Sdk: Tree-shaking and inlining

[ranquild]

Compile this code with dart2js and --trust-type-annotations

import 'dart:html';

void main() {
  HtmlElement element = new DivElement();
  element.classes.add('my-class-name');
}

Main function is compiled to:

var t1 = document;
t1 = t1.createElement("div");
t1.classList.add("my-class-name");

However compiled file size in around 100 kb and contains code for _ElementCssClassSet. However, all used code of this class is inlined. It seems that tree-shaking and code exclusion doesn't work well with inlining/@JS() annotations. Ideally compiler should be able to eliminate code for all dart classes in this example. Resolving this issue might result in huge improvements in compiled dart to js file sizes.

[ranquild]

@rakudrama Please have a look.

[rakudrama]

This is what I see.
I see this at the latest revision, and something similar at 1.22.

$ cat bug23016.dart
import 'dart:html';

void main() {
  HtmlElement element = new DivElement();
  element.classes.add('my-class-name');
}
$ sdk/bin/dart2js --trust-type-annotations bug23016.dart --out=o1.js
Dart file (bug23016.dart) compiled to JavaScript: o1.js
$ grep ElementCss o1.js
$ grep -i Css o1.js
$ wc -c o1.js
76140 o1.js
$ 

75k is annoying.
Most of that is the same for all apps, and is actually needed when the app uses tear-offs, catches exceptions, creates an object, does interpolation, etc.
We could do better here but we have been spending our effort on 50 page angular apps rather than 5 small examples.

[ranquild]

@rakudrama Small example is just to demonstrate that tree-shaking can do much better. In my opinion algorithm for finding unused methods/classes should be the same for small apps and large apps. If something is not used in compiled code it should not be there.