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variable is declared multiple times when variable is reserved and there are 2 passes and target is >=es2015 #8622

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bradzacher opened this issue Feb 8, 2024 · 0 comments · May be fixed by #8883
Open

variable is declared multiple times when variable is reserved and there are 2 passes and target is >=es2015 #8622

bradzacher opened this issue Feb 8, 2024 · 0 comments · May be fixed by #8883
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@kdy1
Labels
C-bug
Milestone
Planned

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@bradzacher
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bradzacher commented Feb 8, 2024 •
edited

Describe the bug

When jsc.minify.compress.passes > 1 and jsx.minify.mangle.reserved includes a reserved name - SWC can produce code that semantically invalid with the same variable being definied multiple times.

Input code

export function foo(cond) {
  let reserved = 1;
  if (cond) {
    reserved = 2;
  }
  return [reserved, bar(cond)];
}

function bar(cond) {
  let reserved = 1;
  if (cond) {
    reserved = 2;
  }
  return reserved;
}

Config

{
  "jsc": {
    "parser": {
      "syntax": "ecmascript",
      "jsx": false
    },
    "target": "es2015",
    "loose": false,
    "minify": {
      "compress": {
        "passes": 2
      },
      "mangle": {
        "reserved": ["reserved"]
      }
    }
  },
  "module": {
    "type": "es6"
  },
  "minify": false,
  "isModule": true
}

Playground link (or link to the minimal reproduction)

https://play.swc.rs/?version=1.4.0&code=H4sIAAAAAAAAA0utKMgvKlFIK81LLsnMz1NIy8%2FXSM7PS9FUqOZSUMhJLVEoSi1OLSpLTVGwVTC0BoplpikgqVBAljcCyddygcRKSovyFKJhcjoKSYlFEF2x1ly1XFxw%2B%2BDi2OwzJmCfCZp9MCmQFQByNT4O2QAAAA%3D%3D&config=H4sIAAAAAAAAA1WOQQ6DIBBF956CzLqL1qRd9A49QdMFwdFgQMgMNhrj3YsoajeEeX%2F%2Bnz8VQkDLCp5iit84eEmMtM%2BR8NgFOUQCqKxkRdoHuGS15UWqpWFMaF4VCJIaDMnF5fV23xxgnGPMjo1Z3el6PN9UznpC5hNL3ZhxYeXG5r2GlV1j8H89BiB9sYr0fQyf7C3ym1LAuqo%2FJUAYPa71H3As5aZ7fdD8ys5APRbzD1wt6BJUAQAA

SWC Info output

No response

Expected behavior

SWC produces valid code

Actual behavior

SWC produces broken code:

export function foo(e) {
    let reserved, reserved = 1;
    return e && (reserved = 2), [
        reserved,
        (reserved = 1, e && (reserved = 2), reserved)
    ];
}

Version

1.4.0

Additional context

Note: When targetting es5 the output uses var so it does not crash in a browser.

For comparison the 1 pass code:

export function foo(e) {
    let reserved = 1;
    return e && (reserved = 2), [
        reserved,
        function(e) {
            let reserved = 1;
            return e && (reserved = 2), reserved;
        }(e)
    ];
}

1 pass code with no reserved names:

export function foo(t) {
    let n = 1;
    return t && (n = 2), [
        n,
        function(t) {
            let n = 1;
            return t && (n = 2), n;
        }(t)
    ];
}

2 pass code with no reserved names:

export function foo(o) {
    let t, e = 1;
    return o && (e = 2), [
        e,
        (t = 1, o && (t = 2), t)
    ];
}
@kdy1 kdy1 self-assigned this Feb 8, 2024
@kdy1 kdy1 added this to the Planned milestone Feb 8, 2024
@Auspicus Auspicus linked a pull request Apr 22, 2024 that will close this issue
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@kdy1 kdy1

Labels
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Successfully merging a pull request may close this issue.

fix(es/minifier): don't reserve identifiers in expressions or patterns Auspicus/swc
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@bradzacher @kdy1