doc.go

/*
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