Source file src/go/printer/printer_test.go

     1  // Copyright 2009 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
     6  
     7  import (
     8  	"bytes"
     9  	"errors"
    10  	"flag"
    11  	"fmt"
    12  	"go/ast"
    13  	"go/parser"
    14  	"go/token"
    15  	"internal/diff"
    16  	"io"
    17  	"os"
    18  	"path/filepath"
    19  	"testing"
    20  	"time"
    21  )
    22  
    23  const (
    24  	dataDir  = "testdata"
    25  	tabwidth = 8
    26  )
    27  
    28  var update = flag.Bool("update", false, "update golden files")
    29  
    30  var fset = token.NewFileSet()
    31  
    32  type checkMode uint
    33  
    34  const (
    35  	export checkMode = 1 << iota
    36  	rawFormat
    37  	normNumber
    38  	idempotent
    39  	allowTypeParams
    40  )
    41  
    42  // format parses src, prints the corresponding AST, verifies the resulting
    43  // src is syntactically correct, and returns the resulting src or an error
    44  // if any.
    45  func format(src []byte, mode checkMode) ([]byte, error) {
    46  	// parse src
    47  	f, err := parser.ParseFile(fset, "", src, parser.ParseComments)
    48  	if err != nil {
    49  		return nil, fmt.Errorf("parse: %s\n%s", err, src)
    50  	}
    51  
    52  	// filter exports if necessary
    53  	if mode&export != 0 {
    54  		ast.FileExports(f) // ignore result
    55  		f.Comments = nil   // don't print comments that are not in AST
    56  	}
    57  
    58  	// determine printer configuration
    59  	cfg := Config{Tabwidth: tabwidth}
    60  	if mode&rawFormat != 0 {
    61  		cfg.Mode |= RawFormat
    62  	}
    63  	if mode&normNumber != 0 {
    64  		cfg.Mode |= normalizeNumbers
    65  	}
    66  
    67  	// print AST
    68  	var buf bytes.Buffer
    69  	if err := cfg.Fprint(&buf, fset, f); err != nil {
    70  		return nil, fmt.Errorf("print: %s", err)
    71  	}
    72  
    73  	// make sure formatted output is syntactically correct
    74  	res := buf.Bytes()
    75  	if _, err := parser.ParseFile(fset, "", res, parser.ParseComments); err != nil {
    76  		return nil, fmt.Errorf("re-parse: %s\n%s", err, buf.Bytes())
    77  	}
    78  
    79  	return res, nil
    80  }
    81  
    82  // lineAt returns the line in text starting at offset offs.
    83  func lineAt(text []byte, offs int) []byte {
    84  	i := offs
    85  	for i < len(text) && text[i] != '\n' {
    86  		i++
    87  	}
    88  	return text[offs:i]
    89  }
    90  
    91  // checkEqual compares a and b.
    92  func checkEqual(aname, bname string, a, b []byte) error {
    93  	if bytes.Equal(a, b) {
    94  		return nil
    95  	}
    96  	return errors.New(string(diff.Diff(aname, a, bname, b)))
    97  }
    98  
    99  func runcheck(t *testing.T, source, golden string, mode checkMode) {
   100  	src, err := os.ReadFile(source)
   101  	if err != nil {
   102  		t.Error(err)
   103  		return
   104  	}
   105  
   106  	res, err := format(src, mode)
   107  	if err != nil {
   108  		t.Error(err)
   109  		return
   110  	}
   111  
   112  	// update golden files if necessary
   113  	if *update {
   114  		if err := os.WriteFile(golden, res, 0644); err != nil {
   115  			t.Error(err)
   116  		}
   117  		return
   118  	}
   119  
   120  	// get golden
   121  	gld, err := os.ReadFile(golden)
   122  	if err != nil {
   123  		t.Error(err)
   124  		return
   125  	}
   126  
   127  	// formatted source and golden must be the same
   128  	if err := checkEqual(fmt.Sprintf("format(%v)", source), golden, res, gld); err != nil {
   129  		t.Error(err)
   130  		return
   131  	}
   132  
   133  	if mode&idempotent != 0 {
   134  		// formatting golden must be idempotent
   135  		// (This is very difficult to achieve in general and for now
   136  		// it is only checked for files explicitly marked as such.)
