Components should be able to explicitly specify 'undefined' as default prop value

[Conduitry]

If a component has

<script>
  export let foo = undefined;
</script>

then instantiating the component without a foo prop shouldn't cause a warning in dev mode. This seems to affect only cases where undefined is the default value - other default values work fine.

[Conduitry]

I believe there's a bug when determining the initialized declarations in a given scope:

diff --git a/src/compile/utils/scope.ts b/src/compile/utils/scope.ts
index 20cca46c..6488986d 100644
--- a/src/compile/utils/scope.ts
+++ b/src/compile/utils/scope.ts
@@ -75,12 +75,10 @@ export class Scope {
 		if (node.kind === 'var' && this.block && this.parent) {
 			this.parent.add_declaration(node);
 		} else if (node.type === 'VariableDeclaration') {
-			const initialised = !!node.init;
-
 			node.declarations.forEach((declarator: Node) => {
 				extract_names(declarator.id).forEach(name => {
 					this.declarations.set(name, node);
-					if (initialised) this.initialised_declarations.add(name);
+					if (declarator.init) this.initialised_declarations.add(name);
 				});
 			});
 		} else {

In the AST, init is a property on the individual VariableDeclarators, not on the VariableDeclaration. I'm not sure whether this has any impact on other things in the code. None that I've seen so far.