Label being incorrectly removed with treeshaking disabled

[guybedford]

• Rollup Version: 2.3.1
• Link to reproduction (IMPORTANT, read below): https://github.com/guybedford/rollup-label-bug

Expected Behavior

There are three labeled while loops in the build with loop: names.

When running the build with treeshaking enabled, all three labels remain in the output.

Actual Behavior

When running the build with treeshaking disabled, the first loop: label is removed! As a result the internal break loop fails further parsing.

[guybedford]

@lukastaegert any ideas why this might be happening?

[lukastaegert]

It is hard to reduce the test case

[guybedford]

Thanks for taking a look - I've managed to isolate it down to three files in a circular reference that use the same label name, where one of the files contains a function from the other. The isolation at https://github.com/guybedford/rollup-label-bug/blob/master/tokenize-string.js now builds the local file directly. It's definitely a complex case - but the fact remains a valid label (and the code is definitely valid) should not be removed when treeshaking is disabled.

[lukastaegert]

Managed to solve it, fix at #3492