REPL force module load as last resort

If there are no members, and it's not a template,
forcibly initialize the enclosing class.

Author: som-snytt

compiler/src/dotty/tools/repl/Rendering.scala

@@ -113,18 +113,25 @@ private[repl] class Rendering(parentClassLoader: Option[ClassLoader] = None) {
     infoDiagnostic(d.symbol.showUser, d)
 
   /** Render value definition result */
-  def renderVal(d: Denotation)(using Context): Option[Diagnostic] = {
+  def renderVal(d: Denotation)(using Context): Option[Diagnostic] =
     val dcl = d.symbol.showUser
 
-    try {
+    try
       if (d.symbol.is(Flags.Lazy)) Some(infoDiagnostic(dcl, d))
       else valueOf(d.symbol).map(value => infoDiagnostic(s"$dcl = $value", d))
-    }
-    catch { case ex: InvocationTargetException => Some(infoDiagnostic(renderError(ex), d)) }
-  }
-
-  /** Render the stack trace of the underlying exception */
-  private def renderError(ex: InvocationTargetException): String = {
+    catch case ex: InvocationTargetException => Some(infoDiagnostic(renderError(ex), d))
+  end renderVal
+
+  /** Force module initialization in the absence of members. */
+  def forceModule(sym: Symbol)(using Context): Seq[Diagnostic] =
+    def load() =
+      val objectName = sym.fullName.encode.toString
+      val resObj: Class[?] = Class.forName(objectName, true, classLoader())
+      Nil
+    try load() catch case e: ExceptionInInitializerError => List(infoDiagnostic(renderError(e), sym.denot))
+
+  /** Render the stack trace of the underlying exception. */
+  private def renderError(ex: InvocationTargetException | ExceptionInInitializerError): String = {
     val cause = ex.getCause match {
       case ex: ExceptionInInitializerError => ex.getCause
       case ex => ex

compiler/src/dotty/tools/repl/ReplDriver.scala

@@ -309,7 +309,9 @@ class ReplDriver(settings: Array[String],
         defs.map(rendering.renderMethod) ++
         vals.flatMap(rendering.renderVal)
 
-      (state.copy(valIndex = state.valIndex - vals.count(resAndUnit)), formattedMembers)
+      val diagnostics = if formattedMembers.isEmpty then rendering.forceModule(symbol) else formattedMembers
+
+      (state.copy(valIndex = state.valIndex - vals.count(resAndUnit)), diagnostics)
     }
     else (state, Seq.empty)
 

compiler/test/dotty/tools/repl/ReplCompilerTests.scala

@@ -203,6 +203,22 @@ class ReplCompilerTests extends ReplTest {
     run("val a: 1 | 0 = 1")
     assertEquals("val a: 1 | 0 = 1", storedOutput().trim)
   }
+
+  @Test def `i10214 must show classic MatchError` = fromInitialState { implicit state =>
+    run("val 1 = 2")
+    assertEquals("scala.MatchError: 2 (of class java.lang.Integer)", storedOutput().linesIterator.next())
+  }
+  @Test def `i10214 must show useful regex MatchError` =
+    fromInitialState { implicit state =>
+      run("""val r = raw"\d+".r""")
+    } andThen { implicit state =>
+      run("""val r() = "abc"""")
+      assertEquals("scala.MatchError: abc (of class java.lang.String)", storedOutput().linesIterator.drop(2).next())
+    }
+  @Test def `i10214 must show MatchError on literal type` = fromInitialState { implicit state =>
+    run("val (x: 1) = 2")
+    assertEquals("scala.MatchError: 2 (of class java.lang.Integer)", storedOutput().linesIterator.next())
+  }
 }
 
 object ReplCompilerTests {