1 files changed, 296 insertions, 0 deletions
diff --git a/src/regexp/syntax/compile.go b/src/regexp/syntax/compile.go
new file mode 100644
index 0000000..c9f9fa0
--- /dev/null
+++ b/src/regexp/syntax/compile.go
@@ -0,0 +1,296 @@
+// Copyright 2011 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package syntax
+
+import "unicode"
+
+// A patchList is a list of instruction pointers that need to be filled in (patched).
+// Because the pointers haven't been filled in yet, we can reuse their storage
+// to hold the list. It's kind of sleazy, but works well in practice.
+// See https://swtch.com/~rsc/regexp/regexp1.html for inspiration.
+//
+// These aren't really pointers: they're integers, so we can reinterpret them
+// this way without using package unsafe. A value l.head denotes
+// p.inst[l.head>>1].Out (l.head&1==0) or .Arg (l.head&1==1).
+// head == 0 denotes the empty list, okay because we start every program
+// with a fail instruction, so we'll never want to point at its output link.
+type patchList struct {
+	head, tail uint32
+}
+
+func makePatchList(n uint32) patchList {
+	return patchList{n, n}
+}
+
+func (l patchList) patch(p *Prog, val uint32) {
+	head := l.head
+	for head != 0 {
+		i := &p.Inst[head>>1]
+		if head&1 == 0 {
+			head = i.Out
+			i.Out = val
+		} else {
+			head = i.Arg
+			i.Arg = val
+		}
+	}
+}
+
+func (l1 patchList) append(p *Prog, l2 patchList) patchList {
+	if l1.head == 0 {
+		return l2
+	}
+	if l2.head == 0 {
+		return l1
+	}
+
+	i := &p.Inst[l1.tail>>1]
+	if l1.tail&1 == 0 {
+		i.Out = l2.head
+	} else {
+		i.Arg = l2.head
+	}
+	return patchList{l1.head, l2.tail}
+}
+
+// A frag represents a compiled program fragment.
+type frag struct {
+	i        uint32    // index of first instruction
+	out      patchList // where to record end instruction
+	nullable bool      // whether fragment can match empty string
+}
+
+type compiler struct {
+	p *Prog
+}
+
+// Compile compiles the regexp into a program to be executed.
+// The regexp should have been simplified already (returned from re.Simplify).
+func Compile(re *Regexp) (*Prog, error) {
+	var c compiler
+	c.init()
+	f := c.compile(re)
+	f.out.patch(c.p, c.inst(InstMatch).i)
+	c.p.Start = int(f.i)
+	return c.p, nil
+}
+
+func (c *compiler) init() {
+	c.p = new(Prog)
+	c.p.NumCap = 2 // implicit ( and ) for whole match $0
+	c.inst(InstFail)
+}
+
+var anyRuneNotNL = []rune{0, '\n' - 1, '\n' + 1, unicode.MaxRune}
+var anyRune = []rune{0, unicode.MaxRune}
+
+func (c *compiler) compile(re *Regexp) frag {
+	switch re.Op {
+	case OpNoMatch:
+		return c.fail()
+	case OpEmptyMatch:
+		return c.nop()
+	case OpLiteral:
+		if len(re.Rune) == 0 {
+			return c.nop()
+		}
+		var f frag
+		for j := range re.Rune {
+			f1 := c.rune(re.Rune[j:j+1], re.Flags)
+			if j == 0 {
+				f = f1
+			} else {
+				f = c.cat(f, f1)
+			}
+		}
+		return f
+	case OpCharClass:
+		return c.rune(re.Rune, re.Flags)
+	case OpAnyCharNotNL:
+		return c.rune(anyRuneNotNL, 0)
+	case OpAnyChar:
+		return c.rune(anyRune, 0)
+	case OpBeginLine:
+		return c.empty(EmptyBeginLine)
+	case OpEndLine:
+		return c.empty(EmptyEndLine)
+	case OpBeginText:
+		return c.empty(EmptyBeginText)
+	case OpEndText:
+		return c.empty(EmptyEndText)
+	case OpWordBoundary:
+		return c.empty(EmptyWordBoundary)
+	case OpNoWordBoundary:
+		return c.empty(EmptyNoWordBoundary)
+	case OpCapture:
+		bra := c.cap(uint32(re.Cap << 1))
+		sub := c.compile(re.Sub[0])
+		ket := c.cap(uint32(re.Cap<<1 | 1))
+		return c.cat(c.cat(bra, sub), ket)
+	case OpStar:
+		return c.star(c.compile(re.Sub[0]), re.Flags&NonGreedy != 0)
+	case OpPlus:
+		return c.plus(c.compile(re.Sub[0]), re.Flags&NonGreedy != 0)
+	case OpQuest:
+		return c.quest(c.compile(re.Sub[0]), re.Flags&NonGreedy != 0)
+	case OpConcat:
+		if len(re.Sub) == 0 {
+			return c.nop()
+		}
+		var f frag
+		for i, sub := range re.Sub {
+			if i == 0 {
+				f = c.compile(sub)
+			} else {
+				f = c.cat(f, c.compile(sub))
+			}
+		}
+		return f
+	case OpAlternate:
+		var f frag
+		for _, sub := range re.Sub {
+			f = c.alt(f, c.compile(sub))
+		}
+		return f
+	}
+	panic("regexp: unhandled case in compile")
+}
+
+func (c *compiler) inst(op InstOp) frag {
+	// TODO: impose length limit
+	f := frag{i: uint32(len(c.p.Inst)), nullable: true}
+	c.p.Inst = append(c.p.Inst, Inst{Op: op})
+	return f
+}
+
+func (c *compiler) nop() frag {
+	f := c.inst(InstNop)
+	f.out = makePatchList(f.i << 1)
+	return f
+}
+
+func (c *compiler) fail() frag {
+	return frag{}
+}
+
+func (c *compiler) cap(arg uint32) frag {
+	f := c.inst(InstCapture)
+	f.out = makePatchList(f.i << 1)
+	c.p.Inst[f.i].Arg = arg
+
+	if c.p.NumCap < int(arg)+1 {
+		c.p.NumCap = int(arg) + 1
+	}
+	return f
+}
+
+func (c *compiler) cat(f1, f2 frag) frag {
+	// concat of failure is failure
+	if f1.i == 0 || f2.i == 0 {
+		return frag{}
+	}
+
+	// TODO: elide nop
+
+	f1.out.patch(c.p, f2.i)
+	return frag{f1.i, f2.out, f1.nullable && f2.nullable}
+}
+
+func (c *compiler) alt(f1, f2 frag) frag {
+	// alt of failure is other
+	if f1.i == 0 {
+		return f2
+	}
+	if f2.i == 0 {
+		return f1
+	}
+
+	f := c.inst(InstAlt)
+	i := &c.p.Inst[f.i]
+	i.Out = f1.i
+	i.Arg = f2.i
+	f.out = f1.out.append(c.p, f2.out)
+	f.nullable = f1.nullable || f2.nullable
+	return f
+}
+
+func (c *compiler) quest(f1 frag, nongreedy bool) frag {
+	f := c.inst(InstAlt)
+	i := &c.p.Inst[f.i]
+	if nongreedy {
+		i.Arg = f1.i
+		f.out = makePatchList(f.i << 1)
+	} else {
+		i.Out = f1.i
+		f.out = makePatchList(f.i<<1 | 1)
+	}
+	f.out = f.out.append(c.p, f1.out)
+	return f
+}
+
+// loop returns the fragment for the main loop of a plus or star.
+// For plus, it can be used after changing the entry to f1.i.
+// For star, it can be used directly when f1 can't match an empty string.
+// (When f1 can match an empty string, f1* must be implemented as (f1+)?
+// to get the priority match order correct.)
+func (c *compiler) loop(f1 frag, nongreedy bool) frag {
+	f := c.inst(InstAlt)
+	i := &c.p.Inst[f.i]
+	if nongreedy {
+		i.Arg = f1.i
+		f.out = makePatchList(f.i << 1)
+	} else {
+		i.Out = f1.i
+		f.out = makePatchList(f.i<<1 | 1)
+	}
+	f1.out.patch(c.p, f.i)
+	return f
+}
+
+func (c *compiler) star(f1 frag, nongreedy bool) frag {
+	if f1.nullable {
+		// Use (f1+)? to get priority match order correct.
+		// See golang.org/issue/46123.
+		return c.quest(c.plus(f1, nongreedy), nongreedy)
+	}
+	return c.loop(f1, nongreedy)
+}
+
+func (c *compiler) plus(f1 frag, nongreedy bool) frag {
+	return frag{f1.i, c.loop(f1, nongreedy).out, f1.nullable}
+}
+
+func (c *compiler) empty(op EmptyOp) frag {
+	f := c.inst(InstEmptyWidth)
+	c.p.Inst[f.i].Arg = uint32(op)
+	f.out = makePatchList(f.i << 1)
+	return f
+}
+
+func (c *compiler) rune(r []rune, flags Flags) frag {
+	f := c.inst(InstRune)
+	f.nullable = false
+	i := &c.p.Inst[f.i]
+	i.Rune = r
+	flags &= FoldCase // only relevant flag is FoldCase
+	if len(r) != 1 || unicode.SimpleFold(r[0]) == r[0] {
+		// and sometimes not even that
+		flags &^= FoldCase
+	}
+	i.Arg = uint32(flags)
+	f.out = makePatchList(f.i << 1)
+
+	// Special cases for exec machine.
+	switch {
+	case flags&FoldCase == 0 && (len(r) == 1 || len(r) == 2 && r[0] == r[1]):
+		i.Op = InstRune1
+	case len(r) == 2 && r[0] == 0 && r[1] == unicode.MaxRune:
+		i.Op = InstRuneAny
+	case len(r) == 4 && r[0] == 0 && r[1] == '\n'-1 && r[2] == '\n'+1 && r[3] == unicode.MaxRune:
+		i.Op = InstRuneAnyNotNL
+	}
+
+	return f
+}