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 needs another primary operand but the stream is already at EOF. This occurs when an operator (&&, ||, or !) is followed by nothing - the expression ends where a tag or group was expected.

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 d568f8ce37)

Solutions

1. Add the missing right-hand operand after the operator: `unit && smoke`.
2. Remove the trailing operator if you did not mean to combine anything.
3. Ensure every `!` is immediately followed by a tag or group.

Example fix

// before
vitest --tag 'unit &&'

// after
vitest --tag 'unit && smoke'

// Reject expressions ending with an operator
function endsWithOperator(expr: string): boolean {
  return /(?:&&|\|\||!|\band\b|\bor\b|\bnot\b)\s*$/i.test(expr.trim())
}

When it happens

Trigger: A trailing operator: `--tag 'unit &&'`, `--tag 'unit ||'`, or a leading/trailing `!` with nothing after, e.g. `--tag '!'`.

Common situations: Accidentally truncating a filter expression. Editing a filter and deleting the last tag. Using `!` alone expecting negation of everything.

Related errors

• Invalid tags expression: unexpected "${formatToken(stream.pe
• Invalid tags expression: missing closing ")" in "${this.expr
• Invalid tags expression: expected "${formatTokenType(type)}"
• Invalid tags expression: unexpected "${formatToken(token)}"
• failed to parse ${options.id}

AI-assisted analysis of vitest-dev/vitest@d568f8ce37 (2026-08-03). Data as JSON: /data/errors/89b61a7f14b3ba53.json. Report an issue: GitHub.