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Typescript

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Typescript

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Although this is not a requirement, we encourage if all new code is developed in Typescript.

Project references

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Kibana has crossed the 2m LoC mark. The current situation creates some scaling problems when the default out-of-the-box setup stops working. As a result, developers suffer from slow project compilation and IDE unresponsiveness. As a part of Developer Experience project, we are migrating our tooling to use built-in TypeScript features addressing the scaling problems - project references & incremental builds

In a nutshell - instead of compiling the whole Kibana codebase at once, this setup enforces splitting the code base into independent projects that form a directed acyclic graph (DAG). This allows the TypeScript compiler (tsc) to apply several advanced optimizations:

Every project emits public interfaces in the form of d.ts type declarations generated by the TypeScript compiler
These generated d.ts type declarations are used whenever a referenced project is imported in a depending project
This makes it possible to determine which project needs rebuilding when the source code has changed to use a more aggressive caching strategy.

More details are available in the official docs

Caveats

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This architecture imposes several limitations to which we must comply:

Projects cannot have circular dependencies. Even though the Kibana platform doesn’t support circular dependencies between Kibana plugins, TypeScript (and ES6 modules) does allow circular imports between files. So in theory, you may face a problem when migrating to the TS project references and you will have to resolve this circular dependency.
A project must emit its type declaration. It’s not always possible to generate a type declaration if the compiler cannot infer a type. There are two basic cases:
1. Your plugin exports a type inferring an internal type declared in Kibana codebase. In this case, you’ll have to either export an internal type or to declare an exported type explicitly.
2. Your plugin exports something inferring a type from a 3rd party library that doesn’t export this type. To fix the problem, you have to declare the exported type manually.

Prerequisites

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Since tsc doesn’t support circular project references, the migration order does matter. You can migrate your plugin only when all the plugin dependencies already have migrated. It creates a situation where commonly used plugins (such as data or kibana_react) have to migrate first.

Implementation

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Make sure all the plugins listed as dependencies in kibana.json file have migrated to TS project references.
Add tsconfig.json in the root folder of your plugin.

{
  "extends": "../../../tsconfig.base.json",
  "compilerOptions": {
    "composite": true,
    "outDir": "./target/types",
    "emitDeclarationOnly": true,
    "declaration": true,
    "declarationMap": true
  },
  "include": [
    // add all the folders containg files to be compiled
  ],
  "references": [
    { "path": "../../core/tsconfig.json" },
    // add references to other TypeScript projects your plugin dependes on
  ]
}

If your plugin imports a file not listed in include, the build will fail with the next message File ‘…’ is not listed within the file list of project …’. Projects must list all files or use an 'include' pattern.

Build you plugin ./node_modules/.bin/tsc -b src/plugins/my_plugin. Fix errors if tsc cannot generate type declarations for your project.
Add your project reference to references property of tsconfig.refs.json
Add your plugin to references property and plugin folder to exclude property of the tsconfig.json it used to belong to (for example, for src/plugins/** it’s tsconfig.json; for x-pack/plugins/** it’s x-pack/tsconfig.json).
List the reference to your newly created project in all the Kibana tsconfig.json files that could import your project: tsconfig.json, test/tsconfig.json, x-pack/tsconfig.json, x-pack/test/tsconfig.json. And in all the plugin-specific tsconfig.refs.json for dependent plugins.
You can measure how your changes affect tsc compiler performance with node --max-old-space-size=4096 ./node_modules/.bin/tsc -p tsconfig.json --extendedDiagnostics --noEmit. Compare with master branch.

You can use https://github.com/elastic/kibana/pull/79446 as an example.

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