Source file src/go/printer/nodes.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  // 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  	"go/ast"
    13  	"go/token"
    14  	"math"
    15  	"strconv"
    16  	"strings"
    17  	"unicode"
    18  	"unicode/utf8"
    19  )
    20  
    21  // Formatting issues:
    22  // - better comment formatting for /*-style comments at the end of a line (e.g. a declaration)
    23  //   when the comment spans multiple lines; if such a comment is just two lines, formatting is
    24  //   not idempotent
    25  // - formatting of expression lists
    26  // - should use blank instead of tab to separate one-line function bodies from
    27  //   the function header unless there is a group of consecutive one-liners
    28  
    29  // ----------------------------------------------------------------------------
    30  // Common AST nodes.
    31  
    32  // Print as many newlines as necessary (but at least min newlines) to get to
    33  // the current line. ws is printed before the first line break. If newSection
    34  // is set, the first line break is printed as formfeed. Returns 0 if no line
    35  // breaks were printed, returns 1 if there was exactly one newline printed,
    36  // and returns a value > 1 if there was a formfeed or more than one newline
    37  // printed.
    38  //
    39  // TODO(gri): linebreak may add too many lines if the next statement at "line"
    40  // is preceded by comments because the computation of n assumes
    41  // the current position before the comment and the target position
    42  // after the comment. Thus, after interspersing such comments, the
    43  // space taken up by them is not considered to reduce the number of
    44  // linebreaks. At the moment there is no easy way to know about
    45  // future (not yet interspersed) comments in this function.
    46  func (p *printer) linebreak(line, min int, ws whiteSpace, newSection bool) (nbreaks int) {
    47  	n := max(nlimit(line-p.pos.Line), min)
    48  	if n > 0 {
    49  		p.print(ws)
    50  		if newSection {
    51  			p.print(formfeed)
    52  			n--
    53  			nbreaks = 2
    54  		}
    55  		nbreaks += n
    56  		for ; n > 0; n-- {
    57  			p.print(newline)
    58  		}
    59  	}
    60  	return
    61  }
    62  
    63  // setComment sets g as the next comment if g != nil and if node comments
    64  // are enabled - this mode is used when printing source code fragments such
    65  // as exports only. It assumes that there is no pending comment in p.comments
    66  // and at most one pending comment in the p.comment cache.
    67  func (p *printer) setComment(g *ast.CommentGroup) {
    68  	if g == nil || !p.useNodeComments {
    69  		return
    70  	}
    71  	if p.comments == nil {
    72  		// initialize p.comments lazily
    73  		p.comments = make([]*ast.CommentGroup, 1)
    74  	} else if p.cindex < len(p.comments) {
    75  		// for some reason there are pending comments; this
    76  		// should never happen - handle gracefully and flush
    77  		// all comments up to g, ignore anything after that
    78  		p.flush(p.posFor(g.List[0].Pos()), token.ILLEGAL)
    79  		p.comments = p.comments[0:1]
    80  		// in debug mode, report error
    81  		p.internalError("setComment found pending comments")
    82  	}
    83  	p.comments[0] = g
    84  	p.cindex = 0
    85  	// don't overwrite any pending comment in the p.comment cache
    86  	// (there may be a pending comment when a line comment is
    87  	// immediately followed by a lead comment with no other
    88  	// tokens between)
    89  	if p.commentOffset == infinity {
    90  		p.nextComment() // get comment ready for use
    91  	}
    92  }
    93  
    94  type exprListMode uint
    95  
    96  const (
    97  	commaTerm exprListMode = 1 << iota // list is optionally terminated by a comma
    98  	noIndent                           // no extra indentation in multi-line lists
    99  )
   100  
   101  // If indent is set, a multi-line identifier list is indented after the
   102  // first linebreak encountered.
   103  func (p *printer) identList(list []*ast.Ident, indent bool) {
   104  	// convert into an expression list so we can re-use exprList formatting
   105  	xlist := make([]ast.Expr, len(list))
   106  	for i, x := range list {
   107  		xlist[i] = x
   108  	}
   109  	var mode exprListMode
   110  	if !indent {
   111  		mode = noIndent
   112  	}
   113  	p.exprList(token.NoPos, xlist, 1, mode, token.NoPos, false)
   114  }
   115  
   116  const filteredMsg = "contains filtered or unexported fields"
   117  
   118  // Print a list of expressions. If the list spans multiple
   119  // source lines, the original line breaks are respected between
   120  // expressions.
   121  //
   122  // TODO(gri) Consider rewriting this to be independent of []ast.Expr
   123  // so that we can use the algorithm for any kind of list
   124  //
   125  //	(e.g., pass list via a channel over which to range).
   126  func (p *printer) exprList(prev0 token.Pos, list []ast.Expr, depth int, mode exprListMode, next0 token.Pos, isIncomplete bool) {
   127  	if len(list) == 0 {
   128  		if isIncomplete {
   129  			prev := p.posFor(prev0)
   130  			next := p.posFor(next0)
   131  			if prev.IsValid() && prev.Line == next.Line {
   132  				p.print("/* " + filteredMsg + " */")
   133  			} else {
   134  				p.print(newline)
   135  				p.print(indent, "// "+filteredMsg, unindent, newline)
   136  			}
   137  		}
   138  		return
   139  	}
   140  
   141  	prev := p.posFor(prev0)
   142  	next := p.posFor(next0)
   143  	line := p.lineFor(list[0].Pos())
   144  	endLine := p.lineFor(list[len(list)-1].End())
   145  
   146  	if prev.IsValid() && prev.Line == line && line == endLine {
   147  		// all list entries on a single line
   148  		for i, x := range list {
   149  			if i > 0 {
   150  				// use position of expression following the comma as
   151  				// comma position for correct comment placement
   152  				p.setPos(x.Pos())
   153  				p.print(token.COMMA, blank)
   154  			}
   155  			p.expr0(x, depth)
   156  		}
   157  		if isIncomplete {
   158  			p.print(token.COMMA, blank, "/* "+filteredMsg+" */")
   159  		}
   160  		return
   161  	}
   162  
   163  	// list entries span multiple lines;
   164  	// use source code positions to guide line breaks
   165  
   166  	// Don't add extra indentation if noIndent is set;
   167  	// i.e., pretend that the first line is already indented.
   168  	ws := ignore
   169  	if mode&noIndent == 0 {
   170  		ws = indent
   171  	}
   172  
   173  	// The first linebreak is always a formfeed since this section must not
   174  	// depend on any previous formatting.
   175  	prevBreak := -1 // index of last expression that was followed by a linebreak
   176  	if prev.IsValid() && prev.Line < line && p.linebreak(line, 0, ws, true) > 0 {
   177  		ws = ignore
   178  		prevBreak = 0
   179  	}
   180  
   181  	// initialize expression/key size: a zero value indicates expr/key doesn't fit on a single line
   182  	size := 0
   183  
   184  	// We use the ratio between the geometric mean of the previous key sizes and
   185  	// the current size to determine if there should be a break in the alignment.
   186  	// To compute the geometric mean we accumulate the ln(size) values (lnsum)
   187  	// and the number of sizes included (count).
   188  	lnsum := 0.0
   189  	count := 0
   190  
   191  	// print all list elements
   192  	prevLine := prev.Line
   193  	for i, x := range list {
   194  		line = p.lineFor(x.Pos())
   195  
   196  		// Determine if the next linebreak, if any, needs to use formfeed:
   197  		// in general, use the entire node size to make the decision; for
   198  		// key:value expressions, use the key size.
   199  		// TODO(gri) for a better result, should probably incorporate both
   200  		//           the key and the node size into the decision process
   201  		useFF := true
   202  
   203  		// Determine element size: All bets are off if we don't have
   204  		// position information for the previous and next token (likely
   205  		// generated code - simply ignore the size in this case by setting
   206  		// it to 0).
   207  		prevSize := size
   208  		const infinity = 1e6 // larger than any source line
   209  		size = p.nodeSize(x, infinity)
   210  		pair, isPair := x.(*ast.KeyValueExpr)
   211  		if size <= infinity && prev.IsValid() && next.IsValid() {
   212  			// x fits on a single line
   213  			if isPair {
   214  				size = p.nodeSize(pair.Key, infinity) // size <= infinity
   215  			}
   216  		} else {
   217  			// size too large or we don't have good layout information
   218  			size = 0
   219  		}
   220  
   221  		// If the previous line and the current line had single-
   222  		// line-expressions and the key sizes are small or the
   223  		// ratio between the current key and the geometric mean
   224  		// if the previous key sizes does not exceed a threshold,
   225  		// align columns and do not use formfeed.
   226  		if prevSize > 0 && size > 0 {
   227  			const smallSize = 40
   228  			if count == 0 || prevSize <= smallSize && size <= smallSize {
   229  				useFF = false
   230  			} else {
   231  				const r = 2.5                               // threshold
   232  				geomean := math.Exp(lnsum / float64(count)) // count > 0
   233  				ratio := float64(size) / geomean
   234  				useFF = r*ratio <= 1 || r <= ratio
   235  			}
   236  		}
   237  
   238  		needsLinebreak := 0 < prevLine && prevLine < line
   239  		if i > 0 {
   240  			// Use position of expression following the comma as
   241  			// comma position for correct comment placement, but
   242  			// only if the expression is on the same line.
   243  			if !needsLinebreak {
   244  				p.setPos(x.Pos())
   245  			}
   246  			p.print(token.COMMA)
   247  			needsBlank := true
   248  			if needsLinebreak {
   249  				// Lines are broken using newlines so comments remain aligned
   250  				// unless useFF is set or there are multiple expressions on
   251  				// the same line in which case formfeed is used.
