support --style-props for <svelte:component>

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

@@ -423,21 +423,73 @@ export default class InlineComponentWrapper extends Wrapper {
 				}
 			`);
 
+			if (has_css_custom_properties) {
+				block.chunks.create.push(b`${css_custom_properties_wrapper} = @element("div");`);
+				block.chunks.hydrate.push(b`@set_style(${css_custom_properties_wrapper}, "display", "contents");`);
+				this.node.css_custom_properties.forEach(attr => {
+					const dependencies = attr.get_dependencies();
+					const should_cache = attr.should_cache();
+					const last = should_cache && block.get_unique_name(`${attr.name.replace(/[^a-zA-Z_$]/g, '_')}_last`);
+					if (should_cache) block.add_variable(last);
+					const value = attr.get_value(block);
+					const init = should_cache ? x`${last} = ${value}` : value;
+
+					block.chunks.hydrate.push(b`@set_style(${css_custom_properties_wrapper}, "${attr.name}", ${init});`);
+					if (dependencies.length > 0) {
+						let condition = block.renderer.dirty(dependencies);
+						if (should_cache) condition = x`${condition} && (${last} !== (${last} = ${value}))`;
+
+						block.chunks.update.push(b`
+							if (${condition}) {
+								@set_style(${css_custom_properties_wrapper}, "${attr.name}", ${should_cache ? last : value});
+							}
+						`);
+					}
+				});
+			}
+
 			block.chunks.create.push(
 				b`if (${name}) @create_component(${name}.$$.fragment);`
 			);
 
 			if (parent_nodes && this.renderer.options.hydratable) {
+				let nodes = parent_nodes;
+				if (has_css_custom_properties) {
+					nodes = block.get_unique_name(`${css_custom_properties_wrapper.name}_nodes`);
+					block.chunks.claim.push(b`
+						${css_custom_properties_wrapper} = @claim_element(${parent_nodes}, "DIV", { style: true })
+						var ${nodes} = @children(${css_custom_properties_wrapper});
+					`);
+				}
 				block.chunks.claim.push(
 					b`if (${name}) @claim_component(${name}.$$.fragment, ${parent_nodes});`
 				);
 			}
 
+			if (has_css_custom_properties) {
+				if (parent_node) {
+					block.chunks.mount.push(b`@append(${parent_node}, ${css_custom_properties_wrapper})`);
+					if (is_head(parent_node)) {
+						block.chunks.destroy.push(b`@detach(${css_custom_properties_wrapper});`);
+					}
+				} else {
+					block.chunks.mount.push(b`@insert(#target, ${css_custom_properties_wrapper}, #anchor);`);
+					// TODO we eventually need to consider what happens to elements
+					// that belong to the same outgroup as an outroing element...
+					block.chunks.destroy.push(b`if (detaching) @detach(${css_custom_properties_wrapper});`);
+				}
+				block.chunks.mount.push(b`
+					if (${name}) {
+						@mount_component(${name}, ${css_custom_properties_wrapper}, ${parent_node ? 'null' : '#anchor'});
+					}
+				`);
+			} else {
 				block.chunks.mount.push(b`
 					if (${name}) {
 						@mount_component(${name}, ${parent_node || '#target'}, ${parent_node ? 'null' : '#anchor'});
 					}
 				`);
+			}
 
 			const anchor = this.get_or_create_anchor(block, parent_node, parent_nodes);
 			const update_mount_node = this.get_update_mount_node(anchor);