Environments:

• Prettier Version: 2.8.4
• Running Prettier via: CLI
• Runtime: NodeJS v16.15.1
• Operating System: macOS

Steps to reproduce:

test.less

@prefix: foo;

@{prefix}-title{
  color: red;
}

prettier -c -w test.less

Expected behavior:

no Css SyntaxError

Actual behavior:

SyntaxError: CssSyntaxError: Unknown word

postcss-less has fix the issue at postcss-less@5

upgrade prettier dependencies postcss-less@3 -> postcss-less@5 can fix the bug.

details: shellscape/postcss-less#159