Allow to skip passing inputs to the run command when the -classpath option is passed

Author: Gedochao

modules/build/src/main/scala/scala/build/Build.scala

@@ -57,7 +57,8 @@ object Build {
     def outputOpt: Some[os.Path]          = Some(output)
     def dependencyClassPath: Seq[os.Path] = sources.resourceDirs ++ artifacts.classPath
     def fullClassPath: Seq[os.Path]       = Seq(output) ++ dependencyClassPath
-    def foundMainClasses(): Seq[String]   = MainClass.find(output)
+    def foundMainClasses(): Seq[String] =
+      MainClass.find(output) ++ options.classPathOptions.extraClassPath.flatMap(MainClass.find)
     def retainedMainClass(
       mainClasses: Seq[String],
       commandString: String,

modules/build/src/main/scala/scala/build/Inputs.scala

@@ -302,10 +302,11 @@ object Inputs {
     directories: Directories,
     forcedWorkspace: Option[os.Path],
     enableMarkdown: Boolean,
-    allowRestrictedFeatures: Boolean
+    allowRestrictedFeatures: Boolean,
+    extraClasspathWasPassed: Boolean
   ): Inputs = {
 
-    assert(validElems.nonEmpty)
+    assert(extraClasspathWasPassed || validElems.nonEmpty)
 
     val (inferredWorkspace, inferredNeedsHash, workspaceOrigin) = {
       val settingsFiles = projectSettingsFiles(validElems)
@@ -490,7 +491,8 @@ object Inputs {
     acceptFds: Boolean,
     forcedWorkspace: Option[os.Path],
     enableMarkdown: Boolean,
-    allowRestrictedFeatures: Boolean
+    allowRestrictedFeatures: Boolean,
+    extraClasspathWasPassed: Boolean
   ): Either[BuildException, Inputs] = {
     val validatedArgs: Seq[Either[String, Seq[Element]]] =
       validateArgs(args, cwd, download, stdinOpt, acceptFds)
@@ -504,15 +506,16 @@ object Inputs {
       val validElems = validatedArgsAndSnippets.collect {
         case Right(elem) => elem
       }.flatten
-      assert(validElems.nonEmpty)
+      assert(extraClasspathWasPassed || validElems.nonEmpty)
 
       Right(forValidatedElems(
         validElems,
         baseProjectName,
         directories,
         forcedWorkspace,
         enableMarkdown,
-        allowRestrictedFeatures
+        allowRestrictedFeatures,
+        extraClasspathWasPassed
       ))
     }
     else
@@ -533,10 +536,11 @@ object Inputs {
     acceptFds: Boolean = false,
     forcedWorkspace: Option[os.Path] = None,
     enableMarkdown: Boolean = false,
-    allowRestrictedFeatures: Boolean
+    allowRestrictedFeatures: Boolean,
+    extraClasspathWasPassed: Boolean
   ): Either[BuildException, Inputs] =
     if (
-      args.isEmpty && scriptSnippetList.isEmpty && scalaSnippetList.isEmpty && javaSnippetList.isEmpty
+      args.isEmpty && scriptSnippetList.isEmpty && scalaSnippetList.isEmpty && javaSnippetList.isEmpty && !extraClasspathWasPassed
     )
       defaultInputs().toRight(new InputsException(
         "No inputs provided (expected files with .scala, .sc, .java or .md extensions, and / or directories)."
@@ -555,7 +559,8 @@ object Inputs {
         acceptFds,
         forcedWorkspace,
         enableMarkdown,
-        allowRestrictedFeatures
+        allowRestrictedFeatures,
+        extraClasspathWasPassed
       )
 
   def default(): Option[Inputs] =

modules/build/src/test/scala/scala/build/tests/TestInputs.scala

@@ -43,7 +43,8 @@ final case class TestInputs(
         tmpDir,
         Directories.under(tmpDir / ".data"),
         forcedWorkspace = forcedWorkspaceOpt.map(_.resolveFrom(tmpDir)),
-        allowRestrictedFeatures = true
+        allowRestrictedFeatures = true,
+        extraClasspathWasPassed = false
       )
       res match {
         case Left(err)     => throw new Exception(err)

