I was surprised when I tried to spread a `Set` in TypeScript and the browser complained about `Set.slice()` not being defined. This is because TypeScript does not automatically enable support for iterators when targeting earlier ES versions, like we do in the browser, unless you use the `"downlevelIteration": true` compiler option. This injects some helpers into the necessary files for reading/spreading iterators, which can be stuffed behind an import statement with using the `"importHelpers": true` compiler option and include `tslib` in our dependencies. This is already a dependency of several of our packages, so it shouldn't cause any additional modules.
* [typescript] continue to use the default config in development
In #21865 we tried to make a separate config file that would be used for
browser TS files by excluding them from the default config file and
adding a second that included them. This works fine in the build, but
IDE integrations rely on being able to automatically discover a
`tsconfig.json` file in a parent directory of the file being edited,
which doesn't work when the tsconfig.json file is found, but excludes
the file being edited. In this situation IDE integrations silently
fallback to the default TSConfig settings, which don't show the types of
compiler errors that will become issues in CI, like implicit any
warnings.
This implements the original strategy we tried in #21865 of mutating the
tsconfig.json file before we run the tsc in the build so that the config
files select the right files at build time.
* [tslint] remove browser config from default projects list since it is empty
* [build/ts] fix typo
Right now the build process is running TypeScript code through a single transpilation process which produces the JS code that ships with the distributable. This process causes problems because when running the optimizer from source we use a slightly different config 33c6ade756/src/optimize/base_optimizer.js (L312-L313), which instructs typescript to build modules using ESM, which webpack understands, but in the build we transpile this TypeScript to commonjs, which does not support features that are important to the strategy we are using to maintain BWC with the legacy platform as we migrate to the new platform.
This implements a `tsconfig.browser.json` file at the root of the repository that extends the default `tsconfig.json` file and includes a `src/**/public/**/*` code, which the root `tsconfig.json` file now excludes. This new config file is added to the list of projects that we lint, is shared with webpack, and is built along with the default project in the build process to create JS code that uses esm for webpack to consume.
Fixes#20694
Implements super basic new platform `core` system, which includes two services: `core.injectedMetadata` and `core.legacyPlatform`. The `core` currently has two responsibilities:
1. read the metadata from the DOM and initialize the `ui/metadata` module with legacy metadata, proving out how we plan to expose data from the new platform through the existing APIs/modules to the legacy platform.
2. bootstrap the legacy platform by loading either `ui/chrome` or `ui/test_harness`
Because `core` mutates the `ui/metadata` module before bootstrapping the legacy platform all existing consumers of `ui/metadata` won't be impacted by the fact that metadata loading was moved into the new platform. We plan to do this for many other services that will need to exist in both the legacy and new platforms, like `ui/chrome` (see #20696).
This upgrades TypeScript to version 2.9.2. My main motivation is the support for generic type arguments in JSX elements and tagged templates (e.g. for `styled-components`).
Problems arising from breaking changes in the new TypeScript version have been mitigated by:
* setting the `keyofStringsOnly` option until impacted code has been
future-proofed
* Restricting some joi-related generics
See the [release notes](https://www.typescriptlang.org/docs/handbook/release-notes/typescript-2-9.html) for details.
Some follow-up tasks should be:
* Update EUI to support the new `keyof` behaviour
* Update new platform TypeScript code to support new `keyof` behaviour
* Remove `keyofStringsOnly` setting
* Typescriptify ui/embeddable folder
* Allow ts modules from ui/public folders to be imported
* Address review comments from Tim
* Address code review from Oleg
* remove lodash usage
* remove mappng to non public folder
* [typescript] add typescript support for the server and browser
* [ts-jest] upgrade to latest version
* [jest] support test.tsx files
* [jest/ts] modify `ts-jest.tsConfigFile` config based on filePath
* [types] use correct major version of minimatch types
* [jest] add ts support to x-pack jest config
* [ts/projects] fix tsconfig.json not found error message
* [optimizer/ts] use lowercase jsx option
* [tsconfig] remove ui/* alias
* [plguin-helpers] remove mention of `buildSourcePatterns`
* [plugin-helpers] expect typescript to be a devDep
* [dev/build] place transpile tasks next to each other
* [ts/x-pack] add common and server directories to ts project
* [dev/ts/project] use a limited set of globs to find tsconfig files
