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

View as plain text