Two @Test funcs with the same name crashes the compiler

[ole]

Motivation

Create a Swift Testing target and define 2 test functions. Give both functions the same name:

import Testing

@Test func someTest() {}

@Test func someTest() {}

Expected behavior:

A nice compiler error of the form "Invalid redeclaration of 'someTest`

Observed behavior:

The compiler crashes during macro expansion.

$ swift build --build-tests
Building for debugging...
error: emit-module command failed with exit code 1 (use -v to see invocation)
macro expansion @Test:2:25: error: invalid redeclaration of '$s41SwiftTestingTwoTestFuncsWithSameNameTests04someD00D0fMp_8f5bed0c2fMu_()'
`- …/SwiftTestingTwoTestFuncsWithSameNameTests.swift:4:25: note: expanded code originates here
2 | import SwiftTestingTwoTestFuncsWithSameName
3 |
4 | @Test func someTest() {}
  +--- macro expansion @Test -------------------------------------------
  | 1 | @available(*, deprecated, message: "This function is an implementation detail of the testing library. Do not use it directly.")
…

macro expansion @Test:10:6: error: invalid redeclaration of '$s41SwiftTestingTwoTestFuncsWithSameNameTests04someD00D0fMp_38__🟠$test_container__function__f5bed0c2fMu_'
`- …/SwiftTestingTwoTestFuncsWithSameNameTests.swift:4:25: note: expanded code originates here

When running the tests in Xcode, you see "Command SwiftCompile failed with a nonzero exit code" and need to dig into the build log to discover the actual issue, which isn't a good user experience.

Proposed solution

It would be nice to have a better diagnostic for this, especially because I believe this is a fairly common error to make when copy-pasting an existing test function.

Alternatives considered

No response

Additional information

I tested this on macOS 15.5 with Swift 6.1 (Xcode 16.4) and Swift 6.2 beta (Xcode 26.0 beta 2). The result is the same in both cases, except that Swift 6.2 also prints a stack trace, presumably because it's built with more assertions enabled?

[grynspan]

The given code is invalid and won't compile anyway.

We don't have a mechanism to distinguish exactly identical test function signatures. There is an issue in swift-syntax tracking this problem that I filed a while back; will transfer and dup this issue later today.

[ole]

The given code is invalid and won't compile anyway.

Sure, but poor diagnostics for invalid code is still worth reporting, isn't it?

We don't have a mechanism to distinguish exactly identical test function signatures. There is an issue in swift-syntax tracking this problem that I filed a while back; will transfer and dup this issue later today.

Thanks!

[stmontgomery]

It seems to me the most urgent problem here is the compiler crash. I agree it would be nice if swift-syntax offered some way for a macro implementation such as ours to detect and report this kind of issue, but that feels slightly lower-priority.

Given that there's (apparently) a compiler crash here, I'd propose we transfer this to the main Swift repo instead of to swift-syntax and duping it.

[grynspan]

Sure, let's start there. I can't for the life of me find the bug I want to dup it to anyway (I swear it's real!)

[ole]

Thanks for transferring it to the right place!

[twhitt14]

I took a look into this and have a fix ready. Could I be assigned to the issue?