typegen: de-novo use fails silently -- serious bug!

[rcoreilly]

Describe the bug

if you run typegen (i.e., core generate) on a type that embeds a core Widget (e.g., core.Frame), in a directory that has no prior successful tree.Node types added, it fails to recognize this as a tree.Node type, and does not generate the proper set of methods (e.g., the New function).

A workaround is to explicitly include the tree type:

var _ tree.Node = (*MyType)(nil)

and then generate. Once this succeeds, then this line can be deleted and it will continue to work.

How to reproduce

see above.

Example code

No response

Relevant output

No response

Platform

macOS