Source file src/go/printer/nodes.go

Documentation: go/printer

     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  // This file implements printing of AST nodes; specifically
     6  // expressions, statements, declarations, and files. It uses
     7  // the print functionality implemented in printer.go.
     8  
     9  package printer
    10  
    11  import (
    12  	"bytes"
    13  	"go/ast"
    14  	"go/internal/typeparams"
    15  	"go/token"
    16  	"math"
    17  	"strconv"
    18  	"strings"
    19  	"unicode"
    20  	"unicode/utf8"
    21  )
    22  
    23  // Formatting issues:
    24  // - better comment formatting for /*-style comments at the end of a line (e.g. a declaration)
    25  //   when the comment spans multiple lines; if such a comment is just two lines, formatting is
    26  //   not idempotent
    27  // - formatting of expression lists
    28  // - should use blank instead of tab to separate one-line function bodies from
    29  //   the function header unless there is a group of consecutive one-liners
    30  
    31  // ----------------------------------------------------------------------------
    32  // Common AST nodes.
    33  
    34  // Print as many newlines as necessary (but at least min newlines) to get to
    35  // the current line. ws is printed before the first line break. If newSection
    36  // is set, the first line break is printed as formfeed. Returns 0 if no line
    37  // breaks were printed, returns 1 if there was exactly one newline printed,
    38  // and returns a value > 1 if there was a formfeed or more than one newline
    39  // printed.
    40  //
    41  // TODO(gri): linebreak may add too many lines if the next statement at "line"
    42  //            is preceded by comments because the computation of n assumes
    43  //            the current position before the comment and the target position
    44  //            after the comment. Thus, after interspersing such comments, the
    45  //            space taken up by them is not considered to reduce the number of
    46  //            linebreaks. At the moment there is no easy way to know about
    47  //            future (not yet interspersed) comments in this function.
    48  //
    49  func (p *printer) linebreak(line, min int, ws whiteSpace, newSection bool) (nbreaks int) {
    50  	n := nlimit(line - p.pos.Line)
    51  	if n < min {
    52  		n = min
    53  	}
    54  	if n > 0 {
    55  		p.print(ws)
    56  		if newSection {
    57  			p.print(formfeed)
    58  			n--
    59  			nbreaks = 2
    60  		}
    61  		nbreaks += n
    62  		for ; n > 0; n-- {
    63  			p.print(newline)
    64  		}
    65  	}
    66  	return
    67  }
    68  
    69  // setComment sets g as the next comment if g != nil and if node comments
    70  // are enabled - this mode is used when printing source code fragments such
    71  // as exports only. It assumes that there is no pending comment in p.comments
    72  // and at most one pending comment in the p.comment cache.
    73  func (p *printer) setComment(g *ast.CommentGroup) {
    74  	if g == nil || !p.useNodeComments {
    75  		return
    76  	}
    77  	if p.comments == nil {
    78  		// initialize p.comments lazily
    79  		p.comments = make([]*ast.CommentGroup, 1)
    80  	} else if p.cindex < len(p.comments) {
    81  		// for some reason there are pending comments; this
    82  		// should never happen - handle gracefully and flush
    83  		// all comments up to g, ignore anything after that
    84  		p.flush(p.posFor(g.List[0].Pos()), token.ILLEGAL)
    85  		p.comments = p.comments[0:1]
    86  		// in debug mode, report error
    87  		p.internalError("setComment found pending comments")
    88  	}
    89  	p.comments[0] = g
    90  	p.cindex = 0
    91  	// don't overwrite any pending comment in the p.comment cache
    92  	// (there may be a pending comment when a line comment is
    93  	// immediately followed by a lead comment with no other
    94  	// tokens between)
    95  	if p.commentOffset == infinity {
    96  		p.nextComment() // get comment ready for use
    97  	}
    98  }
    99  
   100  type exprListMode uint
   101  
   102  const (
   103  	commaTerm exprListMode = 1 << iota // list is optionally terminated by a comma
   104  	noIndent                           // no extra indentation in multi-line lists
   105  )
   106  
   107  // If indent is set, a multi-line identifier list is indented after the
   108  // first linebreak encountered.
   109  func (p *printer) identList(list []*ast.Ident, indent bool) {
   110  	// convert into an expression list so we can re-use exprList formatting
   111  	xlist := make([]ast.Expr, len(list))
   112  	for i, x := range list {
   113  		xlist[i] = x
   114  	}
   115  	var mode exprListMode
   116  	if !indent {
   117  		mode = noIndent
   118  	}
   119  	p.exprList(token.NoPos, xlist, 1, mode, token.NoPos, false)
   120  }
   121  
   122  const filteredMsg = "contains filtered or unexported fields"
   123  
   124  // Print a list of expressions. If the list spans multiple
   125  // source lines, the original line breaks are respected between
   126  // expressions.
   127  //
   128  // TODO(gri) Consider rewriting this to be independent of []ast.Expr
   129  //           so that we can use the algorithm for any kind of list
   130  //           (e.g., pass list via a channel over which to range).
   131  func (p *printer) exprList(prev0 token.Pos, list []ast.Expr, depth int, mode exprListMode, next0 token.Pos, isIncomplete bool) {
   132  	if len(list) == 0 {
   133  		if isIncomplete {
   134  			prev := p.posFor(prev0)
   135  			next := p.posFor(next0)
   136  			if prev.IsValid() && prev.Line == next.Line {
   137  				p.print("/* " + filteredMsg + " */")
   138  			} else {
   139  				p.print(newline)
   140  				p.print(indent, "// "+filteredMsg, unindent, newline)
   141  			}
   142  		}
   143  		return
   144  	}
   145  
   146  	prev := p.posFor(prev0)
   147  	next := p.posFor(next0)
   148  	line := p.lineFor(list[0].Pos())
   149  	endLine := p.lineFor(list[len(list)-1].End())
   150  
   151  	if prev.IsValid() && prev.Line == line && line == endLine {
   152  		// all list entries on a single line
   153  		for i, x := range list {
   154  			if i > 0 {
   155  				// use position of expression following the comma as
   156  				// comma position for correct comment placement
   157  				p.print(x.Pos(), token.COMMA, blank)
   158  			}
   159  			p.expr0(x, depth)
   160  		}
   161  		if isIncomplete {
   162  			p.print(token.COMMA, blank, "/* "+filteredMsg+" */")
   163  		}
   164  		return
   165  	}
   166  
   167  	// list entries span multiple lines;
   168  	// use source code positions to guide line breaks
   169  
   170  	// Don't add extra indentation if noIndent is set;
   171  	// i.e., pretend that the first line is already indented.
   172  	ws := ignore
   173  	if mode&noIndent == 0 {
   174  		ws = indent
   175  	}
   176  
   177  	// The first linebreak is always a formfeed since this section must not
   178  	// depend on any previous formatting.
   179  	prevBreak := -1 // index of last expression that was followed by a linebreak
   180  	if prev.IsValid() && prev.Line < line && p.linebreak(line, 0, ws, true) > 0 {
   181  		ws = ignore
   182  		prevBreak = 0
   183  	}
   184  
   185  	// initialize expression/key size: a zero value indicates expr/key doesn't fit on a single line
   186  	size := 0
   187  
   188  	// We use the ratio between the geometric mean of the previous key sizes and
   189  	// the current size to determine if there should be a break in the alignment.
   190  	// To compute the geometric mean we accumulate the ln(size) values (lnsum)
   191  	// and the number of sizes included (count).
   192  	lnsum := 0.0
   193  	count := 0
   194  
   195  	// print all list elements
   196  	prevLine := prev.Line
   197  	for i, x := range list {
   198  		line = p.lineFor(x.Pos())
   199  
   200  		// Determine if the next linebreak, if any, needs to use formfeed:
   201  		// in general, use the entire node size to make the decision; for
   202  		// key:value expressions, use the key size.
   203  		// TODO(gri) for a better result, should probably incorporate both
   204  		//           the key and the node size into the decision process
   205  		useFF := true
   206  
   207  		// Determine element size: All bets are off if we don't have
   208  		// position information for the previous and next token (likely
   209  		// generated code - simply ignore the size in this case by setting
   210  		// it to 0).
   211  		prevSize := size
   212  		const infinity = 1e6 // larger than any source line
   213  		size = p.nodeSize(x, infinity)
   214  		pair, isPair := x.(*ast.KeyValueExpr)
   215  		if size <= infinity && prev.IsValid() && next.IsValid() {
   216  			// x fits on a single line
   217  			if isPair {
   218  				size = p.nodeSize(pair.Key, infinity) // size <= infinity
   219  			}
   220  		} else {
   221  			// size too large or we don't have good layout information
   222  			size = 0
   223  		}
   224  
   225  		// If the previous line and the current line had single-
   226  		// line-expressions and the key sizes are small or the
   227  		// ratio between the current key and the geometric mean
   228  		// if the previous key sizes does not exceed a threshold,
   229  		// align columns and do not use formfeed.
   230  		if prevSize > 0 && size > 0 {
   231  			const smallSize = 40
   232  			if count == 0 || prevSize <= smallSize && size <= smallSize {
   233  				useFF = false
   234  			} else {
   235  				const r = 2.5                               // threshold
   236  				geomean := math.Exp(lnsum / float64(count)) // count > 0
   237  				ratio := float64(size) / geomean
   238  				useFF = r*ratio <= 1 || r <= ratio
   239  			}
   240  		}
   241  
   242  		needsLinebreak := 0 < prevLine && prevLine < line
   243  		if i > 0 {
   244  			// Use position of expression following the comma as
   245  			// comma position for correct comment placement, but
   246  			// only if the expression is on the same line.