   137  		res, err = format(gld, mode)
   138  		if err != nil {
   139  			t.Error(err)
   140  			return
   141  		}
   142  		if err := checkEqual(golden, fmt.Sprintf("format(%s)", golden), gld, res); err != nil {
   143  			t.Errorf("golden is not idempotent: %s", err)
   144  		}
   145  	}
   146  }
   147  
   148  func check(t *testing.T, source, golden string, mode checkMode) {
   149  	// run the test
   150  	cc := make(chan int, 1)
   151  	go func() {
   152  		runcheck(t, source, golden, mode)
   153  		cc <- 0
   154  	}()
   155  
   156  	// wait with timeout
   157  	select {
   158  	case <-time.After(10 * time.Second): // plenty of a safety margin, even for very slow machines
   159  		// test running past time out
   160  		t.Errorf("%s: running too slowly", source)
   161  	case <-cc:
   162  		// test finished within allotted time margin
   163  	}
   164  }
   165  
   166  type entry struct {
   167  	source, golden string
   168  	mode           checkMode
   169  }
   170  
   171  // Use go test -update to create/update the respective golden files.
   172  var data = []entry{
   173  	{"empty.input", "empty.golden", idempotent},
   174  	{"comments.input", "comments.golden", 0},
   175  	{"comments.input", "comments.x", export},
   176  	{"comments2.input", "comments2.golden", idempotent},
   177  	{"alignment.input", "alignment.golden", idempotent},
   178  	{"linebreaks.input", "linebreaks.golden", idempotent},
   179  	{"expressions.input", "expressions.golden", idempotent},
   180  	{"expressions.input", "expressions.raw", rawFormat | idempotent},
   181  	{"declarations.input", "declarations.golden", 0},
   182  	{"statements.input", "statements.golden", 0},
   183  	{"slow.input", "slow.golden", idempotent},
   184  	{"complit.input", "complit.x", export},
   185  	{"go2numbers.input", "go2numbers.golden", idempotent},
   186  	{"go2numbers.input", "go2numbers.norm", normNumber | idempotent},
   187  	{"generics.input", "generics.golden", idempotent | allowTypeParams},
   188  	{"gobuild1.input", "gobuild1.golden", idempotent},
   189  	{"gobuild2.input", "gobuild2.golden", idempotent},
   190  	{"gobuild3.input", "gobuild3.golden", idempotent},
   191  	{"gobuild4.input", "gobuild4.golden", idempotent},
   192  	{"gobuild5.input", "gobuild5.golden", idempotent},
   193  	{"gobuild6.input", "gobuild6.golden", idempotent},
   194  	{"gobuild7.input", "gobuild7.golden", idempotent},
   195  }
   196  
   197  func TestFiles(t *testing.T) {
   198  	t.Parallel()
   199  	for _, e := range data {
   200  		source := filepath.Join(dataDir, e.source)
   201  		golden := filepath.Join(dataDir, e.golden)
   202  		mode := e.mode
   203  		t.Run(e.source, func(t *testing.T) {
   204  			t.Parallel()
   205  			check(t, source, golden, mode)
   206  			// TODO(gri) check that golden is idempotent
   207  			//check(t, golden, golden, e.mode)
   208  		})
   209  	}
   210  }
   211  
   212  // TestLineComments, using a simple test case, checks that consecutive line
   213  // comments are properly terminated with a newline even if the AST position
   214  // information is incorrect.
