use MethodParameter attribute if code attribute is missing

[char3210]

this applies parameter names for abstract methods and interface methods

[liach]

nameIndex may be 0, indicating null. getEntry does not accept 0 arguments:

cfr/src/org/benf/cfr/reader/entities/constantpool/ConstantPool.java

Line 155 in dd14c75

if (index == 0) throw new ConfusedCFRException("Attempt to fetch element 0 from constant pool");

[liach]

Same here, no good if it's 0-name; it's totally legal to have null name in MethodParameters (storing parameter flags only) but valid name in LocalVariableTable/LocalVariableTypeTable

[char3210]

not sure what exactly isGoodName is supposed to represent, but I don't see a very easy way to fix this currently since this doesn't know which parameter it is until dumpParameter is called...

[liach]

Same, will NPE on .getValue

[liach]

On a side note, I don't know why cfr's author doesn't just implement the length calculation and attribute name reading in the base Attribute class. This brings visible confusion when reviewing the attribute changes, and requires extra overrides and fields for shared content.

[liach]

Also as a side note: javac actually does NOT generate MethodParameters attributes by default! So you can hope Mojang actually added -parameters flag when compiling their binaries, which I don't think is the case.

In Java 20:

public interface Apple {
	int my(int argumentName);
}

compiles with javac Apple.java to javap output:

Classfile /C:/code/test/Apple.class
  Last modified May 3, 2023; size 111 bytes
  SHA-256 checksum c0538a6bdbb501ff27f98571a00bfccf855d25aca7d63ec9a446be8ebb783451
  Compiled from "Apple.java"
public interface Apple
  minor version: 0
  major version: 64
  flags: (0x0601) ACC_PUBLIC, ACC_INTERFACE, ACC_ABSTRACT
  this_class: #1                          // Apple
  super_class: #3                         // java/lang/Object
  interfaces: 0, fields: 0, methods: 1, attributes: 1
Constant pool:
  #1 = Class              #2              // Apple
  #2 = Utf8               Apple
  #3 = Class              #4              // java/lang/Object
  #4 = Utf8               java/lang/Object
  #5 = Utf8               my
  #6 = Utf8               (I)I
  #7 = Utf8               SourceFile
  #8 = Utf8               Apple.java
{
  public abstract int my(int);
    descriptor: (I)I
    flags: (0x0401) ACC_PUBLIC, ACC_ABSTRACT
}
SourceFile: "Apple.java"

No MethodParameters is available.

[char3210]

yeah that's expected, but this is mostly for decompiling remapped jars, and the remapping process (intermediary -> named) does emit the MethodParameters attributes if parameters are present, at least in loom