exp/regexp/syntax: finish Regexp manipulation
Except for the inevitable bug fixes, the Regexp code is done.
R=sam.thorogood, r
CC=golang-dev
https://golang.org/cl/4635082
diff --git a/src/pkg/exp/regexp/syntax/parse.go b/src/pkg/exp/regexp/syntax/parse.go
index ae40d5f..b6c91f7 100644
--- a/src/pkg/exp/regexp/syntax/parse.go
+++ b/src/pkg/exp/regexp/syntax/parse.go
@@ -106,8 +106,6 @@
// push pushes the regexp re onto the parse stack and returns the regexp.
func (p *parser) push(re *Regexp) *Regexp {
- // TODO: compute simple
-
if re.Op == OpCharClass && len(re.Rune) == 2 && re.Rune[0] == re.Rune[1] {
// Single rune.
if p.maybeConcat(re.Rune[0], p.flags&^FoldCase) {
@@ -250,7 +248,7 @@
return p.push(p.newRegexp(OpEmptyMatch))
}
- return p.collapse(subs, OpConcat)
+ return p.push(p.collapse(subs, OpConcat))
}
// alternate replaces the top of the stack (above the topmost '(') with its alternation.
@@ -276,7 +274,7 @@
return p.push(p.newRegexp(OpNoMatch))
}
- return p.collapse(subs, OpAlternate)
+ return p.push(p.collapse(subs, OpAlternate))
}
// cleanAlt cleans re for eventual inclusion in an alternation.
@@ -302,13 +300,13 @@
}
}
-// collapse pushes the result of applying op to sub
-// onto the stack. If sub contains op nodes, they all
-// get flattened into a single node.
-// sub points into p.stack so it cannot be kept.
+// collapse returns the result of applying op to sub.
+// If sub contains op nodes, they all get hoisted up
+// so that there is never a concat of a concat or an
+// alternate of an alternate.
func (p *parser) collapse(subs []*Regexp, op Op) *Regexp {
if len(subs) == 1 {
- return p.push(subs[0])
+ return subs[0]
}
re := p.newRegexp(op)
re.Sub = re.Sub0[:0]
@@ -320,7 +318,295 @@
re.Sub = append(re.Sub, sub)
}
}
- return p.push(re)
+ if op == OpAlternate {
+ re.Sub = p.factor(re.Sub, re.Flags)
+ if len(re.Sub) == 1 {
+ old := re
+ re = re.Sub[0]
+ p.reuse(old)
+ }
+ }
+ return re
+}
+
+// factor factors common prefixes from the alternation list sub.
+// It returns a replacement list that reuses the same storage and
+// frees (passes to p.reuse) any removed *Regexps.
+//
+// For example,
+// ABC|ABD|AEF|BCX|BCY
+// simplifies by literal prefix extraction to
+// A(B(C|D)|EF)|BC(X|Y)
+// which simplifies by character class introduction to
+// A(B[CD]|EF)|BC[XY]
+//
+func (p *parser) factor(sub []*Regexp, flags Flags) []*Regexp {
+ if len(sub) < 2 {
+ return sub
+ }
+
+ // Round 1: Factor out common literal prefixes.
+ var str []int
+ var strflags Flags
+ start := 0
+ out := sub[:0]
+ for i := 0; i <= len(sub); i++ {
+ // Invariant: the Regexps that were in sub[0:start] have been
+ // used or marked for reuse, and the slice space has been reused
+ // for out (len(out) <= start).
+ //
+ // Invariant: sub[start:i] consists of regexps that all begin
+ // with str as modified by strflags.
+ var istr []int
+ var iflags Flags
+ if i < len(sub) {
+ istr, iflags = p.leadingString(sub[i])
+ if iflags == strflags {
+ same := 0
+ for same < len(str) && same < len(istr) && str[same] == istr[same] {
+ same++
+ }
+ if same > 0 {
+ // Matches at least one rune in current range.