   215  func TestLineComments(t *testing.T) {
   216  	const src = `// comment 1
   217  	// comment 2
   218  	// comment 3
   219  	package main
   220  	`
   221  
   222  	fset := token.NewFileSet()
   223  	f, err := parser.ParseFile(fset, "", src, parser.ParseComments)
   224  	if err != nil {
   225  		panic(err) // error in test
   226  	}
   227  
   228  	var buf bytes.Buffer
   229  	fset = token.NewFileSet() // use the wrong file set
   230  	Fprint(&buf, fset, f)
   231  
   232  	nlines := 0
   233  	for _, ch := range buf.Bytes() {
   234  		if ch == '\n' {
   235  			nlines++
   236  		}
   237  	}
   238  
   239  	const expected = 3
   240  	if nlines < expected {
   241  		t.Errorf("got %d, expected %d\n", nlines, expected)
   242  		t.Errorf("result:\n%s", buf.Bytes())
   243  	}
   244  }
   245  
   246  // Verify that the printer can be invoked during initialization.
   247  func init() {
   248  	const name = "foobar"
   249  	var buf bytes.Buffer
   250  	if err := Fprint(&buf, fset, &ast.Ident{Name: name}); err != nil {
   251  		panic(err) // error in test
   252  	}
   253  	// in debug mode, the result contains additional information;
   254  	// ignore it
   255  	if s := buf.String(); !debug && s != name {
   256  		panic("got " + s + ", want " + name)
   257  	}
   258  }
   259  
   260  // Verify that the printer doesn't crash if the AST contains BadXXX nodes.
   261  func TestBadNodes(t *testing.T) {
   262  	const src = "package p\n("
   263  	const res = "package p\nBadDecl\n"
   264  	f, err := parser.ParseFile(fset, "", src, parser.ParseComments)
   265  	if err == nil {
   266  		t.Error("expected illegal program") // error in test
   267  	}
   268  	var buf bytes.Buffer
   269  	Fprint(&buf, fset, f)
   270  	if buf.String() != res {
   271  		t.Errorf("got %q, expected %q", buf.String(), res)
   272  	}
   273  }
   274  
   275  // testComment verifies that f can be parsed again after printing it
   276  // with its first comment set to comment at any possible source offset.
   277  func testComment(t *testing.T, f *ast.File, srclen int, comment *ast.Comment) {
   278  	f.Comments[0].List[0] = comment
   279  	var buf bytes.Buffer
   280  	for offs := 0; offs <= srclen; offs++ {
   281  		buf.Reset()
   282  		// Printing f should result in a correct program no
   283  		// matter what the (incorrect) comment position is.
   284  		if err := Fprint(&buf, fset, f); err != nil {
   285  			t.Error(err)
   286  		}
   287  		if _, err := parser.ParseFile(fset, "", buf.Bytes(), 0); err != nil {
   288  			t.Fatalf("incorrect program for pos = %d:\n%s", comment.Slash, buf.String())
   289  		}
   290  		// Position information is just an offset.
   291  		// Move comment one byte down in the source.
   292  		comment.Slash++
   293  	}
   294  }
   295  
   296  // Verify that the printer produces a correct program
   297  // even if the position information of comments introducing newlines
   298  // is incorrect.
