Joe Savona
723b616c67
See discussion on #2448 for full context. In the new `@enablePreserveExistingMemoizationGuarantees` mode, the goal is to preserve the existing referential equality guarantees from the original code. #2448 lays the groundwork by explicitly marking the _output_ of each useMemo block as memoized, hinting to the compiler that the value cannot subsequently change. This ensures the mutable range doesn't extend _later_, possibly overlapping a hook call and causing memoization to gett pruned. This PR fixes the other direction. There are cases where free variables referenced in the useMemo block could have been inferred as mutated, which could then extend the _start_ of the range earlier past a hook: ```javascript const foo = createObject(); useBar(); const baz = useMemo(() => { const baz = createObject(); maybeMutate(foo, baz); return baz; }, [foo]); ``` Here the compiler would infer that both `baz` and `foo` are mutable at the `maybeMutate()` call, grouping them in the same scope. But that scope would span the `useBar()` call, and be pruned, meaning that `baz` went unmemoized. However, useMemo blocks shouldn't be mutating free variables. Only variables newly created within the useMemo block should be mutable. So this PR extends the feature to treat all free variables referenced in a useMemo block as frozen as of the block itself.
React Forget
React Forget is an experimental Babel plugin to automatically memoize React Hooks and Components.
Development
# tsc --watch
$ yarn dev
# in another terminal window
$ yarn test --watch
Notes
An overview of the implementation can be found in the Architecture Overview.
This transform
- needs plugin-syntax-jsx as a dependency to inherit the syntax from.
- should be run before plugin-transform-react-jsx
- assume the enforcement of rules of hooks, i.e.
- only call hooks from React functions
- only call hooks at the top level
- https://www.npmjs.com/package/eslint-plugin-react-hooks
Scaffolding
- https://github.com/facebook/flow/tree/master/packages/babel-plugin-transform-flow-enums
- https://github.com/babel/babel/blob/main/packages/babel-plugin-transform-react-jsx/src/create-plugin.ts
Reference
Rust Development
First-Time Setup
- Install Rust using
rustup. See the guide at https://www.rust-lang.org/tools/install. - Install Visual Studio Code from https://code.visualstudio.com/. Note to Meta employees: install the stock version from that website, not the pre-installed version.
- Install the Rust Analyzer VSCode extension through the VSCode marketplace. See instructions at https://rust-analyzer.github.io/manual.html#vs-code.
- Install
cargo editwhich extends cargo with commands to manage dependencies. See https://github.com/killercup/cargo-edit#installation - Install
cargo instawhich extens cargo with a command to manage snapshots. See https://insta.rs/docs/cli/
Workspace Hygiene
Adding Dependencies
To add a dependency, add it to the top-level Cargo.toml
// Cargo.toml
[workspace.dependencies]
...
new_dep = { version = "x.y.z" }
...
Then reference it from your crate as follows:
// crates/forget_foo/Cargo.toml
[dependencies]
...
new_dep = { workspace = true }
...
Adding new crates
Rust's compilation strategy is largely based on parallelizing at the granularity of crates, so builds can be faster when projects have more but smaller crates. Where possible it helps to structure crates to minimize dependencies. For example, our various compiler passes depend on each other in the sense that they often must run in a certain order. However, they often don't need to call each other, so they can generally be split into crates of similar types of passes, so that those crates can compile in parallel.
As a rule of thumb, add crates at roughly the granularity of our existing top-level folds. If you have some one-off utility code that
doesn't fit neatly in a crate, add it to forget_utils rather than add a one-off crate for it.
Running Tests
Run all tests with the following from the root directory:
cargo test
The majority of our tests will (should) live in the forget_fixtures crate, which is a test-only crate that runs compilation end-to-end with snapshot
tests. To run just these tests use:
# quiet version
cargo test -p forget_fixtures
# without suppressing stdout/stderr output
cargo test -p forget_fixtures -- --nocapture
Another hint is that VSCode will show a "Run test" option if you hover over a test in the source code, this lets you run a single test easily. The command line will also give you the CLI command to run just that one test.
Updating Snapshots
The above tests make frequent use of snapshot tests. If snapshots do not match the tests will fail with a diff, if the new output is correct you can accept the changes with:
cargo insta accept
If this command fails, see the note in "first-time setup" about installing cargo insta.
CI Configuration
GitHub CI is configured in .github/workflows/rust.yml.