it would be appropriate to only have references to the typealias here.

2. The cursor-info response from sourcekit at the location of the extension only has the reference of the typealias, with no details about the extension. As far as I can tell, there's no way to call cursor info for the offset of the extension and receive semantic information about the extension.

[keith]

My change I guess didn't really touch sourcekit's response at all, so I'm not surprised it's different still 😕 . I'm not sure what other folks think it should be but I guess I would expect them to be the same(ish)