The error message you're getting from go test is what you would get if you passed . as a positional argument

Compare on Linux:

go-bench-recursive-bug$ pwd
/tmp/tmp.KALKdsjINS/go-bench-recursive-bug

go-bench-recursive-bug$ go test -bench= . ./...
no Go files in /tmp/tmp.KALKdsjINS/go-bench-recursive-bug

(Note the extra space after -bench= in that invocation.)

@maruel, can you confirm that the command line you tested with does not contain any Unicode whitespace after the = token?

If you run the program in https://play.golang.org/p/CknqiPUEKR9 using go run main.go -bench=. in PowerShell, what arguments does it print?

https://github.com/maruel/go-bench-recursive-bug/blob/ca0741b30bcc6c61c398d85d85a4cf3648b19e9e/.github/workflows/test.yml#L57

The same string go test -bench=. ./... is used on all OSes.

Your comment made me realize that this works on powershell:

go test -bench . ./...
PASS
ok      github.com/maruel/go-bench-recursive-bug/v1     0.301s
PASS
ok      github.com/maruel/go-bench-recursive-bug/v2     0.295s

So -bench . works but -bench=. doesn't, and this distinction only exists on powershell.

Here's the confirmation:
https://github.com/maruel/go-bench-recursive-bug/runs/1552580624?check_suite_focus=true

And your suspicion is right.

Powershell:

go run main.go -bench=.
["C:\\Users\\parent\\AppData\\Local\\Temp\\go-build894726910\\b001\\exe\\main.exe" "-bench=" "."]
go run main.go "-bench=."
["C:\\Users\\parent\\AppData\\Local\\Temp\\go-build425756990\\b001\\exe\\main.exe" "-bench=."]
go run main.go -bench=. -foo=bar
["C:\\Users\\parent\\AppData\\Local\\Temp\\go-build535392258\\b001\\exe\\main.exe" "-bench=" "." "-foo=bar"]
go run main.go -bench=. -foo=.
["C:\\Users\\parent\\AppData\\Local\\Temp\\go-build471980682\\b001\\exe\\main.exe" "-bench=" "." "-foo=" "."]
go run main.go -bench=a
["C:\\Users\\parent\\AppData\\Local\\Temp\\go-build201397402\\b001\\exe\\main.exe" "-bench=a"]

cmd:

go run main.go -bench=.
["C:\\Users\\parent\\AppData\\Local\\Temp\\go-build817999182\\b001\\exe\\main.exe" "-bench=."]
go run main.go "-bench=."
["C:\\Users\\parent\\AppData\\Local\\Temp\\go-build207076590\\b001\\exe\\main.exe" "-bench=."]

So it looks like it's a parsing bug somewhere in the intersection of go and powershell but I can only confirm with a argument ending with "=.". I'm not familiar enough with powershell to know where the bug is located.

That seem surprising to me that nobody used any form of -foo=. in go with powershell yet and would have not noticed the problem.

$PSVersionTable.PSVersion
Major  Minor  Build  Revision
-----  -----  -----  --------
5      1      19041  610

@4a6f656c @alexbrainman @networkimprov @mattn and any other folks who may know things about PowerShell: is it expected that -bench=. in PowerShell expands to -bench= and . as separate arguments?

I think it's this bug in powershell PowerShell/PowerShell#6291

Thanks Sean, that's it.

I confirmed that it works with the compiled program @bcmills noted above, not just via "go ...". And confirmed that -foo.bar is split up as "-foo" and ".bar". "=" is not needed.

Since it's truly a bug in powershell, we can close this one as there is no AI.