Is "safari10" "mangle" option implementation even necessary?

[joebeachjoebeach]

Hello!

I see from the minify.mangle docs that the safari10 option (available in terser) has not yet been implemented.

That terser option is meant to prevent code like this from being generated:

function loop() {
    let a = someFunc();
    console.log(a);
    for (let a of [1,2,3]) {
        console.log(a);
    }
}

Safari 10 views the second let a (in the for loop) as a syntax error.

---

I took a look at what terser and swc do with this code.

terser

safari10: false

function o(){let o=someFunc();console.log(o);for(let o of[1,2,3])console.log(o)}

Duplicate variable name: o is declared twice. This will be a syntax error in Safari 10.

safari10: true

function o(){let o=someFunc();console.log(o);for(let l of[1,2,3])console.log(l)}

No more duplicate variable name. The second variable gets a new name: l. This will not be a syntax error in Safari 10.

swc

safari10: false (the only option currently)

function a(){let a=someFunc();console.log(a);for(let b of[1,2,3]){console.log(b)}}

No more duplicate variable name. The first one is a and the second is now b. This will not be a syntax error in Safari 10.

---

Given this, is implementing the minify.mangle.safari10 option necessary? Our team is keen on swapping out terser for swc in our build process, and this makes me feel like we don't really need to wait for safari10 to specifically be implemented. Am I right in thinking that the bug is avoided by default?

[kdy1]

Yes, because serde does not provide a way to ignore a field.
It's not used, but it's api of terser.

[kdy1]

You are right, it will not cause an issue.
But removing may create an issue because of serde issue.

[joebeachjoebeach]

Thanks for the quick response!

[taozhou-glean]

looks like safari10 is now supported:

and it seems to have some side effects once enabled:

(the s was redefined within the catch block and also in the catch(s) )

https://play.swc.rs/?version=1.3.104&code=H4sIAAAAAAAAA8VTTY%2FaMBC98ytG2wtIBDdAYaEf0nahWqRdiugeelvZzoS4JDb1OLC02v9eB1q%2BEqnqqXNI%2FPHe5M17CmMgTYTg%2BBI1xNZkkDi3oiFjC%2BWSXLSkydjNj9zizYhlSlpDJnYBz12C2inJnTI6SJWw3G6D2NjgGzGRGsHkoBOG0SDsD7qiH3dFh2PYFtft%2FpuuCNudXr%2FbwxDFNfNklhFPA2HNhtAyspL59dIvte%2B%2Fxo%2F7zXS3eUAivsA7rqMUbcvRq%2Fvwda%2BGzytjHciUE0EVEn7WwBc5fyeB01ZLkBa5w5k1axWhre8ARaVmsUA7hPvdu3k4T3wrSrxXjypDk7sHGoLOM3GKWaH1NmRcS7xNlTdpCJPZ5dkO3RiC%2F3SmCN9VCf7wW%2FFRUMtZLrF%2BVTlecDENSJ6mGLWuGm8PbZzdnjQtShpNDlYWY7QWowP5PWjcVPpYP%2BMfxTVL52W3ypiSW2XIXsRtIZRrR63ZfPxpPJ%2BPR0%2Fjr4%2Fj6ZfJ5%2BnTZHRGOxm5KL7hqmLIFqGO7v6InOP3HMnVL7gWXW51mXxEvXinnUygjo0LcxmDSXykAj471OR%2FGIi5Sgn85LBJfGZr77gPj4xu%2Bqs0FVwuwRnISekFcL0FVUxf5HlsUpFjwctX%2Fz%2FEv4dxrvRfkjhnnsRQ2z9ffgH%2F94Mb1AQAAA%3D%3D&config=H4sIAAAAAAAAA41V22rcQAx9z1cYQ9%2BW0iRQSh%2F6VEopBPoHRuvReCcZj4aR7OwS8u%2BVb5u9jJfC4rV1NLoead7uiqJ85rr8Xrzpq37gXjAF8L%2FRR0ysgKQONxMYITGmo7JK%2BBAE9iop5RCR6%2BSilJsFFd7PBkbJ%2B2xGEgS2lNpTSx4bqA8%2FsaYEQunMscJmAZ5QwIBAzrAnYjwPuXXB2cOpoxZC4%2FFEMkRE0WOPXqUWPB%2FdKvSCGKvaA3OAFnlNw95EY3I9COo%2FxZySw28ZKYOF5O6%2FnKZ6TFbxmtqYkPk8F0hN12KQnB9IiV75orYq3xJ51KasIxVw5YJgM5Hi0nBN3kNkrHpIGStDpJoKU87FAHaC5lidKzwYJ46UlRnUIJiqJoMZyCWsxfWYO6a%2B9FhgGrlwmc8IG9x2TYOXXBympAffaUMzyH5siUabsbojx1LZLuRKOIErNZjAubhX7LFVQulSuD73TC6s9OR%2Fia18Wjt9m%2FQuWB0%2BOWRwHdRclkF3gE6JczZT2aEymMTlupnQdDUOla1z4czwSvnYGazQWuVKxjS%2FOql3OafDxiObAbS%2FYHOsmoDqOIUr%2BDAQN%2BBfmqXkCTZrtCC7dZQP7Zb8DQctyo7MDQVthdA6nHRL7OM63gWDSg00WZWOR%2BB6CegACFUeJccNHQ%2B1WDWeth9rYtmYd8tz3J0lhv7jwmun1VF2DA3OV5d6S%2FhnsFI%2Bfn7U3yLnnYsRzV%2BlIvHlOipFRwVHDpU6VlI8FL1uS%2B3Upvjx8GlTBJJiWFfTm8Pi%2Fn55rVra6ufiR%2FeOdfsz0k2ha7TdyeU1cnDwh%2Fy1PCo5flrUltMf9%2BBc8Pd%2F5hMUQPsHAAA%3D