   252  				nbreaks := p.linebreak(line, 0, ws, useFF || prevBreak+1 < i)
   253  				if nbreaks > 0 {
   254  					ws = ignore
   255  					prevBreak = i
   256  					needsBlank = false // we got a line break instead
   257  				}
   258  				// If there was a new section or more than one new line
   259  				// (which means that the tabwriter will implicitly break
   260  				// the section), reset the geomean variables since we are
   261  				// starting a new group of elements with the next element.
   262  				if nbreaks > 1 {
   263  					lnsum = 0
   264  					count = 0
   265  				}
   266  			}
   267  			if needsBlank {
   268  				p.print(blank)
   269  			}
   270  		}
   271  
   272  		if len(list) > 1 && isPair && size > 0 && needsLinebreak {
   273  			// We have a key:value expression that fits onto one line
   274  			// and it's not on the same line as the prior expression:
   275  			// Use a column for the key such that consecutive entries
   276  			// can align if possible.
   277  			// (needsLinebreak is set if we started a new line before)
   278  			p.expr(pair.Key)
   279  			p.setPos(pair.Colon)
   280  			p.print(token.COLON, vtab)
   281  			p.expr(pair.Value)
   282  		} else {
   283  			p.expr0(x, depth)
   284  		}
   285  
   286  		if size > 0 {
   287  			lnsum += math.Log(float64(size))
   288  			count++
   289  		}
   290  
   291  		prevLine = line
   292  	}
   293  
   294  	if mode&commaTerm != 0 && next.IsValid() && p.pos.Line < next.Line {
   295  		// Print a terminating comma if the next token is on a new line.
   296  		p.print(token.COMMA)
   297  		if isIncomplete {
   298  			p.print(newline)
   299  			p.print("// " + filteredMsg)
   300  		}
   301  		if ws == ignore && mode&noIndent == 0 {
   302  			// unindent if we indented
   303  			p.print(unindent)
   304  		}
   305  		p.print(formfeed) // terminating comma needs a line break to look good
   306  		return
   307  	}
   308  
   309  	if isIncomplete {
   310  		p.print(token.COMMA, newline)
   311  		p.print("// "+filteredMsg, newline)
   312  	}
   313  
   314  	if ws == ignore && mode&noIndent == 0 {
   315  		// unindent if we indented
   316  		p.print(unindent)
   317  	}
   318  }
   319  
   320  type paramMode int
   321  
   322  const (
   323  	funcParam paramMode = iota
   324  	funcTParam
   325  	typeTParam
   326  )
   327  
   328  func (p *printer) parameters(fields *ast.FieldList, mode paramMode) {
   329  	openTok, closeTok := token.LPAREN, token.RPAREN
   330  	if mode != funcParam {
   331  		openTok, closeTok = token.LBRACK, token.RBRACK
   332  	}
   333  	p.setPos(fields.Opening)
   334  	p.print(openTok)
   335  	if len(fields.List) > 0 {
   336  		prevLine := p.lineFor(fields.Opening)
   337  		ws := indent
   338  		for i, par := range fields.List {
   339  			// determine par begin and end line (may be different
   340  			// if there are multiple parameter names for this par
   341  			// or the type is on a separate line)
   342  			parLineBeg := p.lineFor(par.Pos())
   343  			parLineEnd := p.lineFor(par.End())
   344  			// separating "," if needed
   345  			needsLinebreak := 0 < prevLine && prevLine < parLineBeg
   346  			if i > 0 {
   347  				// use position of parameter following the comma as
   348  				// comma position for correct comma placement, but
   349  				// only if the next parameter is on the same line
   350  				if !needsLinebreak {
   351  					p.setPos(par.Pos())
   352  				}
   353  				p.print(token.COMMA)
   354  			}
   355  			// separator if needed (linebreak or blank)
   356  			if needsLinebreak && p.linebreak(parLineBeg, 0, ws, true) > 0 {
   357  				// break line if the opening "(" or previous parameter ended on a different line
   358  				ws = ignore
   359  			} else if i > 0 {
   360  				p.print(blank)
   361  			}
   362  			// parameter names
   363  			if len(par.Names) > 0 {
   364  				// Very subtle: If we indented before (ws == ignore), identList
   365  				// won't indent again. If we didn't (ws == indent), identList will
   366  				// indent if the identList spans multiple lines, and it will outdent
   367  				// again at the end (and still ws == indent). Thus, a subsequent indent
   368  				// by a linebreak call after a type, or in the next multi-line identList
   369  				// will do the right thing.
   370  				p.identList(par.Names, ws == indent)
   371  				p.print(blank)
   372  			}
   373  			// parameter type
   374  			p.expr(stripParensAlways(par.Type))
   375  			prevLine = parLineEnd
   376  		}
   377  
   378  		// if the closing ")" is on a separate line from the last parameter,
   379  		// print an additional "," and line break
   380  		if closing := p.lineFor(fields.Closing); 0 < prevLine && prevLine < closing {
   381  			p.print(token.COMMA)
   382  			p.linebreak(closing, 0, ignore, true)
   383  		} else if mode == typeTParam && fields.NumFields() == 1 && combinesWithName(fields.List[0].Type) {
   384  			// A type parameter list [P T] where the name P and the type expression T syntactically
   385  			// combine to another valid (value) expression requires a trailing comma, as in [P *T,]
   386  			// (or an enclosing interface as in [P interface(*T)]), so that the type parameter list
   387  			// is not parsed as an array length [P*T].
   388  			p.print(token.COMMA)
   389  		}
   390  
   391  		// unindent if we indented
   392  		if ws == ignore {
   393  			p.print(unindent)
   394  		}
   395  	}
   396  
   397  	p.setPos(fields.Closing)
   398  	p.print(closeTok)
   399  }
   400  
   401  // combinesWithName reports whether a name followed by the expression x
   402  // syntactically combines to another valid (value) expression. For instance
   403  // using *T for x, "name *T" syntactically appears as the expression x*T.
   404  // On the other hand, using  P|Q or *P|~Q for x, "name P|Q" or name *P|~Q"
   405  // cannot be combined into a valid (value) expression.
   406  func combinesWithName(x ast.Expr) bool {
   407  	switch x := x.(type) {
   408  	case *ast.StarExpr:
   409  		// name *x.X combines to name*x.X if x.X is not a type element
   410  		return !isTypeElem(x.X)
   411  	case *ast.BinaryExpr:
   412  		return combinesWithName(x.X) && !isTypeElem(x.Y)
   413  	case *ast.ParenExpr:
   414  		// name(x) combines but we are making sure at
   415  		// the call site that x is never parenthesized.
   416  		panic("unexpected parenthesized expression")
   417  	}
   418  	return false
   419  }
   420  
   421  // isTypeElem reports whether x is a (possibly parenthesized) type element expression.
   422  // The result is false if x could be a type element OR an ordinary (value) expression.
   423  func isTypeElem(x ast.Expr) bool {
   424  	switch x := x.(type) {
   425  	case *ast.ArrayType, *ast.StructType, *ast.FuncType, *ast.InterfaceType, *ast.MapType, *ast.ChanType:
   426  		return true
   427  	case *ast.UnaryExpr:
   428  		return x.Op == token.TILDE
   429  	case *ast.BinaryExpr:
   430  		return isTypeElem(x.X) || isTypeElem(x.Y)
   431  	case *ast.ParenExpr:
   432  		return isTypeElem(x.X)
   433  	}
   434  	return false
   435  }
   436  
   437  func (p *printer) signature(sig *ast.FuncType) {
   438  	if sig.TypeParams != nil {
   439  		p.parameters(sig.TypeParams, funcTParam)
   440  	}
   441  	if sig.Params != nil {
   442  		p.parameters(sig.Params, funcParam)
   443  	} else {
   444  		p.print(token.LPAREN, token.RPAREN)
   445  	}
   446  	res := sig.Results
   447  	n := res.NumFields()
   448  	if n > 0 {
   449  		// res != nil
   450  		p.print(blank)
   451  		if n == 1 && res.List[0].Names == nil {
   452  			// single anonymous res; no ()'s
   453  			p.expr(stripParensAlways(res.List[0].Type))
   454  			return
   455  		}
   456  		p.parameters(res, funcParam)
   457  	}
   458  }
   459  
   460  func identListSize(list []*ast.Ident, maxSize int) (size int) {
   461  	for i, x := range list {
   462  		if i > 0 {
   463  			size += len(", ")
   464  		}
   465  		size += utf8.RuneCountInString(x.Name)
   466  		if size >= maxSize {
   467  			break
   468  		}
   469  	}
   470  	return
   471  }
   472  
   473  func (p *printer) isOneLineFieldList(list []*ast.Field) bool {
   474  	if len(list) != 1 {
   475  		return false // allow only one field
   476  	}
   477  	f := list[0]
   478  	if f.Tag != nil || f.Comment != nil {
   479  		return false // don't allow tags or comments
   480  	}
   481  	// only name(s) and type
   482  	const maxSize = 30 // adjust as appropriate, this is an approximate value
   483  	namesSize := identListSize(f.Names, maxSize)
   484  	if namesSize > 0 {
   485  		namesSize = 1 // blank between names and types
   486  	}
   487  	typeSize := p.nodeSize(f.Type, maxSize)
   488  	return namesSize+typeSize <= maxSize
   489  }
   490  
   491  func (p *printer) setLineComment(text string) {
   492  	p.setComment(&ast.CommentGroup{List: []*ast.Comment{{Slash: token.NoPos, Text: text}}})
