compile.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 "unicode"
     8  
     9  // A patchList is a list of instruction pointers that need to be filled in (patched).
    10  // Because the pointers haven't been filled in yet, we can reuse their storage
    11  // to hold the list. It's kind of sleazy, but works well in practice.
    12  // See https://swtch.com/~rsc/regexp/regexp1.html for inspiration.
    13  //
    14  // These aren't really pointers: they're integers, so we can reinterpret them
    15  // this way without using package unsafe. A value l.head denotes
    16  // p.inst[l.head>>1].Out (l.head&1==0) or .Arg (l.head&1==1).
    17  // head == 0 denotes the empty list, okay because we start every program
    18  // with a fail instruction, so we'll never want to point at its output link.
    19  type patchList struct {
    20  	head, tail uint32
    21  }
    22  
    23  func makePatchList(n uint32) patchList {
    24  	return patchList{n, n}
    25  }
    26  
    27  func (l patchList) patch(p *Prog, val uint32) {
    28  	head := l.head
    29  	for head != 0 {
    30  		i := &p.Inst[head>>1]
    31  		if head&1 == 0 {
    32  			head = i.Out
    33  			i.Out = val
    34  		} else {
    35  			head = i.Arg
    36  			i.Arg = val
    37  		}
    38  	}
    39  }
    40  
    41  func (l1 patchList) append(p *Prog, l2 patchList) patchList {
    42  	if l1.head == 0 {
    43  		return l2
    44  	}
    45  	if l2.head == 0 {
    46  		return l1
    47  	}
    48  
    49  	i := &p.Inst[l1.tail>>1]
    50  	if l1.tail&1 == 0 {
    51  		i.Out = l2.head
    52  	} else {
    53  		i.Arg = l2.head
    54  	}
    55  	return patchList{l1.head, l2.tail}
    56  }
    57  
    58  // A frag represents a compiled program fragment.
    59  type frag struct {
    60  	i   uint32    // index of first instruction
    61  	out patchList // where to record end instruction
    62  }
    63  
    64  type compiler struct {
    65  	p *Prog
    66  }
    67  
    68  // Compile compiles the regexp into a program to be executed.
    69  // The regexp should have been simplified already (returned from re.Simplify).
    70  func Compile(re *Regexp) (*Prog, error) {
    71  	var c compiler
    72  	c.init()
    73  	f := c.compile(re)
    74  	f.out.patch(c.p, c.inst(InstMatch).i)
    75  	c.p.Start = int(f.i)
    76  	return c.p, nil
    77  }
    78  
    79  func (c *compiler) init() {
    80  	c.p = new(Prog)
    81  	c.p.NumCap = 2 // implicit ( and ) for whole match $0
    82  	c.inst(InstFail)
    83  }
    84  
    85  var anyRuneNotNL = []rune{0, '\n' - 1, '\n' + 1, unicode.MaxRune}
    86  var anyRune = []rune{0, unicode.MaxRune}
    87  
    88  func (c *compiler) compile(re *Regexp) frag {
    89  	switch re.Op {
    90  	case OpNoMatch:
    91  		return c.fail()
    92  	case OpEmptyMatch:
    93  		return c.nop()
    94  	case OpLiteral:
    95  		if len(re.Rune) == 0 {
    96  			return c.nop()
    97  		}
    98  		var f frag
    99  		for j := range re.Rune {
   100  			f1 := c.rune(re.Rune[j:j+1], re.Flags)
   101  			if j == 0 {
   102  				f = f1
   103  			} else {
   104  				f = c.cat(f, f1)
   105  			}
   106  		}
   107  		return f
   108  	case OpCharClass:
   109  		return c.rune(re.Rune, re.Flags)
   110  	case OpAnyCharNotNL:
   111  		return c.rune(anyRuneNotNL, 0)
   112  	case OpAnyChar:
   113  		return c.rune(anyRune, 0)
   114  	case OpBeginLine:
   115  		return c.empty(EmptyBeginLine)
   116  	case OpEndLine:
   117  		return c.empty(EmptyEndLine)
   118  	case OpBeginText:
   119  		return c.empty(EmptyBeginText)
   120  	case OpEndText:
   121  		return c.empty(EmptyEndText)
   122  	case OpWordBoundary:
   123  		return c.empty(EmptyWordBoundary)
   124  	case OpNoWordBoundary:
   125  		return c.empty(EmptyNoWordBoundary)
   126  	case OpCapture:
   127  		bra := c.cap(uint32(re.Cap << 1))
   128  		sub := c.compile(re.Sub[0])
   129  		ket := c.cap(uint32(re.Cap<<1 | 1))
   130  		return c.cat(c.cat(bra, sub), ket)
   131  	case OpStar:
   132  		return c.star(c.compile(re.Sub[0]), re.Flags&NonGreedy != 0)
   133  	case OpPlus:
   134  		return c.plus(c.compile(re.Sub[0]), re.Flags&NonGreedy != 0)
   135  	case OpQuest:
   136  		return c.quest(c.compile(re.Sub[0]), re.Flags&NonGreedy != 0)
   137  	case OpConcat:
   138  		if len(re.Sub) == 0 {
   139  			return c.nop()
   140  		}
   141  		var f frag
   142  		for i, sub := range re.Sub {
   143  			if i == 0 {
   144  				f = c.compile(sub)
   145  			} else {
   146  				f = c.cat(f, c.compile(sub))
   147  			}
   148  		}
   149  		return f
   150  	case OpAlternate:
   151  		var f frag
   152  		for _, sub := range re.Sub {
   153  			f = c.alt(f, c.compile(sub))
   154  		}
   155  		return f
   156  	}
   157  	panic("regexp: unhandled case in compile")
   158  }
   159  
   160  func (c *compiler) inst(op InstOp) frag {
   161  	// TODO: impose length limit
   162  	f := frag{i: uint32(len(c.p.Inst))}
   163  	c.p.Inst = append(c.p.Inst, Inst{Op: op})
   164  	return f
   165  }
   166  
   167  func (c *compiler) nop() frag {
   168  	f := c.inst(InstNop)
   169  	f.out = makePatchList(f.i << 1)
   170  	return f
   171  }
   172  
   173  func (c *compiler) fail() frag {
   174  	return frag{}
   175  }
   176  
   177  func (c *compiler) cap(arg uint32) frag {
   178  	f := c.inst(InstCapture)
   179  	f.out = makePatchList(f.i << 1)
   180  	c.p.Inst[f.i].Arg = arg
   181  
   182  	if c.p.NumCap < int(arg)+1 {
   183  		c.p.NumCap = int(arg) + 1
   184  	}
   185  	return f
   186  }
   187  
   188  func (c *compiler) cat(f1, f2 frag) frag {
   189  	// concat of failure is failure
   190  	if f1.i == 0 || f2.i == 0 {
   191  		return frag{}
   192  	}
   193  
   194  	// TODO: elide nop
   195  
   196  	f1.out.patch(c.p, f2.i)
   197  	return frag{f1.i, f2.out}
   198  }
   199  
   200  func (c *compiler) alt(f1, f2 frag) frag {
   201  	// alt of failure is other
   202  	if f1.i == 0 {
   203  		return f2
   204  	}
   205  	if f2.i == 0 {
   206  		return f1
   207  	}
   208  
   209  	f := c.inst(InstAlt)
   210  	i := &c.p.Inst[f.i]
   211  	i.Out = f1.i
   212  	i.Arg = f2.i
   213  	f.out = f1.out.append(c.p, f2.out)
   214  	return f
   215  }
   216  
   217  func (c *compiler) quest(f1 frag, nongreedy bool) frag {
   218  	f := c.inst(InstAlt)
   219  	i := &c.p.Inst[f.i]
   220  	if nongreedy {
   221  		i.Arg = f1.i
   222  		f.out = makePatchList(f.i << 1)
   223  	} else {
   224  		i.Out = f1.i
   225  		f.out = makePatchList(f.i<<1 | 1)
   226  	}
   227  	f.out = f.out.append(c.p, f1.out)
   228  	return f
   229  }
   230  
   231  func (c *compiler) star(f1 frag, nongreedy bool) frag {
   232  	f := c.inst(InstAlt)
   233  	i := &c.p.Inst[f.i]
   234  	if nongreedy {
   235  		i.Arg = f1.i
   236  		f.out = makePatchList(f.i << 1)
   237  	} else {
   238  		i.Out = f1.i
   239  		f.out = makePatchList(f.i<<1 | 1)
   240  	}
   241  	f1.out.patch(c.p, f.i)
   242  	return f
   243  }
   244  
   245  func (c *compiler) plus(f1 frag, nongreedy bool) frag {
   246  	return frag{f1.i, c.star(f1, nongreedy).out}
   247  }
   248  
   249  func (c *compiler) empty(op EmptyOp) frag {
   250  	f := c.inst(InstEmptyWidth)
   251  	c.p.Inst[f.i].Arg = uint32(op)
   252  	f.out = makePatchList(f.i << 1)
   253  	return f
   254  }
   255  
   256  func (c *compiler) rune(r []rune, flags Flags) frag {
   257  	f := c.inst(InstRune)
   258  	i := &c.p.Inst[f.i]
   259  	i.Rune = r
   260  	flags &= FoldCase // only relevant flag is FoldCase
   261  	if len(r) != 1 || unicode.SimpleFold(r[0]) == r[0] {
   262  		// and sometimes not even that
   263  		flags &^= FoldCase
   264  	}
   265  	i.Arg = uint32(flags)
   266  	f.out = makePatchList(f.i << 1)
   267  
   268  	// Special cases for exec machine.
   269  	switch {
   270  	case flags&FoldCase == 0 && (len(r) == 1 || len(r) == 2 && r[0] == r[1]):
   271  		i.Op = InstRune1
   272  	case len(r) == 2 && r[0] == 0 && r[1] == unicode.MaxRune:
   273  		i.Op = InstRuneAny
   274  	case len(r) == 4 && r[0] == 0 && r[1] == '\n'-1 && r[2] == '\n'+1 && r[3] == unicode.MaxRune:
   275  		i.Op = InstRuneAnyNotNL
   276  	}
   277  
   278  	return f
   279  }
   280
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