package mainimport ("bytes""fmt""go/ast""go/parser""go/printer""go/token""strings")func parseFunc(filename, functionname string) (fun *ast.FuncDecl, fset *token.FileSet) {fset = token.NewFileSet()if file, err := parser.ParseFile(fset, filename, nil, 0); err == nil {for _, d := range file.Decls {if f, ok := d.(*ast.FuncDecl); ok && f.Name.Name == functionname {fun = freturn}}}panic("function not found")}func printSelf() {// 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", "printSelf")// 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.Bufferprinter.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)}func main() {printSelf()}

Output:funcAST, fset := parseFunc("example_test.go", "printSelf")var buf bytes.Bufferprinter.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)