cmd/go: typo in flag causes panic when running a test file in GOROOT/src

[josharian]

At tip:

$ go test -timeoout=100h fmt
panic: loadPackageData called with empty package path

goroutine 21 [running]:
cmd/go/internal/load.loadPackageData(0x0, 0x0, 0x0, 0x0, 0xc0000240c4, 0x16, 0x0, 0x0, 0x0, 0x0, ...)
	/Users/josh/go/tip/src/cmd/go/internal/load/pkg.go:648 +0x625
cmd/go/internal/load.(*preload).preloadMatches.func1(0xc000068640, 0x0, 0x0)
	/Users/josh/go/tip/src/cmd/go/internal/load/pkg.go:841 +0x80
created by cmd/go/internal/load.(*preload).preloadMatches
	/Users/josh/go/tip/src/cmd/go/internal/load/pkg.go:839 +0x165

Note the typo: timeoout instead of timeout.

cc @bcmills @jayconrod

[wade-welles]

Just pulled down the newest master and checked and was unable to reproduce, was this already fixed? I wanted to fix it :D

./go test -timeoout=100h fmt
flag provided but not defined: -timeoout
Usage of /tmp/go-build643614696/b001/go.test:
  -flaky
...

[josharian]

On my phone, but I wonder whether you have to be in dir $GOROOT/src to reproduce.

[mvdan]

I equally cannot reproduce this on go version devel +0f559941fb Sat Oct 26 15:17:28 2019 +0000 linux/amd64. I tried inside GOROOT/src and with various GO111MODULE values. I wonder if I missed any piece of the puzzle.

[josharian]

Sorry about that. I believe to reproduce you need a test file in GOROOT/src, and then run from that dir. Which means this is pretty low priority. Will re-milestone.

[jayconrod]

Reproduced with the instructions from the last comment.

It looks like go test -timeoout fmt is being interpreted as go test . with some arguments to pass to the tests, since -timeoout is not a flag that go test itself recognizes. So it tries to load the package in the current directory, $GOROOT/src.

The bug is that modload.ImportPaths is returning an empty string as one of the import paths. Which is kind of correct because normally a package path in std is its subdirectory under $GOROOT/src, and since there is no subdirectory in this case, we get "".

Maybe we should detect and reject this case specifically? It's such a small corner case though.