When compiling a package that instantiates a generic type from another
package, info.Types only contains the instantiated *types.Named. The
*types.Struct case in recordFieldToStruct returns early on instantiated
structs (field != field.Origin()), so the origin struct was never
recorded in fieldToStruct. At rewrite time, looking up the origin field
then failed with "could not find struct for field X".
Fix by also recursing into typ.Origin() for instantiated named types,
so the uninstantiated struct is visited and its fields are recorded.
Fixes#1027.
Golo Roden
cdc4b23ac5