Implements so that slot defaults apply when forwarding

src/compiler/compile/render_dom/Block.ts

@@ -43,6 +43,7 @@ export default class Block {
 	binding_groups: Set<BindingGroup> = new Set();
 
 	chunks: {
+		conditional_fragment: Array<Node | Node[]>;
 		declarations: Array<Node | Node[]>;
 		init: Array<Node | Node[]>;
 		create: Array<Node | Node[]>;
@@ -92,6 +93,7 @@ export default class Block {
 		this.bindings = options.bindings;
 
 		this.chunks = {
+			conditional_fragment: [],
 			declarations: [],
 			init: [],
 			create: [],
@@ -381,7 +383,7 @@ export default class Block {
 			}
 		}
 
-		const return_value: any = x`{
+		const return_fragment: any = x`{
 			key: ${properties.key},
 			first: ${properties.first},
 			c: ${properties.create},
@@ -399,6 +401,13 @@ export default class Block {
 		}`;
 
 		const block = dev && this.get_unique_name('block');
+		const conditional_array = {
+			type: 'ArrayExpression',
+			elements: this.chunks.conditional_fragment
+		};
+		const conditional = this.chunks.conditional_fragment.length ? x`${conditional_array}.some(@identity)` : null;
+
+		const return_value = conditional ? x`${conditional} ? ${return_fragment} : null` : return_fragment;
 
 		const body = b`
 			${this.chunks.declarations}

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

@@ -128,6 +128,7 @@ export default class SlotWrapper extends Wrapper {
 		const slot_definition = block.get_unique_name(`${sanitize(slot_name)}_slot_template`);
 		const slot_or_fallback = has_fallback ? block.get_unique_name(`${sanitize(slot_name)}_slot_or_fallback`) : slot;
 
+		block.chunks.conditional_fragment.push(slot_or_fallback);
 		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});

src/compiler/compile/render_ssr/handlers/InlineComponent.ts

@@ -77,9 +77,11 @@ export default function(node: InlineComponent, renderer: Renderer, options: Rend
 			slot_scopes
 		}));
 
-		slot_scopes.forEach(({ input, output, statements }, name) => {
+		slot_scopes.forEach(({ input, output, condition, default_value, statements }, name) => {
 			slot_fns.push(
-				p`${name}: (${input}) => { ${statements}; return ${output}; }`
+				condition && default_value
+					? p`${name}: ${condition} || ${default_value} ? (${input}) => ${output} : null`
+					: p`${name}: (${input}) => { ${statements}; return ${output}; }`
 			);
 		});
 	}

src/compiler/compile/render_ssr/handlers/Slot.ts

@@ -34,7 +34,9 @@ export default function(node: Slot, renderer: Renderer, options: RenderOptions &
 		});
 		options.slot_scopes.set(slot, {
 			input: get_slot_scope(node.lets),
-			output: renderer.pop()
+			condition: x`#slots.${node.slot_name}`,
+			output: renderer.pop(),
+			default_value: result
 		});
 	}
 }