Incorrect handling of mandated parameter names in MethodParameters attributes

When reading MethodParameters attributes, javac reads the names of all provided parameters including 'mandated' parameters (e.g. the enclosing instance parameter of inner classes) [1]. When setting the parameters names of a MethodSymbol it only skips over enclosing instance parameters if the names were inferred from the local variable table, and not if they were read from the MethodParameters attribute [2].

The result is that mandated parameters names read from the MethodParameter attribute are used for non-mandated parameters, and the real names are offset.

[1] http://hg.openjdk.java.net/jdk9/dev/langtools/file/ee787e34231d/src/jdk.compiler/share/classes/com/sun/tools/javac/jvm/ClassReader.java#l1288
[2] http://hg.openjdk.java.net/jdk9/dev/langtools/file/ee787e34231d/src/jdk.compiler/share/classes/com/sun/tools/javac/jvm/ClassReader.java#l2476

Skipping over mandated parameter names in MethodParameter attributes avoids this issue:

diff -r 9b2de82e7e49 src/jdk.compiler/share/classes/com/sun/tools/javac/jvm/ClassReader.java
--- a/src/jdk.compiler/share/classes/com/sun/tools/javac/jvm/ClassReader.java Wed Feb 15 16:18:18 2017 -0800
+++ b/src/jdk.compiler/share/classes/com/sun/tools/javac/jvm/ClassReader.java Thu Mar 23 15:22:23 2017 -0700
@@ -1285,10 +1285,14 @@
                         int numEntries = nextByte();
                         parameterNameIndices = new int[numEntries];
                         haveParameterNameIndices = true;
+ int index = 0;
                         for (int i = 0; i < numEntries; i++) {
                             int nameIndex = nextChar();
                             int flags = nextChar();
- parameterNameIndices[i] = nameIndex;
+ if ((flags & Flags.MANDATED) == Flags.MANDATED) {
+ continue;
+ }
+ parameterNameIndices[index++] = nameIndex;
                         }
                     }
                     bp = newbp;

Repro:

=== ./plugin/module-info.java
module parameterplugin {
  requires transitive jdk.compiler;
  provides com.sun.source.util.Plugin with parameterplugin.ParameterPlugin;
}
=== ./plugin/parameterplugin/ParameterPlugin.java
package parameterplugin;

import static java.util.stream.Collectors.joining;

import com.sun.source.tree.*;
import com.sun.source.util.*;
import javax.lang.model.element.*;

public class ParameterPlugin implements Plugin {

  @Override
  public String getName() {
    return "ParameterPlugin";
  }

  @Override
  public void init(JavacTask javacTask, String... strings) {
    javacTask.addTaskListener(
        new TaskListener() {
          @Override
          public void finished(TaskEvent e) {
            if (e.getKind() != TaskEvent.Kind.ENTER) {
              return;
            }
            new TreePathScanner<Void, Void>() {
              @Override
              public Void visitNewClass(NewClassTree node, Void aVoid) {
                ExecutableElement e =
                    (ExecutableElement) Trees.instance(javacTask).getElement(getCurrentPath());
                System.err.println(
                    e.getParameters()
                        .stream()
                        .map(p -> p.asType() + " " + p.getSimpleName())
                        .collect(joining(", ")));
                return null;
              }
            }.scan(new TreePath(e.getCompilationUnit()), null);
          }
        });
  }
}
=== ./A.java
class A {
  class I {
    I(int a, int b) {}
  }
}
=== ./B.java
class B {
  void f(A a) {
    a.new I(1, 2);
  }
}
===

Actual:

$ javac -parameters $(find . -name "*.java")
$ javac --processor-module-path plugin -Xplugin:Parameter
Plugin B.java -sourcepath : -parameters
int this$0, int a

Expected:

int a, int b