Evaluate expression when compress conditional statement

[Austaras]

Describe the bug

This would require implementing terser evaluate method.

Input code

let a = 'aaaa'

if (a === 'aaaa') {
	console.log(a)
}

Config

No response

Playground link

https://play.swc.rs/?version=1.2.170&code=H4sIAAAAAAAAA8tJLVFIVLBVUE8EAnUursw0BQ0g3xYmoqlQzcWZnJ9XnJ%2BTqpeTn66RqMlVCwBln0kENQAAAA%3D%3D&config=H4sIAAAAAAAAA22TzZLbIAzH38XnHLqdaQ%2F7AL3tMzAKCEdbAx4ksvFk8u4VthfbSW%2Fox19CX9y7T7bd%2B70bITPmeuIpCty69w5tALaZRulOKlPkYWB8nDqB3KNUCf%2F88fZLr4eUGFfBqQsUyU81mE1hzMhcz%2BpUAkbhpoOc05eakota55QGhPhiG2BDUbDHvLnaNAwwMpor5OZRX4NMnOIBFUFnxpzGvXt0JJSimg06BGdsclshjjJaoSvuRBpHRZE1uSN0eC59X5u4PI1XGAoINvs2t0IfbX6XRCzGl8hPaM12cVzQUuiqIm8ySsnxW%2FOZKB568RdR8xyAOULY5T9zr7M4Kv1%2FVBS9DlKmRnXKW1YRey3OEPlWYc0asxA2UUZXLNYK7RZ8hYeCmBwa9F7b3Zz5i8RedlnJNGLy7V7bBn4bwmKa76U60roHL%2FCPpiX7eaw8gFyeGU%2FhnIaXEAHlktwL1k5IeoZZV%2Fg2PtMSHWqf0e0uClezVqm%2FLUDs2649KkiuVHCfGzJ%2Fw9%2FdY%2Ft2S3eIP1bdHOcfmKDn2%2BoDAAA%3D

Expected behavior

console.log('aaaa')

Actual behavior

let a="aaaa";"aaaa"===a&&console.log(a)

Version

1.2.170

Additional context

No response

[kdy1]

We have inliner,

See https://play.swc.rs/?version=1.2.171&code=H4sIAAAAAAAAA6vm4sxJLVFIVLBVMOTi4sxMU9AAsm2BPE2Fai5OzuT8vOL8nFS9nPx0jURNLs5arloAAXFBdjMAAAA%3D&config=H4sIAAAAAAAAA22TQZbbIAyG78I6i077Oos5QHc9A4%2BAcDS1hYtEJn55uXtF7GA76Q59%2FBLSD1zNJ3vzcTWjywy5rngicRfzYcAPjn3GUcxBZYqi6xluByMudyBVwt%2B%2Fvf3U7T4lhkVwMAMSxqkW82kYMzDXNVKPpKIfB6P5ZQASbiku5%2FSloeSi0TGlHhy9xNaxRRLoIK%2BpPvW9Gxns2eWWUQ92GTnRDhWBYMecxm06BRRMpGGDAVywPoV1poAZvOAZNiKtoyJibW4PAxxL11U%2F56Ph7PriBFp8ubuih7a8U0IWGwvxE1q6nRNnNA%2B6qDDaDFIyPTSfCWnnxR8A7bN3zOSGTf93HvUu9sr4HxVS1DuVqVG98LUrgk6Hs4ixTVi7hiwITZQhFA91Qr8WX%2BBuIMYAFmJUu1syf6H406YrmUZIse2rbS6ulzCH9vGo9rS%2Bgxf4S9uS7X0sfHByemY8DcfUv5QYQE4pvGB1QtIzzPqEL%2BMzLRRAfYaw2Shcw8UF%2BFuA%2FMNT%2FYmDo649vlsFKZQKrneH7l%2F03dzWLzkXQv696O51%2FgGRKYQUBgQAAA%3D%3D

Problem is that, inlining a string literal can make output too large. (25 M => 76M, in real case in the past)

[Austaras]

Combined with #4414, I'd say number shouldn't be inlined blindly too.

[Austaras]

The actual process of terser is when check constant conditions, evaluate left side of comparison and find out it's aaaa, so the whole if can be removed

[kdy1]

Hmm, I think we need it.

[nkitku]

version : 1.2.224 playground

this works only when variable contain <= 3 characters

let a = 'aaa'

if (a === 'aaa') {
	console.log(a)
}

gives

console.log("aaa") 

doesn't matter how long the string is in condition, it will evaluate

let a = 'aaa'

if (a === 'aaaaaaaaaaaaaaaaaaaaaaaaa') {
	console.log(a)
}

gives nothing

but if just add one more char in variable

let a = 'aaaa'

if (a === 'aaaaaaaaaaaaaaaaaaaaaaaaa') {
	console.log(a)
}

gives

let l="aaaa";"aaaaaaaaaaaaaaaaaaaaaaaaa"===l&&console.log(l)

[swc-bot]

This closed issue has been automatically locked because it had no new activity for a month. If you are running into a similar issue, please create a new issue with the steps to reproduce. Thank you.