References to each index in keying expression seen as undeclared

[Conduitry]

From sveltejs/eslint-plugin-svelte3#37

Something like

{#each foo as bar, i (i)}hey{/each}

produces an erroneous warning that i is not defined. The key seems to be created correctly from the each block's ctx.i - there's just an incorrect warning from the compiler about it.

[Conduitry]

My first stab at a solution for this was to simply add the EachBlock's index to its scope before creating the Expression for its key:

diff --git a/src/compiler/compile/nodes/EachBlock.ts b/src/compiler/compile/nodes/EachBlock.ts
index adaa46b8..12e6cccb 100644
--- a/src/compiler/compile/nodes/EachBlock.ts
+++ b/src/compiler/compile/nodes/EachBlock.ts
@@ -83,16 +83,16 @@ export default class EachBlock extends AbstractBlock {
 			this.scope.add(context.key.name, this.expression.dependencies, this);
 		});
 
-		this.key = info.key
-			? new Expression(component, this, this.scope, info.key)
-			: null;
-
 		if (this.index) {
 			// index can only change if this is a keyed each block
 			const dependencies = this.key ? this.expression.dependencies : new Set([]);
 			this.scope.add(this.index, dependencies, this);
 		}
 
+		this.key = info.key
+			? new Expression(component, this, this.scope, info.key)
+			: null;
+
 		this.has_animation = false;
 
 		this.children = map_children(component, this, this.scope, info.children);

but this is making the each-block-keyed and each-block-keyed-object-identity runtime tests fail and I'm not sure why.

---

Edit: Whoops, the this.index handling was looking at this.key to see whether there was a key set. With the above change, this of course needs to be looking at info.key instead. With that, there are no failing tests.