a bug about parseFilter

[marzk]

try eslint to reproduce the bug.

<template>
  <div>{{ 1 | identity() || 0 }}</div>
</template>

<script>
export default {};
</script>

This is because identity() || 0 is LogicalExpression but not CallExpression.

This is the bug code.

//  `parseFilter` in `./src/script/index.ts`

if (argsCode != null) {
    const { ast } = parseScriptFragment(
        `0${argsCode}`,
        locationCalculator.getSubCalculatorAfter(paren - 1),
        parserOptions,
    )
    const statement = ast.body[0] as ESLintExpressionStatement
    const callExpression = statement.expression as ESLintCallExpression

    ast.tokens!.shift()
    
    // this is LogicalExpression
    for (const argument of callExpression.arguments) {
        argument.parent = expression
        expression.arguments.push(argument)
    }
    
    // ...
}

im not good at parser, and I dont know how to fix this bug. So i only create an issue but not a pr.

[mysticatea]

Thank you for this report.

It doesn't look a documented behavior (https://vuejs.org/v2/guide/filters.html). Would you explain how it works?

cc: @yyx990803 @michalsnik

[marzk]

Vue parse {{ 1 | identity() || 0 }} as _f("identity")(1,) || 0, its what i means. demo

This is not a standard usage about filter, obviously. But we may make a mistake sometimes, and it can not be debugged easily, because eslint just provide an error 0:0 error Parsing error: callExpression.arguments is not iterable without stack trace.

[mysticatea]

You are right. We should fix this.

@yyx990803 I'd like to ask the specification. Should we go which way?

1. ESLint allows that filters usage.
2. ESLint reports it as a syntax error.

[yyx990803]

I think this should be a syntax error.

[mysticatea]

@yyx990803 Thank you!