cc @kzc

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npm install rollup/rollup#correctly-associate-annotations

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Codecov Report

Merging #4095 (12d5b03) into master (2febefa) will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master    #4095   +/-   ##
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  Coverage   98.01%   98.02%           
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  Files         201      201           
  Lines        6994     7029   +35     
  Branches     2054     2060    +6     
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+ Hits         6855     6890   +35     
  Misses         66       66           
  Partials       73       73           

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Good stuff.

This is difficult to get right. I trust if the results were vetted with terser then it ought to be fine. Should there be pure annotation disagreements between minifiers, use the defacto behavior of uglify-js which happens to support ES2020+ these days.

With the recent PR on sequences it ought to be easy to support pure annotated calls with side effects in their parameters:

$ echo 'var foo = /*@__PURE__*/ bar(0, baz(), /*@__PURE__*/ boo(), 3);' | rollup --silent
/*@__PURE__*/ bar(0, baz(), /*@__PURE__*/ boo(), 3);

$ echo 'var foo = /*@__PURE__*/ bar(0, baz(), /*@__PURE__*/ boo(), 3);' | uglify-js --toplevel -mc
baz();

Side note... the surprising complexity of correctly associating comments with AST nodes and preserving their intent across various javascript tools is why I strongly discourage extending pure annotations beyond calls and new expressions. Anything can be wrapped in pure IIFEs in the worst case anyway.