init: copy .jvmopts to .mill-jvm-opts when converting a sbt project (#5339)

Fix #5335

Pull request: #5339

Author: lefou

integration/migrating/init/src/MillInitSbtTests.scala

@@ -46,6 +46,33 @@ object MillInitScala3ExampleProjectTests extends BuildGenTestSuite {
   }
 }
 
+object MillInitScala3ExampleProjectWithJvmOptsTests extends BuildGenTestSuite {
+  def tests: Tests = Tests {
+    /*
+    - 17 KB
+    - `sbt` 1.10.7
+     */
+    val url =
+      "https://github.com/scala/scala3-example-project/archive/853808c50601e88edaa7272bcfb887b96be0e22a.zip"
+
+    test - integrationTest(url)(it =>
+      os.write(it.workspacePath / ".jvmopts", "-Ddummy=prop -Ddummy2=prop2")
+      testMillInit(
+        it,
+        expectedAllSourceFileNums = Map("allSourceFiles" -> 13, "test.allSourceFiles" -> 1),
+        expectedCompileTaskResults = Some(SplitTaskResults(
+          successful = SortedSet("compile", "test.compile"),
+          failed = SortedSet.empty
+        )),
+        expectedTestTaskResults =
+          Some(SplitTaskResults(successful = SortedSet("test"), failed = SortedSet.empty))
+      )
+      assert(os.exists(it.workspacePath / ".mill-jvm-opts"))
+      assert(os.read(it.workspacePath / ".mill-jvm-opts") == "-Ddummy=prop -Ddummy2=prop2")
+    )
+  }
+}
+
 object MillInitSbtScalaCsv200Tests extends BuildGenTestSuite {
   def tests: Tests = Tests {
     /*

libs/init/sbt/src/mill/main/sbt/SbtBuildGenMain.scala

@@ -157,6 +157,32 @@ object SbtBuildGenMain
     convertWriteOut(cfg, cfg.shared, (buildExport.defaultBuildInfo, projectNodeTree))
 
     println("converted sbt build to Mill")
+
+    {
+      val jvmOptsSbt = workspace / ".jvmopts"
+      val jvmOptsMill = workspace / ".mill-jvm-opts"
+
+      if (os.exists(jvmOptsSbt)) {
+        println(s"copying ${jvmOptsSbt.last} to ${jvmOptsMill.last}")
+        if (os.exists(jvmOptsMill)) {
+          val backup = jvmOptsMill / os.up / s"${jvmOptsMill.last}.bak"
+          println(s"creating backup ${backup.last}")
+          os.move.over(jvmOptsMill, backup)
+        }
+        var reportOnce = true
+        // Since .jvmopts may contain multiple args per line, we warn the user
+        // as Mill wants each arg on a separate line
+        os.read.lines(jvmOptsSbt).collectFirst {
+          // Warn the user once when we find spaces, but ignore comments
+          case x if reportOnce && !x.trim().startsWith("#") && x.trim().contains(" ") =>
+            reportOnce = false
+            println(
+              s"${jvmOptsMill.last}: Please check that each arguments is on a separate line!"
+            )
+        }
+        os.copy(jvmOptsSbt, jvmOptsMill)
+      }
+    }
   }
 
   /**