   493  }
   494  
   495  func (p *printer) fieldList(fields *ast.FieldList, isStruct, isIncomplete bool) {
   496  	lbrace := fields.Opening
   497  	list := fields.List
   498  	rbrace := fields.Closing
   499  	hasComments := isIncomplete || p.commentBefore(p.posFor(rbrace))
   500  	srcIsOneLine := lbrace.IsValid() && rbrace.IsValid() && p.lineFor(lbrace) == p.lineFor(rbrace)
   501  
   502  	if !hasComments && srcIsOneLine {
   503  		// possibly a one-line struct/interface
   504  		if len(list) == 0 {
   505  			// no blank between keyword and {} in this case
   506  			p.setPos(lbrace)
   507  			p.print(token.LBRACE)
   508  			p.setPos(rbrace)
   509  			p.print(token.RBRACE)
   510  			return
   511  		} else if p.isOneLineFieldList(list) {
   512  			// small enough - print on one line
   513  			// (don't use identList and ignore source line breaks)
   514  			p.setPos(lbrace)
   515  			p.print(token.LBRACE, blank)
   516  			f := list[0]
   517  			if isStruct {
   518  				for i, x := range f.Names {
   519  					if i > 0 {
   520  						// no comments so no need for comma position
   521  						p.print(token.COMMA, blank)
   522  					}
   523  					p.expr(x)
   524  				}
   525  				if len(f.Names) > 0 {
   526  					p.print(blank)
   527  				}
   528  				p.expr(f.Type)
   529  			} else { // interface
   530  				if len(f.Names) > 0 {
   531  					name := f.Names[0] // method name
   532  					p.expr(name)
   533  					p.signature(f.Type.(*ast.FuncType)) // don't print "func"
   534  				} else {
   535  					// embedded interface
   536  					p.expr(f.Type)
   537  				}
   538  			}
   539  			p.print(blank)
   540  			p.setPos(rbrace)
   541  			p.print(token.RBRACE)
   542  			return
   543  		}
   544  	}
   545  	// hasComments || !srcIsOneLine
   546  
   547  	p.print(blank)
   548  	p.setPos(lbrace)
   549  	p.print(token.LBRACE, indent)
   550  	if hasComments || len(list) > 0 {
   551  		p.print(formfeed)
   552  	}
   553  
   554  	if isStruct {
   555  
   556  		sep := vtab
   557  		if len(list) == 1 {
   558  			sep = blank
   559  		}
   560  		var line int
   561  		for i, f := range list {
   562  			if i > 0 {
   563  				p.linebreak(p.lineFor(f.Pos()), 1, ignore, p.linesFrom(line) > 0)
   564  			}
   565  			extraTabs := 0
   566  			p.setComment(f.Doc)
   567  			p.recordLine(&line)
   568  			if len(f.Names) > 0 {
   569  				// named fields
   570  				p.identList(f.Names, false)
   571  				p.print(sep)
   572  				p.expr(f.Type)
   573  				extraTabs = 1
   574  			} else {
   575  				// anonymous field
   576  				p.expr(f.Type)
   577  				extraTabs = 2
   578  			}
   579  			if f.Tag != nil {
   580  				if len(f.Names) > 0 && sep == vtab {
   581  					p.print(sep)
   582  				}
   583  				p.print(sep)
   584  				p.expr(f.Tag)
   585  				extraTabs = 0
   586  			}
   587  			if f.Comment != nil {
   588  				for ; extraTabs > 0; extraTabs-- {
   589  					p.print(sep)
   590  				}
   591  				p.setComment(f.Comment)
   592  			}
   593  		}
   594  		if isIncomplete {
   595  			if len(list) > 0 {
   596  				p.print(formfeed)
   597  			}
   598  			p.flush(p.posFor(rbrace), token.RBRACE) // make sure we don't lose the last line comment
   599  			p.setLineComment("// " + filteredMsg)
   600  		}
   601  
   602  	} else { // interface
   603  
   604  		var line int
   605  		var prev *ast.Ident // previous "type" identifier
   606  		for i, f := range list {
   607  			var name *ast.Ident // first name, or nil
   608  			if len(f.Names) > 0 {
   609  				name = f.Names[0]
   610  			}
   611  			if i > 0 {
   612  				// don't do a line break (min == 0) if we are printing a list of types
   613  				// TODO(gri) this doesn't work quite right if the list of types is
   614  				//           spread across multiple lines
   615  				min := 1
   616  				if prev != nil && name == prev {
   617  					min = 0
   618  				}
   619  				p.linebreak(p.lineFor(f.Pos()), min, ignore, p.linesFrom(line) > 0)
   620  			}
   621  			p.setComment(f.Doc)
   622  			p.recordLine(&line)
   623  			if name != nil {
   624  				// method
   625  				p.expr(name)
   626  				p.signature(f.Type.(*ast.FuncType)) // don't print "func"
   627  				prev = nil
   628  			} else {
   629  				// embedded interface
   630  				p.expr(f.Type)
   631  				prev = nil
   632  			}
   633  			p.setComment(f.Comment)
   634  		}
   635  		if isIncomplete {
   636  			if len(list) > 0 {
   637  				p.print(formfeed)
   638  			}
   639  			p.flush(p.posFor(rbrace), token.RBRACE) // make sure we don't lose the last line comment
   640  			p.setLineComment("// contains filtered or unexported methods")
   641  		}
   642  
   643  	}
   644  	p.print(unindent, formfeed)
   645  	p.setPos(rbrace)
   646  	p.print(token.RBRACE)
   647  }
   648  
   649  // ----------------------------------------------------------------------------
   650  // Expressions
   651  
   652  func walkBinary(e *ast.BinaryExpr) (has4, has5 bool, maxProblem int) {
   653  	switch e.Op.Precedence() {
   654  	case 4:
   655  		has4 = true
   656  	case 5:
   657  		has5 = true
   658  	}
   659  
   660  	switch l := e.X.(type) {
   661  	case *ast.BinaryExpr:
   662  		if l.Op.Precedence() < e.Op.Precedence() {
   663  			// parens will be inserted.
   664  			// pretend this is an *ast.ParenExpr and do nothing.
   665  			break
   666  		}
   667  		h4, h5, mp := walkBinary(l)
   668  		has4 = has4 || h4
   669  		has5 = has5 || h5
   670  		maxProblem = max(maxProblem, mp)
   671  	}
   672  
   673  	switch r := e.Y.(type) {
   674  	case *ast.BinaryExpr:
   675  		if r.Op.Precedence() <= e.Op.Precedence() {
   676  			// parens will be inserted.
   677  			// pretend this is an *ast.ParenExpr and do nothing.
   678  			break
   679  		}
   680  		h4, h5, mp := walkBinary(r)
   681  		has4 = has4 || h4
   682  		has5 = has5 || h5
   683  		maxProblem = max(maxProblem, mp)
   684  
   685  	case *ast.StarExpr:
   686  		if e.Op == token.QUO { // `*/`
   687  			maxProblem = 5
   688  		}
   689  
   690  	case *ast.UnaryExpr:
   691  		switch e.Op.String() + r.Op.String() {
   692  		case "/*", "&&", "&^":
   693  			maxProblem = 5
   694  		case "++", "--":
   695  			maxProblem = max(maxProblem, 4)
   696  		}
   697  	}
   698  	return
   699  }
   700  
   701  func cutoff(e *ast.BinaryExpr, depth int) int {
   702  	has4, has5, maxProblem := walkBinary(e)
   703  	if maxProblem > 0 {
   704  		return maxProblem + 1
   705  	}
   706  	if has4 && has5 {
   707  		if depth == 1 {
   708  			return 5
   709  		}
   710  		return 4
   711  	}
   712  	if depth == 1 {
   713  		return 6
   714  	}
   715  	return 4
   716  }
   717  
   718  func diffPrec(expr ast.Expr, prec int) int {
   719  	x, ok := expr.(*ast.BinaryExpr)
   720  	if !ok || prec != x.Op.Precedence() {
   721  		return 1
   722  	}
   723  	return 0
   724  }
   725  
   726  func reduceDepth(depth int) int {
   727  	depth--
   728  	if depth < 1 {
   729  		depth = 1
   730  	}
   731  	return depth
   732  }
   733  
   734  // Format the binary expression: decide the cutoff and then format.
   735  // Let's call depth == 1 Normal mode, and depth > 1 Compact mode.
   736  // (Algorithm suggestion by Russ Cox.)
   737  //
   738  // The precedences are:
   739  //
   740  //	5             *  /  %  <<  >>  &  &^
   741  //	4             +  -  |  ^
   742  //	3             ==  !=  <  <=  >  >=
   743  //	2             &&
   744  //	1             ||
   745  //
   746  // The only decision is whether there will be spaces around levels 4 and 5.
   747  // There are never spaces at level 6 (unary), and always spaces at levels 3 and below.
   748  //
   749  // To choose the cutoff, look at the whole expression but excluding primary
   750  // expressions (function calls, parenthesized exprs), and apply these rules:
   751  //
   752  //  1. If there is a binary operator with a right side unary operand
   753  //     that would clash without a space, the cutoff must be (in order):
   754  //
   755  //     /*	6
   756  //     &&	6
   757  //     &^	6
   758  //     ++	5
   759  //     --	5
   760  //
   761  //     (Comparison operators always have spaces around them.)
   762  //
   763  //  2. If there is a mix of level 5 and level 4 operators, then the cutoff
   764  //     is 5 (use spaces to distinguish precedence) in Normal mode
   765  //     and 4 (never use spaces) in Compact mode.
   766  //
   767  //  3. If there are no level 4 operators or no level 5 operators, then the
   768  //     cutoff is 6 (always use spaces) in Normal mode
   769  //     and 4 (never use spaces) in Compact mode.
   770  func (p *printer) binaryExpr(x *ast.BinaryExpr, prec1, cutoff, depth int) {
   771  	prec := x.Op.Precedence()
   772  	if prec < prec1 {
   773  		// parenthesis needed
   774  		// Note: The parser inserts an ast.ParenExpr node; thus this case
   775  		//       can only occur if the AST is created in a different way.
