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Variable self assignment not removed (x = x) #1081

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Ahnfelt opened this issue Oct 5, 2021 · 4 comments
Closed

Variable self assignment not removed (x = x) #1081

Ahnfelt opened this issue Oct 5, 2021 · 4 comments
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compress Issue in the compression step enhancement

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@Ahnfelt
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Ahnfelt commented Oct 5, 2021

Bug report or Feature request?

Feature request.

Version (complete output of terser -V or specific git commit)

Online REPL 5th of October 2021

Complete CLI command or minify() options used

Default options:

{
  module: true,
  compress: {},
  mangle: {},
  output: {},
  parse: {},
  rename: {},
}

terser input

export function f(x) {
    x = x;
}

terser output or error

export function f(f){f=f}

Expected result

export function f(f){}
@jridgewell
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jridgewell commented Oct 5, 2021

Do you see code like f = f as the output of some build step?

@fabiosantoscode
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fabiosantoscode commented Oct 7, 2021

Sometimes Terser itself outputs x=x IIRC

@Ahnfelt
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Ahnfelt commented Oct 7, 2021

Sometimes Terser itself outputs x=x IIRC

Yeah, e.g. this produces the exact same output:

export function f(x) {
    const y = x;
    const z = y;
    x = z;
}

@jridgewell jridgewell added compress Issue in the compression step enhancement and removed discussion labels Oct 7, 2021
@jridgewell
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jridgewell commented Oct 7, 2021

Alright, let's add a simple assignment case.

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Labels
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