fix(coverage): flaky c8 coverage caused by parallel sourcemap constructing

[AriPerkkio]

• Fixes c8 coverage seems broken when testing vue file with style tag #2539

Currently C8 provider is constructing the sourcemaps using multiple parallel Promises.

vitest/packages/coverage-c8/src/provider.ts

Lines 53 to 56 in e641a11

	await Promise.all(Array
	.from(this.ctx.vitenode.fetchCache.entries())
	.filter(i => !i[0].includes('/node_modules/'))
	.map(async ([file, { result }]) => {

If two requests, e.g. src/components/StyleTag.vue and src/components/StyleTag.vue?vue&type=style&index=0&scoped=88d9cf36&lang.css are running at the same time, it's not guaranteed that sourceMapMeta['src/components/StyleTag.vue'] ends up containing the correct sourcemaps. By running the tests multiple times, the sourceMapMeta may contain incorrect sourcemaps. Sometimes it works fine as correct ones load slower.

I've refactored the Promise.all into a simple for loop, so that sourceMapMeta is not overwritten by parallel promises. Also added a check to see whether sourceMapMeta already contains the file, and skip overwriting it.

I'm not familiar with Vue. It seems that file.vue has correct sourcemaps and result.code is ok. The file.vue?query... is requested afterwards and does not contain actual contents in result.code.

result.code of src/components/StyleTag.vue, this one we want in sourceMapMeta

const __vite_ssr_import_0__ = await __vite_ssr_import__("/node_modules/.pnpm/vue@3.2.45/node_modules/vue/index.mjs");

const _sfc_main = /* @__PURE__ */ __vite_ssr_import_0__.defineComponent({
  __name: "StyleTag",
  setup(__props, { expose }) {
    expose();
    if (false) {
      console.log("false");
    } else {
      console.log("true");
    }
    const __returned__ = {};
    Object.defineProperty(__returned__, "__isScriptSetup", { enumerable: false, value: true });
    return __returned__;
  }
});
function _sfc_render(_ctx, _cache, $props, $setup, $data, $options) {
  return "Component with style tag";
}
const __vite_ssr_import_1__ = await __vite_ssr_import__("/src/components/StyleTag.vue?vue&type=style&index=0&scoped=88d9cf36&lang.css");

const __vite_ssr_import_2__ = await __vite_ssr_import__("/@id/__x00__plugin-vue:export-helper");

__vite_ssr_exports__.default = /* @__PURE__ */ __vite_ssr_import_2__.default(_sfc_main, [["render", _sfc_render], ["__scopeId", "data-v-88d9cf36"], ["__file", "/Users/x/y/demo-c8-issues/src/components/StyleTag.vue"]]);

//# sourceMappingSource=vite-node
//# sourceMappingURL=data:application/json;charset=utf-8;base64,eyJ2ZXJzaW9uIjozLCJtYXBwaW5ncyI6Ijs7Ozs7O0FBQ0EsUUFBSSxPQUFPO0FBQ1QsY0FBUSxJQUFJLE9BQU87QUFBQSxJQUNyQixPQUFPO0FBQ0wsY0FBUSxJQUFJLE1BQU07QUFBQSxJQUNwQjs7Ozs7OztTQUdBIiwibmFtZXMiOltdLCJzb3VyY2VzIjpbIi9Vc2Vycy9hcmkvR2l0L2RlbW8tYzgtaXNzdWVzL3NyYy9jb21wb25lbnRzL1N0eWxlVGFnLnZ1ZSJdLCJzb3VyY2VzQ29udGVudCI6WyI8c2NyaXB0IHNldHVwIGxhbmc9XCJ0c1wiPlxuaWYgKGZhbHNlKSB7XG4gIGNvbnNvbGUubG9nKCdmYWxzZScpO1xufSBlbHNlIHtcbiAgY29uc29sZS5sb2coJ3RydWUnKTtcbn1cbjwvc2NyaXB0PlxuXG48dGVtcGxhdGU+Q29tcG9uZW50IHdpdGggc3R5bGUgdGFnPC90ZW1wbGF0ZT5cblxuPHN0eWxlIGxhbmc9XCJjc3NcIiBzY29wZWQ+XG5ib2R5IHtcbiAgYmFja2dyb3VuZC1jb2xvcjogI2JhZGE1NTtcbn1cbjwvc3R5bGU+XG4iXSwiZmlsZSI6Ii9Vc2Vycy9hcmkvR2l0L2RlbW8tYzgtaXNzdWVzL3NyYy9jb21wb25lbnRzL1N0eWxlVGFnLnZ1ZSJ9\n'

result.code of src/components/StyleTag.vue?vue&type=style&index=0&scoped=88d9cf36&lang.css, breaks coverage if overwrites sourceMapMeta

//# sourceMappingSource=vite-node
//# sourceMappingURL=data:application/json;charset=utf-8;base64,eyJ2ZXJzaW9uIjozLCJmaWxlIjpudWxsLCJzb3VyY2VzIjpbIi9Vc2Vycy9hcmkvR2l0L2RlbW8tYzgtaXNzdWVzL3NyYy9jb21wb25lbnRzL1N0eWxlVGFnLnZ1ZT92dWUmdHlwZT1zdHlsZSZpbmRleD0wJnNjb3BlZD04OGQ5Y2YzNiZsYW5nLmNzcyJdLCJzb3VyY2VzQ29udGVudCI6WyIiXSwibmFtZXMiOltdLCJtYXBwaW5ncyI6IiJ9