fix stringifying of attributes in presence of spread in SSR (#4247)

src/runtime/internal/ssr.ts

@@ -25,9 +25,7 @@ export function spread(args, classes_to_add) {
 		else if (boolean_attributes.has(name.toLowerCase())) {
 			if (value) str += " " + name;
 		} else if (value != null) {
-			str += " " + name + "=" + JSON.stringify(String(value)
-				.replace(/"/g, '"')
-				.replace(/'/g, '''));
+			str += ` ${name}="${String(value).replace(/"/g, '"').replace(/'/g, ''')}"`;
 		}
 	});
 

test/server-side-rendering/samples/spread-attributes-white-space/_expected.html

@@ -0,0 +1,8 @@
+<input value="
+	bar
+">
+
+<input class="
+	white
+	space
+">

test/server-side-rendering/samples/spread-attributes-white-space/main.svelte

@@ -0,0 +1,12 @@
+<script>
+	let props = {
+		value: '\n\tbar\n',
+	};
+</script>
+
+<input {...props} />
+
+<input class="
+	white
+	space
+" {...({})}>