SI-9937 find nested java classes if InnerClass entry is missing

src/compiler/scala/tools/nsc/symtab/classfile/ClassfileParser.scala

@@ -380,11 +380,41 @@ abstract class ClassfileParser {
   }
 
   private def lookupClass(name: Name) = try {
-    if (name containsChar '.')
-      rootMirror getClassByName name
-    else
+    def lookupTopLevel = {
+      if (name containsChar '.')
+        rootMirror getClassByName name
+      else
       // FIXME - we shouldn't be doing ad hoc lookups in the empty package, getClassByName should return the class
-      definitions.getMember(rootMirror.EmptyPackageClass, name.toTypeName)
+        definitions.getMember(rootMirror.EmptyPackageClass, name.toTypeName)
+    }
+
+    // For inner classes we usually don't get here: `classNameToSymbol` already returns the symbol
+    // of the inner class based on the InnerClass table. However, if the classfile is missing the
+    // InnerClass entry for `name`, it might still be that there exists an inner symbol (because
+    // some other classfile _does_ have an InnerClass entry for `name`). In this case, we want to
+    // return the actual inner symbol (C.D, with owner C), not the top-level symbol C$D. This is
+    // what the logic below is for (see PR #5822 / scala/bug#9937).
+    val split = if (isScalaRaw) -1 else name.lastIndexOf('$')
+    if (split > 0 && split < name.length) {
+      val outerName = name.subName(0, split)
+      val innerName = name.subName(split + 1, name.length).toTypeName
+      val outerSym = classNameToSymbol(outerName)
+
+      // If the outer class C cannot be found, look for a top-level class C$D
+      if (outerSym.isInstanceOf[StubSymbol]) lookupTopLevel
+      else {
+        // We have a java-defined class name C$D and look for a member D of C. But we don't know if
+        // D is declared static or not, so we have to search both in class C and its companion.
+        val r = if (outerSym == clazz)
+          staticScope.lookup(innerName) orElse
+            instanceScope.lookup(innerName)
+        else
+          lookupMemberAtTyperPhaseIfPossible(outerSym, innerName) orElse
+            lookupMemberAtTyperPhaseIfPossible(outerSym.companionModule, innerName)
+        r orElse lookupTopLevel
+      }
+    } else
+      lookupTopLevel
   } catch {
     // The handler
     //   - prevents crashes with deficient InnerClassAttributes (scala/bug#2464, 0ce0ad5)

test/files/run/t9937/Test_1.java

@@ -0,0 +1,11 @@
+class C$D { public int i() { return 1; } }
+class C$E { public int i() { return 1; } }
+class C$F$G { public int i() { return 1; } }
+
+// Test1 has a reference to C$D, which is a top-level class in this case,
+// so there's no INNERCLASS attribute in Test1
+class Test_1 {
+  static C$D mD(C$D cd) { return cd; }
+  static C$E mE(C$E ce) { return ce; }
+  static C$F$G mG(C$F$G cg ) { return cg; }
+}

test/files/run/t9937/Test_2.java

@@ -0,0 +1,12 @@
+class C {
+  class D { public int i() { return 2; } }
+  static class E { public int i() { return 2; } }
+  static class F { static class G { public int i() { return 2; } } }
+}
+
+// Test2 has an INNERCLASS attribute for C$D
+class Test_2 {
+  public static int acceptD(C.D cd) { return cd.i(); }
+  public static int acceptE(C.E ce) { return ce.i(); }
+  public static int acceptG(C.F.G cg ) { return cg.i(); }
+}

test/files/run/t9937/Test_3.scala

@@ -0,0 +1,8 @@
+object Test {
+  def main(args: Array[String]): Unit = {
+    val c = new C
+    assert(Test_2.acceptD(Test_1.mD(new c.D)) == 2)
+    assert(Test_2.acceptE(Test_1.mE(new C.E)) == 2)
+    assert(Test_2.acceptG(Test_1.mG(new C.F.G)) == 2)
+  }
+}