SWC compress removes string literal’s .toUpperCase() and produces incorrect code

[controversial]

Describe the bug

The attached playground shows a stripped-down version of a code file that appears in my next.js project.

The SWC minifier/“compressor” removes .toUpperCase() from a string literal without uppercasing the string literal. The result is incorrect output.

Playground link

Input code

export class Renderer {
  renderStaticFrame(string1, string2) {
    const line1Text = `${string1} and ${string2}`.toUpperCase();
    const line2Text = 'line 2 text'.toUpperCase();

    const text = `${line1Text}\n${line2Text}`;
    return text;
  }
}

console.log(new Renderer().renderStaticFrame('a', 'b'));

Output code

export class Renderer {
  renderStaticFrame(string1, string2) {
      let line1Text = `${string1} and ${string2}`.toUpperCase();
      return `${line1Text}\nline 2 text`;
  }
}
console.log(new Renderer().renderStaticFrame('a', 'b'));

Expected behavior

Both lines are uppercase.

❯ node swc-input.js   
A AND B
LINE 2 TEXT

Actual behavior

The second line is printed in lowercase, because the toUpperCase function was removed in the SWC output.

❯ node swc-output.js     
A AND B
line 2 text

SWC Info output

    Operating System:
        Platform: darwin
        Arch: arm64
        Machine Type: arm64
        Version: Darwin Kernel Version 23.4.0: Fri Mar 15 00:10:42 PDT 2024; root:xnu-10063.101.17~1/RELEASE_ARM64_T6000
        CPU: (10 cores)
            Models: Apple M1 Pro

    Binaries:
        Node: 20.12.2
        npm: 10.5.0
        Yarn: 1.22.19
        pnpm: N/A

    Relevant Packages:
        @swc/core: N/A
        @swc/helpers: 0.5.5
        @swc/types: N/A
        typescript: 5.4.5
        next: 14.2.0

    SWC Config:
        output: N/A
        .swcrc path: N/A

    Next.js info:
        output: N/A

Version

1.4.14

Additional context

From playing with the version selector in the playground, it appears this issue was introduced in version 1.3.105.

[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.