   247  			if !needsLinebreak {
   248  				p.print(x.Pos())
   249  			}
   250  			p.print(token.COMMA)
   251  			needsBlank := true
   252  			if needsLinebreak {
   253  				// Lines are broken using newlines so comments remain aligned
   254  				// unless useFF is set or there are multiple expressions on
   255  				// the same line in which case formfeed is used.
   256  				nbreaks := p.linebreak(line, 0, ws, useFF || prevBreak+1 < i)
   257  				if nbreaks > 0 {
   258  					ws = ignore
   259  					prevBreak = i
   260  					needsBlank = false // we got a line break instead
   261  				}
   262  				// If there was a new section or more than one new line
   263  				// (which means that the tabwriter will implicitly break
   264  				// the section), reset the geomean variables since we are
   265  				// starting a new group of elements with the next element.
   266  				if nbreaks > 1 {
   267  					lnsum = 0
   268  					count = 0
   269  				}
   270  			}
   271  			if needsBlank {
   272  				p.print(blank)
   273  			}
   274  		}
   275  
   276  		if len(list) > 1 && isPair && size > 0 && needsLinebreak {
   277  			// We have a key:value expression that fits onto one line
   278  			// and it's not on the same line as the prior expression:
   279  			// Use a column for the key such that consecutive entries
   280  			// can align if possible.
   281  			// (needsLinebreak is set if we started a new line before)
   282  			p.expr(pair.Key)
   283  			p.print(pair.Colon, token.COLON, vtab)
   284  			p.expr(pair.Value)
   285  		} else {
   286  			p.expr0(x, depth)
   287  		}
   288  
   289  		if size > 0 {
   290  			lnsum += math.Log(float64(size))
   291  			count++
   292  		}
   293  
   294  		prevLine = line
   295  	}
   296  
   297  	if mode&commaTerm != 0 && next.IsValid() && p.pos.Line < next.Line {
   298  		// Print a terminating comma if the next token is on a new line.
   299  		p.print(token.COMMA)
   300  		if isIncomplete {
   301  			p.print(newline)
   302  			p.print("// " + filteredMsg)
   303  		}
   304  		if ws == ignore && mode&noIndent == 0 {
   305  			// unindent if we indented
   306  			p.print(unindent)
   307  		}
   308  		p.print(formfeed) // terminating comma needs a line break to look good
   309  		return
   310  	}
   311  
   312  	if isIncomplete {
   313  		p.print(token.COMMA, newline)
   314  		p.print("// "+filteredMsg, newline)
   315  	}
   316  
   317  	if ws == ignore && mode&noIndent == 0 {
   318  		// unindent if we indented
   319  		p.print(unindent)
   320  	}
   321  }
   322  
   323  func (p *printer) parameters(fields *ast.FieldList, isTypeParam bool) {
   324  	openTok, closeTok := token.LPAREN, token.RPAREN
   325  	if isTypeParam {
   326  		openTok, closeTok = token.LBRACK, token.RBRACK
   327  	}
   328  	p.print(fields.Opening, openTok)
   329  	if len(fields.List) > 0 {
   330  		prevLine := p.lineFor(fields.Opening)
   331  		ws := indent
   332  		for i, par := range fields.List {
   333  			// determine par begin and end line (may be different
   334  			// if there are multiple parameter names for this par
   335  			// or the type is on a separate line)
   336  			parLineBeg := p.lineFor(par.Pos())
   337  			parLineEnd := p.lineFor(par.End())
   338  			// separating "," if needed
   339  			needsLinebreak := 0 < prevLine && prevLine < parLineBeg
   340  			if i > 0 {
   341  				// use position of parameter following the comma as
   342  				// comma position for correct comma placement, but
   343  				// only if the next parameter is on the same line
   344  				if !needsLinebreak {
   345  					p.print(par.Pos())
   346  				}
   347  				p.print(token.COMMA)
   348  			}
   349  			// separator if needed (linebreak or blank)
   350  			if needsLinebreak && p.linebreak(parLineBeg, 0, ws, true) > 0 {
   351  				// break line if the opening "(" or previous parameter ended on a different line
   352  				ws = ignore
   353  			} else if i > 0 {
   354  				p.print(blank)
   355  			}
   356  			// parameter names
   357  			if len(par.Names) > 0 {
   358  				// Very subtle: If we indented before (ws == ignore), identList
   359  				// won't indent again. If we didn't (ws == indent), identList will
   360  				// indent if the identList spans multiple lines, and it will outdent
   361  				// again at the end (and still ws == indent). Thus, a subsequent indent
   362  				// by a linebreak call after a type, or in the next multi-line identList
   363  				// will do the right thing.
   364  				p.identList(par.Names, ws == indent)
   365  				p.print(blank)
   366  			}
   367  			// parameter type
   368  			p.expr(stripParensAlways(par.Type))
   369  			prevLine = parLineEnd
   370  		}
   371  		// if the closing ")" is on a separate line from the last parameter,
   372  		// print an additional "," and line break
   373  		if closing := p.lineFor(fields.Closing); 0 < prevLine && prevLine < closing {
   374  			p.print(token.COMMA)
   375  			p.linebreak(closing, 0, ignore, true)
   376  		}
   377  		// unindent if we indented
   378  		if ws == ignore {
   379  			p.print(unindent)
   380  		}
   381  	}
   382  	p.print(fields.Closing, closeTok)
   383  }
   384  
   385  func (p *printer) signature(sig *ast.FuncType) {
   386  	if tparams := typeparams.Get(sig); tparams != nil {
   387  		p.parameters(tparams, true)
   388  	}
   389  	if sig.Params != nil {
   390  		p.parameters(sig.Params, false)
   391  	} else {
   392  		p.print(token.LPAREN, token.RPAREN)
   393  	}
   394  	res := sig.Results
   395  	n := res.NumFields()
   396  	if n > 0 {
   397  		// res != nil
   398  		p.print(blank)
   399  		if n == 1 && res.List[0].Names == nil {
   400  			// single anonymous res; no ()'s
   401  			p.expr(stripParensAlways(res.List[0].Type))
   402  			return
   403  		}
   404  		p.parameters(res, false)
   405  	}
   406  }
   407  
   408  func identListSize(list []*ast.Ident, maxSize int) (size int) {
   409  	for i, x := range list {
   410  		if i > 0 {
   411  			size += len(", ")
   412  		}
   413  		size += utf8.RuneCountInString(x.Name)
   414  		if size >= maxSize {
   415  			break
   416  		}
   417  	}
   418  	return
   419  }
   420  
   421  func (p *printer) isOneLineFieldList(list []*ast.Field) bool {
   422  	if len(list) != 1 {
   423  		return false // allow only one field
   424  	}
   425  	f := list[0]
   426  	if f.Tag != nil || f.Comment != nil {
   427  		return false // don't allow tags or comments
   428  	}
   429  	// only name(s) and type
   430  	const maxSize = 30 // adjust as appropriate, this is an approximate value
   431  	namesSize := identListSize(f.Names, maxSize)
   432  	if namesSize > 0 {
   433  		namesSize = 1 // blank between names and types
   434  	}
   435  	typeSize := p.nodeSize(f.Type, maxSize)
   436  	return namesSize+typeSize <= maxSize
   437  }
   438  
   439  func (p *printer) setLineComment(text string) {
   440  	p.setComment(&ast.CommentGroup{List: []*ast.Comment{{Slash: token.NoPos, Text: text}}})
   441  }
   442  
   443  func (p *printer) fieldList(fields *ast.FieldList, isStruct, isIncomplete bool) {
   444  	lbrace := fields.Opening
   445  	list := fields.List
   446  	rbrace := fields.Closing
   447  	hasComments := isIncomplete || p.commentBefore(p.posFor(rbrace))
   448  	srcIsOneLine := lbrace.IsValid() && rbrace.IsValid() && p.lineFor(lbrace) == p.lineFor(rbrace)
   449  
   450  	if !hasComments && srcIsOneLine {
   451  		// possibly a one-line struct/interface
   452  		if len(list) == 0 {
   453  			// no blank between keyword and {} in this case
   454  			p.print(lbrace, token.LBRACE, rbrace, token.RBRACE)
   455  			return
   456  		} else if p.isOneLineFieldList(list) {
   457  			// small enough - print on one line
   458  			// (don't use identList and ignore source line breaks)
   459  			p.print(lbrace, token.LBRACE, blank)
   460  			f := list[0]
   461  			if isStruct {
   462  				for i, x := range f.Names {
   463  					if i > 0 {
   464  						// no comments so no need for comma position
   465  						p.print(token.COMMA, blank)
   466  					}
   467  					p.expr(x)
   468  				}
   469  				if len(f.Names) > 0 {
   470  					p.print(blank)
   471  				}
   472  				p.expr(f.Type)
   473  			} else { // interface
   474  				if len(f.Names) > 0 {
   475  					// type list type or method
   476  					name := f.Names[0] // "type" or method name
   477  					p.expr(name)
   478  					if name.Name == "type" {
   479  						// type list type
