Disable ExtractSemanticDB phase when writing to output directory de…

…fined as JAR. (#16790)

Change extracted from #15322 where
the issue was discovered

Writing to outputDirectory when it is a JAR can lead to producing
malformed file, it is using FileOutputStream which works somehow
correct, but if we would open the same JAR again in later phase (eg.
genBCode) header of the file would be malformed: the result file grows
in size respectively to provided input, but we can read only files
written by SemanticDB phase.

compiler/src/dotty/tools/dotc/semanticdb/ExtractSemanticDB.scala

@@ -24,6 +24,7 @@ import scala.annotation.{ threadUnsafe => tu, tailrec }
 import scala.PartialFunction.condOpt
 
 import dotty.tools.dotc.{semanticdb => s}
+import dotty.tools.io.{AbstractFile, JarArchive}
 
 /** Extract symbol references and uses to semanticdb files.
  *  See https://scalameta.org/docs/semanticdb/specification.html#symbol-1
@@ -38,7 +39,9 @@ class ExtractSemanticDB extends Phase:
   override val description: String = ExtractSemanticDB.description
 
   override def isRunnable(using Context) =
-    super.isRunnable && ctx.settings.Xsemanticdb.value
+    import ExtractSemanticDB.{semanticdbTarget, outputDirectory}
+    def writesToOutputJar = semanticdbTarget.isEmpty && outputDirectory.isInstanceOf[JarArchive]
+    super.isRunnable && ctx.settings.Xsemanticdb.value && !writesToOutputJar
 
   // Check not needed since it does not transform trees
   override def isCheckable: Boolean = false
@@ -475,21 +478,22 @@ object ExtractSemanticDB:
   val name: String = "extractSemanticDB"
   val description: String = "extract info into .semanticdb files"
 
+  private def semanticdbTarget(using Context): Option[Path] =
+    Option(ctx.settings.semanticdbTarget.value)
+      .filterNot(_.isEmpty)
+      .map(Paths.get(_))
+
+  private def outputDirectory(using Context): AbstractFile = ctx.settings.outputDir.value
+
   def write(
     source: SourceFile,
     occurrences: List[SymbolOccurrence],
     symbolInfos: List[SymbolInformation],
     synthetics: List[Synthetic],
   )(using Context): Unit =
     def absolutePath(path: Path): Path = path.toAbsolutePath.normalize
-    val semanticdbTarget =
-      val semanticdbTargetSetting = ctx.settings.semanticdbTarget.value
-      absolutePath(
-        if semanticdbTargetSetting.isEmpty then ctx.settings.outputDir.value.jpath
-        else Paths.get(semanticdbTargetSetting)
-      )
     val relPath = SourceFile.relativePath(source, ctx.settings.sourceroot.value)
-    val outpath = semanticdbTarget
+    val outpath = absolutePath(semanticdbTarget.getOrElse(outputDirectory.jpath))
       .resolve("META-INF")
       .resolve("semanticdb")
       .resolve(relPath)