example_test.go

Documentation: go/printer

		 1  // Copyright 2012 The Go Authors. All rights reserved.
		 2  // Use of this source code is governed by a BSD-style
		 3  // license that can be found in the LICENSE file.
		 4  
		 5  package printer_test
		 6  
		 7  import (
		 8  	"bytes"
		 9  	"fmt"
		10  	"go/ast"
		11  	"go/parser"
		12  	"go/printer"
		13  	"go/token"
		14  	"strings"
		15  	"testing"
		16  )
		17  
		18  // Dummy test function so that godoc does not use the entire file as example.
		19  func Test(*testing.T) {}
		20  
		21  func parseFunc(filename, functionname string) (fun *ast.FuncDecl, fset *token.FileSet) {
		22  	fset = token.NewFileSet()
		23  	if file, err := parser.ParseFile(fset, filename, nil, 0); err == nil {
		24  		for _, d := range file.Decls {
		25  			if f, ok := d.(*ast.FuncDecl); ok && f.Name.Name == functionname {
		26  				fun = f
		27  				return
		28  			}
		29  		}
		30  	}
		31  	panic("function not found")
		32  }
		33  
		34  func ExampleFprint() {
		35  	// Parse source file and extract the AST without comments for
		36  	// this function, with position information referring to the
		37  	// file set fset.
		38  	funcAST, fset := parseFunc("example_test.go", "ExampleFprint")
		39  
		40  	// Print the function body into buffer buf.
		41  	// The file set is provided to the printer so that it knows
		42  	// about the original source formatting and can add additional
		43  	// line breaks where they were present in the source.
		44  	var buf bytes.Buffer
		45  	printer.Fprint(&buf, fset, funcAST.Body)
		46  
		47  	// Remove braces {} enclosing the function body, unindent,
		48  	// and trim leading and trailing white space.
		49  	s := buf.String()
		50  	s = s[1 : len(s)-1]
		51  	s = strings.TrimSpace(strings.ReplaceAll(s, "\n\t", "\n"))
		52  
		53  	// Print the cleaned-up body text to stdout.
		54  	fmt.Println(s)
		55  
		56  	// output:
		57  	// funcAST, fset := parseFunc("example_test.go", "ExampleFprint")
		58  	//
		59  	// var buf bytes.Buffer
		60  	// printer.Fprint(&buf, fset, funcAST.Body)
		61  	//
		62  	// s := buf.String()
		63  	// s = s[1 : len(s)-1]
		64  	// s = strings.TrimSpace(strings.ReplaceAll(s, "\n\t", "\n"))
		65  	//
		66  	// fmt.Println(s)
		67  }
		68
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