+ // Keep going around.
+ str = str[:same]
+ continue
+ }
+ }
+ }
+
+ // Found end of a run with common leading literal string:
+ // sub[start:i] all begin with str[0:len(str)], but sub[i]
+ // does not even begin with str[0].
+ //
+ // Factor out common string and append factored expression to out.
+ if i == start {
+ // Nothing to do - run of length 0.
+ } else if i == start+1 {
+ // Just one: don't bother factoring.
+ out = append(out, sub[start])
+ } else {
+ // Construct factored form: prefix(suffix1|suffix2|...)
+ prefix := p.newRegexp(OpLiteral)
+ prefix.Flags = strflags
+ prefix.Rune = append(prefix.Rune[:0], str...)
+
+ for j := start; j < i; j++ {
+ sub[j] = p.removeLeadingString(sub[j], len(str))
+ }
+ suffix := p.collapse(sub[start:i], OpAlternate) // recurse
+
+ re := p.newRegexp(OpConcat)
+ re.Sub = append(re.Sub[:0], prefix, suffix)
+ out = append(out, re)
+ }
+
+ // Prepare for next iteration.
+ start = i
+ str = istr
+ strflags = iflags
+ }
+ sub = out
+
+ // Round 2: Factor out common complex prefixes,
+ // just the first piece of each concatenation,
+ // whatever it is. This is good enough a lot of the time.
+ start = 0
+ out = sub[:0]
+ var first *Regexp
+ for i := 0; i <= len(sub); i++ {
+ // Invariant: the Regexps that were in sub[0:start] have been
+ // used or marked for reuse, and the slice space has been reused
+ // for out (len(out) <= start).
+ //
+ // Invariant: sub[start:i] consists of regexps that all begin
+ // with str as modified by strflags.
+ var ifirst *Regexp
+ if i < len(sub) {
+ ifirst = p.leadingRegexp(sub[i])
+ if first != nil && first.Equal(ifirst) {
+ continue
+ }
+ }
+
+ // Found end of a run with common leading regexp:
+ // sub[start:i] all begin with first but sub[i] does not.
+ //
+ // Factor out common regexp and append factored expression to out.
+ if i == start {
+ // Nothing to do - run of length 0.
+ } else if i == start+1 {
+ // Just one: don't bother factoring.
+ out = append(out, sub[start])
+ } else {
+ // Construct factored form: prefix(suffix1|suffix2|...)
+ prefix := first
+
+ for j := start; j < i; j++ {
+ reuse := j != start // prefix came from sub[start]
+ sub[j] = p.removeLeadingRegexp(sub[j], reuse)
+ }
+ suffix := p.collapse(sub[start:i], OpAlternate) // recurse
+
+ re := p.newRegexp(OpConcat)
+ re.Sub = append(re.Sub[:0], prefix, suffix)
+ out = append(out, re)
+ }
+
+ // Prepare for next iteration.
+ start = i
+ first = ifirst
+ }
+ sub = out
+
+ // Round 3: Collapse runs of single literals into character classes.
+ start = 0
+ out = sub[:0]
+ for i := 0; i <= len(sub); i++ {
+ // Invariant: the Regexps that were in sub[0:start] have been
+ // used or marked for reuse, and the slice space has been reused
+ // for out (len(out) <= start).
+ //
+ // Invariant: sub[start:i] consists of regexps that are either
+ // literal runes or character classes.
+ if i < len(sub) && isCharClass(sub[i]) {
+ continue
+ }
+
+ // sub[i] is not a char or char class;
+ // emit char class for sub[start:i]...
+ if i == start {
+ // Nothing to do - run of length 0.
+ } else if i == start+1 {
+ out = append(out, sub[start])
+ } else {
+ // Make new char class.
+ // Start with most complex regexp in sub[start].
