Allow whitespace after = in attributes (#3026)

src/compiler/parse/state/tag.ts

@@ -385,6 +385,7 @@ function read_attribute(parser: Parser, unique_names: Set<string>) {
 
 	let value: any[] | true = true;
 	if (parser.eat('=')) {
+		parser.allow_whitespace();
 		value = read_attribute_value(parser);
 		end = parser.index;
 	} else if (parser.match_regex(/["']/)) {

test/parser/samples/attribute-with-whitespace/input.svelte

@@ -0,0 +1 @@
+<button on:click= {foo}>Click</button>

test/parser/samples/attribute-with-whitespace/output.json

@@ -0,0 +1,39 @@
+{
+	"html": {
+		"start": 0,
+		"end": 38,
+		"type": "Fragment",
+		"children": [
+			{
+				"start": 0,
+				"end": 38,
+				"type": "Element",
+				"name": "button",
+				"attributes": [
+					{
+						"start": 8,
+						"end": 23,
+						"type": "EventHandler",
+						"name": "click",
+						"modifiers": [],
+						"expression": {
+							"type": "Identifier",
+							"start": 19,
+							"end": 22,
+							"name": "foo"
+						}
+					}
+				],
+				"children": [
+					{
+						"start": 24,
+						"end": 29,
+						"type": "Text",
+						"raw": "Click",
+						"data": "Click"
+					}
+				]
+			}
+		]
+	}
+}