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  	"strconv"
     9  	"strings"
    10  	"unicode"
    11  	"unicode/utf8"
    12  )
    13  
    14  // Compiled program.
    15  // May not belong in this package, but convenient for now.
    16  
    17  // A Prog is a compiled regular expression program.
    18  type Prog struct {
    19  	Inst   []Inst
    20  	Start  int // index of start instruction
    21  	NumCap int // number of InstCapture insts in re
    22  }
    23  
    24  // An InstOp is an instruction opcode.
    25  type InstOp uint8
    26  
    27  const (
    28  	InstAlt InstOp = iota
    29  	InstAltMatch
    30  	InstCapture
    31  	InstEmptyWidth
    32  	InstMatch
    33  	InstFail
    34  	InstNop
    35  	InstRune
    36  	InstRune1
    37  	InstRuneAny
    38  	InstRuneAnyNotNL
    39  )
    40  
    41  var instOpNames = []string{
    42  	"InstAlt",
    43  	"InstAltMatch",
    44  	"InstCapture",
    45  	"InstEmptyWidth",
    46  	"InstMatch",
    47  	"InstFail",
    48  	"InstNop",
    49  	"InstRune",
    50  	"InstRune1",
    51  	"InstRuneAny",
    52  	"InstRuneAnyNotNL",
    53  }
    54  
    55  func (i InstOp) String() string {
    56  	if uint(i) >= uint(len(instOpNames)) {
    57  		return ""
    58  	}
    59  	return instOpNames[i]
    60  }
    61  
    62  // An EmptyOp specifies a kind or mixture of zero-width assertions.
    63  type EmptyOp uint8
    64  
    65  const (
    66  	EmptyBeginLine EmptyOp = 1 << iota
    67  	EmptyEndLine
    68  	EmptyBeginText
    69  	EmptyEndText
    70  	EmptyWordBoundary
    71  	EmptyNoWordBoundary
    72  )
    73  
    74  // EmptyOpContext returns the zero-width assertions
    75  // satisfied at the position between the runes r1 and r2.
    76  // Passing r1 == -1 indicates that the position is
    77  // at the beginning of the text.
    78  // Passing r2 == -1 indicates that the position is
    79  // at the end of the text.
    80  func EmptyOpContext(r1, r2 rune) EmptyOp {
    81  	var op EmptyOp = EmptyNoWordBoundary
    82  	var boundary byte
    83  	switch {
    84  	case IsWordChar(r1):
    85  		boundary = 1
    86  	case r1 == '\n':
    87  		op |= EmptyBeginLine
    88  	case r1 < 0:
    89  		op |= EmptyBeginText | EmptyBeginLine
    90  	}
    91  	switch {
    92  	case IsWordChar(r2):
    93  		boundary ^= 1
    94  	case r2 == '\n':
    95  		op |= EmptyEndLine
    96  	case r2 < 0:
    97  		op |= EmptyEndText | EmptyEndLine
    98  	}
    99  	if boundary != 0 { // IsWordChar(r1) != IsWordChar(r2)
   100  		op ^= (EmptyWordBoundary | EmptyNoWordBoundary)
   101  	}
   102  	return op
   103  }
   104  
   105  // IsWordChar reports whether r is considered a “word character”
   106  // during the evaluation of the \b and \B zero-width assertions.
   107  // These assertions are ASCII-only: the word characters are [A-Za-z0-9_].
   108  func IsWordChar(r rune) bool {
   109  	return 'A' <= r && r <= 'Z' || 'a' <= r && r <= 'z' || '0' <= r && r <= '9' || r == '_'
   110  }
   111  
   112  // An Inst is a single instruction in a regular expression program.
   113  type Inst struct {
   114  	Op   InstOp
   115  	Out  uint32 // all but InstMatch, InstFail
   116  	Arg  uint32 // InstAlt, InstAltMatch, InstCapture, InstEmptyWidth
   117  	Rune []rune
   118  }
   119  
   120  func (p *Prog) String() string {
   121  	var b strings.Builder
   122  	dumpProg(&b, p)
   123  	return b.String()
   124  }
   125  
   126  // skipNop follows any no-op or capturing instructions.
