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58/*
go-sumtype takes a list of Go package paths or files and looks for sum type
declarations in each package/file provided. Exhaustiveness checks are then
performed for each use of a declared sum type in a type switch statement.
Namely, go-sumtype will report an error for any type switch statement that
either lacks a default clause or does not account for all possible variants.
Declarations are provided in comments like so:
//go-sumtype:decl MySumType
MySumType must satisfy the following:
1. It is a type defined in the same package.
2. It is an interface.
3. It is *sealed*. That is, part of its interface definition contains an
unexported method.
go-sumtype will produce an error if any of the above is not true.
For valid declarations, go-sumtype will look for all occurrences in which a
value of type MySumType participates in a type switch statement. In those
occurrences, it will attempt to detect whether the type switch is exhaustive
or not. If it's not, go-sumtype will report an error. For example:
$ cat mysumtype.go
package main
//go-sumtype:decl MySumType
type MySumType interface {
sealed()
}
type VariantA struct{}
func (a *VariantA) sealed() {}
type VariantB struct{}
func (b *VariantB) sealed() {}
func main() {
switch MySumType(nil).(type) {
case *VariantA:
}
}
$ go-sumtype mysumtype.go
mysumtype.go:18:2: exhaustiveness check failed for sum type 'MySumType': missing cases for VariantB
Adding either a default clause or a clause to handle *VariantB will cause
exhaustive checks to pass.
As a special case, if the type switch statement contains a default clause
that always panics, then exhaustiveness checks are still performed.
*/
package main