+ max := start
+ for j := start + 1; j < i; j++ {
+ if sub[max].Op < sub[j].Op || sub[max].Op == sub[j].Op && len(sub[max].Rune) < len(sub[j].Rune) {
+ max = j
+ }
+ }
+ sub[start], sub[max] = sub[max], sub[start]
+
+ for j := start + 1; j < i; j++ {
+ mergeCharClass(sub[start], sub[j])
+ p.reuse(sub[j])
+ }
+ cleanAlt(sub[start])
+ out = append(out, sub[start])
+ }
+
+ // ... and then emit sub[i].
+ if i < len(sub) {
+ out = append(out, sub[i])
+ }
+ start = i + 1
+ }
+ sub = out
+
+ // Round 4: Collapse runs of empty matches into a single empty match.
+ start = 0
+ out = sub[:0]
+ for i := range sub {
+ if i+1 < len(sub) && sub[i].Op == OpEmptyMatch && sub[i+1].Op == OpEmptyMatch {
+ continue
+ }
+ out = append(out, sub[i])
+ }
+ sub = out
+
+ return sub
+}
+
+// leadingString returns the leading literal string that re begins with.
+// The string refers to storage in re or its children.
+func (p *parser) leadingString(re *Regexp) ([]int, Flags) {
+ if re.Op == OpConcat && len(re.Sub) > 0 {
+ re = re.Sub[0]
+ }
+ if re.Op != OpLiteral {
+ return nil, 0
+ }
+ return re.Rune, re.Flags & FoldCase
+}
+
+// removeLeadingString removes the first n leading runes
+// from the beginning of re. It returns the replacement for re.
+func (p *parser) removeLeadingString(re *Regexp, n int) *Regexp {
+ if re.Op == OpConcat && len(re.Sub) > 0 {
+ // Removing a leading string in a concatenation
+ // might simplify the concatenation.
+ sub := re.Sub[0]
+ sub = p.removeLeadingString(sub, n)
+ re.Sub[0] = sub
+ if sub.Op == OpEmptyMatch {
+ p.reuse(sub)
+ switch len(re.Sub) {
+ case 0, 1:
+ // Impossible but handle.
+ re.Op = OpEmptyMatch
+ re.Sub = nil
+ case 2:
+ old := re
+ re = re.Sub[1]
+ p.reuse(old)
+ default:
+ copy(re.Sub, re.Sub[1:])
+ re.Sub = re.Sub[:len(re.Sub)-1]
+ }
+ }
+ return re
+ }
+
+ if re.Op == OpLiteral {
+ re.Rune = re.Rune[:copy(re.Rune, re.Rune[n:])]
+ if len(re.Rune) == 0 {
+ re.Op = OpEmptyMatch
+ }
+ }
+ return re
+}
+
+// leadingRegexp returns the leading regexp that re begins with.
+// The regexp refers to storage in re or its children.
+func (p *parser) leadingRegexp(re *Regexp) *Regexp {
+ if re.Op == OpEmptyMatch {
+ return nil
+ }
+ if re.Op == OpConcat && len(re.Sub) > 0 {
+ sub := re.Sub[0]
+ if sub.Op == OpEmptyMatch {
+ return nil
+ }
+ return sub
+ }
+ return re
+}
+
+// removeLeadingRegexp removes the leading regexp in re.
+// It returns the replacement for re.
+// If reuse is true, it passes the removed regexp (if no longer needed) to p.reuse.
+func (p *parser) removeLeadingRegexp(re *Regexp, reuse bool) *Regexp {
+ if re.Op == OpConcat && len(re.Sub) > 0 {
+ if reuse {
+ p.reuse(re.Sub[0])
+ }
+ re.Sub = re.Sub[:copy(re.Sub, re.Sub[1:])]
+ switch len(re.Sub) {
+ case 0:
+ re.Op = OpEmptyMatch
+ re.Sub = nil
+ case 1:
+ old := re
+ re = re.Sub[0]
+ p.reuse(old)
+ }
+ return re
+ }
+ re.Op = OpEmptyMatch
+ return re
}
func literalRegexp(s string, flags Flags) *Regexp {
@@ -752,6 +1038,36 @@
return nil
}
+// mergeCharClass makes dst = dst|src.
