vitest-dev/vitest · error · Error

Invalid tags expression: unexpected end of expression in

Error message

Invalid tags expression: unexpected end of expression in "${this.expr}"

What it means

Thrown by TokenStream.unexpectedToken when the parser is at a position requiring a primary expression (a tag or a `(`) but the current token is EOF — i.e. the expression ended prematurely. This happens when a binary or unary operator has nothing after it.

Solutions

1. Add the missing operand after the trailing operator: `--tags 'foo && bar'`.
2. Remove the trailing operator if no second operand is intended: `--tags 'foo'`.
3. Ensure every `!`/`not` is followed by a tag or parenthesized sub-expression.

Example fix

# before
vitest --tags 'smoke &&'

# after
vitest --tags 'smoke && critical'

function noTrailingOperator(expr: string): boolean {
  return !/(?:&&|\|\||!|\bnot\b|\band\b|\bor\b)\s*$/i.test(expr.trim())
}

When it happens

Trigger: A `--tags` expression ending with a binary operator (`vitest --tags 'foo &&'`, `vitest --tags 'foo ||'`), a `not`/`!` with no following tag (`vitest --tags '!'` or `--tags 'not'`), or an empty expression after an operator inside parens (`--tags '(foo && )'` would surface via 344, but a bare trailing `&&` hits 345).

Common situations: Trailing operator typed by accident; the tag name after an operator was deleted; building the expression programmatically and leaving a dangling operator.

Related errors

• Invalid tags expression: expected
• Invalid tags expression: missing closing ")" in
• Invalid tags expression: unexpected
• Invalid tags expression: unexpected
• Unknown value for "test.listTags

AI-assisted analysis of vitest-dev/vitest@1fa9837ec2 (2026-08-11). Data as JSON: /api/errors/89b61a7f14b3ba53. Report an issue: GitHub.

Appendix: source

Thrown at packages/vitest/src/runtime/runner/utils/tags.ts:192

  next(): Token {
    return this.tokens[this.pos++]
  }

  expect(type: Token['type']): Token {
    const token = this.next()
    if (token.type !== type) {
      if (type === 'RPAREN' && token.type === 'EOF') {
        throw new Error(`Invalid tags expression: missing closing ")" in "${this.expr}"`)
      }
      throw new Error(`Invalid tags expression: expected "${formatTokenType(type)}" but got "${formatToken(token)}" in "${this.expr}"`)
    }
    return token
  }

  unexpectedToken(): never {
    const token = this.peek()
    if (token.type === 'EOF') {
      throw new Error(`Invalid tags expression: unexpected end of expression in "${this.expr}"`)
    }
    throw new Error(`Invalid tags expression: unexpected "${formatToken(token)}" in "${this.expr}"`)
  }
}

function formatTokenType(type: Token['type']): string {
  switch (type) {
    case 'TAG': return 'tag'
    case 'AND': return 'and'
    case 'OR': return 'or'
    case 'NOT': return 'not'
    case 'LPAREN': return '('
    case 'RPAREN': return ')'
    case 'EOF': return 'end of expression'
  }
}

function parseOrExpression(stream: TokenStream, availableTags: TestTagDefinition[]): ASTNode {

View on GitHub (pinned to 1fa9837ec2)