feat(typescript): specify "this" type for "watchLoading"

[Kocal]

Hi,

I'm currently migrating my Vue components from basic syntax to decorated syntax by using vue-class-component and vue-property-decorator, and I faced a problem.

<template>
  <div>...</div>
</template>

<script lang="ts">
import gql from 'graphql-tag';
import { Component, Vue } from 'vue-property-decorator';

@Component({
  apollo: {
    language: {
      query: gql`{ ... }`,
      variables() {
        return {
          language: this.language,
        };
      },
      error() {
        this.error = true;
      },
      watchLoading(isLoading) {
        this.loading = isLoading;
      },
    },
  },
})
export default class HelloWorld extends Vue {
  language = 'fr';
  error = false;
  loading = false;
}
</script>

When compiling this code, I have the following error Property 'loading' does not exist on type 'Vue'. (see Travis).
I first thought it was a problem of decorators or of TypeScript itself, but I had no errors for this.language and this.error. 🤔

Adding this: ApolloVueThisType<V> makes everything works ✨

[Kocal]

Hum, I'm having the same problem with result() method but I'm not able to fix it this time... 😅

Kocal/vue-class-components-with-this-usage-in-decorators@55592cc and https://travis-ci.com/Kocal/vue-class-components-with-this-usage-in-decorators/builds/82144890#L455, thanks!