[Bug]: Cssnano hangs when including `|` character in identifier

[mattcoley]

Describe the bug

Including | at the beginning of a CSS selector results in the cssnano process never terminating. For example minification of:

| h1 {}

does not terminate.

Other combinations of selectors with this character work fine: h1 |, |h1, h1|.

Output from postcss parse:

Root {
  raws: { semicolon: false, after: '' },
  type: 'root',
  nodes: [
    Rule {
      raws: [Object],
      type: 'rule',
      nodes: [Array],
      parent: [Circular *1],
      source: [Object],
      selector: '| body',
      [Symbol(isClean)]: false,
      [Symbol(my)]: true
    }
  ],
  source: {
    input: Input {
      css: '| body { margin:0; }',
      hasBOM: false,
      id: '<input css -2Oudu>',
      [Symbol(fromOffsetCache)]: [Array]
    },
    start: { offset: 0, line: 1, column: 1 }
  },
  [Symbol(isClean)]: false,
  [Symbol(my)]: true
}

Expected behaviour

cssnano should exit on this input.

Steps to reproduce

Problem can be validated via https://cssnano.co/playground/

For cli usage:

postcss test.css --use cssnano --no-map

Version

5.1.11

Preset

(no preset)

Environment

System:
    OS: macOS 11.6.4
    CPU: (12) x64 Intel(R) Core(TM) i7-9750H CPU @ 2.60GHz
    Memory: 50.88 MB / 32.00 GB
    Shell: 5.8 - /bin/zsh

Package details

└── [email protected]

Additional context

No response

[ludofischer]

Including | at the beginning of a CSS selector results in the cssnano process never terminating

Why would the stylesheet include a | at the start of a selector? Is it not invalid CSS?

[mattcoley]

It is invalid CSS (in this case accidental) but the process should still terminate. We came across this bug in our CI/CD pipeline where the builds would timeout rather than fail and display an error message (invalid CSS). Other examples of invalid CSS terminate with an error message.