bd432f6316
Summary: Fixes https://github.com/facebook/prepack/issues/1462. Supersedes my attempts in https://github.com/facebook/prepack/pull/1459, https://github.com/facebook/prepack/pull/1460, and https://github.com/facebook/prepack/pull/1468. The git history reflects a lot of back-and-forth so it might make more sense to look at the final code. There are two separate fixes here: * If we have a partial simple source and then a normal source, we shouldn't attempt to `Set` any further keys after the first partial. Instead we should emit residual `Object.assign` calls. If we set the keys, we end up with a wrong key order (a key gets set earlier than it should have). Key order (AFAIK) isn't mandated by the spec but tends to be relied on in product code because all engines preserve it in the order of assignments. * It is not safe to mutate either a partial source or the target (when some sources are partial) in Prepack land after the `Object.assign` call. This is because Prepack will serialize all those mutations (as the object final state) right into the residual `Object.assign` call. But this is wrong because they haven't happened yet. The second issue is thorny. In many cases sources (and the target) don't get mutated later. So we'd like to keep supporting `Object.assign` with partials when we don't touch them later. To solve it, I introduced new `obj.makeFinal()` and `obj.isFinalObject()` methods. If an object is marked as "final", we cannot make changes to it that would change its emitted form. This is a way for us to say "let's try to continue as far as we can, but if anything tries to touch it, fatal". It doesn't mean the object is "frozen" (technically we didn't freeze it), but it means Prepack can't deal with further mutations to it because Prepack has already "used" its current snapshot and it would be unsafe to change it. I'm not sure I'm checking `isFinalObject()` in all places where it's necessary. If there is a way to do this with stronger guarantees please let me know. I want to still highlight that this fixes multiple existing issues on master so it's a step in a safer duration, even though I'm wary that if the concept is not fully baked, it might give a false sense of security. Here's how we're using this new infra. When we emit a residual `Object.assign()` call because some sources are partial (and simple), I mark all sources and the target as "final". So if they don't get mutated, everything is fine. If they get mutated later, we get a fatal when they do. In the future Prepack might support this better, but the fatal makes it clear which cases it currently doesn't handle (and would produce wrong output for). There might also be other cases where making an object as "final" lets us continue further, although I don't know Prepack codebase well enough to tell for sure. So I'm hoping it is useful as a generic concept outside of the `Object.assign()` use case. The pure mode is treated a bit differently. In the pure mode we can get away with "leaking" final values whenever we need to write to them. Then they're treated like any other "leaked" object. I added regression tests for all existing cases I could find, both in pure and impure mode. Closes https://github.com/facebook/prepack/pull/1469 Reviewed By: trueadm Differential Revision: D7046641 Pulled By: gaearon fbshipit-source-id: 472188eeabe28dcce36ab026ecbcbc4c8e83176b |
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| flow-libs | ||
| flow-typed/npm | ||
| scripts | ||
| src | ||
| test | ||
| website | ||
| .babelrc | ||
| .eslintignore | ||
| .eslintrc | ||
| .flowconfig | ||
| .gitignore | ||
| .gitmodules | ||
| .watchmanconfig | ||
| circle.yml | ||
| CODE_OF_CONDUCT.md | ||
| CONTRIBUTING.md | ||
| LICENSE | ||
| package.json | ||
| PATENTS | ||
| README.md | ||
| webpack.config.js | ||
| yarn.lock | ||
Prepack 
Prepack is a partial evaluator for JavaScript. Prepack rewrites a JavaScript bundle, resulting in JavaScript code that executes more efficiently. For initialization-heavy code, Prepack works best in an environment where JavaScript parsing is effectively cached.
See the official prepack.io website for an introduction and an interactive REPL playground.
How to use Prepack
Install the CLI via npm,
$ npm install -g prepack
Or if you prefer yarn, make sure you get yarn first,
$ npm install -g yarn
and then install the Prepack CLI via yarn:
$ yarn global add prepack
You may need to prepend (pun intended!) the command with sudo in some cases.
Let the party begin
To compile a file and print the output to the console:
$ prepack script.js
If you want to compile a file and output to another file:
$ prepack script.js --out script-processed.js
Detailed instructions and the API can be found at Prepack CLI: Getting Started
Plugins to other tools
The following are a few plugins to other tools. They have been created and are maintained separately from Prepack itself. If you run into any issues with those plugins, please ask the plugin maintainers for support.
- A Rollup plugin for Prepack
- A Webpack plugin for Prepack
- A Visual Studio code plugin for Prepack
- A babel plugin which transforms Flow annotations into prepack model declarations.
Status
- test262 status on master branch
- code coverage report for serialization tests
- To see the status for a pull request, look for the message All checks have passed or All checks have failed. Click on Show all checks, Details, Artifacts, and then test262-status.txt or coverage-report-sourcemapped/index.html.
How to get the code
- Clone repository and make it your current directory.
git submodule initgit submodule update --init- Get yarn and node, then do
yarn
Note: For development work you really need yarn, as many scripts require it.
How to build, lint, type check
- Get the code
yarn build
You can later runyarn watchin the background to just compile changed files on the fly.yarn lintyarn flow
How to run tests
- Get the code
- Make sure the code is built, either by running
yarn buildoryarn watch yarn test
You can run individual test suites as follows:
yarn test-serializer
This tests the interpreter and serializer. All tests should pass.yarn test-test262
This tests conformance against the test262 suite. Not all will pass, increasing conformance is work in progress.
How to run the interpreter
- Get the code
- Make sure the code is built, either by running
yarn buildoryarn watch yarn repl
This starts an interactive interpreter session.
How to run Prepack
-
Get the code
-
Make sure the code is built, either by running
yarn buildoryarn watch. -
Have a JavaScript file handy that you want to prepack, for example:
echo "function hello() { return 'hello'; } function world() { return 'world'; } s = hello() + ' ' + world();" >/tmp/sample.js -
cat /tmp/sample.js | yarn prepack
Try--helpfor more options.
How to validate changes
Instead of building, linting, type checking, testing separately, the following does everything together:
yarn validate
How to edit the website
The content for prepack.io resides in the website directory of this repository. To make changes, submit a pull request, just like for any code changes.
In order to run the website locally at localhost:8000:
- Build prepack into the website:
yarn build-bundle && mv prepack.min.js website/js - Run
python -m SimpleHTTPServer(Python 2) orpython -m http.server(Python 3) from thewebsite/directory
How to contribute
For more information about contributing pull requests and issues, see our Contribution Guidelines.
License
Prepack is BSD-licensed. We also provide an additional patent grant.