x/website/tour: installing @latest gets older version

[dmitshur]

A reasonable way to install the latest version of the tour binary from its latest location is by using go install:

go install golang.org/x/website/tour@latest

However, doing so currently gets a slightly older version of the tour, before the x/website/tour nested module was merged into the x/website module in CL 323897.

$ go install golang.org/x/website/tour@latest
go: downloading golang.org/x/website v0.0.0-20210715154925-11adafea15f8
go: downloading golang.org/x/website/tour v0.0.0-20210616181959-e0d934b43647

$ go version -m $(which tour) | head -n 3
/Users/dmitshur/go/bin/tour: go1.16.6
	path	golang.org/x/website/tour
	mod	golang.org/x/website/tour	v0.0.0-20210616181959-e0d934b43647	h1:IFK+1/z6bm51XIJD3ksijCgwsZXJJxliWFiIYVEG6F8=

Note that module path is golang.org/x/website/tour and version is a month-old v0.0.0-20210616181959-e0d934b43647, rather than the latest commit on master branch:

$ go install golang.org/x/website/tour@HEAD
$ go version -m $(which tour) | head -n 3  
/Users/dmitshur/go/bin/tour: go1.16.6
	path	golang.org/x/website/tour
	mod	golang.org/x/website	v0.0.0-20210715154925-11adafea15f8	h1:xRFLa1Fo4NnOCH0yKaPu6H36MmmA/GJEZyTEO+HOWlI=

A workaround is to specify @HEAD or the exact version of tour one wants.

[dmitshur]

Hmm, this doesn't seem to happen in GOPROXY=direct mode, so maybe the module mirror is playing a role. I'll check again later.

[dmitshur]

I understand why this is happening and can confirm both the go command and module mirror are working as expected. Specifically, https://golang.org/ref/mod#resolve-pkg-mod specifies that:

If one or more modules contain the requested package, the module with the longest path is used.

When the module mirror is used, the latest versions of both x/website and x/website/tour modules are found, both contain the tour package, and the x/website/tour with the its longer module path gets selected (despite being older).

I suspect we'll need to fix this by publishing a newer version of the x/website/tour module that retracts its past versions and/or deletes the tour package.

[bcmills]

#39007 is closely related.

[ericfrederich]

I guess this is still an issue in 2025.
I can only run a 4 year old version (2021) of the tour locally?
Is there a workaround?

This seems like it would be an important bug but no attention in 4 years?

# go install golang.org/x/website/tour@latest
go: downloading golang.org/x/website v0.0.0-20250219015331-21ca6346b037
# ~/go/bin/tour
2025/02/19 09:15:33 Serving content from /home/ubuntu/go/pkg/mod/golang.org/x/website/tour@v0.0.0-20210616181959-e0d934b43647
2025/02/19 09:15:33 Please open your web browser and visit http://127.0.0.1:3999

[dmitshur]

@ericfrederich Yes, there is a workaround, as mentioned in the original report:

A workaround is to specify @HEAD or the exact version of tour one wants.

For example, go run golang.org/x/website/tour@v0.0.0-20250219015331-21ca6346b037 runs a recent version of tour:

$ go run golang.org/x/website/tour@v0.0.0-20250226202246-0620964c30c6 
2025/02/26 16:55:40 A browser window should open. If not, please visit http://127.0.0.1:3999
[…]

That said, I agree this bug is unfortunate and would be good to fix since beginners are less likely to discover that there is a workaround.

CC @golang/tools-team via owners.

[gopherbot]

Change https://go.dev/cl/653155 mentions this issue: tour: deprecate and retract the nested module