Tweak doc version URLs (#3939)

Duplicate `latest` as `0.12.x`, and fix the `.x` URLs and display names
for old versions

docs/package.mill

@@ -163,7 +163,7 @@ object `package` extends RootModule {
     sanitizeAntoraYml(
       dest,
       "main-branch",
-      build.millVersion().split('.').dropRight(1).mkString(".") + ".x",
+      "main-branch",
       build.millLastTag()
     )
     PathRef(dest)
@@ -172,17 +172,15 @@ object `package` extends RootModule {
   def sanitizeAntoraYml(
       dest: os.Path,
       version: String,
-      millVersion: String,
+      displayVersion: String,
       millLastTag: String
   ): Unit = {
-    val isPreRelease = (millVersion != millLastTag) || Seq("-M", "-RC").exists(millVersion.contains)
+    val isPreRelease = version == "main-branch" || Seq("-M", "-RC").exists(version.contains)
+    val preReleaseSuffix = if (isPreRelease) "\nprerelease: true" else ""
     val lines = os.read(dest / "antora.yml").linesIterator.map {
       case s"version:$_" =>
-        if (isPreRelease)
-          s"version: '${version}'\ndisplay-version: 'main-branch'\nprerelease: true"
-        else
-          s"version: '${version}'\ndisplay-version: '${millVersion}'"
-      case s"    mill-version:$_" => s"    mill-version: '$millVersion'"
+        s"version: '$version'\ndisplay-version: '$displayVersion'$preReleaseSuffix"
+      case s"    mill-version:$_" => s"    mill-version: '$millLastTag'"
       case s"    mill-last-tag:$_" => s"    mill-last-tag: '$millLastTag'"
       case l => l
     }
@@ -246,16 +244,23 @@ object `package` extends RootModule {
   }
 
   def oldDocSources: T[Seq[PathRef]] = Task {
-    for (oldVersion <- build.Settings.docTags) yield {
-      val latest = build.Settings.docTags.last == oldVersion
-      val checkout = T.dest / oldVersion
+    val versionLabels =
+      build.Settings.docTags.map{v =>
+        val xVersion = v.split('.').dropRight(1).mkString(".") + ".x"
+        (v, xVersion, xVersion)
+      } ++
+      // Set the latest stable branch as the "master" docs that people default to
+      Seq((build.Settings.docTags.last, "master", s"latest-${build.Settings.docTags.last}"))
+
+    for ((millLastTag, version, displayVersion) <- versionLabels) yield {
+      val checkout = T.dest / displayVersion
       os.proc("git", "clone", T.workspace / ".git", checkout).call(stdout = os.Inherit)
-      os.proc("git", "checkout", oldVersion).call(cwd = checkout, stdout = os.Inherit)
+      os.proc("git", "checkout", millLastTag).call(cwd = checkout, stdout = os.Inherit)
       val outputFolder = checkout / "out" / "docs" / "source.dest"
       os.proc("./mill", "-i", "docs.source").call(cwd = checkout, stdout = os.Inherit)
       expandDiagramsInDirectoryAdocFile(outputFolder, mill.main.VisualizeModule.classpath().map(_.path))
-      // Set the latest stable branch as the "master" docs that people default to
-      sanitizeAntoraYml(outputFolder, if (latest) "master" else oldVersion, oldVersion, oldVersion)
+
+      sanitizeAntoraYml(outputFolder, version, displayVersion, millLastTag)
       PathRef(outputFolder)
     }
   }