   480  						p.print(blank)
   481  						p.expr(f.Type)
   482  					} else {
   483  						// method
   484  						p.signature(f.Type.(*ast.FuncType)) // don't print "func"
   485  					}
   486  				} else {
   487  					// embedded interface
   488  					p.expr(f.Type)
   489  				}
   490  			}
   491  			p.print(blank, rbrace, token.RBRACE)
   492  			return
   493  		}
   494  	}
   495  	// hasComments || !srcIsOneLine
   496  
   497  	p.print(blank, lbrace, token.LBRACE, indent)
   498  	if hasComments || len(list) > 0 {
   499  		p.print(formfeed)
   500  	}
   501  
   502  	if isStruct {
   503  
   504  		sep := vtab
   505  		if len(list) == 1 {
   506  			sep = blank
   507  		}
   508  		var line int
   509  		for i, f := range list {
   510  			if i > 0 {
   511  				p.linebreak(p.lineFor(f.Pos()), 1, ignore, p.linesFrom(line) > 0)
   512  			}
   513  			extraTabs := 0
   514  			p.setComment(f.Doc)
   515  			p.recordLine(&line)
   516  			if len(f.Names) > 0 {
   517  				// named fields
   518  				p.identList(f.Names, false)
   519  				p.print(sep)
   520  				p.expr(f.Type)
   521  				extraTabs = 1
   522  			} else {
   523  				// anonymous field
   524  				p.expr(f.Type)
   525  				extraTabs = 2
   526  			}
   527  			if f.Tag != nil {
   528  				if len(f.Names) > 0 && sep == vtab {
   529  					p.print(sep)
   530  				}
   531  				p.print(sep)
   532  				p.expr(f.Tag)
   533  				extraTabs = 0
   534  			}
   535  			if f.Comment != nil {
   536  				for ; extraTabs > 0; extraTabs-- {
   537  					p.print(sep)
   538  				}
   539  				p.setComment(f.Comment)
   540  			}
   541  		}
   542  		if isIncomplete {
   543  			if len(list) > 0 {
   544  				p.print(formfeed)
   545  			}
   546  			p.flush(p.posFor(rbrace), token.RBRACE) // make sure we don't lose the last line comment
   547  			p.setLineComment("// " + filteredMsg)
   548  		}
   549  
   550  	} else { // interface
   551  
   552  		var line int
   553  		var prev *ast.Ident // previous "type" identifier
   554  		for i, f := range list {
   555  			var name *ast.Ident // first name, or nil
   556  			if len(f.Names) > 0 {
   557  				name = f.Names[0]
   558  			}
   559  			if i > 0 {
   560  				// don't do a line break (min == 0) if we are printing a list of types
   561  				// TODO(gri) this doesn't work quite right if the list of types is
   562  				//           spread across multiple lines
   563  				min := 1
   564  				if prev != nil && name == prev {
   565  					min = 0
   566  				}
   567  				p.linebreak(p.lineFor(f.Pos()), min, ignore, p.linesFrom(line) > 0)
   568  			}
   569  			p.setComment(f.Doc)
   570  			p.recordLine(&line)
   571  			if name != nil {
   572  				// type list type or method
   573  				if name.Name == "type" {
   574  					// type list type
   575  					if name == prev {
   576  						// type is part of a list of types
   577  						p.print(token.COMMA, blank)
   578  					} else {
   579  						// type starts a new list of types
   580  						p.print(name, blank)
   581  					}
   582  					p.expr(f.Type)
   583  					prev = name
   584  				} else {
   585  					// method
   586  					p.expr(name)
   587  					p.signature(f.Type.(*ast.FuncType)) // don't print "func"
   588  					prev = nil
   589  				}
   590  			} else {
   591  				// embedded interface
   592  				p.expr(f.Type)
   593  				prev = nil
   594  			}
   595  			p.setComment(f.Comment)
   596  		}
   597  		if isIncomplete {
   598  			if len(list) > 0 {
   599  				p.print(formfeed)
   600  			}
   601  			p.flush(p.posFor(rbrace), token.RBRACE) // make sure we don't lose the last line comment
   602  			p.setLineComment("// contains filtered or unexported methods")
   603  		}
   604  
   605  	}
   606  	p.print(unindent, formfeed, rbrace, token.RBRACE)
   607  }
   608  
   609  // ----------------------------------------------------------------------------
   610  // Expressions
   611  
   612  func walkBinary(e *ast.BinaryExpr) (has4, has5 bool, maxProblem int) {
   613  	switch e.Op.Precedence() {
   614  	case 4:
   615  		has4 = true
   616  	case 5:
   617  		has5 = true
   618  	}
   619  
   620  	switch l := e.X.(type) {
   621  	case *ast.BinaryExpr:
   622  		if l.Op.Precedence() < e.Op.Precedence() {
   623  			// parens will be inserted.
   624  			// pretend this is an *ast.ParenExpr and do nothing.
   625  			break
   626  		}
   627  		h4, h5, mp := walkBinary(l)
   628  		has4 = has4 || h4
   629  		has5 = has5 || h5
   630  		if maxProblem < mp {
   631  			maxProblem = mp
   632  		}
   633  	}
   634  
   635  	switch r := e.Y.(type) {
   636  	case *ast.BinaryExpr:
   637  		if r.Op.Precedence() <= e.Op.Precedence() {
   638  			// parens will be inserted.
   639  			// pretend this is an *ast.ParenExpr and do nothing.
   640  			break
   641  		}
   642  		h4, h5, mp := walkBinary(r)
   643  		has4 = has4 || h4
   644  		has5 = has5 || h5
   645  		if maxProblem < mp {
   646  			maxProblem = mp
   647  		}
   648  
   649  	case *ast.StarExpr:
   650  		if e.Op == token.QUO { // `*/`
   651  			maxProblem = 5
   652  		}
   653  
   654  	case *ast.UnaryExpr:
   655  		switch e.Op.String() + r.Op.String() {
   656  		case "/*", "&&", "&^":
   657  			maxProblem = 5
   658  		case "++", "--":
   659  			if maxProblem < 4 {
   660  				maxProblem = 4
   661  			}
   662  		}
   663  	}
   664  	return
   665  }
   666  
   667  func cutoff(e *ast.BinaryExpr, depth int) int {
   668  	has4, has5, maxProblem := walkBinary(e)
   669  	if maxProblem > 0 {
   670  		return maxProblem + 1
   671  	}
   672  	if has4 && has5 {
   673  		if depth == 1 {
   674  			return 5
   675  		}
   676  		return 4
   677  	}
   678  	if depth == 1 {
   679  		return 6
   680  	}
   681  	return 4
   682  }
   683  
   684  func diffPrec(expr ast.Expr, prec int) int {
   685  	x, ok := expr.(*ast.BinaryExpr)
   686  	if !ok || prec != x.Op.Precedence() {
   687  		return 1
   688  	}
   689  	return 0
   690  }
   691  
   692  func reduceDepth(depth int) int {
   693  	depth--
   694  	if depth < 1 {
   695  		depth = 1
   696  	}
   697  	return depth
   698  }
   699  
   700  // Format the binary expression: decide the cutoff and then format.
   701  // Let's call depth == 1 Normal mode, and depth > 1 Compact mode.
   702  // (Algorithm suggestion by Russ Cox.)
   703  //
   704  // The precedences are:
   705  //	5             *  /  %  <<  >>  &  &^
   706  //	4             +  -  |  ^
   707  //	3             ==  !=  <  <=  >  >=
   708  //	2             &&
   709  //	1             ||
   710  //
   711  // The only decision is whether there will be spaces around levels 4 and 5.
   712  // There are never spaces at level 6 (unary), and always spaces at levels 3 and below.
   713  //
   714  // To choose the cutoff, look at the whole expression but excluding primary
   715  // expressions (function calls, parenthesized exprs), and apply these rules:
   716  //
   717  //	1) If there is a binary operator with a right side unary operand
   718  //	   that would clash without a space, the cutoff must be (in order):
   719  //
   720  //		/*	6
   721  //		&&	6
   722  //		&^	6
   723  //		++	5
   724  //		--	5
   725  //
   726  //         (Comparison operators always have spaces around them.)
   727  //
   728  //	2) If there is a mix of level 5 and level 4 operators, then the cutoff
   729  //	   is 5 (use spaces to distinguish precedence) in Normal mode
   730  //	   and 4 (never use spaces) in Compact mode.
   731  //
   732  //	3) If there are no level 4 operators or no level 5 operators, then the
   733  //	   cutoff is 6 (always use spaces) in Normal mode
   734  //	   and 4 (never use spaces) in Compact mode.
   735  //
   736  func (p *printer) binaryExpr(x *ast.BinaryExpr, prec1, cutoff, depth int) {
   737  	prec := x.Op.Precedence()
   738  	if prec < prec1 {
   739  		// parenthesis needed
   740  		// Note: The parser inserts an ast.ParenExpr node; thus this case
   741  		//       can only occur if the AST is created in a different way.
   742  		p.print(token.LPAREN)
   743  		p.expr0(x, reduceDepth(depth)) // parentheses undo one level of depth
   744  		p.print(token.RPAREN)
   745  		return
   746  	}
   747  
   748  	printBlank := prec < cutoff
   749  
   750  	ws := indent
   751  	p.expr1(x.X, prec, depth+diffPrec(x.X, prec))
   752  	if printBlank {
   753  		p.print(blank)
   754  	}
   755  	xline := p.pos.Line // before the operator (it may be on the next line!)
