x/pkgsite: “not a valid tag” for commit hashes in the standard library

[bcmills]

What is the URL of the page with the issue?

https://pkg.go.dev/context@3d49b683c6095a9a2681e84f05adfbb8d82882e8

What is your user agent?

Mozilla/5.0 (X11; CrOS x86_64 15183.78.0) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/108.0.0.0 Safari/537.36

Screenshot

What did you do?

1. Navigate to https://pkg.go.dev/context@master.
2. See that it isn't quite up to date.
3. Change @master to @3d49b683c6095a9a2681e84f05adfbb8d82882e8 to try to force-reload the standard library at a specific commit.

What did you expect to see?

Documentation for the context package at Go commit 3d49b68.

What did you see instead?

An error screen.

[findleyr]

Logic here: https://cs.opensource.google/go/x/pkgsite/+/master:internal/frontend/urlinfo.go;l=157;drc=8ea409f829091208d2d0ba4d81ecbe83b0fee9bb

I think we could just let master through, as we do for non-std packages. @jamalc is that right?

[hyangah]

This brings up an interesting question - the stdlib code on master may depend on new, not yet released language features. The pkgsite processes the downloaded code with the newest, stable version of go, but it can be still older than the go the stdlib on master assumes.

Moreover, with the new #57001 proposal, it is almost likely that the go version in stdlib's go.mod is not known to the pkgsite in production. How should pkgsite handle the data that require newer go?

cc @golang/tools-team @rsc