fix(minifier): should not merge conditional function calls if referencing the function has a side-effect

[sapphi-red]

a ? b(c, d) : b(e, d) should not be compressed to b(a ? c : e, d) if b has a side effect.
Because b may update a variable.

For example, compressing the following code changes the behavior.

var foo = () => console.log('foo')
var bar = () => { foo = () => console.log('foo2') }
bar() ? foo(1, 2) : foo(3, 2) // outputs 'foo'

// was compressed into
var foo = () => console.log('foo')
var bar = () => { foo = () => console.log('foo2') }
foo(bar() ? 1 : 3, 2); // outputs 'foo2'

We can improve this if we know that foo is not updated after it was declared (i.e. foo is a const). But I didn't implement it for now.

evaluation steps in detail

Before the compression, the code is evaluated in the following steps:

1. Evaluate a
2. Evaluate b
3. Evaluate c / e
4. Evaluate d
5. Evaluate b(c,d) / b(e,d)

After the compression, the code is evaluated in the following steps:

1. Evaluate b
2. Evaluate a
3. Evaluate c / e
4. Evaluate d
5. Evaluate b(c,d) / b(e,d)

The steps of 1 and 2 are reversed.

References

• Spec of conditional expression
• Spec of call expression

[sapphi-red]

• fix(minifier): should not merge conditional function calls if referencing the function has a side-effect #8922 👈 (View in Graphite)
• main

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[codspeed-hq]

CodSpeed Performance Report

Merging #8922 will not alter performance

_{Comparing 02-03-feat_minifier_merge_conditional_function_calls_with_side-effect_free_conditions (4a723f1) with main (a520986)}

Summary

✅ 33 untouched benchmarks

[Boshen]

Merge activity

• Feb 6, 10:06 AM EST: The merge label '0-merge' was detected. This PR will be added to the Graphite merge queue once it meets the requirements.
• Feb 6, 10:06 AM EST: A user added this pull request to the Graphite merge queue.
• Feb 6, 10:13 AM EST: A user merged this pull request with the Graphite merge queue.