import "go/printer"
Package printer implements printing of AST nodes.
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.
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 struct {
Node interface{} // *ast.File, or ast.Expr, ast.Decl, ast.Spec, or ast.Stmt
Comments []*ast.CommentGroup
}
A CommentedNode bundles an AST node and corresponding comments. It may be provided as argument to any of the Fprint functions.
type Config struct {
Mode Mode // default: 0
Tabwidth int // default: 8
Indent int // default: 0 (all code is indented at least by this much)
}
A Config node controls the output of 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 uint
A Mode value is a set of flags (or 0). They control printing.
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
)