Add -Ylegacy-api-layout to retain previous layout of API

Add option to build 'flat' scaladoc package using `generateScalaDocumentation [output] --justAPI`

Author: romanowski

project/Build.scala

@@ -1325,6 +1325,7 @@ object Build {
       generateScalaDocumentation := Def.inputTaskDyn {
         val extraArgs = spaceDelimited("[output]").parsed
         val dest = file(extraArgs.headOption.getOrElse("scaladoc/output/scala3")).getAbsoluteFile
+        val justAPI = extraArgs.drop(1).headOption == Some("--justAPI")
         val majorVersion = (LocalProject("scala3-library-bootstrapped") / scalaBinaryVersion).value
 
         val dottyJars: Seq[java.io.File] = Seq(
@@ -1346,21 +1347,24 @@ object Build {
 
         val dottyLibRoot = projectRoot.relativize(dottyManagesSources.toPath.normalize())
 
+        def generateDocTask =
+          generateDocumentation(
+            roots, "Scala 3", dest.getAbsolutePath, "master",
+            Seq(
+              "-comment-syntax", "wiki",
+              s"-source-links:docs=github://lampepfl/dotty/master#docs",
+              "-doc-root-content", docRootFile.toString,
+              "-Ydocument-synthetic-types"
+            ) ++ (if (justAPI) Nil else Seq("-siteroot", "docs", "-Ylegacy-api-layout")))
+
         if (dottyJars.isEmpty) Def.task { streams.value.log.error("Dotty lib wasn't found") }
+        else if (justAPI) generateDocTask
         else Def.task{
           IO.write(dest / "versions" / "latest-nightly-base", majorVersion)
 
           // This file is used by GitHub Pages when the page is available in a custom domain
           IO.write(dest / "CNAME", "dotty.epfl.ch")
-        }.dependsOn(generateDocumentation(
-          roots, "Scala 3", dest.getAbsolutePath, "master",
-          Seq(
-            "-comment-syntax", "wiki",
-            "-siteroot", "docs",
-            s"-source-links:docs=github://lampepfl/dotty/master#docs",
-            "-doc-root-content", docRootFile.toString,
-            "-Ydocument-synthetic-types"
-          )))
+        }.dependsOn(generateDocTask)
       }.evaluated,
 
       generateTestcasesDocumentation := Def.taskDyn {

scaladoc/src/dotty/tools/scaladoc/Scaladoc.scala

@@ -58,7 +58,8 @@ object Scaladoc:
     snippetCompilerDebug: Boolean = false,
     noLinkWarnings: Boolean = false,
     versionsDictionaryUrl: Option[String] = None,
-    generateInkuire : Boolean = false
+    generateInkuire : Boolean = false,
+    legacyAPILayout : Boolean = false
   )
 
   def run(args: Array[String], rootContext: CompilerContext): Reporter =
@@ -223,7 +224,8 @@ object Scaladoc:
         noLinkWarnings.get,
         snippetCompilerDebug.get,
         versionsDictionaryUrl.nonDefault,
-        generateInkuire.get
+        generateInkuire.get,
+        legacyAPILayout.get,
       )
       (Some(docArgs), newContext)
     }

scaladoc/src/dotty/tools/scaladoc/ScaladocSettings.scala

@@ -120,5 +120,8 @@ class ScaladocSettings extends SettingGroup with AllScalaSettings:
   val generateInkuire: Setting[Boolean] =
     BooleanSetting("-Ygenerate-inkuire", "Generates InkuireDB and enables Hoogle-like searches", false)
 
+  val legacyAPILayout: Setting[Boolean] =
+    BooleanSetting("-Ylegacy-api-layout", "Keep all api member inside `api` directory", false)
+
   def scaladocSpecificSettings: Set[Setting[_]] =
     Set(sourceLinks, syntax, revision, externalDocumentationMappings, socialLinks, skipById, skipByRegex, deprecatedSkipPackages, docRootContent, snippetCompiler, snippetCompilerDebug, generateInkuire)

scaladoc/src/dotty/tools/scaladoc/renderers/Locations.scala

@@ -32,15 +32,18 @@ trait Locations(using ctx: DocContext):
         val path = dri match
           case `docsRootDRI` => List("docs", "index")
           case `apiPageDRI` =>
-            if ctx.staticSiteContext.fold(false)(_.hasIndexFile) then List("api", "index") else List("index")
+            if ctx.args.legacyAPILayout || ctx.staticSiteContext.fold(false)(_.hasIndexFile)
+              then List("api", "index")
+              else List("index")
           case dri if dri.isStaticFile =>
             Paths.get(dri.location).iterator.asScala.map(_.toString).toList
           case dri =>
             val loc = dri.location
-            loc.split(Array('.')).toList match
+            val fqn = loc.split(Array('.')).toList match
               case "<empty>" :: Nil  => "_empty_" :: Nil
               case "<empty>" :: tail => "_empty_" :: tail
               case other => other
+            if ctx.args.legacyAPILayout then "api" :: fqn else fqn
         cache.put(dri, path)
         path
       case cached => cached