Enhance AstDumper for debugging and testing

[niloc132]

Enhances the AstDumper utility class with the aim of bringing back some of the functionality previously removed in 64f9b00, where individual methods could be traced from source Java all the way to JS output. This is a small step in that direction that nevertheless provides more insight into what the compiler is doing, through a series of changes:

• Improve printed Java output - classes should list their name, enums and records should be labeled as such, etc. AST traversal is made more visitor-like to make filtering easier.
• JS AST should also be printed, rather than ending with the Java optimization loops, allowing insight into JS passes.
• A filter can be applied to the ast at any stage, resulting in only printing code from the specified files or lines, to more easily follow specific changes through a program.

More improvement remains - multiple permutations may end up mixed in the same file, different compiler passes are not individually listed or labeled, arguments are re-parsed every time they are used, but impact to the API is minimal for now.

[niloc132]

Example of generating an AST dump with JS output included, while working on a fix for #9731 - running a build of the Hello sample before and after the change, and running diff -U10 before.dump after.dump results in this sample output (demonstrating two ways that the code is improving):

 function Button(handler){
   $clinit_FocusWidget();
   ButtonBase.call(this, $createPushButtonElement($doc));
   ($clinit_DOM() , this.element).className = 'gwt-Button' || '';
-  ($clinit_DOM() , this.element).innerHTML = 'Click me' || '';
-  $addDomHandler(this, handler, ($clinit_ClickEvent() , $clinit_ClickEvent() , TYPE));
+  this.element.innerHTML = 'Click me' || '';
+  $addDomHandler(this, handler, ($clinit_ClickEvent() , TYPE));
 }

[niloc132]

CompilerTest doesn't fail locally, investigating...

[niloc132]

Failures appear to be an example of #9947, rerunning.

[niloc132]

Here's an example of the output when writing emulation unit testing - if you add -Dgwt.jjs.dumpAst=/tmp/ast.dump -Dgwt.jjs.dumpAst.filter=com/google/gwt/emultest/java/lang/StringTest.java:130-164 to the jvmargs, you will see this method in its various stages of compilation:

gwt/user/test/com/google/gwt/emultest/java/lang/StringTest.java

Lines 130 to 164 in a0bbaf0

	@SuppressWarnings("ReturnValueIgnored")
	public void testConcat() {
	String abc = String.valueOf(new char[] {'a', 'b', 'c'});
	String def = String.valueOf(new char[] {'d', 'e', 'f'});
	String empty = String.valueOf(new char[] {});
	assertEquals("abcdef", abc + def);
	assertEquals("abcdef", abc.concat(def));
	assertEquals("", empty.concat(empty));
	char c = def.charAt(0);
	String s = abc;
	assertEquals("abcd", abc + 'd');
	assertEquals("abcd", abc + c);
	assertEquals("abcd", s + 'd');
	assertEquals("abcd", s + c);
	s += c;
	assertEquals("abcd", s);
	try {
	returnNull().concat("");
	fail();
	} catch (NullPointerException e) {
	// expected
	} catch (JavaScriptException e) {
	// expected
	}
	try {
	hideFromCompiler("").concat(returnNull());
	fail();
	} catch (NullPointerException e) {
	// expected
	} catch (JavaScriptException e) {
	// expected
	}
	}

If you are doing draft tests (e.g. test.draft.htmlunit), you won't see as much, while prod tests (e.g. test.web.htmlunit) will show more steps to get to the final JS. This isn't a particularly interesting method to look at, so I'm not pasting the whole results (see my gist for the whole thing), but one more interesting thing to call out is that by just jumping to the bottom, you can see the unobfuscated (but still optimized) JS method:

_.testConcat = function testConcat(){
  var abc, c, def, empty, s;
  abc = valueOf(stampJavaTypeInfo(getClassLiteralForArray(C_classLit, 1), {8:1, 3:1}, 7, 15, [97, 98, 99]));
  def = valueOf(stampJavaTypeInfo(getClassLiteralForArray(C_classLit, 1), {8:1, 3:1}, 7, 15, [100, 101, 102]));
  empty = valueOf(stampJavaTypeInfo(getClassLiteralForArray(C_classLit, 1), {8:1, 3:1}, 7, 15, []));
  assertEquals('abcdef', abc + def);
  assertEquals('abcdef', (checkCriticalNotNull(abc) , abc + (checkCriticalNotNull(def) , def)));
  assertEquals('', (checkCriticalNotNull(empty) , empty + (checkCriticalNotNull(empty) , empty)));
  c = (checkCriticalStringElementIndex(0, def.length) , def.charCodeAt(0));
  s = abc;
  assertEquals('abcd', abc + 'd');
  assertEquals('abcd', abc + String.fromCharCode(c));
  assertEquals('abcd', s + 'd');
  assertEquals('abcd', s + String.fromCharCode(c));
  s += String.fromCharCode(c);
  assertEquals('abcd', s);
  try {
    ($wnd.Math.random() < -1 && fail() , null).$_nullMethod();
    fail();
  }
   catch ($e0) {
    $e0 = toJava($e0);
    if (!instanceOf($e0, 13))
      if (!instanceOf($e0, 15))
        throw toJs($e0);
  }
  try {
    $concat(($wnd.Math.random() < -1 && fail() , ''), ($wnd.Math.random() < -1 && fail() , null));
    fail();
  }
   catch ($e1) {
    $e1 = toJava($e1);
    if (!instanceOf($e1, 13))
      if (!instanceOf($e1, 15))
        throw toJs($e1);
  }
}