   299  func TestBadComments(t *testing.T) {
   300  	t.Parallel()
   301  	const src = `
   302  // first comment - text and position changed by test
   303  package p
   304  import "fmt"
   305  const pi = 3.14 // rough circle
   306  var (
   307  	x, y, z int = 1, 2, 3
   308  	u, v float64
   309  )
   310  func fibo(n int) {
   311  	if n < 2 {
   312  		return n /* seed values */
   313  	}
   314  	return fibo(n-1) + fibo(n-2)
   315  }
   316  `
   317  
   318  	f, err := parser.ParseFile(fset, "", src, parser.ParseComments)
   319  	if err != nil {
   320  		t.Error(err) // error in test
   321  	}
   322  
   323  	comment := f.Comments[0].List[0]
   324  	pos := comment.Pos()
   325  	if fset.PositionFor(pos, false /* absolute position */).Offset != 1 {
   326  		t.Error("expected offset 1") // error in test
   327  	}
   328  
   329  	testComment(t, f, len(src), &ast.Comment{Slash: pos, Text: "//-style comment"})
   330  	testComment(t, f, len(src), &ast.Comment{Slash: pos, Text: "/*-style comment */"})
   331  	testComment(t, f, len(src), &ast.Comment{Slash: pos, Text: "/*-style \n comment */"})
   332  	testComment(t, f, len(src), &ast.Comment{Slash: pos, Text: "/*-style comment \n\n\n */"})
   333  }
   334  
   335  type visitor chan *ast.Ident
   336  
   337  func (v visitor) Visit(n ast.Node) (w ast.Visitor) {
   338  	if ident, ok := n.(*ast.Ident); ok {
   339  		v <- ident
   340  	}
   341  	return v
   342  }
   343  
   344  // idents is an iterator that returns all idents in f via the result channel.
   345  func idents(f *ast.File) <-chan *ast.Ident {
   346  	v := make(visitor)
   347  	go func() {
   348  		ast.Walk(v, f)
   349  		close(v)
   350  	}()
   351  	return v
   352  }
   353  
   354  // identCount returns the number of identifiers found in f.
   355  func identCount(f *ast.File) int {
   356  	n := 0
   357  	for range idents(f) {
   358  		n++
   359  	}
   360  	return n
   361  }
   362  
   363  // Verify that the SourcePos mode emits correct //line directives
   364  // by testing that position information for matching identifiers
   365  // is maintained.
   366  func TestSourcePos(t *testing.T) {
   367  	const src = `
   368  package p
   369  import ( "go/printer"; "math" )
   370  const pi = 3.14; var x = 0
   371  type t struct{ x, y, z int; u, v, w float32 }
   372  func (t *t) foo(a, b, c int) int {
   373  	return a*t.x + b*t.y +
   374  		// two extra lines here
   375  		// ...
   376  		c*t.z
   377  }
   378  `
   379  
   380  	// parse original
   381  	f1, err := parser.ParseFile(fset, "src", src, parser.ParseComments)
   382  	if err != nil {
   383  		t.Fatal(err)
   384  	}
   385  
   386  	// pretty-print original
   387  	var buf bytes.Buffer
   388  	err = (&Config{Mode: UseSpaces | SourcePos, Tabwidth: 8}).Fprint(&buf, fset, f1)
   389  	if err != nil {
   390  		t.Fatal(err)
   391  	}
   392  
   393  	// parse pretty printed original
   394  	// (//line directives must be interpreted even w/o parser.ParseComments set)
   395  	f2, err := parser.ParseFile(fset, "", buf.Bytes(), 0)
   396  	if err != nil {
   397  		t.Fatalf("%s\n%s", err, buf.Bytes())
   398  	}
   399  
   400  	// At this point the position information of identifiers in f2 should
   401  	// match the position information of corresponding identifiers in f1.
   402  
   403  	// number of identifiers must be > 0 (test should run) and must match
   404  	n1 := identCount(f1)
   405  	n2 := identCount(f2)
   406  	if n1 == 0 {
   407  		t.Fatal("got no idents")
   408  	}
   409  	if n2 != n1 {
   410  		t.Errorf("got %d idents; want %d", n2, n1)
   411  	}
   412  
   413  	// verify that all identifiers have correct line information
   414  	i2range := idents(f2)
   415  	for i1 := range idents(f1) {
   416  		i2 := <-i2range
   417  
   418  		if i2.Name != i1.Name {
   419  			t.Errorf("got ident %s; want %s", i2.Name, i1.Name)
   420  		}
   421  
   422  		// here we care about the relative (line-directive adjusted) positions
   423  		l1 := fset.Position(i1.Pos()).Line
   424  		l2 := fset.Position(i2.Pos()).Line
   425  		if l2 != l1 {
   426  			t.Errorf("got line %d; want %d for %s", l2, l1, i1.Name)
   427  		}
   428  	}
   429  
   430  	if t.Failed() {
   431  		t.Logf("\n%s", buf.Bytes())
   432  	}
   433  }
   434  
   435  // Verify that the SourcePos mode doesn't emit unnecessary //line directives
   436  // before empty lines.
