cmd/go: import paths can contain the .test suffix, breaking the toolchain

[dominikh]

What version of Go are you using (go version)?

$ go version
go version devel go1.21-231f290e51 Sat Apr 8 05:25:04 2023 +0000 linux/amd64

Does this issue reproduce with the latest release?

Yes

What did you do?

Given

-- foo/foo.go --
package foo

import _ "example.com/foo.test"
-- foo/foo_test.go --
package foo
-- foo.test/bar.go --
package bar
-- go.mod --
module example.com

go 1.21

run go test ./foo

What did you expect to see?

One of

• no error
• an explanation for the error
• an explicit error forbidding using foo.test as an import path

What did you see instead?

/home/dominikh/prj/go/pkg/tool/linux_amd64/link: fingerprint mismatch: example.com/foo.test has 36b962da8ceb542c, import from example.com/foo expecting aa419b4c2ff8e5ed

[mvdan]

an explicit error forbidding using foo.test as an import path

This would be my personal choice - even if supporting such package paths is technically possible, it feels like something we should strongly discourage due to the confusion it could cause.

We always have to worry about backwards compatibility, but... is anyone even declaring such packages today?

[bcmills]

(CC @matloob)

[egonelbre]

an explicit error forbidding using foo.test as an import path

This would be my personal choice - even if supporting such package paths is technically possible, it feels like something we should strongly discourage due to the confusion it could cause.

We always have to worry about backwards compatibility, but... is anyone even declaring such packages today?

I've been using .test modules (note, not packages per se) for writing examples or tests, because that TLD is guaranteed not to exist (https://en.wikipedia.org/wiki/.test). But, it's also possible to .example or .invalid as an alternative.

[mvdan]

@egonelbre you can just name those test/..., per #37641.

[gopherbot]

Change https://go.dev/cl/513655 mentions this issue: cmd/go: reject import paths with suffix .test

[gopherbot]

Change https://go.dev/cl/613399 mentions this issue: cmd/go: reject import paths with suffix .test