   776  		p.print(token.LPAREN)
   777  		p.expr0(x, reduceDepth(depth)) // parentheses undo one level of depth
   778  		p.print(token.RPAREN)
   779  		return
   780  	}
   781  
   782  	printBlank := prec < cutoff
   783  
   784  	ws := indent
   785  	p.expr1(x.X, prec, depth+diffPrec(x.X, prec))
   786  	if printBlank {
   787  		p.print(blank)
   788  	}
   789  	xline := p.pos.Line // before the operator (it may be on the next line!)
   790  	yline := p.lineFor(x.Y.Pos())
   791  	p.setPos(x.OpPos)
   792  	p.print(x.Op)
   793  	if xline != yline && xline > 0 && yline > 0 {
   794  		// at least one line break, but respect an extra empty line
   795  		// in the source
   796  		if p.linebreak(yline, 1, ws, true) > 0 {
   797  			ws = ignore
   798  			printBlank = false // no blank after line break
   799  		}
   800  	}
   801  	if printBlank {
   802  		p.print(blank)
   803  	}
   804  	p.expr1(x.Y, prec+1, depth+1)
   805  	if ws == ignore {
   806  		p.print(unindent)
   807  	}
   808  }
   809  
   810  func isBinary(expr ast.Expr) bool {
   811  	_, ok := expr.(*ast.BinaryExpr)
   812  	return ok
   813  }
   814  
   815  func (p *printer) expr1(expr ast.Expr, prec1, depth int) {
   816  	p.setPos(expr.Pos())
   817  
   818  	switch x := expr.(type) {
   819  	case *ast.BadExpr:
   820  		p.print("BadExpr")
   821  
   822  	case *ast.Ident:
   823  		p.print(x)
   824  
   825  	case *ast.BinaryExpr:
   826  		if depth < 1 {
   827  			p.internalError("depth < 1:", depth)
   828  			depth = 1
   829  		}
   830  		p.binaryExpr(x, prec1, cutoff(x, depth), depth)
   831  
   832  	case *ast.KeyValueExpr:
   833  		p.expr(x.Key)
   834  		p.setPos(x.Colon)
   835  		p.print(token.COLON, blank)
   836  		p.expr(x.Value)
   837  
   838  	case *ast.StarExpr:
   839  		const prec = token.UnaryPrec
   840  		if prec < prec1 {
   841  			// parenthesis needed
   842  			p.print(token.LPAREN)
   843  			p.print(token.MUL)
   844  			p.expr(x.X)
   845  			p.print(token.RPAREN)
   846  		} else {
   847  			// no parenthesis needed
   848  			p.print(token.MUL)
   849  			p.expr(x.X)
   850  		}
   851  
   852  	case *ast.UnaryExpr:
   853  		const prec = token.UnaryPrec
   854  		if prec < prec1 {
   855  			// parenthesis needed
   856  			p.print(token.LPAREN)
   857  			p.expr(x)
   858  			p.print(token.RPAREN)
   859  		} else {
   860  			// no parenthesis needed
   861  			p.print(x.Op)
   862  			if x.Op == token.RANGE {
   863  				// TODO(gri) Remove this code if it cannot be reached.
   864  				p.print(blank)
   865  			}
   866  			p.expr1(x.X, prec, depth)
   867  		}
   868  
   869  	case *ast.BasicLit:
   870  		if p.Config.Mode&normalizeNumbers != 0 {
   871  			x = normalizedNumber(x)
   872  		}
   873  		p.print(x)
   874  
   875  	case *ast.FuncLit:
   876  		p.setPos(x.Type.Pos())
   877  		p.print(token.FUNC)
   878  		// See the comment in funcDecl about how the header size is computed.
   879  		startCol := p.out.Column - len("func")
   880  		p.signature(x.Type)
   881  		p.funcBody(p.distanceFrom(x.Type.Pos(), startCol), blank, x.Body)
   882  
   883  	case *ast.ParenExpr:
   884  		if _, hasParens := x.X.(*ast.ParenExpr); hasParens {
   885  			// don't print parentheses around an already parenthesized expression
   886  			// TODO(gri) consider making this more general and incorporate precedence levels
   887  			p.expr0(x.X, depth)
   888  		} else {
   889  			p.print(token.LPAREN)
   890  			p.expr0(x.X, reduceDepth(depth)) // parentheses undo one level of depth
   891  			p.setPos(x.Rparen)
   892  			p.print(token.RPAREN)
   893  		}
   894  
   895  	case *ast.SelectorExpr:
   896  		p.selectorExpr(x, depth, false)
   897  
   898  	case *ast.TypeAssertExpr:
   899  		p.expr1(x.X, token.HighestPrec, depth)
   900  		p.print(token.PERIOD)
   901  		p.setPos(x.Lparen)
   902  		p.print(token.LPAREN)
   903  		if x.Type != nil {
   904  			p.expr(x.Type)
   905  		} else {
   906  			p.print(token.TYPE)
   907  		}
   908  		p.setPos(x.Rparen)
   909  		p.print(token.RPAREN)
   910  
   911  	case *ast.IndexExpr:
   912  		// TODO(gri): should treat[] like parentheses and undo one level of depth
   913  		p.expr1(x.X, token.HighestPrec, 1)
   914  		p.setPos(x.Lbrack)
   915  		p.print(token.LBRACK)
   916  		p.expr0(x.Index, depth+1)
   917  		p.setPos(x.Rbrack)
   918  		p.print(token.RBRACK)
   919  
   920  	case *ast.IndexListExpr:
   921  		// TODO(gri): as for IndexExpr, should treat [] like parentheses and undo
   922  		// one level of depth
   923  		p.expr1(x.X, token.HighestPrec, 1)
   924  		p.setPos(x.Lbrack)
   925  		p.print(token.LBRACK)
   926  		p.exprList(x.Lbrack, x.Indices, depth+1, commaTerm, x.Rbrack, false)
   927  		p.setPos(x.Rbrack)
   928  		p.print(token.RBRACK)
   929  
   930  	case *ast.SliceExpr:
   931  		// TODO(gri): should treat[] like parentheses and undo one level of depth
   932  		p.expr1(x.X, token.HighestPrec, 1)
   933  		p.setPos(x.Lbrack)
   934  		p.print(token.LBRACK)
   935  		indices := []ast.Expr{x.Low, x.High}
   936  		if x.Max != nil {
   937  			indices = append(indices, x.Max)
   938  		}
   939  		// determine if we need extra blanks around ':'
   940  		var needsBlanks bool
   941  		if depth <= 1 {
   942  			var indexCount int
   943  			var hasBinaries bool
   944  			for _, x := range indices {
   945  				if x != nil {
   946  					indexCount++
   947  					if isBinary(x) {
   948  						hasBinaries = true
   949  					}
   950  				}
   951  			}
   952  			if indexCount > 1 && hasBinaries {
   953  				needsBlanks = true
   954  			}
   955  		}
   956  		for i, x := range indices {
   957  			if i > 0 {
   958  				if indices[i-1] != nil && needsBlanks {
   959  					p.print(blank)
   960  				}
   961  				p.print(token.COLON)
   962  				if x != nil && needsBlanks {
   963  					p.print(blank)
   964  				}
   965  			}
   966  			if x != nil {
   967  				p.expr0(x, depth+1)
   968  			}
   969  		}
   970  		p.setPos(x.Rbrack)
   971  		p.print(token.RBRACK)
   972  
   973  	case *ast.CallExpr:
   974  		if len(x.Args) > 1 {
   975  			depth++
   976  		}
   977  
   978  		// Conversions to literal function types or <-chan
   979  		// types require parentheses around the type.
   980  		paren := false
   981  		switch t := x.Fun.(type) {
   982  		case *ast.FuncType:
   983  			paren = true
   984  		case *ast.ChanType:
   985  			paren = t.Dir == ast.RECV
   986  		}
   987  		if paren {
   988  			p.print(token.LPAREN)
   989  		}
   990  		wasIndented := p.possibleSelectorExpr(x.Fun, token.HighestPrec, depth)
   991  		if paren {
   992  			p.print(token.RPAREN)
   993  		}
   994  
   995  		p.setPos(x.Lparen)
   996  		p.print(token.LPAREN)
   997  		if x.Ellipsis.IsValid() {
   998  			p.exprList(x.Lparen, x.Args, depth, 0, x.Ellipsis, false)
   999  			p.setPos(x.Ellipsis)
  1000  			p.print(token.ELLIPSIS)
  1001  			if x.Rparen.IsValid() && p.lineFor(x.Ellipsis) < p.lineFor(x.Rparen) {
  1002  				p.print(token.COMMA, formfeed)
  1003  			}
  1004  		} else {
  1005  			p.exprList(x.Lparen, x.Args, depth, commaTerm, x.Rparen, false)
  1006  		}
  1007  		p.setPos(x.Rparen)
  1008  		p.print(token.RPAREN)
  1009  		if wasIndented {
  1010  			p.print(unindent)
  1011  		}
  1012  
  1013  	case *ast.CompositeLit:
  1014  		// composite literal elements that are composite literals themselves may have the type omitted
  1015  		if x.Type != nil {
  1016  			p.expr1(x.Type, token.HighestPrec, depth)
  1017  		}
  1018  		p.level++
  1019  		p.setPos(x.Lbrace)
  1020  		p.print(token.LBRACE)
  1021  		p.exprList(x.Lbrace, x.Elts, 1, commaTerm, x.Rbrace, x.Incomplete)
  1022  		// do not insert extra line break following a /*-style comment
  1023  		// before the closing '}' as it might break the code if there
  1024  		// is no trailing ','
  1025  		mode := noExtraLinebreak
  1026  		// do not insert extra blank following a /*-style comment
  1027  		// before the closing '}' unless the literal is empty
  1028  		if len(x.Elts) > 0 {
  1029  			mode |= noExtraBlank
  1030  		}
  1031  		// need the initial indent to print lone comments with
  1032  		// the proper level of indentation
  1033  		p.print(indent, unindent, mode)
  1034  		p.setPos(x.Rbrace)
  1035  		p.print(token.RBRACE, mode)
  1036  		p.level--
  1037  
  1038  	case *ast.Ellipsis:
  1039  		p.print(token.ELLIPSIS)
  1040  		if x.Elt != nil {
  1041  			p.expr(x.Elt)
  1042  		}
  1043  
  1044  	case *ast.ArrayType:
  1045  		p.print(token.LBRACK)
  1046  		if x.Len != nil {
  1047  			p.expr(x.Len)
  1048  		}
  1049  		p.print(token.RBRACK)
  1050  		p.expr(x.Elt)
  1051  
  1052  	case *ast.StructType:
  1053  		p.print(token.STRUCT)
  1054  		p.fieldList(x.Fields, true, x.Incomplete)
  1055  
  1056  	case *ast.FuncType:
  1057  		p.print(token.FUNC)
  1058  		p.signature(x)
  1059  
  1060  	case *ast.InterfaceType:
  1061  		p.print(token.INTERFACE)
  1062  		p.fieldList(x.Methods, false, x.Incomplete)
  1063  
  1064  	case *ast.MapType:
  1065  		p.print(token.MAP, token.LBRACK)
  1066  		p.expr(x.Key)
  1067  		p.print(token.RBRACK)
  1068  		p.expr(x.Value)
  1069  
  1070  	case *ast.ChanType:
  1071  		switch x.Dir {
  1072  		case ast.SEND | ast.RECV:
  1073  			p.print(token.CHAN)
  1074  		case ast.RECV:
  1075  			p.print(token.ARROW, token.CHAN) // x.Arrow and x.Pos() are the same
  1076  		case ast.SEND:
  1077  			p.print(token.CHAN)
  1078  			p.setPos(x.Arrow)
  1079  			p.print(token.ARROW)
  1080  		}
  1081  		p.print(blank)
  1082  		p.expr(x.Value)
  1083  
  1084  	default:
  1085  		panic("unreachable")
  1086  	}
  1087  }
  1088  
  1089  // normalizedNumber rewrites base prefixes and exponents
  1090  // of numbers to use lower-case letters (0X123 to 0x123 and 1.2E3 to 1.2e3),
  1091  // and removes leading 0's from integer imaginary literals (0765i to 765i).
