v-for is not parsed correctly when ecmaVersion is set to 5

[dumptyd]

We are trying to introduce Vue into our legacy ES5 codebase and this is proving to be a blocker so any help with this would be greatly appreciated.

It's pretty much this issue but it seems like it was never reported here.
vuejs/eslint-plugin-vue#1089

I've been working on setting up Vue support for eslint in a repo where we use ES5, and the Vue plugin doesn't work well with eslint's ES5 mode.

Installing the Vue plugin silently overwrites certain settings: ecmaVersion is set to 2018, sourceType to module, and JSX is enabled. This caused us to accidentally disable enforcement of our "no ES6" rule for about a month until I found out.

I tried to remedy this by changing these settings back in our .eslintrc.json, but that causes strange errors and even crashes to happen when linting templates that use v-for.

Tell us about your environment

• ESLint version: 6.8.0
• eslint-plugin-vue version: 6.1.2
• Node version: 10.15.2

Please show your full configuration:

{
	"extends": [
		"plugin:vue/recommended"
	],
	"parserOptions": {
		"ecmaVersion": 6,
		"sourceType": "script",
		"ecmaFeatures": {
			"jsx": false
		}
	}
}

What did you do?
First file (simple v-for):

<template>
  <div class="foo">
    <p
      v-for="x in xs"
      :key="x"
    >
      {{ x }}
    </p>
  </div>
</template>

Second file (v-for using parens to get both the value and the index):

<template>
  <div class="foo">
    <p
      v-for="(x, index) in xs"
      :key="index"
    >
      {{ x }}
    </p>
  </div>
</template>

What did you expect to happen?
Both of these files should lint without errors, even in ES5 mode (ecmaVersion: 5 in the eslint config).

What actually happened?
For the first file, I get confusing errors about the v-for line:

  4:7   error  'v-for' directives require that attribute value                                                  vue/valid-v-for
  4:14  error  Parsing error: Unexpected token x                                                                vue/no-parsing-error
  5:7   error  Expected 'v-bind:key' directive to use the variables which are defined by the 'v-for' directive  vue/valid-v-for

For the second file, I get an error message that exposes a JS error / crash in the plugin code, without reference to a line number:

  0:0  error  Parsing error: Cannot read property 'block' of undefined

Both of these errors only happen if ecmaVersion: 5 is set. If I set ecmaVersion: 6, the errors go away.