x/pkgsite: doesn't correctly handle trailing slash in godoc.org redirection

[imjasonh]

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

$ go version
go version go1.15.6 darwin/amd64

Does this issue reproduce with the latest release?

Yes

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

go env Output

$ go env
GO111MODULE=""
GOARCH="amd64"
GOBIN=""
GOCACHE="/Users/jasonhall/Library/Caches/go-build"
GOENV="/Users/jasonhall/Library/Application Support/go/env"
GOEXE=""
GOFLAGS=""
GOHOSTARCH="amd64"
GOHOSTOS="darwin"
GOINSECURE=""
GOMODCACHE="/Users/jasonhall/go/pkg/mod"
GONOPROXY=""
GONOSUMDB=""
GOOS="darwin"
GOPATH="/Users/jasonhall/go"
GOPRIVATE=""
GOPROXY="https://proxy.golang.org,direct"
GOROOT="/usr/local/Cellar/go/1.15.6/libexec"
GOSUMDB="sum.golang.org"
GOTMPDIR=""
GOTOOLDIR="/usr/local/Cellar/go/1.15.6/libexec/pkg/tool/darwin_amd64"
GCCGO="gccgo"
AR="ar"
CC="clang"
CXX="clang++"
CGO_ENABLED="1"
GOMOD="/Users/jasonhall/git/build/go.mod"
CGO_CFLAGS="-g -O2"
CGO_CPPFLAGS=""
CGO_CXXFLAGS="-g -O2"
CGO_FFLAGS="-g -O2"
CGO_LDFLAGS="-g -O2"
PKG_CONFIG="pkg-config"
GOGCCFLAGS="-fPIC -m64 -pthread -fno-caret-diagnostics -Qunused-arguments -fmessage-length=0 -fdebug-prefix-map=/var/folders/bb/l0yfqc6d6kb5zm5f9ktyx0nw0000gn/T/go-build918433136=/tmp/go-build -gno-record-gcc-switches -fno-common"
GOROOT/bin/go version: go version go1.15.6 darwin/amd64
GOROOT/bin/go tool compile -V: compile version go1.15.6
uname -v: Darwin Kernel Version 19.6.0: Mon Aug 31 22:12:52 PDT 2020; root:xnu-6153.141.2~1/RELEASE_X86_64
ProductName:	Mac OS X
ProductVersion:	10.15.7
BuildVersion:	19H2
lldb --version: lldb-1200.0.44.2
Apple Swift version 5.3.2 (swiftlang-1200.0.45 clang-1200.0.32.28)

What did you do?

Browse to https://godoc.org/github.com/google/go-containerregistry/ (with trailing slash)

...or any godoc.org link to a valid package name, with trailing slash:
https://godoc.org/github.com/google/go-github/
https://godoc.org/github.com/gorilla/mux/

What did you expect to see?

I expected to be redirected to https://pkg.go.dev/github.com/google/go-containerregistry/ (with or without the trailing slash, I have no preference)

...and that's what happens when I browse to https://godoc.org/github.com/google/go-containerregistry (no trailing slash)

What did you see instead?

I was redirected to #43036 which is closed working-as-intended, and seemingly unrelated to my issue.

[imjasonh]

Possibly a regression of #40166?

[julieqiu]

Thanks for letting us know, @imjasonh! We're working on a fix.

[gopherbot]

Change https://golang.org/cl/287794 mentions this issue: gddo-server: handle trailing slash in godoc.org redirect

[imjasonh]

Thanks for the quick fix! 👍