#  [](https://cdk.dev) [](#contributors-) [](https://github.com/aws/jsii-rosetta/actions?query=workflow%3Abuild+branch%3Amain) [](https://www.npmjs.com/package/jsii-rosetta) ## Overview `jsii-rosetta` translates code samples contained in jsii libraries from TypeScript to supported *jsii* target languages. This is what enables the [AWS Cloud Development Kit][cdk] to deliver polyglot documentation from a single codebase! `jsii-rosetta` leverages knowledge about jsii language translation conventions in order to produce translations. It only supports a limited set of TypeScript language features (which can be reliably represented in other languages). [cdk]: https://github.com/aws/aws-cdk ## :question: Documentation Head over to our [documentation website](https://aws.github.io/jsii)! The jsii toolchain spreads out on multiple repositories: - [aws/jsii-compiler](https://github.com/aws/jsii-compiler) is where the `jsii` compiler is maintained (except releases in the `1.x` line) - [aws/jsii-rosetta](https://github.com/aws/jsii-rosetta) is where the `jsii-rosetta` sample code transliteration tool is maintained (except releases in the `1.x` line) - [aws/jsii](https://github.com/aws/jsii) is where the rest of the toolchain is maintained, including: - `@jsii/spec`, the package that defines the *`.jsii` assembly* specification - `jsii-config`, an interactive tool to help configure your jsii package - `jsii-pacmak`, the bindings generator for jsii packages - `jsii-reflect`, a higher-level way to process *`.jsii` assemblies* - The jsii runtime libraries for the supported jsii target languages - `1.x` release lines of `jsii` and `jsii-rosetta` # :gear: Contributing See [CONTRIBUTING](./CONTRIBUTING.md). # :school_satchel: Getting Started ## Rosetta for example authors This section describes what to pay attention to when writing examples that will be converted by Rosetta. ### Making examples compile The translator can translate both code that completely compiles and typechecks, as well as code that doesn't. In case of non-compiling samples the translations will be based off of grammatical parsing only. This has the downside that we do not have the type information available to the exact thing in all instances. Specifically struct types will not be able to be inferred from object literals. Have a look at the following piece of code: ```ts someObject.someMethod('foo', { bar: 3, }); ``` In non-TypeScript languages, it is important to know the type of the second argument to the method here. However, without access to the definition of `someMethod()`, it's impossible for Rosetta to know the type, and hence it cannot translate the example. It is therefore important to include necessary imports, variable declarations, etc, to give Rosetta enough information to figure out what's going on in this code, and the example should read like this: ```ts import * as myLib from 'some-library'; declare const someObject: myLib.SomeClass; someObject.someMethod('foo', { bar: 3, }); ``` ### Enforcing correct examples By default, Rosetta will accept non-compiling examples. If you set `jsiiRosetta.strict` to `true` in your `package.json`, the Rosetta command will fail if any example contains an error: ```js /// package.json { "jsiiRosetta": { "strict": true } } ``` ### Fixtures To avoid having to repeat common setup every time, code samples can use "fixtures": a source template where the example is inserted. A fixture must contain the text `/// here` and typically looks like this: ```ts const * as module from '@some/dependency'; class MyClass { constructor() { const obj = new MyObject(); /// here } } ``` The example will be inserted at the location marked as `/// here` and will have access to `module`, `obj` and `this`. Any `import` statements found in the example will automatically be hoisted at the top of the fixture, where they are guaranteed to be syntactically valid. The default file loaded as a fixture is called `rosetta/default.ts-fixture` in the package directory (if it exists). Examples can request an alternative fixture by specifying a `fixture` parameter as part of the code block fence: ````text ```ts fixture=some-fixture ```` Or opt out of using the default fixture by specifying `nofixture`: ````text ```ts nofixture ```` To specify fixtures in an `@example` block, use an accompanying `@exampleMetadata` tag: ````text /** * My cool class * * @exampleMetadata fixture=with-setup * @example * * new MyCoolClass(); */ ```` ### Dependencies When compiling examples, Rosetta will make sure your package itself and all of its `dependencies` and `peerDependencies` are available in the dependency closure that your examples will be compiled in. If there are packages you want to use in an example that should *not* be part of your package's dependencies, declare them in `jsiiRosetta.exampleDependencies` in your `package.json`: ```js /// package.json { "jsiiRosetta": { "exampleDependencies": { "@some-other/package": "^1.2.3", "@yet-another/package": "*", } } } ``` You can also set up a directory with correct dependencies yourself, and pass `--directory` when running `jsii-rosetta extract`. We recommend using the automatic closure building mechanism and specifying `exampleDependencies` though. ## Rosetta for package publishers This section describes how Rosetta integrates into your build process. ### Extract Rosetta has a number of subcommands. The most important one is `jsii-rosetta extract`. The `jsii-rosetta extract` command will take one or more jsii assemblies, extract the snippets from them, will try to compile them with respect to a given home directory, and finally store all translations in something called a "tablet". A couple of things to note here: * Snippets are always read from the jsii assembly. That means if you make changes to examples in source files, you must first re-run `jsii` to regenerate the assembly, before re-running `jsii-rosetta extract`. * The compilation directory will be used to resolve `import`s. Currently, you are responsible for building a directory with the correct `node_modules` directories in there so that a TypeScript compilation step will find all libraries referenced in the examples. This is especially revelant if your examples include libraries that depend on the *current* library: it is not uncommon to write examples in library `A` showing how to use it in combination with library `B`, where `B` depends on `A`. However, since by definition `B` *cannot* be in the set of dependencies of `A`, you must build a directory with both `B` and `A` in it somewhere in your filesystem and run Rosetta in that directory. * "Extract" will compile samples in parallel. The more assemblies you give it at the same time, the more efficient of a job it will be able to do. The extract command will write a file named `.jsii.tabl.json` next to every assembly, containing translations for all samples found in the assembly. You should include this file in your NPM package when you publish, so that downstream consumers of the package have access to the translations. An example invocation of `jsii-rosetta extract` looks like this: ```sh jsii-rosetta extract --directory some/dir $(find . -name .jsii) ``` #### Running in parallel Since TypeScript compilation takes a lot of time, much time can be gained by using the CPUs in your system effectively. `jsii-rosetta extract` will run the compilations in parallel. `jsii-rosetta` will use a number of workers equal to half the number of CPU cores, up to a maximum of 16 workers. This default maximum can be overridden by setting the `JSII_ROSETTA_MAX_WORKER_COUNT` environment variable. If you get out of memory errors running too many workers, run a command like this to raise the memory allowed for your workers: ```sh /sbin/sysctl -w vm.max_map_count=2251954 ``` #### Caching Rosetta extract will translate all examples found in `.jsii` and write the translations to `.jsii.tabl.json`. From compilation to compilation, many of these examples won't have changed. Since TypeScript compilation is a fairly expensive process, we would like to avoid doing unnecessary work as much as possible. To that end, rosetta can reuse translations from a cache, and write new translations into the same cache: ```sh jsii-rosetta extract \ --directory some/dir \ --cache cache.json \ [--trim-cache] \ $(find . -name .jsii) ``` The `--trim-cache` flag will remove any old translations from the cache that don't exist anymore in any of the given assemblies. This prevents the cache from growing endlessly over time (an equivalent `jsii-rosetta trim-cache` command is available if your workflow involves running `extract` in multiple distinct invocations and want to retain the cache between them). ### Infuse The `jsii-rosetta infuse` command increases the coverage of examples for classes in the assembly. It finds classes in the assembly that don't