@puzrin
I'm no expert. Someday I look some source code, found some magic comments, and did some search. (sorry, forget which project)

I have some thinks, but no guarantee if they are right.

Why some functions of js-yaml stays unremoved?

I think ESM is stateless to make tree-shaking happens , so any might be un-stateless code are kept outside that tree. Eg, toplevel function call.

Line 410 in 01d91e5

var str = /*@__PURE__*/new type('tag:yaml.org,2002:str', {

May be we could rewrite those (do some known recipes exist)?

Maybe convert stateful function calls to stateless init functions,
and call them in a big initial function to only keep one __PURE__?

Or just keep multiple __PURE__?

I don't know if there is best practice.

But I'm sure I saw it in some source code, but not generated code, that's how I know this magic comment.

How do you find, which functions should be marked?

echo 'export {} from "./dist/js-yaml.mjs"' | rollup

Besides, I add a test.

Line 23 in 01d91e5

input: 'export {} from "./dist/js-yaml.mjs"; export const foo = "bar"; '

Just see the command line output. Those stateful blocks are kept in output.

Besides, remember the location of those stateful thins, and check the output.
To make sure, certain stateful things are not shaked away.

esm release tree shake is not pure #631

Description