prog.go

Documentation: regexp/syntax

     1  // Copyright 2011 The Go Authors. All rights reserved.
     2  // Use of this source code is governed by a BSD-style
     3  // license that can be found in the LICENSE file.
     4  
     5  package syntax
     6  
     7  import (
     8  	"bytes"
     9  	"strconv"
    10  	"unicode"
    11  )
    12  
    13  // Compiled program.
    14  // May not belong in this package, but convenient for now.
    15  
    16  // A Prog is a compiled regular expression program.
    17  type Prog struct {
    18  	Inst   []Inst
    19  	Start  int // index of start instruction
    20  	NumCap int // number of InstCapture insts in re
    21  }
    22  
    23  // An InstOp is an instruction opcode.
    24  type InstOp uint8
    25  
    26  const (
    27  	InstAlt InstOp = iota
    28  	InstAltMatch
    29  	InstCapture
    30  	InstEmptyWidth
    31  	InstMatch
    32  	InstFail
    33  	InstNop
    34  	InstRune
    35  	InstRune1
    36  	InstRuneAny
    37  	InstRuneAnyNotNL
    38  )
    39  
    40  var instOpNames = []string{
    41  	"InstAlt",
    42  	"InstAltMatch",
    43  	"InstCapture",
    44  	"InstEmptyWidth",
    45  	"InstMatch",
    46  	"InstFail",
    47  	"InstNop",
    48  	"InstRune",
    49  	"InstRune1",
    50  	"InstRuneAny",
    51  	"InstRuneAnyNotNL",
    52  }
    53  
    54  func (i InstOp) String() string {
    55  	if uint(i) >= uint(len(instOpNames)) {
    56  		return ""
    57  	}
    58  	return instOpNames[i]
    59  }
    60  
    61  // An EmptyOp specifies a kind or mixture of zero-width assertions.
    62  type EmptyOp uint8
    63  
    64  const (
    65  	EmptyBeginLine EmptyOp = 1 << iota
    66  	EmptyEndLine
    67  	EmptyBeginText
    68  	EmptyEndText
    69  	EmptyWordBoundary
    70  	EmptyNoWordBoundary
    71  )
    72  
    73  // EmptyOpContext returns the zero-width assertions
    74  // satisfied at the position between the runes r1 and r2.
    75  // Passing r1 == -1 indicates that the position is
    76  // at the beginning of the text.
    77  // Passing r2 == -1 indicates that the position is
    78  // at the end of the text.
    79  func EmptyOpContext(r1, r2 rune) EmptyOp {
    80  	var op EmptyOp = EmptyNoWordBoundary
    81  	var boundary byte
    82  	switch {
    83  	case IsWordChar(r1):
    84  		boundary = 1
    85  	case r1 == '\n':
    86  		op |= EmptyBeginLine
    87  	case r1 < 0:
    88  		op |= EmptyBeginText | EmptyBeginLine
    89  	}
    90  	switch {
    91  	case IsWordChar(r2):
    92  		boundary ^= 1
    93  	case r2 == '\n':
    94  		op |= EmptyEndLine
    95  	case r2 < 0:
    96  		op |= EmptyEndText | EmptyEndLine
    97  	}
    98  	if boundary != 0 { // IsWordChar(r1) != IsWordChar(r2)
    99  		op ^= (EmptyWordBoundary | EmptyNoWordBoundary)
   100  	}
   101  	return op
   102  }
   103  
   104  // IsWordChar reports whether r is consider a ``word character''
   105  // during the evaluation of the \b and \B zero-width assertions.
   106  // These assertions are ASCII-only: the word characters are [A-Za-z0-9_].
   107  func IsWordChar(r rune) bool {
   108  	return 'A' <= r && r <= 'Z' || 'a' <= r && r <= 'z' || '0' <= r && r <= '9' || r == '_'
   109  }
   110  
   111  // An Inst is a single instruction in a regular expression program.