  1092  // It leaves hexadecimal digits alone.
  1093  //
  1094  // normalizedNumber doesn't modify the ast.BasicLit value lit points to.
  1095  // If lit is not a number or a number in canonical format already,
  1096  // lit is returned as is. Otherwise a new ast.BasicLit is created.
  1097  func normalizedNumber(lit *ast.BasicLit) *ast.BasicLit {
  1098  	if lit.Kind != token.INT && lit.Kind != token.FLOAT && lit.Kind != token.IMAG {
  1099  		return lit // not a number - nothing to do
  1100  	}
  1101  	if len(lit.Value) < 2 {
  1102  		return lit // only one digit (common case) - nothing to do
  1103  	}
  1104  	// len(lit.Value) >= 2
  1105  
  1106  	// We ignore lit.Kind because for lit.Kind == token.IMAG the literal may be an integer
  1107  	// or floating-point value, decimal or not. Instead, just consider the literal pattern.
  1108  	x := lit.Value
  1109  	switch x[:2] {
  1110  	default:
  1111  		// 0-prefix octal, decimal int, or float (possibly with 'i' suffix)
  1112  		if i := strings.LastIndexByte(x, 'E'); i >= 0 {
  1113  			x = x[:i] + "e" + x[i+1:]
  1114  			break
  1115  		}
  1116  		// remove leading 0's from integer (but not floating-point) imaginary literals
  1117  		if x[len(x)-1] == 'i' && !strings.ContainsAny(x, ".e") {
  1118  			x = strings.TrimLeft(x, "0_")
  1119  			if x == "i" {
  1120  				x = "0i"
  1121  			}
  1122  		}
  1123  	case "0X":
  1124  		x = "0x" + x[2:]
  1125  		// possibly a hexadecimal float
  1126  		if i := strings.LastIndexByte(x, 'P'); i >= 0 {
  1127  			x = x[:i] + "p" + x[i+1:]
  1128  		}
  1129  	case "0x":
  1130  		// possibly a hexadecimal float
  1131  		i := strings.LastIndexByte(x, 'P')
  1132  		if i == -1 {
  1133  			return lit // nothing to do
  1134  		}
  1135  		x = x[:i] + "p" + x[i+1:]
  1136  	case "0O":
  1137  		x = "0o" + x[2:]
  1138  	case "0o":
  1139  		return lit // nothing to do
  1140  	case "0B":
  1141  		x = "0b" + x[2:]
  1142  	case "0b":
  1143  		return lit // nothing to do
  1144  	}
  1145  
  1146  	return &ast.BasicLit{ValuePos: lit.ValuePos, Kind: lit.Kind, Value: x}
  1147  }
  1148  
  1149  func (p *printer) possibleSelectorExpr(expr ast.Expr, prec1, depth int) bool {
  1150  	if x, ok := expr.(*ast.SelectorExpr); ok {
  1151  		return p.selectorExpr(x, depth, true)
  1152  	}
  1153  	p.expr1(expr, prec1, depth)
  1154  	return false
  1155  }
  1156  
  1157  // selectorExpr handles an *ast.SelectorExpr node and reports whether x spans
  1158  // multiple lines.
  1159  func (p *printer) selectorExpr(x *ast.SelectorExpr, depth int, isMethod bool) bool {
  1160  	p.expr1(x.X, token.HighestPrec, depth)
  1161  	p.print(token.PERIOD)
  1162  	if line := p.lineFor(x.Sel.Pos()); p.pos.IsValid() && p.pos.Line < line {
  1163  		p.print(indent, newline)
  1164  		p.setPos(x.Sel.Pos())
  1165  		p.print(x.Sel)
  1166  		if !isMethod {
  1167  			p.print(unindent)
  1168  		}
  1169  		return true
  1170  	}
  1171  	p.setPos(x.Sel.Pos())
  1172  	p.print(x.Sel)
  1173  	return false
  1174  }
  1175  
  1176  func (p *printer) expr0(x ast.Expr, depth int) {
  1177  	p.expr1(x, token.LowestPrec, depth)
  1178  }
  1179  
  1180  func (p *printer) expr(x ast.Expr) {
  1181  	const depth = 1
  1182  	p.expr1(x, token.LowestPrec, depth)
  1183  }
  1184  
  1185  // ----------------------------------------------------------------------------
  1186  // Statements
  1187  
  1188  // Print the statement list indented, but without a newline after the last statement.
  1189  // Extra line breaks between statements in the source are respected but at most one
  1190  // empty line is printed between statements.
  1191  func (p *printer) stmtList(list []ast.Stmt, nindent int, nextIsRBrace bool) {
  1192  	if nindent > 0 {
  1193  		p.print(indent)
  1194  	}
  1195  	var line int
  1196  	i := 0
  1197  	for _, s := range list {
  1198  		// ignore empty statements (was issue 3466)
  1199  		if _, isEmpty := s.(*ast.EmptyStmt); !isEmpty {
  1200  			// nindent == 0 only for lists of switch/select case clauses;
  1201  			// in those cases each clause is a new section
  1202  			if len(p.output) > 0 {
  1203  				// only print line break if we are not at the beginning of the output
  1204  				// (i.e., we are not printing only a partial program)
  1205  				p.linebreak(p.lineFor(s.Pos()), 1, ignore, i == 0 || nindent == 0 || p.linesFrom(line) > 0)
  1206  			}
  1207  			p.recordLine(&line)
  1208  			p.stmt(s, nextIsRBrace && i == len(list)-1)
  1209  			// labeled statements put labels on a separate line, but here
  1210  			// we only care about the start line of the actual statement
  1211  			// without label - correct line for each label
  1212  			for t := s; ; {
  1213  				lt, _ := t.(*ast.LabeledStmt)
  1214  				if lt == nil {
  1215  					break
  1216  				}
  1217  				line++
  1218  				t = lt.Stmt
  1219  			}
  1220  			i++
  1221  		}
  1222  	}
  1223  	if nindent > 0 {
  1224  		p.print(unindent)
  1225  	}
  1226  }
  1227  
  1228  // block prints an *ast.BlockStmt; it always spans at least two lines.