   437  func TestIssue5945(t *testing.T) {
   438  	const orig = `
   439  package p   // line 2
   440  func f() {} // line 3
   441  
   442  var x, y, z int
   443  
   444  
   445  func g() { // line 8
   446  }
   447  `
   448  
   449  	const want = `//line src.go:2
   450  package p
   451  
   452  //line src.go:3
   453  func f() {}
   454  
   455  var x, y, z int
   456  
   457  //line src.go:8
   458  func g() {
   459  }
   460  `
   461  
   462  	// parse original
   463  	f1, err := parser.ParseFile(fset, "src.go", orig, 0)
   464  	if err != nil {
   465  		t.Fatal(err)
   466  	}
   467  
   468  	// pretty-print original
   469  	var buf bytes.Buffer
   470  	err = (&Config{Mode: UseSpaces | SourcePos, Tabwidth: 8}).Fprint(&buf, fset, f1)
   471  	if err != nil {
   472  		t.Fatal(err)
   473  	}
   474  	got := buf.String()
   475  
   476  	// compare original with desired output
   477  	if got != want {
   478  		t.Errorf("got:\n%s\nwant:\n%s\n", got, want)
   479  	}
   480  }
   481  
   482  var decls = []string{
   483  	`import "fmt"`,
   484  	"const pi = 3.1415\nconst e = 2.71828\n\nvar x = pi",
   485  	"func sum(x, y int) int\t{ return x + y }",
   486  }
   487  
   488  func TestDeclLists(t *testing.T) {
   489  	for _, src := range decls {
   490  		file, err := parser.ParseFile(fset, "", "package p;"+src, parser.ParseComments)
   491  		if err != nil {
   492  			panic(err) // error in test
   493  		}
   494  
   495  		var buf bytes.Buffer
   496  		err = Fprint(&buf, fset, file.Decls) // only print declarations
   497  		if err != nil {
   498  			panic(err) // error in test
   499  		}
   500  
   501  		out := buf.String()
   502  		if out != src {
   503  			t.Errorf("\ngot : %q\nwant: %q\n", out, src)
   504  		}
   505  	}
   506  }
   507  
   508  var stmts = []string{
   509  	"i := 0",
   510  	"select {}\nvar a, b = 1, 2\nreturn a + b",
   511  	"go f()\ndefer func() {}()",
   512  }
   513  
   514  func TestStmtLists(t *testing.T) {
   515  	for _, src := range stmts {
   516  		file, err := parser.ParseFile(fset, "", "package p; func _() {"+src+"}", parser.ParseComments)
   517  		if err != nil {
   518  			panic(err) // error in test
   519  		}
   520  
   521  		var buf bytes.Buffer
   522  		err = Fprint(&buf, fset, file.Decls[0].(*ast.FuncDecl).Body.List) // only print statements
   523  		if err != nil {
   524  			panic(err) // error in test
   525  		}
   526  
   527  		out := buf.String()
   528  		if out != src {
   529  			t.Errorf("\ngot : %q\nwant: %q\n", out, src)
   530  		}
   531  	}
   532  }
   533  
   534  func TestBaseIndent(t *testing.T) {
   535  	t.Parallel()
   536  	// The testfile must not contain multi-line raw strings since those
   537  	// are not indented (because their values must not change) and make
   538  	// this test fail.
