internal/dl: include old unstable release in archive

Updates golang/go#17574
Fixes golang/go#37581
Fixes golang/go#43975

Change-Id: I31cab4b8f8277b3c83ddde001f2649bb5f0bc9c7
Reviewed-on: https://go-review.googlesource.com/c/website/+/290310
Reviewed-by: Dmitri Shuralyov <dmitshur@golang.org>
Trust: Carlos Amedee <carlos@golang.org>
Run-TryBot: Dmitri Shuralyov <dmitshur@golang.org>
TryBot-Result: Go Bot <gobot@golang.org>

internal/dl/dl.go

@@ -209,13 +209,16 @@ func filesToReleases(fs []File) (stable, unstable, archive []Release) {
 		}
 		if !r.Stable {
 			if len(unstable) != 0 {
-				// Only show one (latest) unstable version.
+				// Only show one (latest) unstable version,
+				// consider the older ones to be archived.
+				archive = append(archive, *r)
 				return
 			}
 			maj, min, _ := parseVersion(r.Version)
 			if maj < stableMaj || maj == stableMaj && min <= stableMin {
 				// Display unstable version only if newer than the
-				// latest stable release.
+				// latest stable release, otherwise consider it archived.
+				archive = append(archive, *r)
 				return
 			}
 			unstable = append(unstable, *r)

internal/dl/dl_test.go

@@ -94,7 +94,7 @@ func TestFilesToReleases(t *testing.T) {
 	if got, want := list(unstable), ""; got != want {
 		t.Errorf("unstable = %q; want %q", got, want)
 	}
-	if got, want := list(archive), "go1.7, go1.6, go1.5.2, go1.5"; got != want {
+	if got, want := list(archive), "go1.7, go1.6, go1.5.2, go1.5, go1.5beta1"; got != want {
 		t.Errorf("archive = %q; want %q", got, want)
 	}
 }
@@ -140,10 +140,13 @@ func TestOldUnstableNotShown(t *testing.T) {
 		{Version: "go1.7"},
 		{Version: "go1.7beta1"},
 	}
-	_, unstable, _ := filesToReleases(fs)
+	_, unstable, archive := filesToReleases(fs)
 	if len(unstable) != 0 {
 		t.Errorf("got unstable, want none")
 	}
+	if got, want := list(archive), "go1.7, go1.7beta1"; got != want {
+		t.Errorf("archive = %q; want %q", got, want)
+	}
 }
 
 // A new beta should show up under unstable, but not show up under archive. See golang.org/issue/29669.
@@ -176,11 +179,14 @@ func TestUnstableShown(t *testing.T) {
 		{Version: "go1.7"},
 		{Version: "go1.7beta1"},
 	}
-	_, unstable, _ := filesToReleases(fs)
+	_, unstable, archive := filesToReleases(fs)
 	// Show RCs ahead of betas.
 	if got, want := list(unstable), "go1.8rc1"; got != want {
 		t.Errorf("unstable = %q; want %q", got, want)
 	}
+	if got, want := list(archive), "go1.7, go1.8beta2, go1.7beta1"; got != want {
+		t.Errorf("archive = %q; want %q", got, want)
+	}
 }
 
 // list returns a version list string for the given releases.