Fix( unit ): using the. exact modifier error when all system modifiers

[Zhang-Wei-666]

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

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

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

• Yes
• No

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

The PR fulfills these requirements:

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

[Justineo]

Can you provide a rationale for this change please?

[Zhang-Wei-666]

@Justineo

new Vue({
el: document.createElement('div'),
template: "<div @click.ctrl.alt.shift.meta.exact></div>"
});

if()return null;
↓

vue.js:634 [Vue warn]: Failed to generate render function:

SyntaxError: Unexpected token ) in

with(this){return _c('div',{on:{"click":function($event){if(!$event.ctrlKey)return null;if(!$event.altKey)return null;if(!$event.shiftKey)return null;if(!$event.metaKey)return null;if()return null;}}})}

(found in )

[Justineo]

Never mind, we can use this repro:

https://template-explorer.vuejs.org/#%3Cdiv%20%40click.ctrl.alt.shift.meta.exact%3E%3C%2Fdiv%3E