and on the 7th day, he said, let there be cache

src/compiler/compile/render_dom/wrappers/Element/index.ts

@@ -1125,14 +1125,12 @@ export default class ElementWrapper extends Wrapper {
 
 	add_styles(block: Block) {
 		const has_spread = this.node.attributes.some(attr => attr.is_spread);
-		this.node.styles.forEach((style_directive) => {
-			
-			const { name, expression, important } = style_directive;
+		
+		const style_changed_var =  block.get_unique_name('style_changed');
+		block.chunks.update.push(b`const ${style_changed_var} = ${block.renderer.dirty([...this.dynamic_style_dependencies])};`);
 
-			const should_cache =
-				style_directive.should_cache &&
-				// Avoid caching if we have to override the style attribute
-				!this.dynamic_style_dependencies.size;
+		this.node.styles.forEach((style_directive) => {
+			const { name, expression, important, should_cache } = style_directive;
 
 			const snippet = expression.manipulate(block);
 			let cached_snippet: Identifier | undefined;
@@ -1149,16 +1147,30 @@ export default class ElementWrapper extends Wrapper {
 			if (has_spread) {
 				block.chunks.update.push(updater);
 			} else {
-				const dependencies = [
-					...this.dynamic_style_dependencies,
-					...expression.dynamic_dependencies()
+				const deps = [
+					...expression.dynamic_dependencies(),
+					...this.dynamic_style_dependencies
 				];
 
-				if (dependencies.length > 0) {
-					const is_dirty = block.renderer.dirty(dependencies);
-					const condition = should_cache
-						? x`${is_dirty} && (${cached_snippet} !== (${cached_snippet} = ${snippet}))`
-						: is_dirty;
+				if (deps.length > 0) {
+					if (deps.length === this.dynamic_style_dependencies.size) {
+						block.chunks.update.push(b`
+							if (${style_changed_var}) {
+								${updater}
+							}
+						`);
+						return;
+					}
+
+					let condition =  block.renderer.dirty(deps);
+
+					if (should_cache) {
+						condition = x`${condition} && ${cached_snippet} !== (${cached_snippet} = ${snippet})`;
+
+						if (style_changed_var) {
+							condition = x`${style_changed_var} || ${condition}`;
+						}
+					}
 
 					block.chunks.update.push(b`
 						if (${condition}) {

test/runtime-puppeteer/samples/inline-style-directive-precedence/_config.js

@@ -1,6 +1,6 @@
 export default {
 	html: `
-		<p style="font-size: 32px; color: red;"></p>
+		<p style="font-size: 32px; color: red; background-color: green;"></p>
 	`,
 
 	test({ assert, target, window, component }) {
@@ -8,6 +8,7 @@ export default {
 		const styles = window.getComputedStyle(p);
 		assert.equal(styles.color, 'rgb(255, 0, 0)');
 		assert.equal(styles.fontSize, '32px');
+		assert.equal(styles.backgroundColor, 'rgb(0, 128, 0)');
 
 		component.foo = 'font-size: 50px; color: green;'; // Update style attribute
 		{
@@ -15,6 +16,7 @@ export default {
 			const styles = window.getComputedStyle(p);
 			assert.equal(styles.color, 'rgb(255, 0, 0)');
 			assert.equal(styles.fontSize, '32px');
+			assert.equal(styles.backgroundColor, 'rgb(0, 128, 0)');
 		}
 	}
 };

test/runtime-puppeteer/samples/inline-style-directive-precedence/main.svelte

@@ -2,6 +2,7 @@
 	export let foo = "font-size: 20px; color: blue;";
 	let bar = "32";
 	let baz = "red";
+	export let bg = "gre";
 </script>
 
-<p style:font-size="{bar}px" style:color={baz} style={foo} />
+<p style:font-size="{bar}px" style:color={baz} style="{foo}" style:background-color="{bg}en" />