This makes several changes to flutter web app bootstrapping.
* The build now produces a `flutter_bootstrap.js` file.
* By default, this file does the basic streamlined startup of a flutter app with the service worker settings and no user configuration.
* The user can also put a `flutter_bootstrap.js` file in the `web` subdirectory in the project directory which can have whatever custom bootstrapping logic they'd like to write instead. This file is also templated, and can use any of the tokens that can be used with the `index.html` (with the exception of `{{flutter_bootstrap_js}}`, see below).
* Introduced a few new templating tokens for `index.html`:
* `{{flutter_js}}` => inlines the entirety of `flutter.js`
* `{{flutter_service_worker_version}}` => replaced directly by the service worker version. This can be used instead of the script that sets the `serviceWorkerVersion` local variable that we used to have by default.
* `{{flutter_bootstrap_js}}` => inlines the entirety of `flutter_bootstrap.js` (this token obviously doesn't apply to `flutter_bootstrap.js` itself).
* Changed `IndexHtml` to be called `WebTemplate` instead, since it is used for more than just the index.html now.
* We now emit warnings at build time for certain deprecated flows:
* Warn on the old service worker version pattern (i.e.`(const|var) serviceWorkerVersion = null`) and recommends using `{{flutter_service_worker_version}}` token instead
* Warn on use of `FlutterLoader.loadEntrypoint` and recommend using `FlutterLoader.load` instead
* Warn on manual loading of `flutter_service_worker.js`.
* The default `index.html` on `flutter create` now uses an async script tag with `flutter_bootstrap.js`.
This is an attempt at a reland of https://github.com/flutter/flutter/pull/141396
The main changes here that are different than the original PR is fixes to wire up the `flutter test` command properly with the web renderer.
Dual Web Compile has had some issues where `flutter test` is not respecting the `--web-renderer` flag for some reason. I haven't gotten entirely to the bottom of the issue, but for now we need to rever these changes while I investigate. This reverts the following PRs:
https://github.com/flutter/flutter/pull/143128https://github.com/flutter/flutter/pull/141396
While doing this revert, I had a few merge conflicts with https://github.com/flutter/flutter/pull/142760, and I tried to resolve the merge conflicts within the spirit of that PR's change, but @chingjun I might need your input on whether the imports I have modified are okay with regards to the change you were making.
This implements dual compile via the newly available flutter.js bootstrapping APIs for intelligent build fallback.
* Users can now use the `FlutterLoader.load` API from flutter.js
* Flutter tool injects build info into the `index.html` of the user so that the bootstrapper knows which build variants are available to bootstrap
* The semantics of the `--wasm` flag for `flutter build web` have changed:
- Instead of producing a separate `build/web_wasm` directory, the output goes to the `build/web` directory like a normal web build
- Produces a dual build that contains two build variants: dart2wasm+skwasm and dart2js+CanvasKit. The dart2wasm+skwasm will only work on Chrome in a cross-origin isolated context, all other environments will fall back to dart2js+CanvasKit.
- `--wasm` and `--web-renderer` are now mutually exclusive. Since there are multiple build variants with `--wasm`, the web renderer cannot be expressed via a single command-line flag. For now, we are hard coding what build variants are produced with the `--wasm` flag, but I plan on making this more customizable in the future.
* Build targets now can optionally provide a "build key" which can uniquely identify any specific parameterization of that build target. This way, the build target can invalidate itself by changing its build key. This works a bit better than just stuffing everything into the environment defines because (a) it doesn't invalidate the entire build, just the targets which are affected and (b) settings for multiple build variants don't translate well to the flat map of environment defines.
