These changes pave the way for incrementally converting the implementation
of Meteor's command-line tool to TypeScript, which should have profound
benefits for self-documentation via types, as well as substantially
improving navigability and approachability for community contributors.
Just imagine being able to auto-complete the fields of the various
File-like classes currently floating around the codebase, instead of
having to track down their implementations every time. TypeScript was
designed with large projects like Meteor in mind, and it seems
increasingly irresponsible to forgo the benefits of a type system by
relying on the expertise of a few core contributors who know the codebase
inside and out. I am one of those few people, and I am very excited to
have the assistance of a type system, so I can only imagine how
transformative and empowering it will be for everyone else.
If you've ever wanted to get involved in core Meteor development, picking
a few meteor/tools modules to convert to TypeScript is a great way to get
to know that part of the codebase, while also making things easier for
everyone else who interacts with that code in the future.
Because we already compile meteor/tools using Babel, it makes the most
sense to use Babel's @babel/preset-typescript to compile .ts files:
https://babeljs.io/docs/en/next/babel-preset-typescript.html
Using Babel also means we get to keep all of our current advanced
compilation strategies, such as using Reify to compile module syntax:
https://www.npmjs.com/package/reify
Since we're using Babel, the meteor/tools/tsconfig.json file exists mostly
for the benefit of external tools like VSCode, rather than as a source of
truth for compilation behavior.
Despite our existing convention of including explicit .js file extensions
when importing modules, TypeScript and VSCode strongly encourage omitting
the file extension, so the import can be resolved to a .ts file in
development or a .js file when compiled. Although I find this ambiguity
somewhat unfortunate, it makes sense to follow community norms, at least
until Node.js begins supporting .ts modules by default.
The optimism package no longer knows anything about Fibers, but it does
export various helpers for managing execution contexts, one of which
(noContext) allows us to censor the current context for the duration of a
function call. By wrapping Fiber.yield with noContext, we keep distinct
Fibers from accidentally registering cache dependencies on one another.
Though this is a major update according to the version number (previously
2.0.0 in Meteor 1.8.0.1), we have observed no backwards-incompatible
changes so far.
Note: since Babel 7 is out of beta now, not all Babel-related packages
have been bumped to 7.1.0. In particular, the @babel/runtime package is
still at version 7.0.0. This is great news, because it means we're back to
genuine semantic versioning for all Babel packages!
Short-term fix for #10148.
Unfortunately, unlike most Meteor package and application code, which is
compiled after installation, Meteor compiler plugins are compiled before
they are published, so it's possible for a compiler plugin that uses the
ecmascript package to contain generated code that still uses the
module.watch API, instead of the new and improved module.link API.
A better long-term fix for this problem would be to compile compiler
plugins like any other Meteor code, using whatever version of the
ecmascript plugin the rest of the application is using.
Probably the most notable change in this update is that the Reify compiler
now generates
module.link("./child", { ...setters... });
instead of
module.watch(require("./child"), { ...setters... });
for import and export-from declarations.
This package is already importable because it's a dependency of request,
npm, and http-signature, but it's a good idea to depend on it explicitly
just in case those packages stop depending on it in the future.
