fix(vdom): avoid executing root level script tags

[shadowings-zy]

What kind of change does this PR introduce? (check at least one)

• [ x ] Bugfix
• Feature
• Code style update
• Refactor
• Build-related changes
• Other, please describe:

Does this PR introduce a breaking change? (check one)

• Yes
• [ x ] No

If yes, please describe the impact and migration path for existing applications:

The PR fulfills these requirements:

• [ x ] It's submitted to the dev branch for v2.x (or to a previous version branch), not the master branch
• [ x ] When resolving a specific issue, it's referenced in the PR's title (e.g. fix #xxx[,#xxx], where "xxx" is the issue number)
• [ x ] All tests are passing: https://github.com/vuejs/vue/blob/dev/.github/CONTRIBUTING.md#development-setup
• [ x ] New/updated tests are included

If adding a new feature, the PR's description includes:

• A convincing reason for adding this feature (to avoid wasting your time, it's best to open a suggestion issue first and wait for approval before working on it)

Other information:
Root level <script> tags should not be executed, for consistent behavior. So I remove the code in <script> tag when the <script> tag is the root element of the template.

fix #11483

[posva]

Thanks for the PR! I think this should be done at the compilation level (like the other removal of script). Right now Vue.compile('<script />') still creates a render function that renders the script, but it should just be a render function that returns null

[shadowings-zy]

Aha! I've thought about fix this bug at the compilation level！
But when I read the code I found that if a render function that returns null, the template will render a div as a default element (related codes in file 'src/compiler/codegen/index.js', in 'generate' function). Does this meet our expectations?

If so, I will work on it.

[posva]

if the render function returns null, Vue will output a comment node. But still, it is better that way, yes

[shadowings-zy]

Hi, now I fix this bug at the compilation level.
and Vue.compile('<script />') will creates a render function that returns null.

The output of the render function is as follows:

function anonymous(
) {
with(this){return null}
}

: )

[posva]

can you add a comment above referencing the original issue?

[shadowings-zy]

ok, I will add the issue

[shadowings-zy]

I had added a comment referencing the original issue in the PR.

: )

[posva]

Thanks!

[larson-carter]

These are great changes!