Delegate to `./mill` wrapper script from launcher

Only delegate if the file exists, and we are not currently being delegated to.

This makes the installed launcher automatically download the correct version of
itself to run the build, assuming a `./mill` wrapper script exists

1 files changed, 10 insertions, 1 deletions

diff --git a/build.sc b/build.sc
index aed391d4..dce241b9 100755
--- a/build.sc
+++ b/build.sc
@@ -444,7 +444,16 @@ def launcherScript(shellJvmArgs: Seq[String],
       def java(mainClass: String) =
         s"""exec $$JAVACMD $jvmArgsStr $$JAVA_OPTS -cp "${shellClassPath.mkString(":")}" $mainClass "$$@""""
 
-      s"""if [ -z "$$JAVA_HOME" ] ; then
+      // Delegate to the `./mill` wrapper script if one exists, and we are being
+      // called manually (i.e. the MILL_EXEC_PATH that the wrapper script normally
+      // sets is not present in the environment)
+      s"""if [ -f "$$(dirname "$$BASH_SOURCE")/mill" ] ; then
+         |  if [ ! -z "$$MILL_EXEC_PATH" ] ; then
+         |    exec "$$(dirname "$$BASH_SOURCE")/mill"
+         |  fi
+         |fi
+         |
+         |if [ -z "$$JAVA_HOME" ] ; then
          |  JAVACMD="java"
          |else
          |  JAVACMD="$$JAVA_HOME/bin/java"