Chris's Wiki :: blog/programming/Go122TypesAliasAndCompatibility
Go famously promises backward compatibility to the first release of Go and pretty much delivers on that (although the tools used to build Go programs have changed). Thus, one may be a bit surprised to read the following about go/types in the Go 1.22 Release Notes:
The new Alias type represents type aliases. Previously, type aliases were not represented explicitly, so a reference to a type alias was equivalent to spelling out the aliased type, and the name of the alias was lost. [...]
Because Alias types may break existing type switches that do not know to check for them, this functionality is controlled by a GODEBUG field named gotypesalias. [...] Clients of go/types are urged to adjust their code as soon as possible to work with gotypesalias=1 to eliminate problems early.
A variety of things in go/types return a Type, which is an interface type that 'represents a type of Go'. Well, more specifically these things return values of type Type, and these values have various underlying concrete types. Some code using go/types and dealing with Type values can handle them purely as interfaces, but other code needs to specifically handle all of the particular types (such as Array and so on). Since Type is an interface, such code will use a type switch that is supposed to be exhaustive over all of the concrete types of Type interface values.
