exhaustive

README

exhaustive

The exhaustive package and the related command line program (found in cmd/exhaustive) can be used to check exhaustiveness of enum switch statements in Go code.

Install the command:

go install github.com/nishanths/exhaustive/cmd/exhaustive@latest

For documentation, see the package comment at pkg.go.dev. It describes the flags, the definition of enum, and the definition of exhaustiveness used by this package.

For the changelog, see CHANGELOG in the wiki.

The package provides an Analyzer that follows the guidelines in the go/analysis package; this should make it possible to integrate with external analysis driver programs.

Known issues

The analyzer's behavior is undefined for enum types that are type aliases. See issue #13.

Example

Given the enum

package token

type Token int

const (
	Add Token = iota
	Subtract
	Multiply
+	Quotient
+	Remainder
)

and the switch statement

package calc

import "token"

func processToken(t token.Token) {
	switch t {
	case token.Add: ...
	case token.Subtract: ...
	case token.Multiply: ...
	default: ...
	}
}

running exhaustive

exhaustive ./calc/...

will print

calc.go:6:2: missing cases in switch of type token.Token: Quotient, Remainder

Documentation

Overview

Package exhaustive provides an analyzer that checks exhaustiveness of enum switch statements in Go code.

Definition of enum

The Go language spec does not provide an explicit definition for enums. For the purpose of this analyzer, an enum type is a named (defined) type whose underlying type is an integer (includes byte and rune), a float, or a string type. An enum type must have associated with it one or more constants of the named type. These constants constitute the enum's members.

In the example below, Biome is an enum type with 3 members.

type Biome int

const (
		Tundra  Biome = 1
		Savanna Biome = 2
		Desert  Biome = 3
)

For a constant to be an enum member, it must be declared in the same scope as the enum type. That said, enum member constants don't necessarily have to all be declared in the same const block. Enum member constant values may be specified using iota or using explicit values (like in the example).

The analyzer's behavior is undefined for type aliases. This may change in the future.

Definition of exhaustiveness

An enum switch statement is exhaustive if all of the enum's members are listed in the switch statement's cases.

For an enum type defined in the same package as the switch statement, both exported and unexported enum members must be listed to satisfy exhaustiveness. For an enum type defined in an external package, it is sufficient that only the exported enum members be listed to satisfy exhaustiveness.

Flags

The notable flags used by the analyzer are below. All of these flags are optional.

Flag name						Type	Default value
-check-generated				bool	false
-default-signifies-exhaustive	bool	false
-ignore-enum-members			string	(none)
-package-scope-only				bool	false

If the -check-generated flag is enabled, switch statements in generated Go source files are also checked. Otherwise switch statements in generated files are ignored by default.

If the default-signifies-exhaustive flag is enabled, the presence of a "default" case in switch statements satisfies exhaustiveness, even if all enum members are not listed. It is recommended that you do not enable this flag; enabling it generally defeats the purpose of exhaustiveness checking.

The -ignore-enum-members flag specifies a regular expression, in the syntax accepted by the Go regexp package. Enum members matching the regular expression are ignored, i.e. these enum member names don't have to be listed in switch statements to satisfy exhaustiveness. The specified regular expression is matched against an enum member name inclusive of the enum package import path: for example, "example.com/pkg.Tundra" where where the import path is "example.com/pkg" and the enum member name is "Tundra".

If the -package-scope-only flag is enabled, the analyzer only finds enums defined in package scope, and consequently only switch statements that switch on package-scoped enums will be checked for exhaustiveness. By default, the analyzer finds enums defined in all scopes, and checks switch statements that switch on all these enums.

Skipping analysis

To skip analysis of a specific switch statement, associate the following comment with the switch statement. Note the lack of whitespace between the comment marker ("//") and the comment text.

//exhaustive:ignore

To ignore specific enum members, see the -ignore-enum-members flag.

By default, the analyzer skips analysis of switch statements in generated Go source files. Use the -check-generated flag to change this behavior. See https://golang.org/s/generatedcode for the definition of generated file.

Index

• Constants
• Variables

Constants

const (
	CheckGeneratedFlag             = "check-generated"
	DefaultSignifiesExhaustiveFlag = "default-signifies-exhaustive"
	IgnoreEnumMembersFlag          = "ignore-enum-members"
	PackageScopeOnly               = "package-scope-only"

	IgnorePatternFlag    = "ignore-pattern"    // Deprecated: see IgnoreEnumMembersFlag instead.
	CheckingStrategyFlag = "checking-strategy" // Deprecated.
)

Flag names used by the analyzer. They are exported for use by analyzer driver programs.

const IgnoreDirectivePrefix = "//exhaustive:ignore"

IgnoreDirectivePrefix is used to exclude checking of specific switch statements. See package comment for details.

Variables

var Analyzer = &analysis.Analyzer{
	Name:      "exhaustive",
	Doc:       "check exhaustiveness of enum switch statements",
	Run:       run,
	Requires:  []*analysis.Analyzer{inspect.Analyzer},
	FactTypes: []analysis.Fact{&enumMembersFact{}},
}