Package printer
Package printer
Overview
Package printer implements printing of AST nodes.
Index
- func Fprint(output io.Writer, fset *token.FileSet, node interface{}) error
- type CommentedNode
- type Config
- func (cfg *Config) Fprint(output io.Writer, fset *token.FileSet, node interface{}) error
- type Mode
Examples
Package files
gobuild.go nodes.go printer.go
func Fprint
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
Code:
// Parse source file and extract the AST without comments for
// this function, with position information referring to the
// file set fset.
funcAST, fset := parseFunc("example_test.go", "ExampleFprint")
// Print the function body into buffer buf.
// The file set is provided to the printer so that it knows
// about the original source formatting and can add additional
// line breaks where they were present in the source.
var buf bytes.Buffer
printer.Fprint(&buf, fset, funcAST.Body)
// Remove braces {} enclosing the function body, unindent,
// and trim leading and trailing white space.
s := buf.String()
s = s[1 : len(s)-1]
s = strings.TrimSpace(strings.ReplaceAll(s, "\n\t", "\n"))
// Print the cleaned-up body text to stdout.
fmt.Println(s)
Output:
funcAST, fset := parseFunc("example_test.go", "ExampleFprint")
var buf bytes.Buffer
printer.Fprint(&buf, fset, funcAST.Body)
s := buf.String()
s = s[1 : len(s)-1]
s = strings.TrimSpace(strings.ReplaceAll(s, "\n\t", "\n"))
fmt.Println(s)
type CommentedNode
A CommentedNode bundles an AST node and corresponding comments. It may be provided as argument to any of the Fprint functions.
type CommentedNode struct {
Node interface{} // *ast.File, or ast.Expr, ast.Decl, ast.Spec, or ast.Stmt
Comments []*ast.CommentGroup
}
type Config
A Config node controls the output of Fprint.
type Config struct {
Mode Mode // default: 0
Tabwidth int // default: 8
Indent int // default: 0 (all code is indented at least by this much); added in Go 1.1
}
func (*Config) Fprint
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
A Mode value is a set of flags (or 0). They control printing.
type Mode uint
const (
RawFormat Mode = 1 << iota // do not use a tabwriter; if set, UseSpaces is ignored
TabIndent // use tabs for indentation independent of UseSpaces
UseSpaces // use spaces instead of tabs for alignment
SourcePos // emit //line directives to preserve original source positions
)
© Google, Inc.
Licensed under the Creative Commons Attribution License 3.0.
http://golang.org/pkg/go/printer/