Design Meeting Notes, 3/8/2023

[DanielRosenwasser]

Reusing Type Nodes from Assertion Expressions

#57587

Set impliedNodeFormat in Every Module Mode

#57570

• Expanded traversal with
• mdast-util-to-string exports a named toString binding.

  • However in moduleResolution: esnext and others, we permit a default import of the module.

    import mdast from "mdast-util-to-string";
    mdast.toString; // TypeScript INCORRECTLY allows this.

• We don't under nodenext etc.
  • Because we actually track this information.
• Idea is to consider this information in all module modes.
• Under an older mode like commonjs/node10, we look for high-confidence indicators (e.g. mts files, package.json information).
• Avoids issues where people have an unchecked .cjs file with module.exports incorrectly transformed to include an export {} at the end of the file.
• We can't do perfectly, but we can catch a certain class of errors!
• Doing package.json resolution in all modes slows things down slightly, but we might be able to optimize more.

Proactively Ship esXXXX Emit Targets

#57683

• Some editions of the language will have no changes, or people want to just speculate and say "whatever is stable for this upcoming year.
• Expectation among users
• But there's a royalty-free opt-out period where features can be removed from an edition.
  • Well...this has never happened.
  • How is this possibly not at odds with the stage 3 "start implementing and possibly ship" indicator?
• Seems reasonable to place a schedule for the target versions and libs
• Regardless of whether there are any actual changes, it feels like adding a new "no-op" year isn't a problem.
• Creating a version specifically seems like it's not a problem?
  • What is the strategy? Saying es2024 is an alias for es2023 means that when es2024 gets solidified, syntax stops getting transformed. That's a break.
  • Saying it's an alias for esnext is less breaky - but a feature can be stalled in stage 3 for a long time.
    • But there is a break! If TS is not able to downlevel a feature and then says "oops, we can't downlevel this for es2024".
• Conclusion: start establishing new esXXXX targets following ratification in the standards body. Typically the 2nd plenary meeting of the year.