   112  type Inst struct {
   113  	Op   InstOp
   114  	Out  uint32 // all but InstMatch, InstFail
   115  	Arg  uint32 // InstAlt, InstAltMatch, InstCapture, InstEmptyWidth
   116  	Rune []rune
   117  }
   118  
   119  func (p *Prog) String() string {
   120  	var b bytes.Buffer
   121  	dumpProg(&b, p)
   122  	return b.String()
   123  }
   124  
   125  // skipNop follows any no-op or capturing instructions
   126  // and returns the resulting pc.
   127  func (p *Prog) skipNop(pc uint32) (*Inst, uint32) {
   128  	i := &p.Inst[pc]
   129  	for i.Op == InstNop || i.Op == InstCapture {
   130  		pc = i.Out
   131  		i = &p.Inst[pc]
   132  	}
   133  	return i, pc
   134  }
   135  
   136  // op returns i.Op but merges all the Rune special cases into InstRune
   137  func (i *Inst) op() InstOp {
   138  	op := i.Op
   139  	switch op {
   140  	case InstRune1, InstRuneAny, InstRuneAnyNotNL:
   141  		op = InstRune
   142  	}
   143  	return op
   144  }
   145  
   146  // Prefix returns a literal string that all matches for the
   147  // regexp must start with. Complete is true if the prefix
   148  // is the entire match.
   149  func (p *Prog) Prefix() (prefix string, complete bool) {
   150  	i, _ := p.skipNop(uint32(p.Start))
   151  
   152  	// Avoid allocation of buffer if prefix is empty.
   153  	if i.op() != InstRune || len(i.Rune) != 1 {
   154  		return "", i.Op == InstMatch
   155  	}
   156  
   157  	// Have prefix; gather characters.
   158  	var buf bytes.Buffer
   159  	for i.op() == InstRune && len(i.Rune) == 1 && Flags(i.Arg)&FoldCase == 0 {
   160  		buf.WriteRune(i.Rune[0])
   161  		i, _ = p.skipNop(i.Out)
   162  	}
   163  	return buf.String(), i.Op == InstMatch
   164  }
   165  
   166  // StartCond returns the leading empty-width conditions that must
   167  // be true in any match. It returns ^EmptyOp(0) if no matches are possible.
   168  func (p *Prog) StartCond() EmptyOp {
   169  	var flag EmptyOp
   170  	pc := uint32(p.Start)
   171  	i := &p.Inst[pc]
   172  Loop:
   173  	for {
   174  		switch i.Op {
   175  		case InstEmptyWidth:
   176  			flag |= EmptyOp(i.Arg)
   177  		case InstFail:
   178  			return ^EmptyOp(0)
   179  		case InstCapture, InstNop:
   180  			// skip
   181  		default:
   182  			break Loop
   183  		}
   184  		pc = i.Out
   185  		i = &p.Inst[pc]
   186  	}
   187  	return flag
   188  }
   189  
   190  const noMatch = -1
   191  
   192  // MatchRune reports whether the instruction matches (and consumes) r.
   193  // It should only be called when i.Op == InstRune.
   194  func (i *Inst) MatchRune(r rune) bool {
   195  	return i.MatchRunePos(r) != noMatch
   196  }
   197  
   198  // MatchRunePos checks whether the instruction matches (and consumes) r.
   199  // If so, MatchRunePos returns the index of the matching rune pair
   200  // (or, when len(i.Rune) == 1, rune singleton).
   201  // If not, MatchRunePos returns -1.
   202  // MatchRunePos should only be called when i.Op == InstRune.
   203  func (i *Inst) MatchRunePos(r rune) int {
   204  	rune := i.Rune
   205  
   206  	// Special case: single-rune slice is from literal string, not char class.
   207  	if len(rune) == 1 {
   208  		r0 := rune[0]
   209  		if r == r0 {
   210  			return 0
   211  		}
   212  		if Flags(i.Arg)&FoldCase != 0 {
   213  			for r1 := unicode.SimpleFold(r0); r1 != r0; r1 = unicode.SimpleFold(r1) {
   214  				if r == r1 {
   215  					return 0
   216  				}
   217  			}
   218  		}
   219  		return noMatch
   220  	}
   221  
   222  	// Peek at the first few pairs.
   223  	// Should handle ASCII well.