   127  func (p *Prog) skipNop(pc uint32) *Inst {
   128  	i := &p.Inst[pc]
   129  	for i.Op == InstNop || i.Op == InstCapture {
   130  		i = &p.Inst[i.Out]
   131  	}
   132  	return i
   133  }
   134  
   135  // op returns i.Op but merges all the Rune special cases into InstRune
   136  func (i *Inst) op() InstOp {
   137  	op := i.Op
   138  	switch op {
   139  	case InstRune1, InstRuneAny, InstRuneAnyNotNL:
   140  		op = InstRune
   141  	}
   142  	return op
   143  }
   144  
   145  // Prefix returns a literal string that all matches for the
   146  // regexp must start with. Complete is true if the prefix
   147  // is the entire match.
   148  func (p *Prog) Prefix() (prefix string, complete bool) {
   149  	i := p.skipNop(uint32(p.Start))
   150  
   151  	// Avoid allocation of buffer if prefix is empty.
   152  	if i.op() != InstRune || len(i.Rune) != 1 {
   153  		return "", i.Op == InstMatch
   154  	}
   155  
   156  	// Have prefix; gather characters.
   157  	var buf strings.Builder
   158  	for i.op() == InstRune && len(i.Rune) == 1 && Flags(i.Arg)&FoldCase == 0 && i.Rune[0] != utf8.RuneError {
   159  		buf.WriteRune(i.Rune[0])
   160  		i = p.skipNop(i.Out)
   161  	}
   162  	return buf.String(), i.Op == InstMatch
   163  }
   164  
   165  // StartCond returns the leading empty-width conditions that must
   166  // be true in any match. It returns ^EmptyOp(0) if no matches are possible.
   167  func (p *Prog) StartCond() EmptyOp {
   168  	var flag EmptyOp
   169  	pc := uint32(p.Start)
   170  	i := &p.Inst[pc]
   171  Loop:
   172  	for {
   173  		switch i.Op {
   174  		case InstEmptyWidth:
   175  			flag |= EmptyOp(i.Arg)
   176  		case InstFail:
   177  			return ^EmptyOp(0)
   178  		case InstCapture, InstNop:
   179  			// skip
   180  		default:
   181  			break Loop
   182  		}
   183  		pc = i.Out
   184  		i = &p.Inst[pc]
   185  	}
   186  	return flag
   187  }
   188  
   189  const noMatch = -1
   190  
   191  // MatchRune reports whether the instruction matches (and consumes) r.
   192  // It should only be called when i.Op == InstRune.
   193  func (i *Inst) MatchRune(r rune) bool {
   194  	return i.MatchRunePos(r) != noMatch
   195  }
   196  
   197  // MatchRunePos checks whether the instruction matches (and consumes) r.
   198  // If so, MatchRunePos returns the index of the matching rune pair
   199  // (or, when len(i.Rune) == 1, rune singleton).
   200  // If not, MatchRunePos returns -1.
   201  // MatchRunePos should only be called when i.Op == InstRune.
   202  func (i *Inst) MatchRunePos(r rune) int {
   203  	rune := i.Rune
   204  
   205  	switch len(rune) {
   206  	case 0:
   207  		return noMatch
   208  
   209  	case 1:
   210  		// Special case: single-rune slice is from literal string, not char class.
   211  		r0 := rune[0]
   212  		if r == r0 {
   213  			return 0
   214  		}
   215  		if Flags(i.Arg)&FoldCase != 0 {
   216  			for r1 := unicode.SimpleFold(r0); r1 != r0; r1 = unicode.SimpleFold(r1) {
   217  				if r == r1 {
   218  					return 0
   219  				}
   220  			}
   221  		}
   222  		return noMatch
   223  
   224  	case 2:
   225  		if r >= rune[0] && r <= rune[1] {
   226  			return 0
   227  		}
   228  		return noMatch
   229  
   230  	case 4, 6, 8:
   231  		// Linear search for a few pairs.
   232  		// Should handle ASCII well.
