feat: added a util for counting element occurences

Author: marekdedic

packages/eslint-plugin-svelte/src/utils/element-occurences.ts

@@ -0,0 +1,55 @@
+import type { AST } from 'svelte-eslint-parser';
+
+export enum ElementOccurenceCount {
+	ZeroOrOne,
+	One,
+	ZeroToInf
+}
+
+function multiplyCounts(
+	left: ElementOccurenceCount,
+	right: ElementOccurenceCount
+): ElementOccurenceCount {
+	if (left === ElementOccurenceCount.One) {
+		return right;
+	}
+	if (right === ElementOccurenceCount.One) {
+		return left;
+	}
+	if (left === right) {
+		return left;
+	}
+	return ElementOccurenceCount.ZeroToInf;
+}
+
+function childElementOccurenceCount(parent: AST.SvelteHTMLNode | null): ElementOccurenceCount {
+	if (parent === null) {
+		return ElementOccurenceCount.One;
+	}
+	if (
+		[
+			'SvelteIfBlock',
+			'SvelteElseBlock',
+			'SvelteAwaitBlock',
+			'SvelteAwaitPendingBlock',
+			'SvelteAwaitThenBlock',
+			'SvelteAwaitCatchBlock'
+		].includes(parent.type)
+	) {
+		return ElementOccurenceCount.ZeroOrOne;
+	}
+	if (
+		['SvelteEachBlock', 'SvelteSnippetBlock'].includes(parent.type) ||
+		(parent.type === 'SvelteElement' && parent.kind === 'component')
+	) {
+		return ElementOccurenceCount.ZeroToInf;
+	}
+	return ElementOccurenceCount.One;
+}
+
+export function elementOccurrenceCount(element: AST.SvelteHTMLNode): ElementOccurenceCount {
+	const parentCount =
+		element.parent !== null ? elementOccurrenceCount(element.parent) : ElementOccurenceCount.One;
+	const parentChildCount = childElementOccurenceCount(element.parent);
+	return multiplyCounts(parentCount, parentChildCount);
+}