map/filter/reduce on constant arrays with property access isn't treeshaken

[teidesu]

Rollup Version

v4.0.2

Operating System (or Browser)

n/a

Node Version (if applicable)

No response

Link To Reproduction

https://rollupjs.org/repl/?version=4.0.2&shareable=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

Expected Behaviour

the export is stripped away

Actual Behaviour

it is not stripped.

i believe this is happening due to rollup not being able to determine the type of the argument, since similar exports are all correctly stripped in all these cases:

export const a = 'foo'[0]
export const b = ['foo'][0][0]

const arr = ['foo']
export const c = arr[0][0]

export const d = ['foo'].map(s => s)
export const e = ['foo'].filter(s => true)
export const f = ['foo'].reduce((a, s) => a + s, '')

[lukastaegert]

The problem is indeed that for technical and performance reasons, rollup does not make assumptions about the argument of the map function, otherwise it would need to iterate through all possible arguments, which can easily add up if an array is passed around in the code. Therefore, Rollup needs to assume that accessing a property could have a side effect.

There are two possible ways to address this:

1. Manually declare those mappings as pure via comments https://rollupjs.org/repl/?version=4.0.2&shareable=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
2. Disable side effect detection for property accesses. This is usually a safe choice in most projects unless you explicitly rely on getters with side effects. https://rollupjs.org/repl/?version=4.0.2&shareable=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