+// The caller must ensure that dst.Op >= src.Op,
+// to reduce the amount of copying.
+func mergeCharClass(dst, src *Regexp) {
+ switch dst.Op {
+ case OpAnyChar:
+ // src doesn't add anything.
+ case OpAnyCharNotNL:
+ // src might add \n
+ if matchRune(src, '\n') {
+ dst.Op = OpAnyChar
+ }
+ case OpCharClass:
+ // src is simpler, so either literal or char class
+ if src.Op == OpLiteral {
+ dst.Rune = appendRange(dst.Rune, src.Rune[0], src.Rune[0])
+ } else {
+ dst.Rune = appendClass(dst.Rune, src.Rune)
+ }
+ case OpLiteral:
+ // both literal
+ if src.Rune[0] == dst.Rune[0] {
+ break
+ }
+ dst.Op = OpCharClass
+ dst.Rune = append(dst.Rune, dst.Rune[0])
+ dst.Rune = appendRange(dst.Rune, src.Rune[0], src.Rune[0])
+ }
+}
+
// If the top of the stack is an element followed by an opVerticalBar
// swapVerticalBar swaps the two and returns true.
// Otherwise it returns false.
@@ -767,30 +1083,7 @@
re1, re3 = re3, re1
p.stack[n-3] = re3
}
- switch re3.Op {
- case OpAnyChar:
- // re1 doesn't add anything.
- case OpAnyCharNotNL:
- // re1 might add \n
- if matchRune(re1, '\n') {
- re3.Op = OpAnyChar
- }
- case OpCharClass:
- // re1 is simpler, so either literal or char class
- if re1.Op == OpLiteral {
- re3.Rune = appendRange(re3.Rune, re1.Rune[0], re1.Rune[0])
- } else {
- re3.Rune = appendClass(re3.Rune, re1.Rune)
- }
- case OpLiteral:
- // both literal
- if re1.Rune[0] == re3.Rune[0] {
- break
- }
- re3.Op = OpCharClass
- re3.Rune = append(re3.Rune, re3.Rune[0])
- re3.Rune = appendRange(re3.Rune, re1.Rune[0], re1.Rune[0])
- }
+ mergeCharClass(re3, re1)
p.reuse(re1)
p.stack = p.stack[:n-1]
return true
@@ -1432,10 +1725,11 @@
}
nextLo = hi + 1
}
+ r = r[:w]
if nextLo <= unicode.MaxRune {
// It's possible for the negation to have one more
// range - this one - than the original class, so use append.
- r = append(r[:w], nextLo, unicode.MaxRune)
+ r = append(r, nextLo, unicode.MaxRune)
}
return r
}
diff --git a/src/pkg/exp/regexp/syntax/parse_test.go b/src/pkg/exp/regexp/syntax/parse_test.go
index 51856b6..779b9afd 100644
--- a/src/pkg/exp/regexp/syntax/parse_test.go
+++ b/src/pkg/exp/regexp/syntax/parse_test.go
@@ -39,8 +39,7 @@
{`a{2,3}?`, `nrep{2,3 lit{a}}`},
{`a{2,}?`, `nrep{2,-1 lit{a}}`},
{``, `emp{}`},
- // { `|`, `emp{}` }, // alt{emp{}emp{}} but got factored
- {`|`, `alt{emp{}emp{}}`},
+ {`|`, `emp{}`}, // alt{emp{}emp{}} but got factored
{`|x|`, `alt{emp{}lit{x}emp{}}`},
{`.`, `dot{}`},
{`^`, `bol{}`},
@@ -64,6 +63,9 @@
{`\-`, `lit{-}`},
{`-`, `lit{-}`},
{`\_`, `lit{_}`},
+ {`abc`, `str{abc}`},
+ {`abc|def`, `alt{str{abc}str{def}}`},
+ {`abc|def|ghi`, `alt{str{abc}str{def}str{ghi}}`},
// Posix and Perl extensions
{`[[:lower:]]`, `cc{0x61-0x7a}`},
@@ -156,6 +158,10 @@
// Strings
{`abcde`, `str{abcde}`},
{`[Aa][Bb]cd`, `cat{strfold{AB}str{cd}}`},
+
+ // Factoring.
