Style properties update unnecessarily

[Rich-Harris]

Describe the bug

Svelte generates code that updates style properties when nothing could change.

To Reproduce

https://svelte.dev/repl/fa82902dbf5e442a92217e6d6fa6c078?version=3.8.1

Expected behavior

Given this code...

<script>
	let color = 'red';
</script>

<h1 class={color} style="color: {color}">color: {color}</h1>

...no update could should be generated, since color could not change. This works correctly for regular attributes:

	return {
		c() {
			h1 = element("h1");
			t0 = text("color: ");
			t1 = text(color);
			attr(h1, "class", "" + null_to_empty(color) + " svelte-1fyrt1w");
			set_style(h1, "color", color);
		},

		m(target, anchor) {
			insert(target, h1, anchor);
			append(h1, t0);
			append(h1, t1);
		},

-		p(changed, ctx) {
-			if (changed.color) {
-				set_style(h1, "color", color);
-			}
-		},
-
+		p: noop,
		i: noop,
		o: noop,

		d(detaching) {
			if (detaching) {
				detach(h1);
			}
		}
	};

Severity

Minor

[Rich-Harris]

closed via #3439