exhaustive

README

exhaustive

exhaustive checks exhaustiveness of enum switch statements in Go source code.

For the definition of enum and the definition of exhaustiveness used by this program, see godoc. For the changelog, see CHANGELOG in the GitHub wiki. The program can be configured to additionally check exhaustiveness of keys in map literals whose key type is an enum.

Usage

Command:

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

exhaustive [flags] [packages]

For available flags, refer to the Flags section in godoc or run exhaustive -h.

Package:

go get github.com/nishanths/exhaustive

import "github.com/nishanths/exhaustive"

The exhaustive.Analyzer variable follows guidelines in the golang.org/x/tools/go/analysis package. This should make it possible to integrate exhaustive with your own analysis driver program.

Example

Given an enum:

package token // import "example.org/token"

type Token int

const (
	Add Token = iota
	Subtract
	Multiply
	Quotient
	Remainder
)

and code that switches on the enum:

package calc

import "example.org/token"

func x(t token.Token) {
	switch t {
	case token.Add:
	case token.Subtract:
	case token.Remainder:
	default:
	}
}

running exhaustive with default flags will produce:

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

Specify flag -check=switch,map to additionally check exhaustiveness of keys in map literals. For example:

var m = map[token.Token]rune{
	token.Add:      '+',
	token.Subtract: '-',
	token.Multiply: '*',
	token.Quotient: '/',
}

calc.go:14:9: missing keys in map of key type token.Token: token.Remainder

Contributing

Issues and changes are welcome. Please discuss substantial changes in an issue first.

Documentation

Overview

Package exhaustive defines an analyzer that checks exhaustiveness of switch statements of enum-like constants in Go source code. The analyzer can optionally also check exhaustiveness of keys in map literals whose key type is enum-like.

Definition of enum

The Go language spec does not have an explicit definition for enums. For the purpose of this analyzer, and by convention, an enum type is any named type that:

• has an underlying type of float, string, or integer (includes byte and rune); and
• has at least one constant of its type defined in the same block.

In the example below, Biome is an enum type. The three constants are its enum members.

package eco

type Biome int

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

Enum member constants for an enum type must be declared in the same block as the type. The constant values may be specified using iota, literal values, or any valid means for declaring a Go constant. It is allowed for multiple enum member constants for an enum type to have the same constant value.

Definition of exhaustiveness

A switch statement that switches on a value of an enum type is exhaustive if all enum members are listed in the switch statement's cases. If multiple enum members have the same constant value, it is sufficient for any one of these same-valued members to be listed.

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 exported enum members are listed. Only constant identifiers (e.g. Tundra, eco.Desert) listed in a switch statement's case clause can contribute towards satisfying exhaustiveness; other expressions, such as literal values and function calls, listed in case clauses do not contribute towards satisfying exhaustiveness.

By default, the existence of a default case in a switch statement does not unconditionally make a switch statement exhaustive. Use the -default-signifies-exhaustive flag to adjust this behavior.

For a map literal whose key type is an enum type, a similar definition of exhaustiveness applies. The map literal is considered exhaustive if all enum members are be listed in its keys. Empty map literals are never checked for exhaustiveness.

Type parameters

A switch statement that switches on a value whose type is a type parameter is checked for exhaustiveness if and only if each type element in the type constraint is an enum type and the type elements share the same underlying BasicKind.

For example, the switch statement below will be checked because each type element (i.e. M and N) in the type constraint is an enum type and the type elements share the same underlying BasicKind, namely int8. To satisfy exhaustiveness, the enum members collectively belonging to the enum types M and N (i.e. A, B, and C) must be listed in the switch statement's cases.

func bar[T M | I](v T) {
	switch v {
	case T(A):
	case T(B):
	case T(C):
	}
}

type I interface{ N }

type M int8
const A M = 1

type N int8
const B N = 2
const C N = 3

Type aliases

The analyzer handles type aliases as shown in the example below. newpkg.M is an enum type. oldpkg.M is an alias for newpkg.M. Note that oldpkg.M isn't itself an enum type; oldpkg.M is simply an alias for the actual enum type newpkg.M.

