package token

import "go/token"

Package token defines constants representing the lexical tokens of the Go programming language and basic operations on tokens (printing, predicates).

Example (RetrievePositionInfo) 
package main

import (
	"fmt"
	"go/ast"
	"go/parser"
	"go/token"
)

func main() {
	fset := token.NewFileSet()

	const src = `package main

import "fmt"

import "go/token"

//line :1:5
type p = token.Pos

const bad = token.NoPos

//line fake.go:42:11
func ok(pos p) bool {
	return pos != bad
}

/*line :7:9*/func main() {
	fmt.Println(ok(bad) == bad.IsValid())
}
`

	f, err := parser.ParseFile(fset, "main.go", src, 0)
	if err != nil {
		fmt.Println(err)
		return
	}

	// Print the location and kind of each declaration in f.
	for _, decl := range f.Decls {
		// Get the filename, line, and column back via the file set.
		// We get both the relative and absolute position.
		// The relative position is relative to the last line directive.
		// The absolute position is the exact position in the source.
		pos := decl.Pos()
		relPosition := fset.Position(pos)
		absPosition := fset.PositionFor(pos, false)

		// Either a FuncDecl or GenDecl, since we exit on error.
		kind := "func"
		if gen, ok := decl.(*ast.GenDecl); ok {
			kind = gen.Tok.String()
		}

		// If the relative and absolute positions differ, show both.
		fmtPosition := relPosition.String()
		if relPosition != absPosition {
			fmtPosition += "[" + absPosition.String() + "]"
		}

		fmt.Printf("%s: %s\n", fmtPosition, kind)
	}

}

Output:

main.go:3:1: import
main.go:5:1: import
main.go:1:5[main.go:8:1]: type
main.go:3:1[main.go:10:1]: const
fake.go:42:11[main.go:13:1]: func
fake.go:7:9[main.go:17:14]: func

Index

Examples

Constants

const (
	LowestPrec  = 0 // non-operators
	UnaryPrec   = 6
	HighestPrec = 7
)

A set of constants for precedence-based expression parsing. Non-operators have lowest precedence, followed by operators starting with precedence 1 up to unary operators. The highest precedence serves as "catch-all" precedence for selector, indexing, and other operator and delimiter tokens.

Functions

func IsExported

func IsExported(name string) bool

IsExported reports whether name starts with an upper-case letter.

func IsIdentifier

func IsIdentifier(name string) bool

IsIdentifier reports whether name is a Go identifier, that is, a non-empty string made up of letters, digits, and underscores, where the first character is not a digit. Keywords are not identifiers.

func IsKeyword

func IsKeyword(name string) bool

IsKeyword reports whether name is a Go keyword, such as "func" or "return".

Types

type File

type File struct {
	// contains filtered or unexported fields
}

A File is a handle for a file belonging to a FileSet. A File has a name, size, and line offset table.

func (*File) AddLine

func (f *File) AddLine(offset int)

AddLine adds the line offset for a new line. The line offset must be larger than the offset for the previous line and smaller than the file size; otherwise the line offset is ignored.

func (*File) AddLineColumnInfo

func (f *File) AddLineColumnInfo(offset int, filename string, line, column int)

AddLineColumnInfo adds alternative file, line, and column number information for a given file offset. The offset must be larger than the offset for the previously added alternative line info and smaller than the file size; otherwise the information is ignored.

AddLineColumnInfo is typically used to register alternative position information for line directives such as //line filename:line:column.

func (*File) AddLineInfo

func (f *File) AddLineInfo(offset int, filename string, line int)

AddLineInfo is like File.AddLineColumnInfo with a column = 1 argument. It is here for backward-compatibility for code prior to Go 1.11.

func (*File) Base

func (f *File) Base() int

Base returns the base offset of file f as registered with AddFile.

func (*File) Line

func (f *File) Line(p Pos) int

Line returns the line number for the given file position p; p must be a Pos value in that file or NoPos.

func (*File) LineCount

func (f *File) LineCount() int

LineCount returns the number of lines in file f.

func (*File) LineStart

func (f *File) LineStart(line int) Pos

LineStart returns the Pos value of the start of the specified line. It ignores any alternative positions set using File.AddLineColumnInfo. LineStart panics if the 1-based line number is invalid.

func (*File) Lines

func (f *File) Lines() []int

Lines returns the effective line offset table of the form described by File.SetLines. Callers must not mutate the result.

func (*File) MergeLine

func (f *File) MergeLine(line int)

MergeLine merges a line with the following line. It is akin to replacing the newline character at the end of the line with a space (to not change the remaining offsets). To obtain the line number, consult e.g. [Position.Line]. MergeLine will panic if given an invalid line number.

func (*File) Name

func (f *File) Name() string

Name returns the file name of file f as registered with AddFile.

func (*File) Offset

func (f *File) Offset(p Pos) int

Offset returns the offset for the given file position p; p must be a valid Pos value in that file. f.Offset(f.Pos(offset)) == offset.

