Change the scala compiler version, not scala library version + tests.

Author: arturaz

core/constants/src/mill/constants/CacheFiles.java

@@ -0,0 +1,15 @@
+package mill.constants;
+
+public class CacheFiles {
+  /** Prefix for all cache files. */
+  public static final String prefix = "mill-";
+
+  public static String filename(String name) {
+    return prefix + name;
+  }
+
+  public static final String javaHome = "java-home";
+
+  /** Caches the classpath for the mill runner. */
+  public static final String resolveRunner = "resolve-runner";
+}

integration/feature/mill-scala-version/resources/.directory

@@ -0,0 +1,82 @@
+package mill.integration
+
+import mill.constants.CacheFiles
+import mill.testkit.{IntegrationTester, UtestIntegrationTestSuite}
+import utest.*
+
+object MillScalaVersionTests extends UtestIntegrationTestSuite {
+  private def writeBuildMill(tester: IntegrationTester, scalaVersion: Option[String]): Unit = {
+    val scalaVersionLine = scalaVersion.fold("")(v => s"//| mill-scala-version: $v")
+    os.write.over(
+      tester.workspacePath / "build.mill",
+      s"""$scalaVersionLine
+         |package build
+         |
+         |// empty file
+         |""".stripMargin
+    )
+  }
+
+  private def readResolveRunner(tester: IntegrationTester) =
+    os.read.lines(tester.workspacePath / "out" / CacheFiles.filename(CacheFiles.resolveRunner))
+
+  private def scalaLibraryFor(version: String) =
+    s"org/scala-lang/scala3-library_3/$version/scala3-library_3-$version.jar"
+
+  private def scalaCompilerFor(version: String) =
+    s"org/scala-lang/scala3-compiler_3/$version/scala3-compiler_3-$version.jar"
+
+  private val ScalaVersion = "3.7.2-RC1"
+
+  val tests: Tests = Tests {
+    test("noDirective") - integrationTest { tester =>
+      import tester.*
+
+      writeBuildMill(tester, scalaVersion = None)
+      val res = eval("version")
+      assert(res.isSuccess)
+
+      val lines = readResolveRunner(tester)
+      assert(!lines.exists(_.contains(scalaCompilerFor(ScalaVersion))))
+      assert(!lines.exists(_.contains(scalaLibraryFor(ScalaVersion))))
+    }
+
+    test("withDirective") - integrationTest { tester =>
+      import tester.*
+
+      writeBuildMill(tester, scalaVersion = Some(ScalaVersion))
+      val res = eval("version")
+      assert(res.isSuccess)
+
+      val lines = readResolveRunner(tester)
+      assert(lines.exists(_.contains(scalaCompilerFor(ScalaVersion))))
+      assert(lines.exists(_.contains(scalaLibraryFor(ScalaVersion))))
+    }
+
+    test("withDirectiveAndThenWithout") - integrationTest { tester =>
+      import tester.*
+
+      {
+        writeBuildMill(tester, scalaVersion = Some(ScalaVersion))
+        val res = eval("version")
+        assert(res.isSuccess)
+
+        val lines = readResolveRunner(tester)
+        assert(lines.exists(_.contains(scalaCompilerFor(ScalaVersion))))
+        assert(lines.exists(_.contains(scalaLibraryFor(ScalaVersion))))
+      }
+
+      {
+        // This should recompile the build with the new version.
+        writeBuildMill(tester, scalaVersion = None)
+        val res = eval("version")
+        assert(res.isSuccess)
+
+        val lines = readResolveRunner(tester)
+        assert(!lines.exists(_.contains(scalaCompilerFor(ScalaVersion))))
+        assert(!lines.exists(_.contains(scalaLibraryFor(ScalaVersion))))
+      }
+    }
+
+  }
+}

integration/feature/mill-scala-version/src/MillScalaVersionTests.scala

@@ -15,10 +15,7 @@
 import java.util.function.Supplier;
 import java.util.stream.Stream;
 import mill.client.ClientUtil;
-import mill.constants.BuildInfo;
-import mill.constants.CodeGenConstants;
-import mill.constants.DaemonFiles;
-import mill.constants.EnvVars;
+import mill.constants.*;
 import scala.Option$;
 
 public class MillProcessLauncher {
@@ -192,7 +189,7 @@ static String javaHome() throws Exception {
     if (jvmId != null) {
       final String jvmIdFinal = jvmId;
       javaHome = cachedComputedValue0(
-          "java-home",
+          CacheFiles.javaHome,
           jvmId,
           () -> new String[] {CoursierClient.resolveJavaHome(jvmIdFinal).getAbsolutePath()},
           // Make sure we check to see if the saved java home exists before using
@@ -241,10 +238,10 @@ static List<String> millLaunchJvmCommand() throws Exception {
     vmOptions.add("-XX:+HeapDumpOnOutOfMemoryError");
     vmOptions.add("-cp");
     var classPathCacheKey = 
-      "mill:" + BuildInfo.millVersion + 
+      "mill:" + BuildInfo.millVersion +
       ",scala:" + (maybeScalaVersion == null ? "default" : maybeScalaVersion);
     String[] runnerClasspath = cachedComputedValue0(
-        "resolve-runner", classPathCacheKey,
+         CacheFiles.resolveRunner, classPathCacheKey,
          () -> CoursierClient.resolveMillDaemon(Option$.MODULE$.apply(maybeScalaVersion)),
       arr -> {
           for (String s : arr) {
@@ -277,7 +274,7 @@ static String[] cachedComputedValue(String name, String key, Supplier<String[]>
   static String[] cachedComputedValue0(
       String name, String key, Supplier<String[]> block, Function<String[], Boolean> validate) {
     try {
-      Path cacheFile = Paths.get(".").resolve(out).resolve("mill-" + name);
+      Path cacheFile = Paths.get(".").resolve(out).resolve(CacheFiles.filename(name));
       String[] value = null;
       if (Files.exists(cacheFile)) {
         String[] savedInfo = Files.readString(cacheFile).split("\n");