Explore improving support for embedded languages in JS/TS template strings

[mjbvz]

Investigation of how we can improve support for languages embedded in JavaScript / TypeScript template strings. A few example embedded languages: css, html, glsl, graphql, ...

[mjbvz]

Here's a prototype extension that contributes intellisense and syntax highlighting for css strings: https://github.com/mjbvz/vscode-css-template-strings-prototype

This prototype makes use of a TS Server plugin and VS Code's css language library. VS Code extensions can contribute a global TS Server plugin, however this API is not ready for production yet. Here are a few issues with contributed plugins:

• Global plugins do not work for inferred projects (you need a tsconfig): TSServer --globalPlugins not working for inferred projects TypeScript#18322

• No way to pass configuration from VSCode to a global tsserver plugin: [Proposal] TS Server plugins configuration requests TypeScript#18604

• The current story of when we load global plugins is confusing. Right now, we only load the contirbuted TS Server plugins when using a global version of TypeScript (not the version from the workspace). This was done for versioning reasons. We should investigate this more because IMO the global plugins should always be loaded unless you are using a version of TypeScript that is too old

[mjbvz]

Closing out this exploration.

Progress:

• Reset default theme styling on meta.embedded grammar scopes: Reset styling for embedded languages in grammars? #33120
• Support embeddedLanguages inside injected grammars: Injection grammars with embeddedLanguages #34316
• Submitted PRs against some popular template string extensions to make sure they use embeddedLanguages: kumarharsh/graphql-for-vscode@131fa98, Mark template strings with correct language modes natewallace/angular2-inline#29, Mark styled contents as language:css styled-components/vscode-styled-components#34
• TypeScript plugin for styled components: https://github.com/Microsoft/typescript-styled-plugin

Ongoing:

• Provide way to re-enable quick suggestions in a string: Provide way for a language to re-enable editor.quickSuggestions inside of a string or comment #34857
• Polish means for VSCode extensions to contribute global TS server plugins
• Move styled plugin in to a VS code extension
• Write TS plugin for html