   539  	const filename = "printer.go"
   540  	src, err := os.ReadFile(filename)
   541  	if err != nil {
   542  		panic(err) // error in test
   543  	}
   544  
   545  	file, err := parser.ParseFile(fset, filename, src, 0)
   546  	if err != nil {
   547  		panic(err) // error in test
   548  	}
   549  
   550  	for indent := 0; indent < 4; indent++ {
   551  		indent := indent
   552  		t.Run(fmt.Sprint(indent), func(t *testing.T) {
   553  			t.Parallel()
   554  			var buf bytes.Buffer
   555  			(&Config{Tabwidth: tabwidth, Indent: indent}).Fprint(&buf, fset, file)
   556  			// all code must be indented by at least 'indent' tabs
   557  			lines := bytes.Split(buf.Bytes(), []byte{'\n'})
   558  			for i, line := range lines {
   559  				if len(line) == 0 {
   560  					continue // empty lines don't have indentation
   561  				}
   562  				n := 0
   563  				for j, b := range line {
   564  					if b != '\t' {
   565  						// end of indentation
   566  						n = j
   567  						break
   568  					}
   569  				}
   570  				if n < indent {
   571  					t.Errorf("line %d: got only %d tabs; want at least %d: %q", i, n, indent, line)
   572  				}
   573  			}
   574  		})
   575  	}
   576  }
   577  
   578  // TestFuncType tests that an ast.FuncType with a nil Params field
   579  // can be printed (per go/ast specification). Test case for issue 3870.
   580  func TestFuncType(t *testing.T) {
   581  	src := &ast.File{
   582  		Name: &ast.Ident{Name: "p"},
   583  		Decls: []ast.Decl{
   584  			&ast.FuncDecl{
   585  				Name: &ast.Ident{Name: "f"},
   586  				Type: &ast.FuncType{},
   587  			},
   588  		},
   589  	}
   590  
   591  	var buf bytes.Buffer
   592  	if err := Fprint(&buf, fset, src); err != nil {
   593  		t.Fatal(err)
   594  	}
   595  	got := buf.String()
   596  
   597  	const want = `package p
   598  
   599  func f()
   600  `
   601  
   602  	if got != want {
   603  		t.Fatalf("got:\n%s\nwant:\n%s\n", got, want)
   604  	}
   605  }
   606  
   607  // TestChanType tests that the tree for <-(<-chan int), without
   608  // ParenExpr, is correctly formatted with parens.
   609  // Test case for issue #63362.
   610  func TestChanType(t *testing.T) {
   611  	expr := &ast.UnaryExpr{
   612  		Op: token.ARROW,
   613  		X: &ast.CallExpr{
   614  			Fun: &ast.ChanType{
   615  				Dir:   ast.RECV,
   616  				Value: &ast.Ident{Name: "int"},
   617  			},
   618  			Args: []ast.Expr{&ast.Ident{Name: "nil"}},
   619  		},
   620  	}
   621  	var buf bytes.Buffer
   622  	if err := Fprint(&buf, fset, expr); err != nil {
   623  		t.Fatal(err)
   624  	}
   625  	if got, want := buf.String(), `<-(<-chan int)(nil)`; got != want {
   626  		t.Fatalf("got:\n%s\nwant:\n%s\n", got, want)
   627  	}
   628  }
   629  
   630  type limitWriter struct {
   631  	remaining int
   632  	errCount  int
   633  }
   634  
   635  func (l *limitWriter) Write(buf []byte) (n int, err error) {
   636  	n = len(buf)
   637  	if n >= l.remaining {
   638  		n = l.remaining
   639  		err = io.EOF
   640  		l.errCount++
   641  	}
   642  	l.remaining -= n
   643  	return n, err
   644  }
   645  
   646  // Test whether the printer stops writing after the first error
   647  func TestWriteErrors(t *testing.T) {
   648  	t.Parallel()
   649  	const filename = "printer.go"
   650  	src, err := os.ReadFile(filename)
   651  	if err != nil {
   652  		panic(err) // error in test
   653  	}
   654  	file, err := parser.ParseFile(fset, filename, src, 0)
   655  	if err != nil {
   656  		panic(err) // error in test
   657  	}
   658  	for i := 0; i < 20; i++ {
   659  		lw := &limitWriter{remaining: i}
   660  		err := (&Config{Mode: RawFormat}).Fprint(lw, fset, file)
   661  		if lw.errCount > 1 {
   662  			t.Fatal("Writes continued after first error returned")
   663  		}
   664  		// We expect errCount be 1 iff err is set
   665  		if (lw.errCount != 0) != (err != nil) {
   666  			t.Fatal("Expected err when errCount != 0")
   667  		}
   668  	}
   669  }
   670  
   671  // TestX is a skeleton test that can be filled in for debugging one-off cases.