  1229  func (p *printer) block(b *ast.BlockStmt, nindent int) {
  1230  	p.setPos(b.Lbrace)
  1231  	p.print(token.LBRACE)
  1232  	p.stmtList(b.List, nindent, true)
  1233  	p.linebreak(p.lineFor(b.Rbrace), 1, ignore, true)
  1234  	p.setPos(b.Rbrace)
  1235  	p.print(token.RBRACE)
  1236  }
  1237  
  1238  func isTypeName(x ast.Expr) bool {
  1239  	switch t := x.(type) {
  1240  	case *ast.Ident:
  1241  		return true
  1242  	case *ast.SelectorExpr:
  1243  		return isTypeName(t.X)
  1244  	}
  1245  	return false
  1246  }
  1247  
  1248  func stripParens(x ast.Expr) ast.Expr {
  1249  	if px, strip := x.(*ast.ParenExpr); strip {
  1250  		// parentheses must not be stripped if there are any
  1251  		// unparenthesized composite literals starting with
  1252  		// a type name
  1253  		ast.Inspect(px.X, func(node ast.Node) bool {
  1254  			switch x := node.(type) {
  1255  			case *ast.ParenExpr:
  1256  				// parentheses protect enclosed composite literals
  1257  				return false
  1258  			case *ast.CompositeLit:
  1259  				if isTypeName(x.Type) {
  1260  					strip = false // do not strip parentheses
  1261  				}
  1262  				return false
  1263  			}
  1264  			// in all other cases, keep inspecting
  1265  			return true
  1266  		})
  1267  		if strip {
  1268  			return stripParens(px.X)
  1269  		}
  1270  	}
  1271  	return x
  1272  }
  1273  
  1274  func stripParensAlways(x ast.Expr) ast.Expr {
  1275  	if x, ok := x.(*ast.ParenExpr); ok {
  1276  		return stripParensAlways(x.X)
  1277  	}
  1278  	return x
  1279  }
  1280  
  1281  func (p *printer) controlClause(isForStmt bool, init ast.Stmt, expr ast.Expr, post ast.Stmt) {
  1282  	p.print(blank)
  1283  	needsBlank := false
  1284  	if init == nil && post == nil {
  1285  		// no semicolons required
  1286  		if expr != nil {
  1287  			p.expr(stripParens(expr))
  1288  			needsBlank = true
  1289  		}
  1290  	} else {
  1291  		// all semicolons required
  1292  		// (they are not separators, print them explicitly)
  1293  		if init != nil {
  1294  			p.stmt(init, false)
  1295  		}
  1296  		p.print(token.SEMICOLON, blank)
  1297  		if expr != nil {
  1298  			p.expr(stripParens(expr))
  1299  			needsBlank = true
  1300  		}
  1301  		if isForStmt {
  1302  			p.print(token.SEMICOLON, blank)
  1303  			needsBlank = false
  1304  			if post != nil {
  1305  				p.stmt(post, false)
  1306  				needsBlank = true
  1307  			}
  1308  		}
  1309  	}
  1310  	if needsBlank {
  1311  		p.print(blank)
  1312  	}
  1313  }
  1314  
  1315  // indentList reports whether an expression list would look better if it
  1316  // were indented wholesale (starting with the very first element, rather
  1317  // than starting at the first line break).
  1318  func (p *printer) indentList(list []ast.Expr) bool {
  1319  	// Heuristic: indentList reports whether there are more than one multi-
  1320  	// line element in the list, or if there is any element that is not
  1321  	// starting on the same line as the previous one ends.
  1322  	if len(list) >= 2 {
  1323  		var b = p.lineFor(list[0].Pos())
  1324  		var e = p.lineFor(list[len(list)-1].End())
  1325  		if 0 < b && b < e {
  1326  			// list spans multiple lines
  1327  			n := 0 // multi-line element count
  1328  			line := b
  1329  			for _, x := range list {
  1330  				xb := p.lineFor(x.Pos())
  1331  				xe := p.lineFor(x.End())
  1332  				if line < xb {
  1333  					// x is not starting on the same
  1334  					// line as the previous one ended
  1335  					return true
  1336  				}
  1337  				if xb < xe {
  1338  					// x is a multi-line element
  1339  					n++
  1340  				}
  1341  				line = xe
  1342  			}
  1343  			return n > 1
  1344  		}
  1345  	}
  1346  	return false
  1347  }
  1348  
  1349  func (p *printer) stmt(stmt ast.Stmt, nextIsRBrace bool) {
  1350  	p.setPos(stmt.Pos())
  1351  
  1352  	switch s := stmt.(type) {
  1353  	case *ast.BadStmt:
  1354  		p.print("BadStmt")
  1355  
  1356  	case *ast.DeclStmt:
  1357  		p.decl(s.Decl)
  1358  
  1359  	case *ast.EmptyStmt:
  1360  		// nothing to do
  1361  
  1362  	case *ast.LabeledStmt:
  1363  		// a "correcting" unindent immediately following a line break
  1364  		// is applied before the line break if there is no comment
  1365  		// between (see writeWhitespace)
  1366  		p.print(unindent)
  1367  		p.expr(s.Label)
  1368  		p.setPos(s.Colon)
  1369  		p.print(token.COLON, indent)
  1370  		if e, isEmpty := s.Stmt.(*ast.EmptyStmt); isEmpty {
  1371  			if !nextIsRBrace {
  1372  				p.print(newline)
  1373  				p.setPos(e.Pos())
  1374  				p.print(token.SEMICOLON)
  1375  				break
  1376  			}
  1377  		} else {
  1378  			p.linebreak(p.lineFor(s.Stmt.Pos()), 1, ignore, true)
  1379  		}
  1380  		p.stmt(s.Stmt, nextIsRBrace)
  1381  
  1382  	case *ast.ExprStmt:
  1383  		const depth = 1
  1384  		p.expr0(s.X, depth)
  1385  
  1386  	case *ast.SendStmt:
  1387  		const depth = 1
  1388  		p.expr0(s.Chan, depth)
  1389  		p.print(blank)
  1390  		p.setPos(s.Arrow)
  1391  		p.print(token.ARROW, blank)
  1392  		p.expr0(s.Value, depth)
  1393  
  1394  	case *ast.IncDecStmt:
  1395  		const depth = 1
  1396  		p.expr0(s.X, depth+1)
  1397  		p.setPos(s.TokPos)
  1398  		p.print(s.Tok)
  1399  
  1400  	case *ast.AssignStmt:
  1401  		var depth = 1
  1402  		if len(s.Lhs) > 1 && len(s.Rhs) > 1 {
  1403  			depth++
  1404  		}
  1405  		p.exprList(s.Pos(), s.Lhs, depth, 0, s.TokPos, false)
  1406  		p.print(blank)
  1407  		p.setPos(s.TokPos)
  1408  		p.print(s.Tok, blank)
  1409  		p.exprList(s.TokPos, s.Rhs, depth, 0, token.NoPos, false)
  1410  
  1411  	case *ast.GoStmt:
  1412  		p.print(token.GO, blank)
  1413  		p.expr(s.Call)
  1414  
  1415  	case *ast.DeferStmt:
  1416  		p.print(token.DEFER, blank)
  1417  		p.expr(s.Call)
  1418  
  1419  	case *ast.ReturnStmt:
  1420  		p.print(token.RETURN)
  1421  		if s.Results != nil {
  1422  			p.print(blank)
  1423  			// Use indentList heuristic to make corner cases look
  1424  			// better (issue 1207). A more systematic approach would
  1425  			// always indent, but this would cause significant
  1426  			// reformatting of the code base and not necessarily
  1427  			// lead to more nicely formatted code in general.
  1428  			if p.indentList(s.Results) {
  1429  				p.print(indent)
  1430  				// Use NoPos so that a newline never goes before
  1431  				// the results (see issue #32854).
  1432  				p.exprList(token.NoPos, s.Results, 1, noIndent, token.NoPos, false)
  1433  				p.print(unindent)
  1434  			} else {
  1435  				p.exprList(token.NoPos, s.Results, 1, 0, token.NoPos, false)
  1436  			}
  1437  		}
  1438  
  1439  	case *ast.BranchStmt:
  1440  		p.print(s.Tok)
  1441  		if s.Label != nil {
  1442  			p.print(blank)
  1443  			p.expr(s.Label)
  1444  		}
  1445  
  1446  	case *ast.BlockStmt:
  1447  		p.block(s, 1)
  1448  
  1449  	case *ast.IfStmt:
  1450  		p.print(token.IF)
  1451  		p.controlClause(false, s.Init, s.Cond, nil)
  1452  		p.block(s.Body, 1)
  1453  		if s.Else != nil {
  1454  			p.print(blank, token.ELSE, blank)
  1455  			switch s.Else.(type) {
  1456  			case *ast.BlockStmt, *ast.IfStmt:
  1457  				p.stmt(s.Else, nextIsRBrace)
  1458  			default:
  1459  				// This can only happen with an incorrectly
  1460  				// constructed AST. Permit it but print so
  1461  				// that it can be parsed without errors.
  1462  				p.print(token.LBRACE, indent, formfeed)
  1463  				p.stmt(s.Else, true)
  1464  				p.print(unindent, formfeed, token.RBRACE)
  1465  			}
  1466  		}
  1467  
  1468  	case *ast.CaseClause:
  1469  		if s.List != nil {
  1470  			p.print(token.CASE, blank)
  1471  			p.exprList(s.Pos(), s.List, 1, 0, s.Colon, false)
  1472  		} else {
  1473  			p.print(token.DEFAULT)
  1474  		}
  1475  		p.setPos(s.Colon)
  1476  		p.print(token.COLON)
  1477  		p.stmtList(s.Body, 1, nextIsRBrace)
  1478  
  1479  	case *ast.SwitchStmt:
  1480  		p.print(token.SWITCH)
  1481  		p.controlClause(false, s.Init, s.Tag, nil)
  1482  		p.block(s.Body, 0)
  1483  
  1484  	case *ast.TypeSwitchStmt:
  1485  		p.print(token.SWITCH)
  1486  		if s.Init != nil {
  1487  			p.print(blank)
  1488  			p.stmt(s.Init, false)
  1489  			p.print(token.SEMICOLON)
  1490  		}
  1491  		p.print(blank)
  1492  		p.stmt(s.Assign, false)
  1493  		p.print(blank)
  1494  		p.block(s.Body, 0)
  1495  
  1496  	case *ast.CommClause:
  1497  		if s.Comm != nil {
  1498  			p.print(token.CASE, blank)
  1499  			p.stmt(s.Comm, false)
  1500  		} else {
  1501  			p.print(token.DEFAULT)
  1502  		}
  1503  		p.setPos(s.Colon)
  1504  		p.print(token.COLON)
  1505  		p.stmtList(s.Body, 1, nextIsRBrace)
  1506  
  1507  	case *ast.SelectStmt:
  1508  		p.print(token.SELECT, blank)
  1509  		body := s.Body
  1510  		if len(body.List) == 0 && !p.commentBefore(p.posFor(body.Rbrace)) {
  1511  			// print empty select statement w/o comments on one line
  1512  			p.setPos(body.Lbrace)
  1513  			p.print(token.LBRACE)
  1514  			p.setPos(body.Rbrace)
  1515  			p.print(token.RBRACE)
  1516  		} else {
  1517  			p.block(body, 0)
  1518  		}
  1519  
  1520  	case *ast.ForStmt:
  1521  		p.print(token.FOR)
  1522  		p.controlClause(true, s.Init, s.Cond, s.Post)
  1523  		p.block(s.Body, 1)
  1524  
  1525  	case *ast.RangeStmt:
  1526  		p.print(token.FOR, blank)
  1527  		if s.Key != nil {
  1528  			p.expr(s.Key)
  1529  			if s.Value != nil {
  1530  				// use position of value following the comma as
  1531  				// comma position for correct comment placement
  1532  				p.setPos(s.Value.Pos())
  1533  				p.print(token.COMMA, blank)
  1534  				p.expr(s.Value)
  1535  			}
  1536  			p.print(blank)
  1537  			p.setPos(s.TokPos)
  1538  			p.print(s.Tok, blank)
  1539  		}
  1540  		p.print(token.RANGE, blank)
  1541  		p.expr(stripParens(s.X))
  1542  		p.print(blank)
  1543  		p.block(s.Body, 1)
  1544  
  1545  	default:
  1546  		panic("unreachable")
  1547  	}
  1548  }
  1549  
  1550  // ----------------------------------------------------------------------------
  1551  // Declarations
  1552  
  1553  // The keepTypeColumn function determines if the type column of a series of
  1554  // consecutive const or var declarations must be kept, or if initialization
  1555  // values (V) can be placed in the type column (T) instead. The i'th entry
  1556  // in the result slice is true if the type column in spec[i] must be kept.
