source compatibility project violet fails with a compiler error

[eeckstein]

Description

/build/swift-source-compat-suite/project_cache/violet/Sources/Compiler/Implementation/CompilerImpl+Expr.swift:14:31: error: 'Expression' is ambiguous for type lookup in this context
 12 | extension CompilerImpl {
 13 | 
 14 |   internal func visit(_ node: Expression) throws {
    |                               `- error: 'Expression' is ambiguous for type lookup in this context
 15 |     self.setAppendLocation(node)
 16 |     try node.accept(self)

Reproduction

builds:
https://ci.swift.org/job/swift-6.0-source-compat-suite-debug-ubuntu-2004/121/
https://ci.swift.org/job/swift-6.0-source-compat-suite-ubuntu-2004/121/
https://ci.swift.org/job/swift-source-compat-suite-debug-ubuntu-2004/499/
https://ci.swift.org/job/swift-source-compat-suite-ubuntu-2004/599/

log: https://ci.swift.org/job/swift-6.0-source-compat-suite-debug-ubuntu-2004/121/artifact/build/swift-source-compat-suite/FAIL_violet_5.3_BuildSwiftPackage.log

Expected behavior

should build fine

Environment

CI

Additional information

No response

[AnthonyLatsis]

Could this error actually be legit due to https://forums.swift.org/t/review-sf-0006-expression-macro-and-type/70211? Now there are two distinct extramodular Expression decls visible in this file — one from import Foundation and the other from import VioletParser.

[jmschonfeld]

Yes @AnthonyLatsis I believe you're correct. I think the module that imports both Foundation and VioletParser will need to be updated to disambiguate between the two types (either via fully qualified names, or via a typealias)

[AnthonyLatsis]

@xedin Since by all appearances this is not a compiler issue, could you please transfer it to the compat suite?

[justice-adams-apple]

Hi @LiarPrincess , it appears the source compatibility suite has discovered an issue building violet.

This will likely be uncovered in the next SDK update on our CI. Would you be interested in updating the violet source to account for this? If you find there is no longer any value in testing violet builds nightly, please let me know and I can remove it from the source compatability suite

[LiarPrincess]

Just a PR with an updated tag will suffice?

[justice-adams-apple]

Just a PR with an updated tag will suffice?

Yep, or you can just send me an updated revision and I can open a PR quick and tag you for review

[LiarPrincess]

I created a PR (link above).

There may be a defect in the ambiguity resolution. Tested on: swift-6.1-DEVELOPMENT-SNAPSHOT-2025-02-10-a-ubuntu24.04.

This will NOT compile:

protocol Proto {}

extension Proto {
  typealias Expression = Int
}

class X: Proto {
  // 🔴 main.swift:60:15: error: reference to generic type 'Expression' requires arguments in <...>
  // FoundationEssentials.Expression:2:15: note: generic type 'Expression' declared here
  func foo(n: Expression) {}
}

This will compile:

class Base {
  typealias Expression = Int
}
class Child: Base {
  // 🟢 Works.
  func foo(n: Expression) {}
}

In other words:

• types coming from the class inheritance are recognized as a part of the type
• types coming from the protocol conformance are skipped

I think that both of them should be recognized as a part of the type.