svelte/src/compiler/phases/2-analyze/visitors/IfBlock.js

Cybernetically enhanced web apps

/** @import { AST } from '#compiler' */
/** @import { Context } from '../types' */
import { mark_subtree_dynamic } from './shared/fragment.js';
import { validate_block_not_empty, validate_opening_tag } from './shared/utils.js';

/**
 * @param {AST.IfBlock} node
 * @param {Context} context
 */
export function IfBlock(node, context) {
	validate_block_not_empty(node.consequent, context);
	validate_block_not_empty(node.alternate, context);

	if (context.state.analysis.runes) {
		validate_opening_tag(node, context.state, node.elseif ? ':' : '#');
	}

	mark_subtree_dynamic(context.path);

	context.visit(node.test, {
		...context.state,
		expression: node.metadata.expression
	});

	context.visit(node.consequent);
	if (node.alternate) context.visit(node.alternate);

	// Check if we can flatten branches
	const alt = node.alternate;

	if (alt && alt.nodes.length === 1 && alt.nodes[0].type === 'IfBlock' && alt.nodes[0].elseif) {
		const elseif = alt.nodes[0];

		// Don't flatten if this else-if has an await expression or new blockers
		// TODO would be nice to check the await expression itself to see if it's awaiting the same thing as a previous if expression
		if (
			!elseif.metadata.expression.has_await &&
			!elseif.metadata.expression.has_more_blockers_than(node.metadata.expression)
		) {
			// Roll the existing flattened branches (if any) into this one, then delete those of the else-if block
			// to avoid processing them multiple times as we walk down the chain during code transformation.
			node.metadata.flattened = [elseif, ...(elseif.metadata.flattened ?? [])];
			elseif.metadata.flattened = undefined;
		}
	}
}