  1557  //
  1558  // For example, the declaration:
  1559  //
  1560  //		const (
  1561  //			foobar int = 42 // comment
  1562  //			x          = 7  // comment
  1563  //			foo
  1564  //	             bar = 991
  1565  //		)
  1566  //
  1567  // leads to the type/values matrix below. A run of value columns (V) can
  1568  // be moved into the type column if there is no type for any of the values
  1569  // in that column (we only move entire columns so that they align properly).
  1570  //
  1571  //		matrix        formatted     result
  1572  //	                   matrix
  1573  //		T  V    ->    T  V     ->   true      there is a T and so the type
  1574  //		-  V          -  V          true      column must be kept
  1575  //		-  -          -  -          false
  1576  //		-  V          V  -          false     V is moved into T column
  1577  func keepTypeColumn(specs []ast.Spec) []bool {
  1578  	m := make([]bool, len(specs))
  1579  
  1580  	populate := func(i, j int, keepType bool) {
  1581  		if keepType {
  1582  			for ; i < j; i++ {
  1583  				m[i] = true
  1584  			}
  1585  		}
  1586  	}
  1587  
  1588  	i0 := -1 // if i0 >= 0 we are in a run and i0 is the start of the run
  1589  	var keepType bool
  1590  	for i, s := range specs {
  1591  		t := s.(*ast.ValueSpec)
  1592  		if t.Values != nil {
  1593  			if i0 < 0 {
  1594  				// start of a run of ValueSpecs with non-nil Values
  1595  				i0 = i
  1596  				keepType = false
  1597  			}
  1598  		} else {
  1599  			if i0 >= 0 {
  1600  				// end of a run
  1601  				populate(i0, i, keepType)
  1602  				i0 = -1
  1603  			}
  1604  		}
  1605  		if t.Type != nil {
  1606  			keepType = true
  1607  		}
  1608  	}
  1609  	if i0 >= 0 {
  1610  		// end of a run
  1611  		populate(i0, len(specs), keepType)
  1612  	}
  1613  
  1614  	return m
  1615  }
  1616  
  1617  func (p *printer) valueSpec(s *ast.ValueSpec, keepType bool) {
  1618  	p.setComment(s.Doc)
  1619  	p.identList(s.Names, false) // always present
  1620  	extraTabs := 3
  1621  	if s.Type != nil || keepType {
  1622  		p.print(vtab)
  1623  		extraTabs--
  1624  	}
  1625  	if s.Type != nil {
  1626  		p.expr(s.Type)
  1627  	}
  1628  	if s.Values != nil {
  1629  		p.print(vtab, token.ASSIGN, blank)
  1630  		p.exprList(token.NoPos, s.Values, 1, 0, token.NoPos, false)
  1631  		extraTabs--
  1632  	}
  1633  	if s.Comment != nil {
  1634  		for ; extraTabs > 0; extraTabs-- {
  1635  			p.print(vtab)
  1636  		}
  1637  		p.setComment(s.Comment)
  1638  	}
  1639  }
  1640  
  1641  func sanitizeImportPath(lit *ast.BasicLit) *ast.BasicLit {
  1642  	// Note: An unmodified AST generated by go/parser will already
  1643  	// contain a backward- or double-quoted path string that does
  1644  	// not contain any invalid characters, and most of the work
  1645  	// here is not needed. However, a modified or generated AST
  1646  	// may possibly contain non-canonical paths. Do the work in
  1647  	// all cases since it's not too hard and not speed-critical.
  1648  
  1649  	// if we don't have a proper string, be conservative and return whatever we have
  1650  	if lit.Kind != token.STRING {
  1651  		return lit
  1652  	}
  1653  	s, err := strconv.Unquote(lit.Value)
  1654  	if err != nil {
  1655  		return lit
  1656  	}
  1657  
  1658  	// if the string is an invalid path, return whatever we have
  1659  	//
  1660  	// spec: "Implementation restriction: A compiler may restrict
  1661  	// ImportPaths to non-empty strings using only characters belonging
  1662  	// to Unicode's L, M, N, P, and S general categories (the Graphic
  1663  	// characters without spaces) and may also exclude the characters
  1664  	// !"#$%&'()*,:;<=>?[\]^`{|} and the Unicode replacement character
  1665  	// U+FFFD."
  1666  	if s == "" {
  1667  		return lit
  1668  	}
  1669  	const illegalChars = `!"#$%&'()*,:;<=>?[\]^{|}` + "`\uFFFD"
  1670  	for _, r := range s {
  1671  		if !unicode.IsGraphic(r) || unicode.IsSpace(r) || strings.ContainsRune(illegalChars, r) {
  1672  			return lit
  1673  		}
  1674  	}
  1675  
  1676  	// otherwise, return the double-quoted path
  1677  	s = strconv.Quote(s)
  1678  	if s == lit.Value {
  1679  		return lit // nothing wrong with lit
  1680  	}
  1681  	return &ast.BasicLit{ValuePos: lit.ValuePos, Kind: token.STRING, Value: s}
  1682  }
  1683  
  1684  // The parameter n is the number of specs in the group. If doIndent is set,
  1685  // multi-line identifier lists in the spec are indented when the first
  1686  // linebreak is encountered.
  1687  func (p *printer) spec(spec ast.Spec, n int, doIndent bool) {
  1688  	switch s := spec.(type) {
  1689  	case *ast.ImportSpec:
  1690  		p.setComment(s.Doc)
  1691  		if s.Name != nil {
  1692  			p.expr(s.Name)
  1693  			p.print(blank)
  1694  		}
  1695  		p.expr(sanitizeImportPath(s.Path))
  1696  		p.setComment(s.Comment)
  1697  		p.setPos(s.EndPos)
  1698  
  1699  	case *ast.ValueSpec:
  1700  		if n != 1 {
  1701  			p.internalError("expected n = 1; got", n)
  1702  		}
  1703  		p.setComment(s.Doc)
  1704  		p.identList(s.Names, doIndent) // always present
  1705  		if s.Type != nil {
  1706  			p.print(blank)
  1707  			p.expr(s.Type)
  1708  		}
  1709  		if s.Values != nil {
  1710  			p.print(blank, token.ASSIGN, blank)
  1711  			p.exprList(token.NoPos, s.Values, 1, 0, token.NoPos, false)
  1712  		}
  1713  		p.setComment(s.Comment)
  1714  
  1715  	case *ast.TypeSpec:
  1716  		p.setComment(s.Doc)
  1717  		p.expr(s.Name)
  1718  		if s.TypeParams != nil {
  1719  			p.parameters(s.TypeParams, typeTParam)
  1720  		}
  1721  		if n == 1 {
  1722  			p.print(blank)
  1723  		} else {
  1724  			p.print(vtab)
  1725  		}
  1726  		if s.Assign.IsValid() {
  1727  			p.print(token.ASSIGN, blank)
  1728  		}
  1729  		p.expr(s.Type)
  1730  		p.setComment(s.Comment)
  1731  
  1732  	default:
  1733  		panic("unreachable")
  1734  	}
  1735  }
  1736  
  1737  func (p *printer) genDecl(d *ast.GenDecl) {
  1738  	p.setComment(d.Doc)
  1739  	p.setPos(d.Pos())
  1740  	p.print(d.Tok, blank)
  1741  
  1742  	if d.Lparen.IsValid() || len(d.Specs) != 1 {
  1743  		// group of parenthesized declarations
  1744  		p.setPos(d.Lparen)
  1745  		p.print(token.LPAREN)
  1746  		if n := len(d.Specs); n > 0 {
  1747  			p.print(indent, formfeed)
  1748  			if n > 1 && (d.Tok == token.CONST || d.Tok == token.VAR) {
  1749  				// two or more grouped const/var declarations:
  1750  				// determine if the type column must be kept
  1751  				keepType := keepTypeColumn(d.Specs)
  1752  				var line int
  1753  				for i, s := range d.Specs {
  1754  					if i > 0 {
  1755  						p.linebreak(p.lineFor(s.Pos()), 1, ignore, p.linesFrom(line) > 0)
  1756  					}
  1757  					p.recordLine(&line)
  1758  					p.valueSpec(s.(*ast.ValueSpec), keepType[i])
  1759  				}
  1760  			} else {
  1761  				var line int
  1762  				for i, s := range d.Specs {
  1763  					if i > 0 {
  1764  						p.linebreak(p.lineFor(s.Pos()), 1, ignore, p.linesFrom(line) > 0)
  1765  					}
  1766  					p.recordLine(&line)
  1767  					p.spec(s, n, false)
  1768  				}
  1769  			}
  1770  			p.print(unindent, formfeed)
  1771  		}
  1772  		p.setPos(d.Rparen)
  1773  		p.print(token.RPAREN)
  1774  
  1775  	} else if len(d.Specs) > 0 {
  1776  		// single declaration
  1777  		p.spec(d.Specs[0], 1, true)
  1778  	}
  1779  }
  1780  
  1781  // sizeCounter is an io.Writer which counts the number of bytes written,
  1782  // as well as whether a newline character was seen.
