Remove unused calls to pure functions

[j-f1]

Babili could use an @pure JSDoc tag to determine which functions are pure, then remove unused calls to them.

AST Explorer with code + example: https://astexplorer.net/#/gist/bdcbc34df3916d324454a332988503c7/7c39cede7af9cc9244f89876bb8339a5a4fb3d37

In:

/** @pure */
const myPureFunc = () => {}
myPureFunc()

Out:

/** @pure */
const myPureFunc = () => {}

[nicolo-ribaudo]

Instead of @pure Babili could use #__PURE__, like Uglify: mishoo/UglifyJS#1448, babel/babel#5632

[hzoo]

This is a similar request to babel/babel#5632? Referencing the same issue too. I'm already in favor of doing it

[j-f1]

Sort of — this one will strip out calls to pure functions, while that one wants to add an annotation to functions wrapping transpiled classes.

[boopathi]

Duplicate #520