package constraint

import "go/build/constraint"

Package constraint implements parsing and evaluation of build constraint lines. See https://golang.org/cmd/go/#hdr-Build_constraints for documentation about build constraints themselves.

This package parses both the original “// +build” syntax and the “//go:build” syntax that was added in Go 1.17. See https://golang.org/design/draft-gobuild for details about the “//go:build” syntax.

Index ¶

• func IsGoBuild(line string) bool
• func IsPlusBuild(line string) bool
• func PlusBuildLines(x Expr) ([]string, error)
• type AndExpr
• func (x *AndExpr) Eval(ok func(tag string) bool) bool
• func (x *AndExpr) String() string
• type Expr
• func Parse(line string) (Expr, error)
• type NotExpr
• func (x *NotExpr) Eval(ok func(tag string) bool) bool
• func (x *NotExpr) String() string
• type OrExpr
• func (x *OrExpr) Eval(ok func(tag string) bool) bool
• func (x *OrExpr) String() string
• type SyntaxError
• func (e *SyntaxError) Error() string
• type TagExpr
• func (x *TagExpr) Eval(ok func(tag string) bool) bool
• func (x *TagExpr) String() string

Functions ¶

func IsGoBuild ¶

func IsGoBuild(line string) bool

IsGoBuild reports whether the line of text is a “//go:build” constraint. It only checks the prefix of the text, not that the expression itself parses.

func IsPlusBuild ¶

func IsPlusBuild(line string) bool

IsPlusBuild reports whether the line of text is a “// +build” constraint. It only checks the prefix of the text, not that the expression itself parses.

func PlusBuildLines ¶

func PlusBuildLines(x Expr) ([]string, error)

PlusBuildLines returns a sequence of “// +build” lines that evaluate to the build expression x. If the expression is too complex to convert directly to “// +build” lines, PlusBuildLines returns an error.

Types ¶

type AndExpr ¶

type AndExpr struct {
	X, Y Expr
}

An AndExpr represents the expression X && Y.

func (*AndExpr) Eval ¶

func (x *AndExpr) Eval(ok func(tag string) bool) bool

func (*AndExpr) String ¶

func (x *AndExpr) String() string

type Expr ¶

type Expr interface {
	// String returns the string form of the expression,
	// using the boolean syntax used in //go:build lines.
	String() string

	// Eval reports whether the expression evaluates to true.
	// It calls ok(tag) as needed to find out whether a given build tag
	// is satisfied by the current build configuration.
	Eval(ok func(tag string) bool) bool
	// contains filtered or unexported methods
}

An Expr is a build tag constraint expression. The underlying concrete type is *AndExpr, *OrExpr, *NotExpr, or *TagExpr.

func Parse ¶

func Parse(line string) (Expr, error)

Parse parses a single build constraint line of the form “//go:build ...” or “// +build ...” and returns the corresponding boolean expression.

type NotExpr ¶

type NotExpr struct {
	X Expr
}

A NotExpr represents the expression !X (the negation of X).

func (*NotExpr) Eval ¶

func (x *NotExpr) Eval(ok func(tag string) bool) bool

func (*NotExpr) String ¶

func (x *NotExpr) String() string

type OrExpr ¶

type OrExpr struct {
	X, Y Expr
}

An OrExpr represents the expression X || Y.

func (*OrExpr) Eval ¶

func (x *OrExpr) Eval(ok func(tag string) bool) bool

func (*OrExpr) String ¶

func (x *OrExpr) String() string

type SyntaxError ¶

type SyntaxError struct {
	Offset int    // byte offset in input where error was detected
	Err    string // description of error
}

A SyntaxError reports a syntax error in a parsed build expression.

func (*SyntaxError) Error ¶

func (e *SyntaxError) Error() string

type TagExpr ¶

type TagExpr struct {
	Tag string // for example, “linux” or “cgo”
}

A TagExpr is an Expr for the single tag Tag.

func (*TagExpr) Eval ¶

func (x *TagExpr) Eval(ok func(tag string) bool) bool

func (*TagExpr) String ¶

func (x *TagExpr) String() string

Source Files ¶

expr.go