+ {`abc|abd|aef|bcx|bcy`, `alt{cat{lit{a}alt{cat{lit{b}cc{0x63-0x64}}str{ef}}}cat{str{bc}cc{0x78-0x79}}}`},
+ {`ax+y|ax+z|ay+w`, `cat{lit{a}alt{cat{plus{lit{x}}cc{0x79-0x7a}}cat{plus{lit{y}}lit{w}}}}`},
}
const testFlags = MatchNL | PerlX | UnicodeGroups
diff --git a/src/pkg/exp/regexp/syntax/regexp.go b/src/pkg/exp/regexp/syntax/regexp.go
index 248ace5..00a4add 100644
--- a/src/pkg/exp/regexp/syntax/regexp.go
+++ b/src/pkg/exp/regexp/syntax/regexp.go
@@ -60,6 +60,59 @@
const opPseudo Op = 128 // where pseudo-ops start
+// Equal returns true if x and y have identical structure.
+func (x *Regexp) Equal(y *Regexp) bool {
+ if x == nil || y == nil {
+ return x == y
+ }
+ if x.Op != y.Op {
+ return false
+ }
+ switch x.Op {
+ case OpEndText:
+ // The parse flags remember whether this is \z or \Z.
+ if x.Flags&WasDollar != y.Flags&WasDollar {
+ return false
+ }
+
+ case OpLiteral, OpCharClass:
+ if len(x.Rune) != len(y.Rune) {
+ return false
+ }
+ for i, r := range x.Rune {
+ if r != y.Rune[i] {
+ return false
+ }
+ }
+
+ case OpAlternate, OpConcat:
+ if len(x.Sub) != len(y.Sub) {
+ return false
+ }
+ for i, sub := range x.Sub {
+ if !sub.Equal(y.Sub[i]) {
+ return false
+ }
+ }
+
+ case OpStar, OpPlus, OpQuest:
+ if x.Flags&NonGreedy != y.Flags&NonGreedy || !x.Sub[0].Equal(y.Sub[0]) {
+ return false
+ }
+
+ case OpRepeat:
+ if x.Flags&NonGreedy != y.Flags&NonGreedy || x.Min != y.Min || x.Max != y.Max || !x.Sub[0].Equal(y.Sub[0]) {
+ return false
+ }
+
+ case OpCapture:
+ if x.Cap != y.Cap || x.Name != y.Name || !x.Sub[0].Equal(y.Sub[0]) {
+ return false
+ }
+ }
+ return true
+}
+
// writeRegexp writes the Perl syntax for the regular expression re to b.
func writeRegexp(b *bytes.Buffer, re *Regexp) {
switch re.Op {
@@ -70,16 +123,24 @@
case OpEmptyMatch:
b.WriteString(`(?:)`)
case OpLiteral:
+ if re.Flags&FoldCase != 0 {
+ b.WriteString(`(?i:`)
+ }
for _, r := range re.Rune {
escape(b, r, false)
}
+ if re.Flags&FoldCase != 0 {
+ b.WriteString(`)`)
+ }
case OpCharClass:
if len(re.Rune)%2 != 0 {
b.WriteString(`[invalid char class]`)
break
}
b.WriteRune('[')
- if len(re.Rune) > 0 && re.Rune[0] == 0 && re.Rune[len(re.Rune)-1] == unicode.MaxRune {
+ if len(re.Rune) == 0 {
+ b.WriteString(`^\x00-\x{10FFFF}`)
+ } else if re.Rune[0] == 0 && re.Rune[len(re.Rune)-1] == unicode.MaxRune {
// Contains 0 and MaxRune. Probably a negated class.
