x/pkgsite: GetLatestMajorVersion in proxydatasource does not support incompatible modules

[catzkorn]

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

go1.15.5

Does this issue reproduce with the latest release?

Yes

What operating system and processor architecture are you using (go env)?

go env Output

GO111MODULE=""
GOARCH="amd64"
GOBIN=""
GOCACHE="/Users/charlotte/Library/Caches/go-build"
GOENV="/Users/charlotte/Library/Application Support/go/env"
GOEXE=""
GOFLAGS=""
GOHOSTARCH="amd64"
GOHOSTOS="darwin"
GOINSECURE=""
GOMODCACHE="/Users/charlotte/go/pkg/mod"
GONOPROXY=""
GONOSUMDB=""
GOOS="darwin"
GOPATH="/Users/charlotte/go"
GOPRIVATE=""
GOPROXY="https://proxy.golang.org,direct"
GOROOT="/usr/local/Cellar/go/1.15.5/libexec"
GOSUMDB="sum.golang.org"
GOTMPDIR=""
GOTOOLDIR="/usr/local/Cellar/go/1.15.5/libexec/pkg/tool/darwin_amd64"
GCCGO="gccgo"
AR="ar"
CC="clang"
CXX="clang++"
CGO_ENABLED="1"
GOMOD="/Users/charlotte/src/pkgsite/go.mod"
CGO_CFLAGS="-g -O2"
CGO_CPPFLAGS=""
CGO_CXXFLAGS="-g -O2"
CGO_FFLAGS="-g -O2"
CGO_LDFLAGS="-g -O2"
PKG_CONFIG="pkg-config"

What did you do?

I started the frontend locally with the direct proxy flag set.

$ go run ./cmd/frontend -direct_proxy

Navigated to http://localhost:8080/github.com/golang-migrate/migrate/v3@v3.5.2

What did you expect to see?

I expected to see a warning that there was a greater version available as it does on the pkg.go.dev.

What did you see instead?

I saw no banner.

Discussion

I found this issue while working on and testing #42292. The problem appears to be that GetLatestMajorVersion in the proxydatasource assumes that the first suffixed module uses a v2 suffix. In the case of golang migrate, the first suffixed module appears to be /v3 given that both v1 and v2 are on a non suffixed module.

I would assume we could fix this by parsing the version returned from the first GetInfo call and using that as a basis for subsequent suffixed module names.

[sudo-sturbia]

@julieqiu I would like to claim this, if it's no problem.

[julieqiu]

Please do!

[gopherbot]

Change https://golang.org/cl/277472 mentions this issue: internal/proxydatasource: support incompatible modules in GetLatestMajorVersion