version: 1.10

package printer

import "go/printer"

Overview

Package printer implements printing of AST nodes.

Index

Examples

Package files

nodes.go printer.go

func Fprint

  1. func Fprint(output io.Writer, fset *token.FileSet, node interface{}) error

Fprint “pretty-prints” an AST node to output. It calls Config.Fprint with
default settings. Note that gofmt uses tabs for indentation but spaces for
alignment; use format.Node (package go/format) for output that matches gofmt.


Example:

  1. // Parse source file and extract the AST without comments for
  2. // this function, with position information referring to the
  3. // file set fset.
  4. funcAST, fset := parseFunc("example_test.go", "ExampleFprint")
  6. // Print the function body into buffer buf.
  7. // The file set is provided to the printer so that it knows
  8. // about the original source formatting and can add additional
  9. // line breaks where they were present in the source.
  10. var buf bytes.Buffer
  11. printer.Fprint(&buf, fset, funcAST.Body)
  13. // Remove braces {} enclosing the function body, unindent,
  14. // and trim leading and trailing white space.
  15. s := buf.String()
  16. s = s[1 : len(s)-1]
  17. s = strings.TrimSpace(strings.Replace(s, "\n\t", "\n", -1))
  19. // Print the cleaned-up body text to stdout.
  20. fmt.Println(s)
  22. // output:
  23. // funcAST, fset := parseFunc("example_test.go", "ExampleFprint")
  24. //
  25. // var buf bytes.Buffer
  26. // printer.Fprint(&buf, fset, funcAST.Body)
  27. //
  28. // s := buf.String()
  29. // s = s[1 : len(s)-1]
  30. // s = strings.TrimSpace(strings.Replace(s, "\n\t", "\n", -1))
  31. //
  32. // fmt.Println(s)

type CommentedNode

  1. type CommentedNode struct {
  2.     Node     interface{} // *ast.File, or ast.Expr, ast.Decl, ast.Spec, or ast.Stmt
  3.     Comments []*ast.CommentGroup
  4. }

A CommentedNode bundles an AST node and corresponding comments. It may be
provided as argument to any of the Fprint functions.

type Config

  1. type Config struct {
  2.     Mode     Mode // default: 0
  3.     Tabwidth int  // default: 8
  4.     Indent   int  // default: 0 (all code is indented at least by this much)
  5. }

A Config node controls the output of Fprint.

func (*Config) Fprint

  1. func (cfg *Config) Fprint(output io.Writer, fset *token.FileSet, node interface{}) error

Fprint “pretty-prints” an AST node to output for a given configuration cfg.
Position information is interpreted relative to the file set fset. The node type
must be ast.File, CommentedNode, []ast.Decl, []ast.Stmt, or
assignment-compatible to ast.Expr, ast.Decl, ast.Spec, or ast.Stmt.

type Mode

  1. type Mode uint

A Mode value is a set of flags (or 0). They control printing.

  1. const (
  2.     RawFormat Mode = 1 << iota // do not use a tabwriter; if set, UseSpaces is ignored
  3.     TabIndent                  // use tabs for indentation independent of UseSpaces
  4.     UseSpaces                  // use spaces instead of tabs for alignment
  5.     SourcePos                  // emit //line directives to preserve original source positions
  6. )