have an example associated with them yet (as specified via the `@example` tag in the doc comments), but that are used in another example found elsewhere—in either a `README` or an example of another class—it will copy the example to all classes involved. This will make sure your handwritten examples go as far as possible. Note that in order to do this, `infuse` will *modify* the assemblies it is given. `rosetta infuse` depends on the analysis perfomed by `rosetta extract`, and must therefore be run after `extract`. It can also be run as part of `extract`, by passing the `--infuse` flag: ```sh jsii-rosetta extract \ --directory some/dir \ --infuse \ $(find . -name .jsii) ``` ### Translations and pacmak `jsii-pacmak` will read translation from tablets to substitute translated examples into the generated source bindings. `pacmak` will automatically read individual `.jsii.tabl.json` files if present, and can additionally also read from a global tablet file. When a translation for a code sample cannot be found, `pacmak` can be configured to do one of the following: * Leave the sample untranslated (default) * Translate the sample in-place (this will slow down generation a lot, and you will not have the fine control over the compilation environment that you would have if you were to use the `extract` command) * Fail Example: ```sh jsii-pacmak \ [--rosetta-tablet=global.json] \ [--rosetta-unknown-snippets=verbatim|translate|fail] ``` ### Data flow The diagram below shows how data flows through the jsii tools when used together: ```text ┌───────────┐ │ │ │ Source ├───┐ │ │ │ ╔══════════╗ ┌────────────┐ ╔═══════════════╗ ┌──────────┐ └───────────┘ │ ║ ║ │ │ ║ rosetta ║ │ │ ├───▶║ jsii ║───▶│ assembly │────▶║ extract ║───▶│ tablet │ ┌───────────┐ │ ║ ║ │ │ ║ ║ │ │ │ │ │ ╚══════════╝ └────────────┘ ╚═══════════════╝ └──────────┘ │ README │───┘ │ │ │ │ │ │ └───────────┘ │ ╔═══════════════╗ │ │ ║ rosetta ║ │ └──────────▶║ infuse ║◀─────────┘ ║ ║ ╚═══════════════╝ │ ┌───────────────────┴───────────────────┐ │ │ ▼ ▼ ┌────────────┐ ┌──────────┐ │ │ │ │ │ assembly' │ │ tablet' │ │ │ │ │ └────────────┘ └──────────┘ │ │ │ │ │ ▼ ┌─────────────┐ │ ╔═══════════════╗ ┌┴────────────┐│ │ ║ ║ │ ││ └──────────────────────────────▶║ pacmak ║────▶│ packages ││ ║ ║ │ ├┘ ╚═══════════════╝ └─────────────┘ (potentially live-translates) ``` ## Advanced topics ### Hiding code from samples In order to make examples compile, boilerplate code may need to be added that detracts from the example at hand (such as variable declarations and imports). This package supports hiding parts of the original source after translation. To mark special locations in the source tree, we can use one of three mechanisms: * Use a `void` expression statement to mark statement locations in the AST. * Use the `comma` operator combined with a `void` expression to mark expression locations in the AST. * Use special directive comments (`/// !hide`, `/// !show`) to mark locations that span AST nodes. This is less reliable (because the source location of translated syntax sometimes will have to be estimated) but the only option if you want to mark non-contiguous nodes (such as hide part of a class declaration but show statements inside the constructor). The `void` expression keyword and or the `comma` operator feature are little-used JavaScript features that are reliably parsed by TypeScript and do not affect the semantics of the application in which they appear (so the program executes the same with or without them). A handy mnemonic for this feature is that you can use it to "send your code into the void". #### Hiding statements Statement hiding looks like this: ```ts before(); // will be shown void 0; // start hiding (the argument to 'void' doesn't matter) middle(); // will not be shown void 'show'; // stop hiding after(); // will be shown again ``` #### Hiding expressions For hiding expressions, we use `comma` expressions to attach a `void` statement to an expression value without changing the meaning of the code. Example: ```ts foo(1, 2, (void 1, 3)); ``` Will render as ```ts foo(1, 2) ``` Also supports a visible ellipsis: ```ts const x = (void '...', 3); ``` Renders to: ```ts x = ... ``` #### Hiding across AST nodes Use special comment directives: ```ts before(); /// !hide notShown(); /// !show after(); ``` ## Contributors ✨ Thanks goes to these wonderful people ([emoji key](https://allcontributors.org/docs/en/emoji-key)):