remove unneeded fragment block (#4568)

Author: tanhauhau

src/compiler/compile/render_dom/Block.ts

@@ -419,8 +419,8 @@ export default class Block {
 		return body;
 	}
 
-	has_content() {
-		return this.first ||
+	has_content(): boolean {
+		return !!this.first ||
 			this.event_listeners.length > 0 ||
 			this.chunks.intro.length > 0 ||
 			this.chunks.outro.length > 0  ||

src/compiler/compile/render_dom/Renderer.ts

@@ -284,4 +284,8 @@ export default class Renderer {
 
 		return node;
 	}
+
+	remove_block(block: Block | Node | Node[]) {
+		this.blocks.splice(this.blocks.indexOf(block), 1);
+	}
 }

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

@@ -155,6 +155,7 @@ export default class InlineComponentWrapper extends Wrapper {
 		// removing empty slot
 		for (const slot of this.slots.keys()) {
 			if (!this.slots.get(slot).block.has_content()) {
+				this.renderer.remove_block(this.slots.get(slot).block);
 				this.slots.delete(slot);
 			}
 		}

src/compiler/compile/render_dom/wrappers/Slot.ts

@@ -114,18 +114,23 @@ export default class SlotWrapper extends Wrapper {
 			get_slot_context_fn = 'null';
 		}
 
+		let has_fallback = !!this.fallback;
 		if (this.fallback) {
 			this.fragment.render(this.fallback, null, x`#nodes` as Identifier);
+			has_fallback = this.fallback.has_content();
+			if (!has_fallback) {
+				renderer.remove_block(this.fallback);
+			}
 		}
 
 		const slot = block.get_unique_name(`${sanitize(slot_name)}_slot`);
 		const slot_definition = block.get_unique_name(`${sanitize(slot_name)}_slot_template`);
-		const slot_or_fallback = this.fallback ? block.get_unique_name(`${sanitize(slot_name)}_slot_or_fallback`) : slot;
+		const slot_or_fallback = has_fallback ? block.get_unique_name(`${sanitize(slot_name)}_slot_or_fallback`) : slot;
 
 		block.chunks.init.push(b`
 			const ${slot_definition} = ${renderer.reference('$$slots')}.${slot_name};
 			const ${slot} = @create_slot(${slot_definition}, #ctx, ${renderer.reference('$$scope')}, ${get_slot_context_fn});
-			${this.fallback ? b`const ${slot_or_fallback} = ${slot} || ${this.fallback.name}(#ctx);` : null}
+			${has_fallback ? b`const ${slot_or_fallback} = ${slot} || ${this.fallback.name}(#ctx);` : null}
 		`);
 
 		block.chunks.create.push(
@@ -161,7 +166,7 @@ export default class SlotWrapper extends Wrapper {
 
 		const dynamic_dependencies = Array.from(this.dependencies).filter(is_dependency_dynamic);
 
-		const fallback_dynamic_dependencies = this.fallback
+		const fallback_dynamic_dependencies = has_fallback
 			? Array.from(this.fallback.dependencies).filter(is_dependency_dynamic)
 			: [];
 
@@ -173,7 +178,7 @@ export default class SlotWrapper extends Wrapper {
 				);
 			}
 		`;
-		const fallback_update = this.fallback && fallback_dynamic_dependencies.length > 0 && b`
+		const fallback_update = has_fallback && fallback_dynamic_dependencies.length > 0 && b`
 			if (${slot_or_fallback} && ${slot_or_fallback}.p && ${renderer.dirty(fallback_dynamic_dependencies)}) {
 				${slot_or_fallback}.p(#ctx, #dirty);
 			}