// Print the gaps.
b.WriteRune('^')
@@ -126,7 +187,9 @@
} else {
b.WriteRune('(')
}
- writeRegexp(b, re.Sub[0])
+ if re.Sub[0].Op != OpEmptyMatch {
+ writeRegexp(b, re.Sub[0])
+ }
b.WriteRune(')')
case OpStar, OpPlus, OpQuest, OpRepeat:
if sub := re.Sub[0]; sub.Op > OpCapture {
@@ -205,6 +268,15 @@
case '\v':
b.WriteString(`\v`)
default:
+ if r < 0x100 {
+ b.WriteString(`\x`)
+ s := strconv.Itob(r, 16)
+ if len(s) == 1 {
+ b.WriteRune('0')
+ }
+ b.WriteString(s)
+ break
+ }
b.WriteString(`\x{`)
b.WriteString(strconv.Itob(r, 16))
b.WriteString(`}`)
diff --git a/src/pkg/exp/regexp/syntax/simplify.go b/src/pkg/exp/regexp/syntax/simplify.go
new file mode 100644
index 0000000..7239041
--- /dev/null
+++ b/src/pkg/exp/regexp/syntax/simplify.go
@@ -0,0 +1,151 @@
+// 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
+
+// Simplify returns a regexp equivalent to re but without counted repetitions
+// and with various other simplifications, such as rewriting /(?:a+)+/ to /a+/.
+// The resulting regexp will execute correctly but its string representation
+// will not produce the same parse tree, because capturing parentheses
+// may have been duplicated or removed. For example, the simplified form
+// for /(x){1,2}/ is /(x)(x)?/ but both parentheses capture as $1.
+// The returned regexp may share structure with or be the original.
+func (re *Regexp) Simplify() *Regexp {
+ if re == nil {
+ return nil
+ }
+ switch re.Op {
+ case OpCapture, OpConcat, OpAlternate:
+ // Simplify children, building new Regexp if children change.
+ nre := re
+ for i, sub := range re.Sub {
+ nsub := sub.Simplify()
+ if nre == re && nsub != sub {
+ // Start a copy.
+ nre = new(Regexp)
+ *nre = *re
+ nre.Rune = nil
+ nre.Sub = append(nre.Sub0[:0], re.Sub[:i]...)
+ }
+ if nre != re {
+ nre.Sub = append(nre.Sub, nsub)
+ }
+ }
+ return nre
+
+ case OpStar, OpPlus, OpQuest:
+ sub := re.Sub[0].Simplify()
+ return simplify1(re.Op, re.Flags, sub, re)
+
+ case OpRepeat:
+ // Special special case: x{0} matches the empty string
+ // and doesn't even need to consider x.
+ if re.Min == 0 && re.Max == 0 {
+ return &Regexp{Op: OpEmptyMatch}
+ }
+
+ // The fun begins.
+ sub := re.Sub[0].Simplify()
+
+ // x{n,} means at least n matches of x.
+ if re.Max == -1 {
+ // Special case: x{0,} is x*.
+ if re.Min == 0 {
+ return simplify1(OpStar, re.Flags, sub, nil)
+ }
+
+ // Special case: x{1,} is x+.
+ if re.Min == 1 {
+ return simplify1(OpPlus, re.Flags, sub, nil)
+ }
+
+ // General case: x{4,} is xxxx+.
+ nre := &Regexp{Op: OpConcat}
+ nre.Sub = nre.Sub0[:0]
+ for i := 0; i < re.Min-1; i++ {
+ nre.Sub = append(nre.Sub, sub)
+ }
+ nre.Sub = append(nre.Sub, simplify1(OpPlus, re.Flags, sub, nil))
+ return nre
+ }
+
+ // Special case x{0} handled above.