   756  	yline := p.lineFor(x.Y.Pos())
   757  	p.print(x.OpPos, x.Op)
   758  	if xline != yline && xline > 0 && yline > 0 {
   759  		// at least one line break, but respect an extra empty line
   760  		// in the source
   761  		if p.linebreak(yline, 1, ws, true) > 0 {
   762  			ws = ignore
   763  			printBlank = false // no blank after line break
   764  		}
   765  	}
   766  	if printBlank {
   767  		p.print(blank)
   768  	}
   769  	p.expr1(x.Y, prec+1, depth+1)
   770  	if ws == ignore {
   771  		p.print(unindent)
   772  	}
   773  }
   774  
   775  func isBinary(expr ast.Expr) bool {
   776  	_, ok := expr.(*ast.BinaryExpr)
   777  	return ok
   778  }
   779  
   780  func (p *printer) expr1(expr ast.Expr, prec1, depth int) {
   781  	p.print(expr.Pos())
   782  
   783  	switch x := expr.(type) {
   784  	case *ast.BadExpr:
   785  		p.print("BadExpr")
   786  
   787  	case *ast.Ident:
   788  		p.print(x)
   789  
   790  	case *ast.BinaryExpr:
   791  		if depth < 1 {
   792  			p.internalError("depth < 1:", depth)
   793  			depth = 1
   794  		}
   795  		p.binaryExpr(x, prec1, cutoff(x, depth), depth)
   796  
   797  	case *ast.KeyValueExpr:
   798  		p.expr(x.Key)
   799  		p.print(x.Colon, token.COLON, blank)
   800  		p.expr(x.Value)
   801  
   802  	case *ast.StarExpr:
   803  		const prec = token.UnaryPrec
   804  		if prec < prec1 {
   805  			// parenthesis needed
   806  			p.print(token.LPAREN)
   807  			p.print(token.MUL)
   808  			p.expr(x.X)
   809  			p.print(token.RPAREN)
   810  		} else {
   811  			// no parenthesis needed
   812  			p.print(token.MUL)
   813  			p.expr(x.X)
   814  		}
   815  
   816  	case *ast.UnaryExpr:
   817  		const prec = token.UnaryPrec
   818  		if prec < prec1 {
   819  			// parenthesis needed
   820  			p.print(token.LPAREN)
   821  			p.expr(x)
   822  			p.print(token.RPAREN)
   823  		} else {
   824  			// no parenthesis needed
   825  			p.print(x.Op)
   826  			if x.Op == token.RANGE {
   827  				// TODO(gri) Remove this code if it cannot be reached.
   828  				p.print(blank)
   829  			}
   830  			p.expr1(x.X, prec, depth)
   831  		}
   832  
   833  	case *ast.BasicLit:
   834  		if p.Config.Mode&normalizeNumbers != 0 {
   835  			x = normalizedNumber(x)
   836  		}
   837  		p.print(x)
   838  
   839  	case *ast.FuncLit:
   840  		p.print(x.Type.Pos(), token.FUNC)
   841  		// See the comment in funcDecl about how the header size is computed.
   842  		startCol := p.out.Column - len("func")
   843  		p.signature(x.Type)
   844  		p.funcBody(p.distanceFrom(x.Type.Pos(), startCol), blank, x.Body)
   845  
   846  	case *ast.ParenExpr:
   847  		if _, hasParens := x.X.(*ast.ParenExpr); hasParens {
   848  			// don't print parentheses around an already parenthesized expression
   849  			// TODO(gri) consider making this more general and incorporate precedence levels
   850  			p.expr0(x.X, depth)
   851  		} else {
   852  			p.print(token.LPAREN)
   853  			p.expr0(x.X, reduceDepth(depth)) // parentheses undo one level of depth
   854  			p.print(x.Rparen, token.RPAREN)
   855  		}
   856  
   857  	case *ast.SelectorExpr:
   858  		p.selectorExpr(x, depth, false)
   859  
   860  	case *ast.TypeAssertExpr:
   861  		p.expr1(x.X, token.HighestPrec, depth)
   862  		p.print(token.PERIOD, x.Lparen, token.LPAREN)
   863  		if x.Type != nil {
   864  			p.expr(x.Type)
   865  		} else {
   866  			p.print(token.TYPE)
   867  		}
   868  		p.print(x.Rparen, token.RPAREN)
   869  
   870  	case *ast.IndexExpr:
   871  		// TODO(gri): should treat[] like parentheses and undo one level of depth
   872  		p.expr1(x.X, token.HighestPrec, 1)
   873  		p.print(x.Lbrack, token.LBRACK)
   874  		// Note: we're a bit defensive here to handle the case of a ListExpr of
   875  		// length 1.
   876  		if list := typeparams.UnpackExpr(x.Index); len(list) > 0 {
   877  			if len(list) > 1 {
   878  				p.exprList(x.Lbrack, list, depth+1, commaTerm, x.Rbrack, false)
   879  			} else {
   880  				p.expr0(list[0], depth+1)
   881  			}
   882  		} else {
   883  			p.expr0(x.Index, depth+1)
   884  		}
   885  		p.print(x.Rbrack, token.RBRACK)
   886  
   887  	case *ast.SliceExpr:
   888  		// TODO(gri): should treat[] like parentheses and undo one level of depth
   889  		p.expr1(x.X, token.HighestPrec, 1)
   890  		p.print(x.Lbrack, token.LBRACK)
   891  		indices := []ast.Expr{x.Low, x.High}
   892  		if x.Max != nil {
   893  			indices = append(indices, x.Max)
   894  		}
   895  		// determine if we need extra blanks around ':'
   896  		var needsBlanks bool
   897  		if depth <= 1 {
   898  			var indexCount int
   899  			var hasBinaries bool
   900  			for _, x := range indices {
   901  				if x != nil {
   902  					indexCount++
   903  					if isBinary(x) {
   904  						hasBinaries = true
   905  					}
   906  				}
   907  			}
   908  			if indexCount > 1 && hasBinaries {
   909  				needsBlanks = true
   910  			}
   911  		}
   912  		for i, x := range indices {
   913  			if i > 0 {
   914  				if indices[i-1] != nil && needsBlanks {
   915  					p.print(blank)
   916  				}
   917  				p.print(token.COLON)
   918  				if x != nil && needsBlanks {
   919  					p.print(blank)
   920  				}
   921  			}
   922  			if x != nil {
   923  				p.expr0(x, depth+1)
   924  			}
   925  		}
   926  		p.print(x.Rbrack, token.RBRACK)
   927  
   928  	case *ast.CallExpr:
   929  		if len(x.Args) > 1 {
   930  			depth++
   931  		}
   932  		var wasIndented bool
   933  		if _, ok := x.Fun.(*ast.FuncType); ok {
   934  			// conversions to literal function types require parentheses around the type
   935  			p.print(token.LPAREN)
   936  			wasIndented = p.possibleSelectorExpr(x.Fun, token.HighestPrec, depth)
   937  			p.print(token.RPAREN)
   938  		} else {
   939  			wasIndented = p.possibleSelectorExpr(x.Fun, token.HighestPrec, depth)
   940  		}
   941  		p.print(x.Lparen, token.LPAREN)
   942  		if x.Ellipsis.IsValid() {
   943  			p.exprList(x.Lparen, x.Args, depth, 0, x.Ellipsis, false)
   944  			p.print(x.Ellipsis, token.ELLIPSIS)
   945  			if x.Rparen.IsValid() && p.lineFor(x.Ellipsis) < p.lineFor(x.Rparen) {
   946  				p.print(token.COMMA, formfeed)
   947  			}
   948  		} else {
   949  			p.exprList(x.Lparen, x.Args, depth, commaTerm, x.Rparen, false)
   950  		}
   951  		p.print(x.Rparen, token.RPAREN)
   952  		if wasIndented {
   953  			p.print(unindent)
   954  		}
   955  
   956  	case *ast.CompositeLit:
   957  		// composite literal elements that are composite literals themselves may have the type omitted
   958  		if x.Type != nil {
   959  			p.expr1(x.Type, token.HighestPrec, depth)
   960  		}
   961  		p.level++
   962  		p.print(x.Lbrace, token.LBRACE)
   963  		p.exprList(x.Lbrace, x.Elts, 1, commaTerm, x.Rbrace, x.Incomplete)
   964  		// do not insert extra line break following a /*-style comment
   965  		// before the closing '}' as it might break the code if there
   966  		// is no trailing ','
   967  		mode := noExtraLinebreak
   968  		// do not insert extra blank following a /*-style comment
   969  		// before the closing '}' unless the literal is empty
   970  		if len(x.Elts) > 0 {
   971  			mode |= noExtraBlank
   972  		}
   973  		// need the initial indent to print lone comments with
   974  		// the proper level of indentation
   975  		p.print(indent, unindent, mode, x.Rbrace, token.RBRACE, mode)
   976  		p.level--
   977  
   978  	case *ast.Ellipsis:
   979  		p.print(token.ELLIPSIS)
   980  		if x.Elt != nil {
   981  			p.expr(x.Elt)
   982  		}
   983  
   984  	case *ast.ArrayType:
   985  		p.print(token.LBRACK)
   986  		if x.Len != nil {
   987  			p.expr(x.Len)
   988  		}
   989  		p.print(token.RBRACK)
   990  		p.expr(x.Elt)
   991  
   992  	case *ast.StructType:
   993  		p.print(token.STRUCT)
   994  		p.fieldList(x.Fields, true, x.Incomplete)
   995  
   996  	case *ast.FuncType:
   997  		p.print(token.FUNC)
   998  		p.signature(x)
   999  
  1000  	case *ast.InterfaceType:
  1001  		p.print(token.INTERFACE)
  1002  		p.fieldList(x.Methods, false, x.Incomplete)
  1003  
  1004  	case *ast.MapType:
  1005  		p.print(token.MAP, token.LBRACK)
  1006  		p.expr(x.Key)
  1007  		p.print(token.RBRACK)
  1008  		p.expr(x.Value)
  1009  
  1010  	case *ast.ChanType:
  1011  		switch x.Dir {
  1012  		case ast.SEND | ast.RECV:
  1013  			p.print(token.CHAN)
  1014  		case ast.RECV:
  1015  			p.print(token.ARROW, token.CHAN) // x.Arrow and x.Pos() are the same
  1016  		case ast.SEND:
  1017  			p.print(token.CHAN, x.Arrow, token.ARROW)
  1018  		}
  1019  		p.print(blank)
  1020  		p.expr(x.Value)
  1021  
  1022  	default:
  1023  		panic("unreachable")
  1024  	}
  1025  }
  1026  
  1027  // normalizedNumber rewrites base prefixes and exponents
  1028  // of numbers to use lower-case letters (0X123 to 0x123 and 1.2E3 to 1.2e3),
  1029  // and removes leading 0's from integer imaginary literals (0765i to 765i).
