fix(820): label has associated control

src/compiler/compile/nodes/Element.ts

@@ -507,6 +507,16 @@ export default class Element extends Node {
 			}
 		}
 
+		if (this.name === 'label') {
+			const has_input_child = this.children.some(i => (i instanceof Element && i.name === 'input' ));
+			if (!attribute_map.has('for') && !has_input_child) {
+				component.warn(this, {
+					code: `a11y-label-has-associated-control`,
+					message: `A11y: A form label must be associated with a control.`
+				});
+			}
+		}
+
 		if (a11y_no_onchange.has(this.name)) {
 			if (handlers_map.has('change') && !handlers_map.has('blur')) {
 				component.warn(this, {

test/validator/samples/a11y-label-has-associated-control/input.svelte

@@ -0,0 +1,5 @@
+<label>A</label>
+<label for="id">B</label>
+
+<label>C <input type="text" /></label>
+<label>D <span></span></label>

test/validator/samples/a11y-label-has-associated-control/warnings.json

@@ -0,0 +1,32 @@
+[
+	{
+		"code": "a11y-label-has-associated-control",
+		"end": {
+			"character": 16,
+			"column": 16,
+			"line": 1
+		},
+		"message": "A11y: A form label must be associated with a control.",
+		"pos": 0,
+		"start": {
+			"character": 0,
+			"column": 0,
+			"line": 1
+		}
+	},
+	{
+		"code": "a11y-label-has-associated-control",
+		"end": {
+			"character": 113,
+			"column": 30,
+			"line": 5
+		},
+		"message": "A11y: A form label must be associated with a control.",
+		"pos": 83,
+		"start": {
+			"character": 83,
+			"column": 0,
+			"line": 5
+		}
+	}
+]