apollo-engine-reporting doesn't put errors associated with list elements on the right node

[glasser]

This else path in treeBuilder.ts:

      const specificNode = this.nodes.get(path.join('.'));
      if (specificNode) {
        node = specificNode;
      } else {
        this.logger.warn(
          `Could not find node with path ${path.join(
            '.',
          )}; defaulting to put errors on root node.`,

is supposed to be a "can't happen" case, but it can happen. Nodes are added to this.nodes by willResolveField. There's no specific callback that adds list elements to this.nodes; they get there when some field below them is resolved. But if an error occurs associated with (by err.path) a list element rather than a field, the list element won't have a node and this path is triggered, spewing a warning and losing the correct location for the error.

This was reported by a user, and by code inspection I believe that there are a lot of ways for errors to be generated with a path that ends in a list element:

• a resolver can return a list containing a Promise that rejects
• a resolver whose return type is [X!] can return a list containing null
• a resolver whose return type is a list of union or interface elements can return a list containing an element that cannot be resolved to an appropriate object type

This list is nonexhaustive.

[glasser]

The fix is probably just to call newNode (converting the array to the ResponsePath linked list) from addProtobufError instead of redirecting to the root.

[github-actions]

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