modules/cli/src/main/scala/scala/cli/commands/Clean.scala

@@ -17,7 +17,8 @@ object Clean extends ScalaCommand[CleanOptions] {
       options.directories.directories,
       defaultInputs = () => Inputs.default(),
       forcedWorkspace = options.workspace.forcedWorkspaceOpt,
-      allowRestrictedFeatures = ScalaCli.allowRestrictedFeatures
+      allowRestrictedFeatures = ScalaCli.allowRestrictedFeatures,
+      extraClasspathWasPassed = false
     ) match {
       case Left(message) =>
         System.err.println(message)

modules/cli/src/main/scala/scala/cli/commands/util/SharedOptionsUtil.scala

@@ -60,7 +60,8 @@ object SharedOptionsUtil extends CommandHelpers {
     scriptSnippetList: List[String],
     scalaSnippetList: List[String],
     javaSnippetList: List[String],
-    enableMarkdown: Boolean = false
+    enableMarkdown: Boolean = false,
+    extraClasspathWasPassed: Boolean = false
   ): Either[BuildException, Inputs] = {
     val resourceInputs = resourceDirs
       .map(os.Path(_, Os.pwd))
@@ -83,7 +84,8 @@ object SharedOptionsUtil extends CommandHelpers {
       acceptFds = !Properties.isWin,
       forcedWorkspace = forcedWorkspaceOpt,
       enableMarkdown = enableMarkdown,
-      allowRestrictedFeatures = ScalaCli.allowRestrictedFeatures
+      allowRestrictedFeatures = ScalaCli.allowRestrictedFeatures,
+      extraClasspathWasPassed = extraClasspathWasPassed
     )
     maybeInputs.map { inputs =>
       val forbiddenDirs =
@@ -349,7 +351,8 @@ object SharedOptionsUtil extends CommandHelpers {
         scriptSnippetList = allScriptSnippets,
         scalaSnippetList = allScalaSnippets,
         javaSnippetList = allJavaSnippets,
-        enableMarkdown = v.markdown.enableMarkdown
+        enableMarkdown = v.markdown.enableMarkdown,
+        extraClasspathWasPassed = v.extraJarsAndClasspath.nonEmpty
       )
 
     def allScriptSnippets: List[String] = v.snippet.scriptSnippet ++ v.snippet.executeScript

modules/integration/src/test/scala/scala/cli/integration/RunTestDefinitions.scala

@@ -2295,6 +2295,34 @@ abstract class RunTestDefinitions(val scalaVersionOpt: Option[String])
     }
   }
 
+  test("run main class from -classpath even when no explicit inputs are passed") {
+    val expectedOutput = "Hello"
+    TestInputs(
+      os.rel / "Main.scala" -> s"""object Main extends App { println("$expectedOutput") }"""
+    ).fromRoot { (root: os.Path) =>
+      val compilationOutputDir = os.rel / "compilationOutput"
+      // first, precompile to an explicitly specified output directory with -d
+      os.proc(
+        TestUtil.cli,
+        "compile",
+        ".",
+        "-d",
+        compilationOutputDir,
+        extraOptions
+      ).call(cwd = root)
+
+      // next, run while relying on the pre-compiled class instead of passing inputs
+      val runRes = os.proc(
+        TestUtil.cli,
+        "run",
+        "-classpath",
+        (os.rel / compilationOutputDir).toString,
+        extraOptions
+      ).call(cwd = root)
+      expect(runRes.out.trim == expectedOutput)
+    }
+  }
+
   if (actualScalaVersion.startsWith("3"))
     test("should throw exception for code compiled by scala 3.1.3") {
       val exceptionMsg = "Throw exception in Scala"