gddo-server: handle trailing slash in godoc.org redirect

Fixes golang/go#43979

Change-Id: I3d02cdbfbf9ad7e76ae143b2d78aa9a7dde2097d
Reviewed-on: https://go-review.googlesource.com/c/gddo/+/287794
Trust: Julie Qiu <julie@golang.org>
Run-TryBot: Julie Qiu <julie@golang.org>
Reviewed-by: Jonathan Amsterdam <jba@google.com>

gddo-server/pkgsite.go

diff --git a/gddo-server/pkgsite.go b/gddo-server/pkgsite.go
index bf683a0..9ac53a3 100644
--- a/gddo-server/pkgsite.go
+++ b/gddo-server/pkgsite.go
@@ -358,6 +358,7 @@
 		q.Set("q", "golang.org/x")
 	default:
 		{
+			godocURL.Path = strings.TrimSuffix(godocURL.Path, "/")
 			// If the import path is invalid, redirect to
 			// https://golang.org/issue/43036, so that the users has more context
 			// on why this path does not work on pkg.go.dev.

gddo-server/pkgsite_test.go

diff --git a/gddo-server/pkgsite_test.go b/gddo-server/pkgsite_test.go
index 1acfee8..061a6cd 100644
--- a/gddo-server/pkgsite_test.go
+++ b/gddo-server/pkgsite_test.go
@@ -171,18 +171,23 @@
 			from: "https://godoc.org/cryptoscope.co/go/specialκ",
 			to:   "https://golang.org/issue/43036",
 		},
+		{
+			from: "https://godoc.org/github.com/google/go-containerregistry/",
+			to:   "https://pkg.go.dev/github.com/google/go-containerregistry?utm_source=godoc",
+		},
 	}
 
 	for _, tc := range testCases {
-		u, err := url.Parse(tc.from)
-		if err != nil {
-			t.Errorf("url.Parse(%q): %v", tc.from, err)
-			continue
-		}
-		to := pkgGoDevURL(u)
-		if got, want := to.String(), tc.to; got != want {
-			t.Errorf("pkgGoDevURL(%q) = %q; want %q", u, got, want)
-		}
+		t.Run(strings.ReplaceAll(tc.from, "/", " "), func(t *testing.T) {
+			u, err := url.Parse(tc.from)
+			if err != nil {
+				t.Fatalf("url.Parse(%q): %v", tc.from, err)
+			}
+			to := pkgGoDevURL(u)
+			if got, want := to.String(), tc.to; got != want {
+				t.Errorf("pkgGoDevURL(%q) = %q; want %q", u, got, want)
+			}
+		})
 	}
 }