  1030  // It leaves hexadecimal digits alone.
  1031  //
  1032  // normalizedNumber doesn't modify the ast.BasicLit value lit points to.
  1033  // If lit is not a number or a number in canonical format already,
  1034  // lit is returned as is. Otherwise a new ast.BasicLit is created.
  1035  func normalizedNumber(lit *ast.BasicLit) *ast.BasicLit {
  1036  	if lit.Kind != token.INT && lit.Kind != token.FLOAT && lit.Kind != token.IMAG {
  1037  		return lit // not a number - nothing to do
  1038  	}
  1039  	if len(lit.Value) < 2 {
  1040  		return lit // only one digit (common case) - nothing to do
  1041  	}
  1042  	// len(lit.Value) >= 2
  1043  
  1044  	// We ignore lit.Kind because for lit.Kind == token.IMAG the literal may be an integer
  1045  	// or floating-point value, decimal or not. Instead, just consider the literal pattern.
  1046  	x := lit.Value
  1047  	switch x[:2] {
  1048  	default:
  1049  		// 0-prefix octal, decimal int, or float (possibly with 'i' suffix)
  1050  		if i := strings.LastIndexByte(x, 'E'); i >= 0 {
  1051  			x = x[:i] + "e" + x[i+1:]
  1052  			break
  1053  		}
  1054  		// remove leading 0's from integer (but not floating-point) imaginary literals
  1055  		if x[len(x)-1] == 'i' && strings.IndexByte(x, '.') < 0 && strings.IndexByte(x, 'e') < 0 {
  1056  			x = strings.TrimLeft(x, "0_")
  1057  			if x == "i" {
  1058  				x = "0i"
  1059  			}
  1060  		}
  1061  	case "0X":
  1062  		x = "0x" + x[2:]
  1063  		// possibly a hexadecimal float
  1064  		if i := strings.LastIndexByte(x, 'P'); i >= 0 {
  1065  			x = x[:i] + "p" + x[i+1:]
  1066  		}
  1067  	case "0x":
  1068  		// possibly a hexadecimal float
  1069  		i := strings.LastIndexByte(x, 'P')
  1070  		if i == -1 {
  1071  			return lit // nothing to do
  1072  		}
  1073  		x = x[:i] + "p" + x[i+1:]
  1074  	case "0O":
  1075  		x = "0o" + x[2:]
  1076  	case "0o":
  1077  		return lit // nothing to do
  1078  	case "0B":
  1079  		x = "0b" + x[2:]
  1080  	case "0b":
  1081  		return lit // nothing to do
  1082  	}
  1083  
  1084  	return &ast.BasicLit{ValuePos: lit.ValuePos, Kind: lit.Kind, Value: x}
  1085  }
  1086  
  1087  func (p *printer) possibleSelectorExpr(expr ast.Expr, prec1, depth int) bool {
  1088  	if x, ok := expr.(*ast.SelectorExpr); ok {
  1089  		return p.selectorExpr(x, depth, true)
  1090  	}
  1091  	p.expr1(expr, prec1, depth)
  1092  	return false
  1093  }
  1094  
  1095  // selectorExpr handles an *ast.SelectorExpr node and reports whether x spans
  1096  // multiple lines.
  1097  func (p *printer) selectorExpr(x *ast.SelectorExpr, depth int, isMethod bool) bool {
  1098  	p.expr1(x.X, token.HighestPrec, depth)
  1099  	p.print(token.PERIOD)
  1100  	if line := p.lineFor(x.Sel.Pos()); p.pos.IsValid() && p.pos.Line < line {
  1101  		p.print(indent, newline, x.Sel.Pos(), x.Sel)
  1102  		if !isMethod {
  1103  			p.print(unindent)
  1104  		}
  1105  		return true
  1106  	}
  1107  	p.print(x.Sel.Pos(), x.Sel)
  1108  	return false
  1109  }
  1110  
  1111  func (p *printer) expr0(x ast.Expr, depth int) {
  1112  	p.expr1(x, token.LowestPrec, depth)
  1113  }
  1114  
  1115  func (p *printer) expr(x ast.Expr) {
  1116  	const depth = 1
  1117  	p.expr1(x, token.LowestPrec, depth)
  1118  }
  1119  
  1120  // ----------------------------------------------------------------------------
  1121  // Statements
  1122  
  1123  // Print the statement list indented, but without a newline after the last statement.
  1124  // Extra line breaks between statements in the source are respected but at most one
  1125  // empty line is printed between statements.
  1126  func (p *printer) stmtList(list []ast.Stmt, nindent int, nextIsRBrace bool) {
  1127  	if nindent > 0 {
  1128  		p.print(indent)
  1129  	}
  1130  	var line int
  1131  	i := 0
  1132  	for _, s := range list {
  1133  		// ignore empty statements (was issue 3466)
  1134  		if _, isEmpty := s.(*ast.EmptyStmt); !isEmpty {
  1135  			// nindent == 0 only for lists of switch/select case clauses;
  1136  			// in those cases each clause is a new section
  1137  			if len(p.output) > 0 {
  1138  				// only print line break if we are not at the beginning of the output
  1139  				// (i.e., we are not printing only a partial program)
  1140  				p.linebreak(p.lineFor(s.Pos()), 1, ignore, i == 0 || nindent == 0 || p.linesFrom(line) > 0)
  1141  			}
  1142  			p.recordLine(&line)
  1143  			p.stmt(s, nextIsRBrace && i == len(list)-1)
  1144  			// labeled statements put labels on a separate line, but here
  1145  			// we only care about the start line of the actual statement
  1146  			// without label - correct line for each label
  1147  			for t := s; ; {
  1148  				lt, _ := t.(*ast.LabeledStmt)
  1149  				if lt == nil {
  1150  					break
  1151  				}
  1152  				line++
  1153  				t = lt.Stmt
  1154  			}
  1155  			i++
  1156  		}
  1157  	}
  1158  	if nindent > 0 {
  1159  		p.print(unindent)
  1160  	}
  1161  }
  1162  
  1163  // block prints an *ast.BlockStmt; it always spans at least two lines.
  1164  func (p *printer) block(b *ast.BlockStmt, nindent int) {
  1165  	p.print(b.Lbrace, token.LBRACE)
  1166  	p.stmtList(b.List, nindent, true)
  1167  	p.linebreak(p.lineFor(b.Rbrace), 1, ignore, true)
  1168  	p.print(b.Rbrace, token.RBRACE)
  1169  }
  1170  
  1171  func isTypeName(x ast.Expr) bool {
  1172  	switch t := x.(type) {
  1173  	case *ast.Ident:
  1174  		return true
  1175  	case *ast.SelectorExpr:
  1176  		return isTypeName(t.X)
  1177  	}
  1178  	return false
  1179  }
  1180  
  1181  func stripParens(x ast.Expr) ast.Expr {
  1182  	if px, strip := x.(*ast.ParenExpr); strip {
  1183  		// parentheses must not be stripped if there are any
  1184  		// unparenthesized composite literals starting with
  1185  		// a type name
  1186  		ast.Inspect(px.X, func(node ast.Node) bool {
  1187  			switch x := node.(type) {
  1188  			case *ast.ParenExpr:
  1189  				// parentheses protect enclosed composite literals
  1190  				return false
  1191  			case *ast.CompositeLit:
  1192  				if isTypeName(x.Type) {
  1193  					strip = false // do not strip parentheses
  1194  				}
  1195  				return false
  1196  			}
  1197  			// in all other cases, keep inspecting
  1198  			return true
  1199  		})
  1200  		if strip {
  1201  			return stripParens(px.X)
  1202  		}
  1203  	}
  1204  	return x
  1205  }
  1206  
  1207  func stripParensAlways(x ast.Expr) ast.Expr {
  1208  	if x, ok := x.(*ast.ParenExpr); ok {
  1209  		return stripParensAlways(x.X)
  1210  	}
  1211  	return x
  1212  }
  1213  
  1214  func (p *printer) controlClause(isForStmt bool, init ast.Stmt, expr ast.Expr, post ast.Stmt) {
  1215  	p.print(blank)
  1216  	needsBlank := false
  1217  	if init == nil && post == nil {
  1218  		// no semicolons required
  1219  		if expr != nil {
  1220  			p.expr(stripParens(expr))
  1221  			needsBlank = true
  1222  		}
  1223  	} else {
  1224  		// all semicolons required
  1225  		// (they are not separators, print them explicitly)
  1226  		if init != nil {
  1227  			p.stmt(init, false)
  1228  		}
  1229  		p.print(token.SEMICOLON, blank)
  1230  		if expr != nil {
  1231  			p.expr(stripParens(expr))
  1232  			needsBlank = true
  1233  		}
  1234  		if isForStmt {
  1235  			p.print(token.SEMICOLON, blank)
  1236  			needsBlank = false
  1237  			if post != nil {
  1238  				p.stmt(post, false)
  1239  				needsBlank = true
  1240  			}
  1241  		}
  1242  	}
  1243  	if needsBlank {
  1244  		p.print(blank)
  1245  	}
  1246  }
  1247  
  1248  // indentList reports whether an expression list would look better if it
  1249  // were indented wholesale (starting with the very first element, rather
  1250  // than starting at the first line break).