+
+ // Special case: x{1} is just x.
+ if re.Min == 1 && re.Max == 1 {
+ return sub
+ }
+
+ // General case: x{n,m} means n copies of x and m copies of x?
+ // The machine will do less work if we nest the final m copies,
+ // so that x{2,5} = xx(x(x(x)?)?)?
+
+ // Build leading prefix: xx.
+ var prefix *Regexp
+ if re.Min > 0 {
+ prefix = &Regexp{Op: OpConcat}
+ prefix.Sub = prefix.Sub0[:0]
+ for i := 0; i < re.Min; i++ {
+ prefix.Sub = append(prefix.Sub, sub)
+ }
+ }
+
+ // Build and attach suffix: (x(x(x)?)?)?
+ if re.Max > re.Min {
+ suffix := simplify1(OpQuest, re.Flags, sub, nil)
+ for i := re.Min + 1; i < re.Max; i++ {
+ nre2 := &Regexp{Op: OpConcat}
+ nre2.Sub = append(nre2.Sub0[:0], sub, suffix)
+ suffix = simplify1(OpQuest, re.Flags, nre2, nil)
+ }
+ if prefix == nil {
+ return suffix
+ }
+ prefix.Sub = append(prefix.Sub, suffix)
+ }
+ if prefix != nil {
+ return prefix
+ }
+
+ // Some degenerate case like min > max or min < max < 0.
+ // Handle as impossible match.
+ return &Regexp{Op: OpNoMatch}
+ }
+
+ return re
+}
+
+// simplify1 implements Simplify for the unary OpStar,
+// OpPlus, and OpQuest operators. It returns the simple regexp
+// equivalent to
+//
+// Regexp{Op: op, Flags: flags, Sub: {sub}}
+//
+// under the assumption that sub is already simple, and
+// without first allocating that structure. If the regexp
+// to be returned turns out to be equivalent to re, simplify1
+// returns re instead.
+//
+// simplify1 is factored out of Simplify because the implementation
+// for other operators generates these unary expressions.
+// Letting them call simplify1 makes sure the expressions they
+// generate are simple.
+func simplify1(op Op, flags Flags, sub, re *Regexp) *Regexp {
+ // Special case: repeat the empty string as much as
+ // you want, but it's still the empty string.
+ if sub.Op == OpEmptyMatch {
+ return sub
+ }
+ // The operators are idempotent if the flags match.
+ if op == sub.Op && flags&NonGreedy == sub.Flags&NonGreedy {
+ return sub
+ }
+ if re != nil && re.Op == op && re.Flags&NonGreedy == flags&NonGreedy && sub == re.Sub[0] {
+ return re
+ }
+
+ re = &Regexp{Op: op, Flags: flags}
+ re.Sub = append(re.Sub0[:0], sub)
+ return re
+}
diff --git a/src/pkg/exp/regexp/syntax/simplify_test.go b/src/pkg/exp/regexp/syntax/simplify_test.go
new file mode 100644
index 0000000..c8cec21
--- /dev/null
+++ b/src/pkg/exp/regexp/syntax/simplify_test.go