   224  	for j := 0; j < len(rune) && j <= 8; j += 2 {
   225  		if r < rune[j] {
   226  			return noMatch
   227  		}
   228  		if r <= rune[j+1] {
   229  			return j / 2
   230  		}
   231  	}
   232  
   233  	// Otherwise binary search.
   234  	lo := 0
   235  	hi := len(rune) / 2
   236  	for lo < hi {
   237  		m := lo + (hi-lo)/2
   238  		if c := rune[2*m]; c <= r {
   239  			if r <= rune[2*m+1] {
   240  				return m
   241  			}
   242  			lo = m + 1
   243  		} else {
   244  			hi = m
   245  		}
   246  	}
   247  	return noMatch
   248  }
   249  
   250  // MatchEmptyWidth reports whether the instruction matches
   251  // an empty string between the runes before and after.
   252  // It should only be called when i.Op == InstEmptyWidth.
   253  func (i *Inst) MatchEmptyWidth(before rune, after rune) bool {
   254  	switch EmptyOp(i.Arg) {
   255  	case EmptyBeginLine:
   256  		return before == '\n' || before == -1
   257  	case EmptyEndLine:
   258  		return after == '\n' || after == -1
   259  	case EmptyBeginText:
   260  		return before == -1
   261  	case EmptyEndText:
   262  		return after == -1
   263  	case EmptyWordBoundary:
   264  		return IsWordChar(before) != IsWordChar(after)
   265  	case EmptyNoWordBoundary:
   266  		return IsWordChar(before) == IsWordChar(after)
   267  	}
   268  	panic("unknown empty width arg")
   269  }
   270  
   271  func (i *Inst) String() string {
   272  	var b bytes.Buffer
   273  	dumpInst(&b, i)
   274  	return b.String()
   275  }
   276  
   277  func bw(b *bytes.Buffer, args ...string) {
   278  	for _, s := range args {
   279  		b.WriteString(s)
   280  	}
   281  }
   282  
   283  func dumpProg(b *bytes.Buffer, p *Prog) {
   284  	for j := range p.Inst {
   285  		i := &p.Inst[j]
   286  		pc := strconv.Itoa(j)
   287  		if len(pc) < 3 {
   288  			b.WriteString("   "[len(pc):])
   289  		}
   290  		if j == p.Start {
   291  			pc += "*"
   292  		}
   293  		bw(b, pc, "\t")
   294  		dumpInst(b, i)
   295  		bw(b, "\n")
   296  	}
   297  }
   298  
   299  func u32(i uint32) string {
   300  	return strconv.FormatUint(uint64(i), 10)
   301  }
   302  
   303  func dumpInst(b *bytes.Buffer, i *Inst) {
   304  	switch i.Op {
   305  	case InstAlt:
   306  		bw(b, "alt -> ", u32(i.Out), ", ", u32(i.Arg))
   307  	case InstAltMatch:
   308  		bw(b, "altmatch -> ", u32(i.Out), ", ", u32(i.Arg))
   309  	case InstCapture:
   310  		bw(b, "cap ", u32(i.Arg), " -> ", u32(i.Out))
   311  	case InstEmptyWidth:
   312  		bw(b, "empty ", u32(i.Arg), " -> ", u32(i.Out))
   313  	case InstMatch:
   314  		bw(b, "match")
   315  	case InstFail:
   316  		bw(b, "fail")
   317  	case InstNop:
   318  		bw(b, "nop -> ", u32(i.Out))
   319  	case InstRune:
   320  		if i.Rune == nil {
   321  			// shouldn't happen
   322  			bw(b, "rune <nil>")
   323  		}
   324  		bw(b, "rune ", strconv.QuoteToASCII(string(i.Rune)))
   325  		if Flags(i.Arg)&FoldCase != 0 {
   326  			bw(b, "/i")
   327  		}
   328  		bw(b, " -> ", u32(i.Out))
   329  	case InstRune1:
   330  		bw(b, "rune1 ", strconv.QuoteToASCII(string(i.Rune)), " -> ", u32(i.Out))
   331  	case InstRuneAny:
   332  		bw(b, "any -> ", u32(i.Out))
   333  	case InstRuneAnyNotNL:
   334  		bw(b, "anynotnl -> ", u32(i.Out))
   335  	}
   336  }
   337
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