Add option to deoptimize var declarations for tree-shaking #4139
+94
−38
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Description
This will add a new option
treeshake.correctVarValueBeforeDeclaration
. This option will deoptimize the value of anyvar
declarations to make sure that Rollup does not make wrong assumptions when variables are accessed before their declaration. This will even work in pathological examples likewithout this option, this will be simplified to
which is obviously wrong. As this option can lead to heavy deoptimizations depending on the code, it is not switched on by default. It is still better than turning of tree-shaking altogether as basic tree-shaking will still work well: If a variable is not used, it will be removed.
In the meantime, we can work on finding a proper fix for this situation, at which point this option will be deprecated again.
Currently, it will be part of the "safest" tree-shaking preset introduced in #4131.