  1251  //
  1252  func (p *printer) indentList(list []ast.Expr) bool {
  1253  	// Heuristic: indentList reports whether there are more than one multi-
  1254  	// line element in the list, or if there is any element that is not
  1255  	// starting on the same line as the previous one ends.
  1256  	if len(list) >= 2 {
  1257  		var b = p.lineFor(list[0].Pos())
  1258  		var e = p.lineFor(list[len(list)-1].End())
  1259  		if 0 < b && b < e {
  1260  			// list spans multiple lines
  1261  			n := 0 // multi-line element count
  1262  			line := b
  1263  			for _, x := range list {
  1264  				xb := p.lineFor(x.Pos())
  1265  				xe := p.lineFor(x.End())
  1266  				if line < xb {
  1267  					// x is not starting on the same
  1268  					// line as the previous one ended
  1269  					return true
  1270  				}
  1271  				if xb < xe {
  1272  					// x is a multi-line element
  1273  					n++
  1274  				}
  1275  				line = xe
  1276  			}
  1277  			return n > 1
  1278  		}
  1279  	}
  1280  	return false
  1281  }
  1282  
  1283  func (p *printer) stmt(stmt ast.Stmt, nextIsRBrace bool) {
  1284  	p.print(stmt.Pos())
  1285  
  1286  	switch s := stmt.(type) {
  1287  	case *ast.BadStmt:
  1288  		p.print("BadStmt")
  1289  
  1290  	case *ast.DeclStmt:
  1291  		p.decl(s.Decl)
  1292  
  1293  	case *ast.EmptyStmt:
  1294  		// nothing to do
  1295  
  1296  	case *ast.LabeledStmt:
  1297  		// a "correcting" unindent immediately following a line break
  1298  		// is applied before the line break if there is no comment
  1299  		// between (see writeWhitespace)
  1300  		p.print(unindent)
  1301  		p.expr(s.Label)
  1302  		p.print(s.Colon, token.COLON, indent)
  1303  		if e, isEmpty := s.Stmt.(*ast.EmptyStmt); isEmpty {
  1304  			if !nextIsRBrace {
  1305  				p.print(newline, e.Pos(), token.SEMICOLON)
  1306  				break
  1307  			}
  1308  		} else {
  1309  			p.linebreak(p.lineFor(s.Stmt.Pos()), 1, ignore, true)
  1310  		}
  1311  		p.stmt(s.Stmt, nextIsRBrace)
  1312  
  1313  	case *ast.ExprStmt:
  1314  		const depth = 1
  1315  		p.expr0(s.X, depth)
  1316  
  1317  	case *ast.SendStmt:
  1318  		const depth = 1
  1319  		p.expr0(s.Chan, depth)
  1320  		p.print(blank, s.Arrow, token.ARROW, blank)
  1321  		p.expr0(s.Value, depth)
  1322  
  1323  	case *ast.IncDecStmt:
  1324  		const depth = 1
  1325  		p.expr0(s.X, depth+1)
  1326  		p.print(s.TokPos, s.Tok)
  1327  
  1328  	case *ast.AssignStmt:
  1329  		var depth = 1
  1330  		if len(s.Lhs) > 1 && len(s.Rhs) > 1 {
  1331  			depth++
  1332  		}
  1333  		p.exprList(s.Pos(), s.Lhs, depth, 0, s.TokPos, false)
  1334  		p.print(blank, s.TokPos, s.Tok, blank)
  1335  		p.exprList(s.TokPos, s.Rhs, depth, 0, token.NoPos, false)
  1336  
  1337  	case *ast.GoStmt:
  1338  		p.print(token.GO, blank)
  1339  		p.expr(s.Call)
  1340  
  1341  	case *ast.DeferStmt:
  1342  		p.print(token.DEFER, blank)
  1343  		p.expr(s.Call)
  1344  
  1345  	case *ast.ReturnStmt:
  1346  		p.print(token.RETURN)
  1347  		if s.Results != nil {
  1348  			p.print(blank)
  1349  			// Use indentList heuristic to make corner cases look
  1350  			// better (issue 1207). A more systematic approach would
  1351  			// always indent, but this would cause significant
  1352  			// reformatting of the code base and not necessarily
  1353  			// lead to more nicely formatted code in general.
  1354  			if p.indentList(s.Results) {
  1355  				p.print(indent)
  1356  				// Use NoPos so that a newline never goes before
  1357  				// the results (see issue #32854).
  1358  				p.exprList(token.NoPos, s.Results, 1, noIndent, token.NoPos, false)
  1359  				p.print(unindent)
  1360  			} else {
  1361  				p.exprList(token.NoPos, s.Results, 1, 0, token.NoPos, false)
  1362  			}
  1363  		}
  1364  
  1365  	case *ast.BranchStmt:
  1366  		p.print(s.Tok)
  1367  		if s.Label != nil {
  1368  			p.print(blank)
  1369  			p.expr(s.Label)
  1370  		}
  1371  
  1372  	case *ast.BlockStmt:
  1373  		p.block(s, 1)
  1374  
  1375  	case *ast.IfStmt:
  1376  		p.print(token.IF)
  1377  		p.controlClause(false, s.Init, s.Cond, nil)
  1378  		p.block(s.Body, 1)
  1379  		if s.Else != nil {
  1380  			p.print(blank, token.ELSE, blank)
  1381  			switch s.Else.(type) {
  1382  			case *ast.BlockStmt, *ast.IfStmt:
  1383  				p.stmt(s.Else, nextIsRBrace)
  1384  			default:
  1385  				// This can only happen with an incorrectly
  1386  				// constructed AST. Permit it but print so
  1387  				// that it can be parsed without errors.
  1388  				p.print(token.LBRACE, indent, formfeed)
  1389  				p.stmt(s.Else, true)
  1390  				p.print(unindent, formfeed, token.RBRACE)
  1391  			}
  1392  		}
  1393  
  1394  	case *ast.CaseClause:
  1395  		if s.List != nil {
  1396  			p.print(token.CASE, blank)
  1397  			p.exprList(s.Pos(), s.List, 1, 0, s.Colon, false)
  1398  		} else {
  1399  			p.print(token.DEFAULT)
  1400  		}
  1401  		p.print(s.Colon, token.COLON)
  1402  		p.stmtList(s.Body, 1, nextIsRBrace)
  1403  
  1404  	case *ast.SwitchStmt:
  1405  		p.print(token.SWITCH)
  1406  		p.controlClause(false, s.Init, s.Tag, nil)
  1407  		p.block(s.Body, 0)
  1408  
  1409  	case *ast.TypeSwitchStmt:
  1410  		p.print(token.SWITCH)
  1411  		if s.Init != nil {
  1412  			p.print(blank)
  1413  			p.stmt(s.Init, false)
  1414  			p.print(token.SEMICOLON)
  1415  		}
  1416  		p.print(blank)
  1417  		p.stmt(s.Assign, false)
  1418  		p.print(blank)
  1419  		p.block(s.Body, 0)
  1420  
  1421  	case *ast.CommClause:
  1422  		if s.Comm != nil {
  1423  			p.print(token.CASE, blank)
  1424  			p.stmt(s.Comm, false)
  1425  		} else {
  1426  			p.print(token.DEFAULT)
  1427  		}
  1428  		p.print(s.Colon, token.COLON)
  1429  		p.stmtList(s.Body, 1, nextIsRBrace)
  1430  
  1431  	case *ast.SelectStmt:
  1432  		p.print(token.SELECT, blank)
  1433  		body := s.Body
  1434  		if len(body.List) == 0 && !p.commentBefore(p.posFor(body.Rbrace)) {
  1435  			// print empty select statement w/o comments on one line
  1436  			p.print(body.Lbrace, token.LBRACE, body.Rbrace, token.RBRACE)
  1437  		} else {
  1438  			p.block(body, 0)
  1439  		}
  1440  
  1441  	case *ast.ForStmt:
  1442  		p.print(token.FOR)
  1443  		p.controlClause(true, s.Init, s.Cond, s.Post)
  1444  		p.block(s.Body, 1)
  1445  
  1446  	case *ast.RangeStmt:
  1447  		p.print(token.FOR, blank)
  1448  		if s.Key != nil {
  1449  			p.expr(s.Key)
  1450  			if s.Value != nil {
  1451  				// use position of value following the comma as
  1452  				// comma position for correct comment placement
  1453  				p.print(s.Value.Pos(), token.COMMA, blank)
  1454  				p.expr(s.Value)
  1455  			}
  1456  			p.print(blank, s.TokPos, s.Tok, blank)
  1457  		}
  1458  		p.print(token.RANGE, blank)
  1459  		p.expr(stripParens(s.X))
  1460  		p.print(blank)
  1461  		p.block(s.Body, 1)
  1462  
  1463  	default:
  1464  		panic("unreachable")
  1465  	}
  1466  }
  1467  
  1468  // ----------------------------------------------------------------------------
  1469  // Declarations
  1470  
  1471  // The keepTypeColumn function determines if the type column of a series of
  1472  // consecutive const or var declarations must be kept, or if initialization
  1473  // values (V) can be placed in the type column (T) instead. The i'th entry
  1474  // in the result slice is true if the type column in spec[i] must be kept.