  1783  type sizeCounter struct {
  1784  	hasNewline bool
  1785  	size       int
  1786  }
  1787  
  1788  func (c *sizeCounter) Write(p []byte) (int, error) {
  1789  	if !c.hasNewline {
  1790  		for _, b := range p {
  1791  			if b == '\n' || b == '\f' {
  1792  				c.hasNewline = true
  1793  				break
  1794  			}
  1795  		}
  1796  	}
  1797  	c.size += len(p)
  1798  	return len(p), nil
  1799  }
  1800  
  1801  // nodeSize determines the size of n in chars after formatting.
  1802  // The result is <= maxSize if the node fits on one line with at
  1803  // most maxSize chars and the formatted output doesn't contain
  1804  // any control chars. Otherwise, the result is > maxSize.
  1805  func (p *printer) nodeSize(n ast.Node, maxSize int) (size int) {
  1806  	// nodeSize invokes the printer, which may invoke nodeSize
  1807  	// recursively. For deep composite literal nests, this can
  1808  	// lead to an exponential algorithm. Remember previous
  1809  	// results to prune the recursion (was issue 1628).
  1810  	if size, found := p.nodeSizes[n]; found {
  1811  		return size
  1812  	}
  1813  
  1814  	size = maxSize + 1 // assume n doesn't fit
  1815  	p.nodeSizes[n] = size
  1816  
  1817  	// nodeSize computation must be independent of particular
  1818  	// style so that we always get the same decision; print
  1819  	// in RawFormat
  1820  	cfg := Config{Mode: RawFormat}
  1821  	var counter sizeCounter
  1822  	if err := cfg.fprint(&counter, p.fset, n, p.nodeSizes); err != nil {
  1823  		return
  1824  	}
  1825  	if counter.size <= maxSize && !counter.hasNewline {
  1826  		// n fits in a single line
  1827  		size = counter.size
  1828  		p.nodeSizes[n] = size
  1829  	}
  1830  	return
  1831  }
  1832  
  1833  // numLines returns the number of lines spanned by node n in the original source.
  1834  func (p *printer) numLines(n ast.Node) int {
  1835  	if from := n.Pos(); from.IsValid() {
  1836  		if to := n.End(); to.IsValid() {
  1837  			return p.lineFor(to) - p.lineFor(from) + 1
  1838  		}
  1839  	}
  1840  	return infinity
  1841  }
  1842  
  1843  // bodySize is like nodeSize but it is specialized for *ast.BlockStmt's.
  1844  func (p *printer) bodySize(b *ast.BlockStmt, maxSize int) int {
  1845  	pos1 := b.Pos()
  1846  	pos2 := b.Rbrace
  1847  	if pos1.IsValid() && pos2.IsValid() && p.lineFor(pos1) != p.lineFor(pos2) {
  1848  		// opening and closing brace are on different lines - don't make it a one-liner
  1849  		return maxSize + 1
  1850  	}
  1851  	if len(b.List) > 5 {
  1852  		// too many statements - don't make it a one-liner
  1853  		return maxSize + 1
  1854  	}
  1855  	// otherwise, estimate body size
  1856  	bodySize := p.commentSizeBefore(p.posFor(pos2))
  1857  	for i, s := range b.List {
  1858  		if bodySize > maxSize {
  1859  			break // no need to continue
  1860  		}
  1861  		if i > 0 {
  1862  			bodySize += 2 // space for a semicolon and blank
  1863  		}
  1864  		bodySize += p.nodeSize(s, maxSize)
  1865  	}
  1866  	return bodySize
  1867  }
  1868  
  1869  // funcBody prints a function body following a function header of given headerSize.
  1870  // If the header's and block's size are "small enough" and the block is "simple enough",
  1871  // the block is printed on the current line, without line breaks, spaced from the header
  1872  // by sep. Otherwise the block's opening "{" is printed on the current line, followed by
  1873  // lines for the block's statements and its closing "}".
  1874  func (p *printer) funcBody(headerSize int, sep whiteSpace, b *ast.BlockStmt) {
  1875  	if b == nil {
  1876  		return
  1877  	}
  1878  
  1879  	// save/restore composite literal nesting level
  1880  	defer func(level int) {
  1881  		p.level = level
  1882  	}(p.level)
  1883  	p.level = 0
  1884  
  1885  	const maxSize = 100
  1886  	if headerSize+p.bodySize(b, maxSize) <= maxSize {
  1887  		p.print(sep)
  1888  		p.setPos(b.Lbrace)
  1889  		p.print(token.LBRACE)
  1890  		if len(b.List) > 0 {
  1891  			p.print(blank)
  1892  			for i, s := range b.List {
  1893  				if i > 0 {
  1894  					p.print(token.SEMICOLON, blank)
  1895  				}
  1896  				p.stmt(s, i == len(b.List)-1)
  1897  			}
  1898  			p.print(blank)
  1899  		}
  1900  		p.print(noExtraLinebreak)
  1901  		p.setPos(b.Rbrace)
  1902  		p.print(token.RBRACE, noExtraLinebreak)
  1903  		return
  1904  	}
  1905  
  1906  	if sep != ignore {
  1907  		p.print(blank) // always use blank
  1908  	}
  1909  	p.block(b, 1)
  1910  }
  1911  
  1912  // distanceFrom returns the column difference between p.out (the current output
  1913  // position) and startOutCol. If the start position is on a different line from
  1914  // the current position (or either is unknown), the result is infinity.
  1915  func (p *printer) distanceFrom(startPos token.Pos, startOutCol int) int {
  1916  	if startPos.IsValid() && p.pos.IsValid() && p.posFor(startPos).Line == p.pos.Line {
  1917  		return p.out.Column - startOutCol
  1918  	}
  1919  	return infinity
  1920  }
  1921  
  1922  func (p *printer) funcDecl(d *ast.FuncDecl) {
  1923  	p.setComment(d.Doc)
  1924  	p.setPos(d.Pos())
  1925  	p.print(token.FUNC, blank)
  1926  	// We have to save startCol only after emitting FUNC; otherwise it can be on a
  1927  	// different line (all whitespace preceding the FUNC is emitted only when the
  1928  	// FUNC is emitted).
  1929  	startCol := p.out.Column - len("func ")
  1930  	if d.Recv != nil {
  1931  		p.parameters(d.Recv, funcParam) // method: print receiver
  1932  		p.print(blank)
  1933  	}
  1934  	p.expr(d.Name)
  1935  	p.signature(d.Type)
  1936  	p.funcBody(p.distanceFrom(d.Pos(), startCol), vtab, d.Body)
  1937  }
  1938  
  1939  func (p *printer) decl(decl ast.Decl) {
  1940  	switch d := decl.(type) {
  1941  	case *ast.BadDecl:
  1942  		p.setPos(d.Pos())
  1943  		p.print("BadDecl")
  1944  	case *ast.GenDecl:
  1945  		p.genDecl(d)
  1946  	case *ast.FuncDecl:
  1947  		p.funcDecl(d)
  1948  	default:
  1949  		panic("unreachable")
  1950  	}
  1951  }
  1952  
  1953  // ----------------------------------------------------------------------------
  1954  // Files
  1955  
  1956  func declToken(decl ast.Decl) (tok token.Token) {
  1957  	tok = token.ILLEGAL
  1958  	switch d := decl.(type) {
  1959  	case *ast.GenDecl:
  1960  		tok = d.Tok
  1961  	case *ast.FuncDecl:
  1962  		tok = token.FUNC
  1963  	}
  1964  	return
  1965  }
  1966  
  1967  func (p *printer) declList(list []ast.Decl) {
  1968  	tok := token.ILLEGAL
  1969  	for _, d := range list {
  1970  		prev := tok
  1971  		tok = declToken(d)
  1972  		// If the declaration token changed (e.g., from CONST to TYPE)
  1973  		// or the next declaration has documentation associated with it,
  1974  		// print an empty line between top-level declarations.
  1975  		// (because p.linebreak is called with the position of d, which
  1976  		// is past any documentation, the minimum requirement is satisfied
  1977  		// even w/o the extra getDoc(d) nil-check - leave it in case the
  1978  		// linebreak logic improves - there's already a TODO).
  1979  		if len(p.output) > 0 {
  1980  			// only print line break if we are not at the beginning of the output
  1981  			// (i.e., we are not printing only a partial program)
  1982  			min := 1
  1983  			if prev != tok || getDoc(d) != nil {
  1984  				min = 2
  1985  			}
  1986  			// start a new section if the next declaration is a function
  1987  			// that spans multiple lines (see also issue #19544)
  1988  			p.linebreak(p.lineFor(d.Pos()), min, ignore, tok == token.FUNC && p.numLines(d) > 1)
  1989  		}
  1990  		p.decl(d)
  1991  	}
  1992  }
  1993  
  1994  func (p *printer) file(src *ast.File) {
  1995  	p.setComment(src.Doc)
  1996  	p.setPos(src.Pos())
  1997  	p.print(token.PACKAGE, blank)
  1998  	p.expr(src.Name)
  1999  	p.declList(src.Decls)
  2000  	p.print(newline)
  2001  }
  2002  

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