From 3a9e1ec725a33ca6265732b2f3577757a0cb999b Mon Sep 17 00:00:00 2001
From: Satoshi Dev <162055292+0xsatoshi99@users.noreply.github.com>
Date: Mon, 12 Jan 2026 19:44:49 -0800
Subject: [PATCH] [2.x] fix: Fix pipelining flags applied to unsupported Scala
 versions (#8499)

Scala 2.x has supported pipelining since 2020. The fix now allows:
- All Scala 2.x versions (pipelining supported)
- Scala 3.5.0+ (pipelining added in 3.5)

Generated-by: AI-assisted
---
 main/src/main/scala/sbt/Defaults.scala | 18 ++++++++++--------
 1 file changed, 10 insertions(+), 8 deletions(-)

diff --git a/main/src/main/scala/sbt/Defaults.scala b/main/src/main/scala/sbt/Defaults.scala
index 5e3809fee..e98de6f8c 100644
--- a/main/src/main/scala/sbt/Defaults.scala
+++ b/main/src/main/scala/sbt/Defaults.scala
@@ -1016,15 +1016,17 @@ object Defaults extends BuildCommon {
       },
       scalacOptions := {
         val old = scalacOptions.value
-        if (exportPipelining.value)
-          Def.uncached(
-            Vector(
-              "-Ypickle-java",
-              "-Ypickle-write",
-              earlyOutput.value.toString
-            ) ++ old
+        if (exportPipelining.value) {
+          val sv = scalaVersion.value
+          val shouldApplyFlags = !ScalaArtifacts.isScala3(sv) || VersionNumber(sv).matchesSemVer(
+            SemanticSelector(">=3.5.0")
           )
-        else Def.uncached(old)
+          if (shouldApplyFlags)
+            Def.uncached(
+              Vector("-Ypickle-java", "-Ypickle-write", earlyOutput.value.toString) ++ old
+            )
+          else Def.uncached(old)
+        } else Def.uncached(old)
       },
       scalacOptions := {
         val old = scalacOptions.value