func (*File) Pos

func (f *File) Pos(offset int) Pos

Pos returns the Pos value for the given file offset; the offset must be <= f.Size(). f.Pos(f.Offset(p)) == p.

func (*File) Position

func (f *File) Position(p Pos) (pos Position)

Position returns the Position value for the given file position p. Calling f.Position(p) is equivalent to calling f.PositionFor(p, true).

func (*File) PositionFor

func (f *File) PositionFor(p Pos, adjusted bool) (pos Position)

PositionFor returns the Position value for the given file position p. If adjusted is set, the position may be adjusted by position-altering //line comments; otherwise those comments are ignored. p must be a Pos value in f or NoPos.

func (*File) SetLines

func (f *File) SetLines(lines []int) bool

SetLines sets the line offsets for a file and reports whether it succeeded. The line offsets are the offsets of the first character of each line; for instance for the content "ab\nc\n" the line offsets are {0, 3}. An empty file has an empty line offset table. Each line offset must be larger than the offset for the previous line and smaller than the file size; otherwise SetLines fails and returns false. Callers must not mutate the provided slice after SetLines returns.

func (*File) SetLinesForContent

func (f *File) SetLinesForContent(content []byte)

SetLinesForContent sets the line offsets for the given file content. It ignores position-altering //line comments.

func (*File) Size

func (f *File) Size() int

Size returns the size of file f as registered with AddFile.

type FileSet

type FileSet struct {
	// contains filtered or unexported fields
}

A FileSet represents a set of source files. Methods of file sets are synchronized; multiple goroutines may invoke them concurrently.

The byte offsets for each file in a file set are mapped into distinct (integer) intervals, one interval [base, base+size] per file. FileSet.Base represents the first byte in the file, and size is the corresponding file size. A Pos value is a value in such an interval. By determining the interval a Pos value belongs to, the file, its file base, and thus the byte offset (position) the Pos value is representing can be computed.

When adding a new file, a file base must be provided. That can be any integer value that is past the end of any interval of any file already in the file set. For convenience, FileSet.Base provides such a value, which is simply the end of the Pos interval of the most recently added file, plus one. Unless there is a need to extend an interval later, using the FileSet.Base should be used as argument for FileSet.AddFile.

A File may be removed from a FileSet when it is no longer needed. This may reduce memory usage in a long-running application.

func NewFileSet

func NewFileSet() *FileSet

NewFileSet creates a new file set.

func (*FileSet) AddFile

func (s *FileSet) AddFile(filename string, base, size int) *File

AddFile adds a new file with a given filename, base offset, and file size to the file set s and returns the file. Multiple files may have the same name. The base offset must not be smaller than the FileSet.Base, and size must not be negative. As a special case, if a negative base is provided, the current value of the FileSet.Base is used instead.

Adding the file will set the file set's FileSet.Base value to base + size + 1 as the minimum base value for the next file. The following relationship exists between a Pos value p for a given file offset offs: 

int(p) = base + offs

with offs in the range [0, size] and thus p in the range [base, base+size]. For convenience, File.Pos may be used to create file-specific position values from a file offset.

func (*FileSet) Base

func (s *FileSet) Base() int

Base returns the minimum base offset that must be provided to FileSet.AddFile when adding the next file.

func (*FileSet) File

func (s *FileSet) File(p Pos) (f *File)

File returns the file that contains the position p. If no such file is found (for instance for p == NoPos), the result is nil.

func (*FileSet) Iterate

func (s *FileSet) Iterate(f func(*File) bool)

Iterate calls f for the files in the file set in the order they were added until f returns false.

func (*FileSet) Position

func (s *FileSet) Position(p Pos) (pos Position)

Position converts a Pos p in the fileset into a Position value. Calling s.Position(p) is equivalent to calling s.PositionFor(p, true).

func (*FileSet) PositionFor

func (s *FileSet) PositionFor(p Pos, adjusted bool) (pos Position)

PositionFor converts a Pos p in the fileset into a Position value. If adjusted is set, the position may be adjusted by position-altering //line comments; otherwise those comments are ignored. p must be a Pos value in s or NoPos.

func (*FileSet) Read

func (s *FileSet) Read(decode func(any) error) error

Read calls decode to deserialize a file set into s; s must not be nil.

func (*FileSet) RemoveFile

func (s *FileSet) RemoveFile(file *File)

RemoveFile removes a file from the FileSet so that subsequent queries for its Pos interval yield a negative result. This reduces the memory usage of a long-lived FileSet that encounters an unbounded stream of files.

Removing a file that does not belong to the set has no effect.

func (*FileSet) Write

func (s *FileSet) Write(encode func(any) error) error

Write calls encode to serialize the file set s.

type Pos

type Pos int

Pos is a compact encoding of a source position within a file set. It can be converted into a Position for a more convenient, but much larger, representation.

