diff -r ad063ac1f617 -r f5dd0abd49d1 src/Pure/Tools/build.scala
--- a/src/Pure/Tools/build.scala	Sun May 24 12:38:41 2020 +0200
+++ b/src/Pure/Tools/build.scala	Sun May 24 12:43:04 2020 +0200
@@ -216,7 +216,7 @@
           }
           else Nil
 
-        if (options.bool("pide_build")) {
+        if (options.bool("pide_session")) {
           val resources = new Resources(sessions_structure, deps(parent))
           val session = new Session(options, resources)