package oldpkg
type M = newpkg.M
const (
	A = newpkg.A
	B = newpkg.B
)

package newpkg
type M int
const (
	A M = 1
	B M = 2
)

A switch statement that switches either on a value of type newpkg.M or of type oldpkg.M (which, being an alias, is just an alternative spelling for newpkg.M) is exhaustive if all of newpkg.M's enum members are listed in the switch statement's cases. The following switch statement is exhaustive.

func f(v newpkg.M) {
	switch v {
	case newpkg.A: // or equivalently oldpkg.A
	case newpkg.B: // or equivalently oldpkg.B
	}
}

The analyzer guarantees that introducing a type alias (such as type M = newpkg.M) will not result in new diagnostics if the set of enum member constant values of the RHS type is a subset of the set of enum member constant values of the LHS type.

Flags

Summary:

flag                           type                     default value
----                           ----                     -------------
-check                         comma-separated strings  switch
-explicit-exhaustive-switch    bool                     false
-explicit-exhaustive-map       bool                     false
-check-generated               bool                     false
-default-signifies-exhaustive  bool                     false
-ignore-enum-members           regexp pattern           (none)
-ignore-enum-types             regexp pattern           (none)
-package-scope-only            bool                     false

Descriptions:

-check
	Comma-separated list of program elements to check for
	exhaustiveness.  Supported program element values are
	"switch" and "map". The default value is "switch", which
	means that only switch statements are checked.

-explicit-exhaustive-switch
	Check a switch statement only if it is associated with a
	"//exhaustive:enforce" comment. By default the analyzer
	checks every switch statement that isn't associated with a
	"//exhaustive:ignore" comment.

-explicit-exhaustive-map
	Similar to -explicit-exhaustive-switch but for map literals.

-check-generated
	Check generated files. For the definition of a generated
	file, see https://golang.org/s/generatedcode.

-default-signifies-exhaustive
	Consider a switch statement to be exhaustive
	unconditionally if it has a default case. (In other words,
	all enum members do not have to be listed in its cases if a
	default case is present.) Setting this flag usually is
	counter to the purpose of exhaustiveness checks, so it is
	not recommended to set this flag.

-ignore-enum-members
	Constants that match the specified regular expression (in
	package regexp syntax) are not considered enum members and
	hence do not have to be listed to satisfy exhaustiveness.
	The specified regular expression is matched against the
	constant name inclusive of import path. For example, if the
	import path for the constant is "example.org/eco" and the
	constant name is "Tundra", then the specified regular
	expression is matched against the string
	"example.org/eco.Tundra".

-ignore-enum-types
	Similar to -ignore-enum-members but for types.

-package-scope-only
	Only discover enums declared in file-level blocks. By
	default, the analyzer discovers enums defined in all
	blocks.

Skip analysis

To skip analysis of a switch statement or a map literal, associate it with a comment that begins with "//exhaustive:ignore". For example:

//exhaustive:ignore ... an optional explanation goes here ...
switch v {
case A:
case B:
}

To ignore specific constants in exhaustiveness checks, specify the -ignore-enum-members flag:

exhaustive -ignore-enum-members '^example\.org/eco\.Tundra$'

To ignore specific types, specify the -ignore-enum-types flag:

exhaustive -ignore-enum-types '^time\.Duration$|^example\.org/measure\.Unit$'

Index

• Constants
• Variables

Constants

const (
	CheckFlag                      = "check"
	ExplicitExhaustiveSwitchFlag   = "explicit-exhaustive-switch"
	ExplicitExhaustiveMapFlag      = "explicit-exhaustive-map"
	CheckGeneratedFlag             = "check-generated"
	DefaultSignifiesExhaustiveFlag = "default-signifies-exhaustive"
	DefaultCaseRequiredFlag        = "default-case-required"
	IgnoreEnumMembersFlag          = "ignore-enum-members"
	IgnoreEnumTypesFlag            = "ignore-enum-types"
	PackageScopeOnlyFlag           = "package-scope-only"

	// Deprecated flag names.
	IgnorePatternFlag    = "ignore-pattern"    // Deprecated: use IgnoreEnumMembersFlag.
	CheckingStrategyFlag = "checking-strategy" // Deprecated: no longer applicable.
)

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

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{}},
}