  1475  //
  1476  // For example, the declaration:
  1477  //
  1478  //	const (
  1479  //		foobar int = 42 // comment
  1480  //		x          = 7  // comment
  1481  //		foo
  1482  //              bar = 991
  1483  //	)
  1484  //
  1485  // leads to the type/values matrix below. A run of value columns (V) can
  1486  // be moved into the type column if there is no type for any of the values
  1487  // in that column (we only move entire columns so that they align properly).
  1488  //
  1489  //	matrix        formatted     result
  1490  //                    matrix
  1491  //	T  V    ->    T  V     ->   true      there is a T and so the type
  1492  //	-  V          -  V          true      column must be kept
  1493  //	-  -          -  -          false
  1494  //	-  V          V  -          false     V is moved into T column
  1495  //
  1496  func keepTypeColumn(specs []ast.Spec) []bool {
  1497  	m := make([]bool, len(specs))
  1498  
  1499  	populate := func(i, j int, keepType bool) {
  1500  		if keepType {
  1501  			for ; i < j; i++ {
  1502  				m[i] = true
  1503  			}
  1504  		}
  1505  	}
  1506  
  1507  	i0 := -1 // if i0 >= 0 we are in a run and i0 is the start of the run
  1508  	var keepType bool
  1509  	for i, s := range specs {
  1510  		t := s.(*ast.ValueSpec)
  1511  		if t.Values != nil {
  1512  			if i0 < 0 {
  1513  				// start of a run of ValueSpecs with non-nil Values
  1514  				i0 = i
  1515  				keepType = false
  1516  			}
  1517  		} else {
  1518  			if i0 >= 0 {
  1519  				// end of a run
  1520  				populate(i0, i, keepType)
  1521  				i0 = -1
  1522  			}
  1523  		}
  1524  		if t.Type != nil {
  1525  			keepType = true
  1526  		}
  1527  	}
  1528  	if i0 >= 0 {
  1529  		// end of a run
  1530  		populate(i0, len(specs), keepType)
  1531  	}
  1532  
  1533  	return m
  1534  }
  1535  
  1536  func (p *printer) valueSpec(s *ast.ValueSpec, keepType bool) {
  1537  	p.setComment(s.Doc)
  1538  	p.identList(s.Names, false) // always present
  1539  	extraTabs := 3
  1540  	if s.Type != nil || keepType {
  1541  		p.print(vtab)
  1542  		extraTabs--
  1543  	}
  1544  	if s.Type != nil {
  1545  		p.expr(s.Type)
  1546  	}
  1547  	if s.Values != nil {
  1548  		p.print(vtab, token.ASSIGN, blank)
  1549  		p.exprList(token.NoPos, s.Values, 1, 0, token.NoPos, false)
  1550  		extraTabs--
  1551  	}
  1552  	if s.Comment != nil {
  1553  		for ; extraTabs > 0; extraTabs-- {
  1554  			p.print(vtab)
  1555  		}
  1556  		p.setComment(s.Comment)
  1557  	}
  1558  }
  1559  
  1560  func sanitizeImportPath(lit *ast.BasicLit) *ast.BasicLit {
  1561  	// Note: An unmodified AST generated by go/parser will already
  1562  	// contain a backward- or double-quoted path string that does
  1563  	// not contain any invalid characters, and most of the work
  1564  	// here is not needed. However, a modified or generated AST
  1565  	// may possibly contain non-canonical paths. Do the work in
  1566  	// all cases since it's not too hard and not speed-critical.
  1567  
  1568  	// if we don't have a proper string, be conservative and return whatever we have
  1569  	if lit.Kind != token.STRING {
  1570  		return lit
  1571  	}
  1572  	s, err := strconv.Unquote(lit.Value)
  1573  	if err != nil {
  1574  		return lit
  1575  	}
  1576  
  1577  	// if the string is an invalid path, return whatever we have
  1578  	//
  1579  	// spec: "Implementation restriction: A compiler may restrict
  1580  	// ImportPaths to non-empty strings using only characters belonging
  1581  	// to Unicode's L, M, N, P, and S general categories (the Graphic
  1582  	// characters without spaces) and may also exclude the characters
  1583  	// !"#$%&'()*,:;<=>?[\]^`{|} and the Unicode replacement character
  1584  	// U+FFFD."
  1585  	if s == "" {
  1586  		return lit
  1587  	}
  1588  	const illegalChars = `!"#$%&'()*,:;<=>?[\]^{|}` + "`\uFFFD"
  1589  	for _, r := range s {
  1590  		if !unicode.IsGraphic(r) || unicode.IsSpace(r) || strings.ContainsRune(illegalChars, r) {
  1591  			return lit
  1592  		}
  1593  	}
  1594  
  1595  	// otherwise, return the double-quoted path
  1596  	s = strconv.Quote(s)
  1597  	if s == lit.Value {
  1598  		return lit // nothing wrong with lit
  1599  	}
  1600  	return &ast.BasicLit{ValuePos: lit.ValuePos, Kind: token.STRING, Value: s}
  1601  }
  1602  
  1603  // The parameter n is the number of specs in the group. If doIndent is set,
  1604  // multi-line identifier lists in the spec are indented when the first
  1605  // linebreak is encountered.
  1606  //
  1607  func (p *printer) spec(spec ast.Spec, n int, doIndent bool) {
  1608  	switch s := spec.(type) {
  1609  	case *ast.ImportSpec:
  1610  		p.setComment(s.Doc)
  1611  		if s.Name != nil {
  1612  			p.expr(s.Name)
  1613  			p.print(blank)
  1614  		}
  1615  		p.expr(sanitizeImportPath(s.Path))
  1616  		p.setComment(s.Comment)
  1617  		p.print(s.EndPos)
  1618  
  1619  	case *ast.ValueSpec:
  1620  		if n != 1 {
  1621  			p.internalError("expected n = 1; got", n)
  1622  		}
  1623  		p.setComment(s.Doc)
  1624  		p.identList(s.Names, doIndent) // always present
  1625  		if s.Type != nil {
  1626  			p.print(blank)
  1627  			p.expr(s.Type)
  1628  		}
  1629  		if s.Values != nil {
  1630  			p.print(blank, token.ASSIGN, blank)
  1631  			p.exprList(token.NoPos, s.Values, 1, 0, token.NoPos, false)
  1632  		}
  1633  		p.setComment(s.Comment)
  1634  
  1635  	case *ast.TypeSpec:
  1636  		p.setComment(s.Doc)
  1637  		p.expr(s.Name)
  1638  		if tparams := typeparams.Get(s); tparams != nil {
  1639  			p.parameters(tparams, true)
  1640  		}
  1641  		if n == 1 {
  1642  			p.print(blank)
  1643  		} else {
  1644  			p.print(vtab)
  1645  		}
  1646  		if s.Assign.IsValid() {
  1647  			p.print(token.ASSIGN, blank)
  1648  		}
  1649  		p.expr(s.Type)
  1650  		p.setComment(s.Comment)
  1651  
  1652  	default:
  1653  		panic("unreachable")
  1654  	}
  1655  }
  1656  
  1657  func (p *printer) genDecl(d *ast.GenDecl) {
  1658  	p.setComment(d.Doc)
  1659  	p.print(d.Pos(), d.Tok, blank)
  1660  
  1661  	if d.Lparen.IsValid() || len(d.Specs) > 1 {
  1662  		// group of parenthesized declarations
  1663  		p.print(d.Lparen, token.LPAREN)
  1664  		if n := len(d.Specs); n > 0 {
  1665  			p.print(indent, formfeed)
  1666  			if n > 1 && (d.Tok == token.CONST || d.Tok == token.VAR) {
  1667  				// two or more grouped const/var declarations:
  1668  				// determine if the type column must be kept
  1669  				keepType := keepTypeColumn(d.Specs)
  1670  				var line int
  1671  				for i, s := range d.Specs {
  1672  					if i > 0 {
  1673  						p.linebreak(p.lineFor(s.Pos()), 1, ignore, p.linesFrom(line) > 0)
  1674  					}
  1675  					p.recordLine(&line)
  1676  					p.valueSpec(s.(*ast.ValueSpec), keepType[i])
  1677  				}
  1678  			} else {
  1679  				var line int
  1680  				for i, s := range d.Specs {
  1681  					if i > 0 {
  1682  						p.linebreak(p.lineFor(s.Pos()), 1, ignore, p.linesFrom(line) > 0)
  1683  					}
  1684  					p.recordLine(&line)
  1685  					p.spec(s, n, false)
  1686  				}
  1687  			}
  1688  			p.print(unindent, formfeed)
  1689  		}
  1690  		p.print(d.Rparen, token.RPAREN)
  1691  
  1692  	} else if len(d.Specs) > 0 {
  1693  		// single declaration
  1694  		p.spec(d.Specs[0], 1, true)
  1695  	}
  1696  }
  1697  
  1698  // nodeSize determines the size of n in chars after formatting.