   672  // Do not remove.
   673  func TestX(t *testing.T) {
   674  	const src = `
   675  package p
   676  func _() {}
   677  `
   678  	_, err := format([]byte(src), 0)
   679  	if err != nil {
   680  		t.Error(err)
   681  	}
   682  }
   683  
   684  func TestCommentedNode(t *testing.T) {
   685  	const (
   686  		input = `package main
   687  
   688  func foo() {
   689  	// comment inside func
   690  }
   691  
   692  // leading comment
   693  type bar int // comment2
   694  
   695  `
   696  
   697  		foo = `func foo() {
   698  	// comment inside func
   699  }`
   700  
   701  		bar = `// leading comment
   702  type bar int	// comment2
   703  `
   704  	)
   705  
   706  	fset := token.NewFileSet()
   707  	f, err := parser.ParseFile(fset, "input.go", input, parser.ParseComments)
   708  	if err != nil {
   709  		t.Fatal(err)
   710  	}
   711  
   712  	var buf bytes.Buffer
   713  
   714  	err = Fprint(&buf, fset, &CommentedNode{Node: f.Decls[0], Comments: f.Comments})
   715  	if err != nil {
   716  		t.Fatal(err)
   717  	}
   718  
   719  	if buf.String() != foo {
   720  		t.Errorf("got %q, want %q", buf.String(), foo)
   721  	}
   722  
   723  	buf.Reset()
   724  
   725  	err = Fprint(&buf, fset, &CommentedNode{Node: f.Decls[1], Comments: f.Comments})
   726  	if err != nil {
   727  		t.Fatal(err)
   728  	}
   729  
   730  	if buf.String() != bar {
   731  		t.Errorf("got %q, want %q", buf.String(), bar)
   732  	}
   733  }
   734  
   735  func TestIssue11151(t *testing.T) {
   736  	const src = "package p\t/*\r/1\r*\r/2*\r\r\r\r/3*\r\r+\r\r/4*/\n"
   737  	fset := token.NewFileSet()
   738  	f, err := parser.ParseFile(fset, "", src, parser.ParseComments)
   739  	if err != nil {
   740  		t.Fatal(err)
   741  	}
   742  
   743  	var buf bytes.Buffer
   744  	Fprint(&buf, fset, f)
   745  	got := buf.String()
   746  	const want = "package p\t/*/1*\r/2*\r/3*+/4*/\n" // \r following opening /* should be stripped
   747  	if got != want {
   748  		t.Errorf("\ngot : %q\nwant: %q", got, want)
   749  	}
   750  
   751  	// the resulting program must be valid
   752  	_, err = parser.ParseFile(fset, "", got, 0)
   753  	if err != nil {
   754  		t.Errorf("%v\norig: %q\ngot : %q", err, src, got)
   755  	}
   756  }
   757  
   758  // If a declaration has multiple specifications, a parenthesized
   759  // declaration must be printed even if Lparen is token.NoPos.
