Method _renderMergedCss

lib/css/CssGenerator.js:814–847

* Recursively merge `@import`'d CSS into a single Source (text/css-style-sheet only). * @param {NormalModule} module the module to render * @param {GenerateContext} generateContext the generate context * @param {Set<NormalModule>} ancestors modules on the current path (cycle guard) * @return

(module, generateContext, ancestors)

	 * @returns {Source | null} merged CSS source, or null when the module has no content
	 */
	_renderMergedCss(module, generateContext, ancestors) {
		if (ancestors.has(module)) return null;
		ancestors.add(module);
		try {
			const { moduleGraph } = generateContext;
			/** @type {Source[]} */
			const parts = [];

			for (const dep of module.dependencies) {
				if (!(dep instanceof CssImportDependency)) continue;
				const depModule = /** @type {CssModule} */ (moduleGraph.getModule(dep));
				if (!depModule) continue;
				const depExportType = depModule.exportType;
				if (depExportType !== "text" && depExportType !== "css-style-sheet") {
					continue;
				}
				const depMerged = this._renderMergedCss(
					depModule,
					generateContext,
					ancestors
				);
				if (depMerged) parts.push(depMerged);
			}

			const own = this._renderCss(module, generateContext);
			if (own) parts.push(own);

			if (parts.length === 0) return null;
			if (parts.length === 1) return parts[0];
			return new ConcatSource(...parts);
		} finally {
			ancestors.delete(module);
		}
	}

	/**
	 * Generate CSS source for the current module