Purify should annotate the top level function call before parenthesis.

[mhevery]

Consider this line

export const Injectable: InjectableDecorator = <InjectableDecorator>makeDecorator('Injectable');

The cast <InjectableDecorater> causes this code in tsickle

export const Injectable = (/**@type{InjectableDecortaro}*/makeDecorator('Injectable'));

This generates (notice the parenthesis)

var Injectable = (/*@__PURE__*/ makeDecorator('Injectable'));

Which than makes it retained as parenthesis defeats the @__PURE__. This than retains large portion of code.

[mhevery]

/cc @IgorMinar