Add dotty bisection tool

project/scripts/dottyCompileBisect.scala

@@ -0,0 +1,73 @@
+// Usage
+// > scala-cli project/scripts/dottyCompileBisect.scala -- File.scala
+//
+// This script will bisect the compilation failure starting with a fast bisection on released nightly builds.
+// Then it will bisect the commits between the last nightly that worked and the first nightly that failed.
+
+
+import sys.process._
+import scala.io.Source
+import Releases.Release
+
+@main def dottyCompileBisect(file: String): Unit =
+  val releaseBisect = ReleaseBisect(file)
+  val fistBadRelease = releaseBisect.bisect(Releases.allReleases)
+  println("\nFinished bisecting releases\n")
+  fistBadRelease.previous match
+    case Some(lastGoodRelease) =>
+      println(s"Last good release: $lastGoodRelease\nFirst bad release: $fistBadRelease\n")
+      val commitBisect = CommitBisect(file)
+      commitBisect.bisect(lastGoodRelease.hash, fistBadRelease.hash)
+    case None =>
+      println(s"No good release found")
+
+class ReleaseBisect(file: String):
+
+  def bisect(releases: Vector[Release]): Release =
+    assert(releases.length > 1, "Need at least 2 releases to bisect")
+    if releases.length == 2 then
+      if isGoodRelease(releases.head) then releases.last
+      else releases.head
+    else
+      val mid = releases(releases.length / 2)
+      if isGoodRelease(mid) then bisect(releases.drop(releases.length / 2))
+      else bisect(releases.take(releases.length / 2 + 1))
+
+  private def isGoodRelease(release: Release): Boolean =
+    println(s"Testing ${release.version}")
+    val res = s"""scala-cli compile $file -S "${release.version}"""".!
+    val isGood = res == 0
+    println(s"Test result: ${release.version} is a ${if isGood then "good" else "bad"} release\n")
+    isGood
+
+object Releases:
+  lazy val allReleases: Vector[Release] =
+    val re = raw"(?<=title=$")(.+-bin-\d{8}-\w{7}-NIGHTLY)(?=/$")".r
+    val html = Source.fromURL("https://repo1.maven.org/maven2/org/scala-lang/scala3-compiler_3/")
+    re.findAllIn(html.mkString).map(Release.apply).toVector
+
+  case class Release(version: String):
+    private val re = raw".+-bin-(\d{8})-(\w{7})-NIGHTLY".r
+    def date: String =
+      version match
+        case re(date, _) => date
+        case _ => sys.error(s"Could not extract date from version $version")
+    def hash: String =
+      version match
+        case re(_, hash) => hash
+        case _ => sys.error(s"Could not extract hash from version $version")
+
+    def previous: Option[Release] =
+      val idx = allReleases.indexOf(this)
+      if idx == 0 then None
+      else Some(allReleases(idx - 1))
+
+    override def toString: String = version
+
+class CommitBisect(file: String):
+  def bisect(lastGoodHash: String, fistBadHash: String): Unit =
+    println(s"Starting bisecting commits $lastGoodHash..$fistBadHash\n")
+    "git bisect start".!
+    s"git bisect bad $fistBadHash".!
+    s"git bisect good $lastGoodHash".!
+    s"git bisect run sh project/scripts/dottyCompileBisect.sh $file".!

project/scripts/dottyCompileBisect.sh

@@ -0,0 +1,16 @@
+# Usage
+# > git bisect start
+# > git bisect bad <bad-commit>
+# > git bisect good <good-commit>
+# > git bisect run project/scripts/dottyCompileBisect.sh <file.scala>
+#
+# Note: Use dottyCompileBisect.scala for faster bisection over commits that spans several days
+
+file="$1"
+shift
+
+rm -r out
+mkdir out
+mkdir out/bisect
+
+sbt "clean; scalac -d out/bisect $file"