The Pos value for a given file is a number in the range [base, base+size], where base and size are specified when a file is added to the file set. The difference between a Pos value and the corresponding file base corresponds to the byte offset of that position (represented by the Pos value) from the beginning of the file. Thus, the file base offset is the Pos value representing the first byte in the file.

To create the Pos value for a specific source offset (measured in bytes), first add the respective file to the current file set using FileSet.AddFile and then call File.Pos(offset) for that file. Given a Pos value p for a specific file set fset, the corresponding Position value is obtained by calling fset.Position(p).

Pos values can be compared directly with the usual comparison operators: If two Pos values p and q are in the same file, comparing p and q is equivalent to comparing the respective source file offsets. If p and q are in different files, p < q is true if the file implied by p was added to the respective file set before the file implied by q. 

const NoPos Pos = 0

The zero value for Pos is NoPos; there is no file and line information associated with it, and NoPos.IsValid() is false. NoPos is always smaller than any other Pos value. The corresponding Position value for NoPos is the zero value for Position.

func (Pos) IsValid

func (p Pos) IsValid() bool

IsValid reports whether the position is valid.

type Position

type Position struct {
	Filename string // filename, if any
	Offset   int    // offset, starting at 0
	Line     int    // line number, starting at 1
	Column   int    // column number, starting at 1 (byte count)
}

Position describes an arbitrary source position including the file, line, and column location. A Position is valid if the line number is > 0.

func (*Position) IsValid

func (pos *Position) IsValid() bool

IsValid reports whether the position is valid.

func (Position) String

func (pos Position) String() string

String returns a string in one of several forms: 

file:line:column    valid position with file name
file:line           valid position with file name but no column (column == 0)
line:column         valid position without file name
line                valid position without file name and no column (column == 0)
file                invalid position with file name
-                   invalid position without file name

type Token

type Token int

Token is the set of lexical tokens of the Go programming language. 

const (
	// Special tokens
	ILLEGAL Token = iota
	EOF
	COMMENT

	// Identifiers and basic type literals
	// (these tokens stand for classes of literals)
	IDENT  // main
	INT    // 12345
	FLOAT  // 123.45
	IMAG   // 123.45i
	CHAR   // 'a'
	STRING // "abc"

	// Operators and delimiters
	ADD // +
	SUB // -
	MUL // *
	QUO // /
	REM // %

	AND     // &
	OR      // |
	XOR     // ^
	SHL     // <<
	SHR     // >>
	AND_NOT // &^

	ADD_ASSIGN // +=
	SUB_ASSIGN // -=
	MUL_ASSIGN // *=
	QUO_ASSIGN // /=
	REM_ASSIGN // %=

	AND_ASSIGN     // &=
	OR_ASSIGN      // |=
	XOR_ASSIGN     // ^=
	SHL_ASSIGN     // <<=
	SHR_ASSIGN     // >>=
	AND_NOT_ASSIGN // &^=

	LAND  // &&
	LOR   // ||
	ARROW // <-
	INC   // ++
	DEC   // --

	EQL    // ==
	LSS    // <
	GTR    // >
	ASSIGN // =
	NOT    // !

	NEQ      // !=
	LEQ      // <=
	GEQ      // >=
	DEFINE   // :=
	ELLIPSIS // ...

	LPAREN // (
	LBRACK // [
	LBRACE // {
	COMMA  // ,
	PERIOD // .

	RPAREN    // )
	RBRACK    // ]
	RBRACE    // }
	SEMICOLON // ;
	COLON     // :

	// Keywords
	BREAK
	CASE
	CHAN
	CONST
	CONTINUE

	DEFAULT
	DEFER
	ELSE
	FALLTHROUGH
	FOR

	FUNC
	GO
	GOTO
	IF
	IMPORT

	INTERFACE
	MAP
	PACKAGE
	RANGE
	RETURN

	SELECT
	STRUCT
	SWITCH
	TYPE
	VAR

	// additional tokens, handled in an ad-hoc manner
	TILDE
)

The list of tokens.

func Lookup

func Lookup(ident string) Token

Lookup maps an identifier to its keyword token or IDENT (if not a keyword).

func (Token) IsKeyword

func (tok Token) IsKeyword() bool

IsKeyword returns true for tokens corresponding to keywords; it returns false otherwise.

func (Token) IsLiteral

func (tok Token) IsLiteral() bool

IsLiteral returns true for tokens corresponding to identifiers and basic type literals; it returns false otherwise.

func (Token) IsOperator

func (tok Token) IsOperator() bool

IsOperator returns true for tokens corresponding to operators and delimiters; it returns false otherwise.

func (Token) Precedence

func (op Token) Precedence() int

Precedence returns the operator precedence of the binary operator op. If op is not a binary operator, the result is LowestPrecedence.

func (Token) String

func (tok Token) String() string

String returns the string corresponding to the token tok. For operators, delimiters, and keywords the string is the actual token character sequence (e.g., for the token ADD, the string is "+"). For all other tokens the string corresponds to the token constant name (e.g. for the token IDENT, the string is "IDENT").