   233  		for j := 0; j < len(rune); j += 2 {
   234  			if r < rune[j] {
   235  				return noMatch
   236  			}
   237  			if r <= rune[j+1] {
   238  				return j / 2
   239  			}
   240  		}
   241  		return noMatch
   242  	}
   243  
   244  	// Otherwise binary search.
   245  	lo := 0
   246  	hi := len(rune) / 2
   247  	for lo < hi {
   248  		m := lo + (hi-lo)/2
   249  		if c := rune[2*m]; c <= r {
   250  			if r <= rune[2*m+1] {
   251  				return m
   252  			}
   253  			lo = m + 1
   254  		} else {
   255  			hi = m
   256  		}
   257  	}
   258  	return noMatch
   259  }
   260  
   261  // MatchEmptyWidth reports whether the instruction matches
   262  // an empty string between the runes before and after.
   263  // It should only be called when i.Op == InstEmptyWidth.
   264  func (i *Inst) MatchEmptyWidth(before rune, after rune) bool {
   265  	switch EmptyOp(i.Arg) {
   266  	case EmptyBeginLine:
   267  		return before == '\n' || before == -1
   268  	case EmptyEndLine:
   269  		return after == '\n' || after == -1
   270  	case EmptyBeginText:
   271  		return before == -1
   272  	case EmptyEndText:
   273  		return after == -1
   274  	case EmptyWordBoundary:
   275  		return IsWordChar(before) != IsWordChar(after)
   276  	case EmptyNoWordBoundary:
   277  		return IsWordChar(before) == IsWordChar(after)
   278  	}
   279  	panic("unknown empty width arg")
   280  }
   281  
   282  func (i *Inst) String() string {
   283  	var b strings.Builder
   284  	dumpInst(&b, i)
   285  	return b.String()
   286  }
   287  
   288  func bw(b *strings.Builder, args ...string) {
   289  	for _, s := range args {
   290  		b.WriteString(s)
   291  	}
   292  }
   293  
   294  func dumpProg(b *strings.Builder, p *Prog) {
   295  	for j := range p.Inst {
   296  		i := &p.Inst[j]
   297  		pc := strconv.Itoa(j)
   298  		if len(pc) < 3 {
   299  			b.WriteString("   "[len(pc):])
   300  		}
   301  		if j == p.Start {
   302  			pc += "*"
   303  		}
   304  		bw(b, pc, "\t")
   305  		dumpInst(b, i)
   306  		bw(b, "\n")
   307  	}
   308  }
   309  
   310  func u32(i uint32) string {
   311  	return strconv.FormatUint(uint64(i), 10)
   312  }
   313  
   314  func dumpInst(b *strings.Builder, i *Inst) {
   315  	switch i.Op {
   316  	case InstAlt:
   317  		bw(b, "alt -> ", u32(i.Out), ", ", u32(i.Arg))
   318  	case InstAltMatch:
   319  		bw(b, "altmatch -> ", u32(i.Out), ", ", u32(i.Arg))
   320  	case InstCapture:
   321  		bw(b, "cap ", u32(i.Arg), " -> ", u32(i.Out))
   322  	case InstEmptyWidth:
   323  		bw(b, "empty ", u32(i.Arg), " -> ", u32(i.Out))
   324  	case InstMatch:
   325  		bw(b, "match")
   326  	case InstFail:
   327  		bw(b, "fail")
   328  	case InstNop:
   329  		bw(b, "nop -> ", u32(i.Out))
   330  	case InstRune:
   331  		if i.Rune == nil {
   332  			// shouldn't happen
   333  			bw(b, "rune <nil>")
   334  		}
   335  		bw(b, "rune ", strconv.QuoteToASCII(string(i.Rune)))
   336  		if Flags(i.Arg)&FoldCase != 0 {
   337  			bw(b, "/i")
   338  		}
   339  		bw(b, " -> ", u32(i.Out))
   340  	case InstRune1:
   341  		bw(b, "rune1 ", strconv.QuoteToASCII(string(i.Rune)), " -> ", u32(i.Out))
   342  	case InstRuneAny:
   343  		bw(b, "any -> ", u32(i.Out))
   344  	case InstRuneAnyNotNL:
   345  		bw(b, "anynotnl -> ", u32(i.Out))
   346  	}
   347  }
   348
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