Copy GraalVM install under shorter path on Windows

Makes it less likely for GraalVM to refer to header files whose path has
more than 256 characters, which seems to be a problem sometimes when
passed to cl.exe by native-image.

Author: alexarchambault

.github/scripts/generate-native-image.sh

@@ -6,6 +6,11 @@ COMMAND="cli.base-image.writeNativeImageScript"
 # Using 'mill -i' so that the Mill process doesn't outlive this invocation
 
 if [[ "$OSTYPE" == "msys" ]]; then
+  ./mill.bat -i ci.copyJvm --dest jvm
+  export JAVA_HOME="$(pwd -W | sed 's,/,\\,g')\\jvm"
+  export GRAALVM_HOME="$JAVA_HOME"
+  export PATH="$(pwd)/bin:$PATH"
+  echo "PATH=$PATH"
   ./mill.bat -i "$COMMAND" generate-native-image.bat
   # Ideally, the generated script should create that directory itself
   mkdir -p out/cli/base-image/nativeImage/dest

build.sc

@@ -1069,4 +1069,23 @@ object ci extends Module {
   def setShouldPublish() = T.command {
     publish.setShouldPublish()
   }
+
+  def copyJvm(jvm: String = deps.graalVmJvmId, dest: String = "jvm") = T.command {
+    import sys.process._
+    val command = Seq(
+      settings.cs(),
+      "java-home",
+      "--jvm",
+      jvm,
+      "--update",
+      "--ttl",
+      "0"
+    )
+    val baseJavaHome = os.Path(command.!!.trim, os.pwd)
+    System.err.println(s"Initial Java home $baseJavaHome")
+    val destJavaHome = os.Path(dest, os.pwd)
+    os.copy(baseJavaHome, destJavaHome, createFolders = true)
+    System.err.println(s"New Java home $destJavaHome")
+    destJavaHome
+  }
 }