Fix #13221: Set JavaStatic on Module fields of module classes in JSCodeGen.

compiler/src/dotty/tools/backend/jvm/BCodeSkelBuilder.scala

@@ -139,6 +139,7 @@ trait BCodeSkelBuilder extends BCodeHelpers {
         // See `tests/run/given-var.scala`
         //
 
+        // !!! Part of this logic is duplicated in JSCodeGen.genCompilationUnit
         claszSymbol.info.decls.foreach { f =>
           if f.isField && !f.name.is(LazyBitMapName) then
             f.setFlag(JavaStatic)

compiler/src/dotty/tools/backend/sjs/JSCodeGen.scala

@@ -198,6 +198,23 @@ class JSCodeGen()(using genCtx: Context) {
     }
     val allTypeDefs = collectTypeDefs(cunit.tpdTree)
 
+    /* #13221 Set JavaStatic on all the Module fields of static module classes.
+     * This is necessary for `desugarIdent` not to crash in some obscure
+     * scenarios.
+     *
+     * !!! Part of this logic is duplicated in BCodeSkelBuilder.genPlainClass
+     *
+     * However, here we only do this for Module fields, not all fields.
+     */
+    for (typeDef <- allTypeDefs) {
+      if (typeDef.symbol.is(ModuleClass)) {
+        typeDef.symbol.info.decls.foreach { f =>
+          if (f.isField && f.is(Module))
+            f.setFlag(JavaStatic)
+        }
+      }
+    }
+
     val (anonJSClassTypeDefs, otherTypeDefs) =
       allTypeDefs.partition(td => td.symbol.isAnonymousClass && td.symbol.isJSType)
 
@@ -1957,12 +1974,7 @@ class JSCodeGen()(using genCtx: Context) {
     val args = tree.args
     val sym = tree.fun.symbol
 
-    val fun = tree.fun match {
-      case fun: Ident => desugarIdent(fun)
-      case fun => fun
-    }
-
-    fun match {
+    tree.fun match {
       case _ if sym.isJSDefaultParam =>
         js.Transient(UndefinedParam)
 

tests/sjs-junit/test/org/scalajs/testsuite/compiler/RegressionTestScala3.scala

@@ -39,6 +39,11 @@ class RegressionTestScala3 {
   @Test def defaultAccessorBridgesIssue12572(): Unit = {
     new MyPromiseIssue12572[Int](5)
   }
+
+  @Test def desugarIdentCrashIssue13221(): Unit = {
+    assertEquals(1, X_Issue13221.I.i)
+    assertEquals(1, X_Issue13221.blah)
+  }
 }
 
 object RegressionTestScala3 {
@@ -76,6 +81,17 @@ object RegressionTestScala3 {
       ???
     }
   }
+
+  object X_Issue13221 extends Y_Issue13221 {
+    object I {
+      def i = 1
+    }
+  }
+
+  abstract class Y_Issue13221 { self: X_Issue13221.type =>
+    import I._
+    def blah = i
+  }
 }
 
 // This class needs to be at the top-level, not in an object, to reproduce the issue