   760  func TestParenthesizedDecl(t *testing.T) {
   761  	// a package with multiple specs in a single declaration
   762  	const src = "package p; var ( a float64; b int )"
   763  	fset := token.NewFileSet()
   764  	f, err := parser.ParseFile(fset, "", src, 0)
   765  	if err != nil {
   766  		t.Fatal(err)
   767  	}
   768  
   769  	// print the original package
   770  	var buf bytes.Buffer
   771  	err = Fprint(&buf, fset, f)
   772  	if err != nil {
   773  		t.Fatal(err)
   774  	}
   775  	original := buf.String()
   776  
   777  	// now remove parentheses from the declaration
   778  	for i := 0; i != len(f.Decls); i++ {
   779  		f.Decls[i].(*ast.GenDecl).Lparen = token.NoPos
   780  	}
   781  	buf.Reset()
   782  	err = Fprint(&buf, fset, f)
   783  	if err != nil {
   784  		t.Fatal(err)
   785  	}
   786  	noparen := buf.String()
   787  
   788  	if noparen != original {
   789  		t.Errorf("got %q, want %q", noparen, original)
   790  	}
   791  }
   792  
   793  // Verify that we don't print a newline between "return" and its results, as
   794  // that would incorrectly cause a naked return.
   795  func TestIssue32854(t *testing.T) {
   796  	src := `package foo
   797  
   798  func f() {
   799          return Composite{
   800                  call(),
   801          }
   802  }`
   803  	fset := token.NewFileSet()
   804  	file, err := parser.ParseFile(fset, "", src, 0)
   805  	if err != nil {
   806  		panic(err)
   807  	}
   808  
   809  	// Replace the result with call(), which is on the next line.
   810  	fd := file.Decls[0].(*ast.FuncDecl)
   811  	ret := fd.Body.List[0].(*ast.ReturnStmt)
   812  	ret.Results[0] = ret.Results[0].(*ast.CompositeLit).Elts[0]
   813  
   814  	var buf bytes.Buffer
   815  	if err := Fprint(&buf, fset, ret); err != nil {
   816  		t.Fatal(err)
   817  	}
   818  	want := "return call()"
   819  	if got := buf.String(); got != want {
   820  		t.Fatalf("got %q, want %q", got, want)
   821  	}
   822  }
   823  
   824  func TestSourcePosNewline(t *testing.T) {
   825  	// We don't provide a syntax for escaping or unescaping characters in line
   826  	// directives (see https://go.dev/issue/24183#issuecomment-372449628).
   827  	// As a result, we cannot write a line directive with the correct path for a
   828  	// filename containing newlines. We should return an error rather than
   829  	// silently dropping or mangling it.
   830  
   831  	fname := "foo\nbar/bar.go"
   832  	src := `package bar`
   833  	fset := token.NewFileSet()
   834  	f, err := parser.ParseFile(fset, fname, src, parser.ParseComments|parser.AllErrors|parser.SkipObjectResolution)
   835  	if err != nil {
   836  		t.Fatal(err)
   837  	}
   838  
   839  	cfg := &Config{
   840  		Mode:     SourcePos, // emit line comments
   841  		Tabwidth: 8,
   842  	}
   843  	var buf bytes.Buffer
   844  	if err := cfg.Fprint(&buf, fset, f); err == nil {
   845  		t.Errorf("Fprint did not error for source file path containing newline")
   846  	}
   847  	if buf.Len() != 0 {
   848  		t.Errorf("unexpected Fprint output:\n%s", buf.Bytes())
   849  	}
   850  }
   851  
   852  // TestEmptyDecl tests that empty decls for const, var, import are printed with
   853  // valid syntax e.g "var ()" instead of just "var", which is invalid and cannot
   854  // be parsed.
   855  func TestEmptyDecl(t *testing.T) { // issue 63566
   856  	for _, tok := range []token.Token{token.IMPORT, token.CONST, token.TYPE, token.VAR} {
   857  		var buf bytes.Buffer
   858  		Fprint(&buf, token.NewFileSet(), &ast.GenDecl{Tok: tok})
   859  		got := buf.String()
   860  		want := tok.String() + " ()"
   861  		if got != want {
   862  			t.Errorf("got %q, want %q", got, want)
   863  		}
   864  	}
   865  }
   866  

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