  1699  // The result is <= maxSize if the node fits on one line with at
  1700  // most maxSize chars and the formatted output doesn't contain
  1701  // any control chars. Otherwise, the result is > maxSize.
  1702  //
  1703  func (p *printer) nodeSize(n ast.Node, maxSize int) (size int) {
  1704  	// nodeSize invokes the printer, which may invoke nodeSize
  1705  	// recursively. For deep composite literal nests, this can
  1706  	// lead to an exponential algorithm. Remember previous
  1707  	// results to prune the recursion (was issue 1628).
  1708  	if size, found := p.nodeSizes[n]; found {
  1709  		return size
  1710  	}
  1711  
  1712  	size = maxSize + 1 // assume n doesn't fit
  1713  	p.nodeSizes[n] = size
  1714  
  1715  	// nodeSize computation must be independent of particular
  1716  	// style so that we always get the same decision; print
  1717  	// in RawFormat
  1718  	cfg := Config{Mode: RawFormat}
  1719  	var buf bytes.Buffer
  1720  	if err := cfg.fprint(&buf, p.fset, n, p.nodeSizes); err != nil {
  1721  		return
  1722  	}
  1723  	if buf.Len() <= maxSize {
  1724  		for _, ch := range buf.Bytes() {
  1725  			if ch < ' ' {
  1726  				return
  1727  			}
  1728  		}
  1729  		size = buf.Len() // n fits
  1730  		p.nodeSizes[n] = size
  1731  	}
  1732  	return
  1733  }
  1734  
  1735  // numLines returns the number of lines spanned by node n in the original source.
  1736  func (p *printer) numLines(n ast.Node) int {
  1737  	if from := n.Pos(); from.IsValid() {
  1738  		if to := n.End(); to.IsValid() {
  1739  			return p.lineFor(to) - p.lineFor(from) + 1
  1740  		}
  1741  	}
  1742  	return infinity
  1743  }
  1744  
  1745  // bodySize is like nodeSize but it is specialized for *ast.BlockStmt's.
  1746  func (p *printer) bodySize(b *ast.BlockStmt, maxSize int) int {
  1747  	pos1 := b.Pos()
  1748  	pos2 := b.Rbrace
  1749  	if pos1.IsValid() && pos2.IsValid() && p.lineFor(pos1) != p.lineFor(pos2) {
  1750  		// opening and closing brace are on different lines - don't make it a one-liner
  1751  		return maxSize + 1
  1752  	}
  1753  	if len(b.List) > 5 {
  1754  		// too many statements - don't make it a one-liner
  1755  		return maxSize + 1
  1756  	}
  1757  	// otherwise, estimate body size
  1758  	bodySize := p.commentSizeBefore(p.posFor(pos2))
  1759  	for i, s := range b.List {
  1760  		if bodySize > maxSize {
  1761  			break // no need to continue
  1762  		}
  1763  		if i > 0 {
  1764  			bodySize += 2 // space for a semicolon and blank
  1765  		}
  1766  		bodySize += p.nodeSize(s, maxSize)
  1767  	}
  1768  	return bodySize
  1769  }
  1770  
  1771  // funcBody prints a function body following a function header of given headerSize.
  1772  // If the header's and block's size are "small enough" and the block is "simple enough",
  1773  // the block is printed on the current line, without line breaks, spaced from the header
  1774  // by sep. Otherwise the block's opening "{" is printed on the current line, followed by
  1775  // lines for the block's statements and its closing "}".
  1776  //
  1777  func (p *printer) funcBody(headerSize int, sep whiteSpace, b *ast.BlockStmt) {
  1778  	if b == nil {
  1779  		return
  1780  	}
  1781  
  1782  	// save/restore composite literal nesting level
  1783  	defer func(level int) {
  1784  		p.level = level
  1785  	}(p.level)
  1786  	p.level = 0
  1787  
  1788  	const maxSize = 100
  1789  	if headerSize+p.bodySize(b, maxSize) <= maxSize {
  1790  		p.print(sep, b.Lbrace, token.LBRACE)
  1791  		if len(b.List) > 0 {
  1792  			p.print(blank)
  1793  			for i, s := range b.List {
  1794  				if i > 0 {
  1795  					p.print(token.SEMICOLON, blank)
  1796  				}
  1797  				p.stmt(s, i == len(b.List)-1)
  1798  			}
  1799  			p.print(blank)
  1800  		}
  1801  		p.print(noExtraLinebreak, b.Rbrace, token.RBRACE, noExtraLinebreak)
  1802  		return
  1803  	}
  1804  
  1805  	if sep != ignore {
  1806  		p.print(blank) // always use blank
  1807  	}
  1808  	p.block(b, 1)
  1809  }
  1810  
  1811  // distanceFrom returns the column difference between p.out (the current output
  1812  // position) and startOutCol. If the start position is on a different line from
  1813  // the current position (or either is unknown), the result is infinity.
  1814  func (p *printer) distanceFrom(startPos token.Pos, startOutCol int) int {
  1815  	if startPos.IsValid() && p.pos.IsValid() && p.posFor(startPos).Line == p.pos.Line {
  1816  		return p.out.Column - startOutCol
  1817  	}
  1818  	return infinity
  1819  }
  1820  
  1821  func (p *printer) funcDecl(d *ast.FuncDecl) {
  1822  	p.setComment(d.Doc)
  1823  	p.print(d.Pos(), token.FUNC, blank)
  1824  	// We have to save startCol only after emitting FUNC; otherwise it can be on a
  1825  	// different line (all whitespace preceding the FUNC is emitted only when the
  1826  	// FUNC is emitted).
  1827  	startCol := p.out.Column - len("func ")
  1828  	if d.Recv != nil {
  1829  		p.parameters(d.Recv, false) // method: print receiver
  1830  		p.print(blank)
  1831  	}
  1832  	p.expr(d.Name)
  1833  	p.signature(d.Type)
  1834  	p.funcBody(p.distanceFrom(d.Pos(), startCol), vtab, d.Body)
  1835  }
  1836  
  1837  func (p *printer) decl(decl ast.Decl) {
  1838  	switch d := decl.(type) {
  1839  	case *ast.BadDecl:
  1840  		p.print(d.Pos(), "BadDecl")
  1841  	case *ast.GenDecl:
  1842  		p.genDecl(d)
  1843  	case *ast.FuncDecl:
  1844  		p.funcDecl(d)
  1845  	default:
  1846  		panic("unreachable")
  1847  	}
  1848  }
  1849  
  1850  // ----------------------------------------------------------------------------
  1851  // Files
  1852  
  1853  func declToken(decl ast.Decl) (tok token.Token) {
  1854  	tok = token.ILLEGAL
  1855  	switch d := decl.(type) {
  1856  	case *ast.GenDecl:
  1857  		tok = d.Tok
  1858  	case *ast.FuncDecl:
  1859  		tok = token.FUNC
  1860  	}
  1861  	return
  1862  }
  1863  
  1864  func (p *printer) declList(list []ast.Decl) {
  1865  	tok := token.ILLEGAL
  1866  	for _, d := range list {
  1867  		prev := tok
  1868  		tok = declToken(d)
  1869  		// If the declaration token changed (e.g., from CONST to TYPE)
  1870  		// or the next declaration has documentation associated with it,
  1871  		// print an empty line between top-level declarations.
  1872  		// (because p.linebreak is called with the position of d, which
  1873  		// is past any documentation, the minimum requirement is satisfied
  1874  		// even w/o the extra getDoc(d) nil-check - leave it in case the
  1875  		// linebreak logic improves - there's already a TODO).
  1876  		if len(p.output) > 0 {
  1877  			// only print line break if we are not at the beginning of the output
  1878  			// (i.e., we are not printing only a partial program)
  1879  			min := 1
  1880  			if prev != tok || getDoc(d) != nil {
  1881  				min = 2
  1882  			}
  1883  			// start a new section if the next declaration is a function
  1884  			// that spans multiple lines (see also issue #19544)
  1885  			p.linebreak(p.lineFor(d.Pos()), min, ignore, tok == token.FUNC && p.numLines(d) > 1)
  1886  		}
  1887  		p.decl(d)
  1888  	}
  1889  }
  1890  
  1891  func (p *printer) file(src *ast.File) {
  1892  	p.setComment(src.Doc)
  1893  	p.print(src.Pos(), token.PACKAGE, blank)
  1894  	p.expr(src.Name)
  1895  	p.declList(src.Decls)
  1896  	p.print(newline)
  1897  }
  1898  

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