[project wizard] Fall back to hardcoded Scala/sbt versions when the version download fails with a non-OK HTTP status #SCL-25707 fixed

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

Author: vasilmkd

sbt/sbt-impl/src/org/jetbrains/sbt/project/template/wizard/ScalaVersionStepLike.scala

@@ -57,8 +57,10 @@ trait ScalaVersionStepLike extends IndentationSyntaxStepLike with AsynchronousVe
       Versions.Scala.loadVersionsWithProgress(indicator)
     }
     downloadVersionsAsynchronously(isScalaLoading, disposable, scalaDownloadVersions, Versions.Scala.toString) { versions =>
-      val stringRepresentation = filterAvailableScalaVersions(versions.map(_.presentation))
-      updateSelectionsAndElementsModelForScala(stringRepresentation)
+      if (versions.nonEmpty) {
+        val stringRepresentation = filterAvailableScalaVersions(versions.map(_.presentation))
+        updateSelectionsAndElementsModelForScala(stringRepresentation)
+      }
     }
   }
 

sbt/sbt-impl/src/org/jetbrains/sbt/project/template/wizard/buildSystem/SbtScalaNewProjectWizardStep.scala

@@ -157,8 +157,8 @@ final class SbtScalaNewProjectWizardStep(parent: ScalaNewProjectWizardMultiStep)
   }
 
   override def setDownloadedSbtVersions(versions: Seq[SbtVersion]): Unit = {
-    availableSbtVersions.set(versions.toOption)
-    availableSbtVersionsForScala3.set(Versions.SBT.sbtVersionsForScala3(versions).toOption)
+    availableSbtVersions.set(versions.toOption.filter(_.nonEmpty))
+    availableSbtVersionsForScala3.set(Versions.SBT.sbtVersionsForScala3(versions).toOption.filter(_.nonEmpty))
     updateSupportedSbtVersionsForSelectedScalaVersion(selections.scalaVersion)
   }
 

scala/scala-impl/src/org/jetbrains/plugins/scala/project/Versions.scala

@@ -1,5 +1,6 @@
 package org.jetbrains.plugins.scala.project
 
+import com.intellij.openapi.diagnostic.Logger
 import com.intellij.openapi.progress.{ProcessCanceledException, ProgressIndicator, ProgressManager}
 import com.intellij.util.concurrency.AppExecutorUtil
 import com.intellij.util.concurrency.annotations.RequiresBackgroundThread
@@ -22,6 +23,8 @@ object Versions {
 
   import Entity._
 
+  private val Log: Logger = Logger.getInstance(this.getClass)
+
   sealed abstract class Kind(private[Versions] val entities: List[Entity]) {
 
     @throws[InterruptedException]
@@ -136,17 +139,15 @@ object Versions {
     }
 
     val downloadedVersionStringsFutures: Seq[CompletableFuture[(DownloadableEntity, Seq[String])]] = downloadable.zip(httpFutures).map {
-      case (entity@DownloadableEntity(_, _, hardcodedVersions, versionPattern), future) =>
+      case (entity@DownloadableEntity(url, _, hardcodedVersions, versionPattern), future) =>
         future
-          .thenApply[Seq[String]] { responseStream =>
-            val bodyLines = responseStream.body().toList.asScala.toSeq
-            bodyLines
-          }
-          .thenApply[(DownloadableEntity, Seq[String])] { lines =>
-            val versionStrings =
-              if (lines.isEmpty) hardcodedVersions
-              else extractVersions(lines, versionPattern)
-
+          .thenApply[(DownloadableEntity, Seq[String])] { response =>
+            val statusCode = response.statusCode()
+            val bodyLines = response.body().toList.asScala.toSeq
+            val versionStrings = extractVersionsFromResponse(statusCode, bodyLines, versionPattern).getOrElse {
+              Log.warn(s"Failed to extract versions from $url (status code: $statusCode), falling back to hardcoded versions")
+              hardcodedVersions
+            }
             entity -> versionStrings
           }
           .whenComplete((_, _) => latch.countDown())
@@ -219,6 +220,17 @@ object Versions {
       case pattern(number) => number
     }
 
+  /**
+   * @return `None` if the response was not successful (e.g., HTTP 429 from Maven Central, SCL-25707)
+   *         or if no versions could be extracted from the body (e.g., unexpected page format).
+   *         Callers are expected to fall back to the hardcoded versions in this case.
+   */
+  private[project] def extractVersionsFromResponse(statusCode: Int, bodyLines: Seq[String], versionPattern: Regex): Option[Seq[String]] =
+    statusCode match {
+      case 200 => Some(extractVersions(bodyLines, versionPattern)).filter(_.nonEmpty)
+      case _ => None
+    }
+
   @RequiresBackgroundThread
   @throws[ExecutionException]
   @throws[InterruptedException]

scala/scala-impl/test/org/jetbrains/plugins/scala/project/VersionsTest.scala

@@ -46,4 +46,24 @@ class VersionsTest {
       assertTrue(s"Hardcoded Scala 3 versions should contain $version", hardcodedVersions.contains(version))
     }
   }
+
+  //SCL-25707
+  @Test
+  def testExtractVersionsFromResponse(): Unit = {
+    val pattern = """.+>(\d+\.\d+\.\d+)/<.*""".r // same shape as the Scala version pattern in Versions.Entity
+    val validBody = Seq(
+      """<a href="2.13.15/" title="2.13.15/">2.13.15/</a>""",
+      """<a href="3.3.4/" title="3.3.4/">3.3.4/</a>"""
+    )
+
+    assertEquals(Some(Seq("2.13.15", "3.3.4")), Versions.extractVersionsFromResponse(200, validBody, pattern))
+    // an error response body (e.g., HTTP 429 Too Many Requests from Maven Central) must not be treated as a successful download
+    assertEquals(None, Versions.extractVersionsFromResponse(429, Seq("<html><body>429 Too Many Requests</body></html>"), pattern))
+    // redirects are not followed by the HTTP client
+    assertEquals(None, Versions.extractVersionsFromResponse(301, Seq.empty, pattern))
+    // a successful response in an unexpected format
+    assertEquals(None, Versions.extractVersionsFromResponse(200, Seq("<html>totally new layout</html>"), pattern))
+    // a successful response with an empty body
+    assertEquals(None, Versions.extractVersionsFromResponse(200, Seq.empty, pattern))
+  }
 }