IOORE importing type with name ending in a period

[jpobst]

Context: com.google.firebase.firestore.model.Document

The following code:

  private static final Comparator<Document> KEY_COMPARATOR =
      (left, right) -> left.getKey().compareTo(right.getKey());

  /** A document comparator that returns document by key and key only. */
  public static Comparator<Document> keyComparator() {
    return KEY_COMPARATOR;
  }

is being parsed out as:

<class abstract="false" deprecated="not deprecated" extends="java.lang.Object" extends-generic-aware="java.lang.Object" jni-extends="Ljava/lang/Object;" final="false" name="Document." static="false" visibility="public" jni-signature="Lcom/google/firebase/firestore/model/Document$;"></class>

The name='Document.' causes an IndexOutOfRangeException building the model from the XML:

   at System.String.get_Chars(Int32 index)
   at MonoDroid.Generation.XmlApiImporter.CreateGenBaseSupport(XElement pkg, XElement elem, Boolean isInterface) in C:\code\xamarin-android-backport\external\Java.Interop\tools\generator\Java.Interop.Tools.Generator.Importers\XmlApiImporter.cs:line 290
   at MonoDroid.Generation.XmlApiImporter.CreateClass(XElement pkg, XElement elem, CodeGenerationOptions options) in C:\code\xamarin-android-backport\external\Java.Interop\tools\generator\Java.Interop.Tools.Generator.Importers\XmlApiImporter.cs:line 110
   at MonoDroid.Generation.XmlApiImporter.ParsePackage(XElement ns, CodeGenerationOptions options) in C:\code\xamarin-android-backport\external\Java.Interop\tools\generator\Java.Interop.Tools.Generator.Importers\XmlApiImporter.cs:line 66
   at MonoDroid.Generation.XmlApiImporter.Parse(XDocument doc, CodeGenerationOptions options) in C:\code\xamarin-android-backport\external\Java.Interop\tools\generator\Java.Interop.Tools.Generator.Importers\XmlApiImporter.cs:line 35

[jpobst]

Notes:

This is an issue caused by a change between firebase-firestore 22.1.1 and 22.1.2.

Java source code: https://github.com/firebase/firebase-android-sdk/blob/master/firebase-firestore/src/main/java/com/google/firebase/firestore/model/Document.java

Java library: https://maven.google.com/web/index.html?q=firestore#com.google.firebase:firebase-firestore:22.1.2

Decompilation:

class-parse

    <class
      abstract="false"
      deprecated="not deprecated"
      jni-extends="Ljava/lang/Object;"
      extends="java.lang.Object"
      extends-generic-aware="java.lang.Object"
      final="false"
      name="Document."
      jni-signature="Lcom/google/firebase/firestore/model/Document$;"
      source-file-name="Document.java"
      static="false"
      visibility="public" />

adjusted

    <class abstract="false" deprecated="not deprecated" extends="java.lang.Object" 
extends-generic-aware="java.lang.Object" jni-extends="Ljava/lang/Object;" final="false" 
name="Document." static="false" visibility="public" 
jni-signature="Lcom/google/firebase/firestore/model/Document$;"></class>

[AmrAlSayed0]

This would also help with this issue #789 (comment).

[jonpryor]

I'm wondering about how specifically this is happening, as I cannot repro it:

import java.util.Comparator;

class Example implements Comparable<Example> {
    public int compareTo(Example a) {return 0;}

    static final Comparator<Example> COMPARATOR = (left, right) -> left.compareTo(right);

    public static Comparator<Example> keyComparator() { return COMPARATOR; }
}

Using both JDK 1.8 and JDK 11's javac, I do not get an Example$.class file as output. Instead, Example.COMPARATOR is implemented in terms of InvokeDynamic & a static method:

$ javap -l -constants -c -private -s Example.class
…
  private static int lambda$static$0(Example, Example);
    descriptor: (LExample;LExample;)I
    Code:
       0: aload_0
       1: aload_1
       2: invokevirtual #4                  // Method compareTo:(LExample;)I
       5: ireturn
    LineNumberTable:
      line 6: 0

  static {};
    descriptor: ()V
    Code:
       0: invokedynamic #5,  0              // InvokeDynamic #0:compare:()Ljava/util/Comparator;
       5: putstatic     #2                  // Field COMPARATOR:Ljava/util/Comparator;
       8: return
    LineNumberTable:
      line 6: 0

The lambda$static$0 method is from the lambda expression.

(My Kotlin toolchain is screwed up, so I can't currently try to see what Kotlin would do in a similar scenario.)

I thus don't understand where Document. is coming from. I certainly don't understand why Document. is public, of all things.

[jonpryor]

Doubly odd is that Document.class doesn't even mention Document$.class:

$ javap -constants -p -l -c -verbose -private -s  Document.class| grep 'Document\$'
  #28 = Utf8               com/google/firebase/firestore/model/Document$$Lambda$1
  #29 = Class              #28            // com/google/firebase/firestore/model/Document$$Lambda$1
  #33 = Methodref          #29.#32        // com/google/firebase/firestore/model/Document$$Lambda$1.lambdaFactory$:()Ljava/util/Comparator;
         0: invokestatic  #33                 // Method com/google/firebase/firestore/model/Document$$Lambda$1.lambdaFactory$:()Ljava/util/Comparator;
# note: no mention of `Document$`,
# except as part of a larger `Document$$Lambda$1`

Document$$Lambda$1.class does mention Document$, as an invokestatic target:

  public int compare(java.lang.Object, java.lang.Object);
    descriptor: (Ljava/lang/Object;Ljava/lang/Object;)I
    flags: (0x0001) ACC_PUBLIC
    Code:
      stack=2, locals=3, args_size=3
         0: aload_1
         1: checkcast     #14                 // class com/google/firebase/firestore/model/Document
         4: aload_2
         5: checkcast     #14                 // class com/google/firebase/firestore/model/Document
         8: invokestatic  #20                 // Method com/google/firebase/firestore/model/Document$.lambda$static$0:(Lcom/google/firebase/firestore/model/Document;Lcom/google/firebase/firestore/model/Document;)I
        11: ireturn

I have to wonder if there's some "Java bytecode post processing" going on…

[jonpryor]

Meanwhile, @jpobst mentioned:

My current thought is to skip types with no effective "name" in XmlApiImporter in generator with a warning or a debug message.

We already skip types with "obfuscated" names:

https://github.com/xamarin/java.interop/blob/12e670a8560f69581d3a3adf0a9d91e8ce8c9afa/tools/generator/Java.Interop.Tools.Generator.Importers/XmlApiImporter.cs#L63-L72

https://github.com/xamarin/java.interop/blob/12e670a8560f69581d3a3adf0a9d91e8ce8c9afa/tools/generator/Java.Interop.Tools.Generator.Importers/XmlApiImporter.cs#L490-L507

so perhaps the "easy" fix is to extend IsObfuscatedName() so that Document. is treated as "obfuscated"?

[jpobst]

I have to wonder if there's some "Java bytecode post processing" going on…

Yeah, I couldn't repro it either, and thought this might be the case.