@@ -0,0 +1,151 @@
+// 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 "testing"
+
+var simplifyTests = []struct {
+ Regexp string
+ Simple string
+}{
+ // Already-simple constructs
+ {`a`, `a`},
+ {`ab`, `ab`},
+ {`a|b`, `[a-b]`},
+ {`ab|cd`, `ab|cd`},
+ {`(ab)*`, `(ab)*`},
+ {`(ab)+`, `(ab)+`},
+ {`(ab)?`, `(ab)?`},
+ {`.`, `.`},
+ {`^`, `^`},
+ {`$`, `$`},
+ {`[ac]`, `[ac]`},
+ {`[^ac]`, `[^ac]`},
+
+ // Posix character classes
+ {`[[:alnum:]]`, `[0-9A-Za-z]`},
+ {`[[:alpha:]]`, `[A-Za-z]`},
+ {`[[:blank:]]`, `[\t ]`},
+ {`[[:cntrl:]]`, `[\x00-\x1f\x7f]`},
+ {`[[:digit:]]`, `[0-9]`},
+ {`[[:graph:]]`, `[!-~]`},
+ {`[[:lower:]]`, `[a-z]`},
+ {`[[:print:]]`, `[ -~]`},
+ {`[[:punct:]]`, "[!-/:-@\\[-`\\{-~]"},
+ {`[[:space:]]`, `[\t-\r ]`},
+ {`[[:upper:]]`, `[A-Z]`},
+ {`[[:xdigit:]]`, `[0-9A-Fa-f]`},
+
+ // Perl character classes
+ {`\d`, `[0-9]`},
+ {`\s`, `[\t-\n\f-\r ]`},
+ {`\w`, `[0-9A-Z_a-z]`},
+ {`\D`, `[^0-9]`},
+ {`\S`, `[^\t-\n\f-\r ]`},
+ {`\W`, `[^0-9A-Z_a-z]`},
+ {`[\d]`, `[0-9]`},
+ {`[\s]`, `[\t-\n\f-\r ]`},
+ {`[\w]`, `[0-9A-Z_a-z]`},
+ {`[\D]`, `[^0-9]`},
+ {`[\S]`, `[^\t-\n\f-\r ]`},
+ {`[\W]`, `[^0-9A-Z_a-z]`},
+
+ // Posix repetitions
+ {`a{1}`, `a`},
+ {`a{2}`, `aa`},
+ {`a{5}`, `aaaaa`},
+ {`a{0,1}`, `a?`},
+ // The next three are illegible because Simplify inserts (?:)
+ // parens instead of () parens to avoid creating extra
+ // captured subexpressions. The comments show a version with fewer parens.
+ {`(a){0,2}`, `(?:(a)(a)?)?`}, // (aa?)?
+ {`(a){0,4}`, `(?:(a)(?:(a)(?:(a)(a)?)?)?)?`}, // (a(a(aa?)?)?)?
+ {`(a){2,6}`, `(a)(a)(?:(a)(?:(a)(?:(a)(a)?)?)?)?`}, // aa(a(a(aa?)?)?)?
+ {`a{0,2}`, `(?:aa?)?`}, // (aa?)?
+ {`a{0,4}`, `(?:a(?:a(?:aa?)?)?)?`}, // (a(a(aa?)?)?)?
+ {`a{2,6}`, `aa(?:a(?:a(?:aa?)?)?)?`}, // aa(a(a(aa?)?)?)?
+ {`a{0,}`, `a*`},
+ {`a{1,}`, `a+`},
+ {`a{2,}`, `aa+`},
+ {`a{5,}`, `aaaaa+`},
+
+ // Test that operators simplify their arguments.
+ {`(?:a{1,}){1,}`, `a+`},
+ {`(a{1,}b{1,})`, `(a+b+)`},
+ {`a{1,}|b{1,}`, `a+|b+`},
+ {`(?:a{1,})*`, `(?:a+)*`},
+ {`(?:a{1,})+`, `a+`},
+ {`(?:a{1,})?`, `(?:a+)?`},
+ {``, `(?:)`},
+ {`a{0}`, `(?:)`},
+
+ // Character class simplification
+ {`[ab]`, `[a-b]`},
+ {`[a-za-za-z]`, `[a-z]`},
+ {`[A-Za-zA-Za-z]`, `[A-Za-z]`},
+ {`[ABCDEFGH]`, `[A-H]`},
+ {`[AB-CD-EF-GH]`, `[A-H]`},
+ {`[W-ZP-XE-R]`, `[E-Z]`},
+ {`[a-ee-gg-m]`, `[a-m]`},
+ {`[a-ea-ha-m]`, `[a-m]`},
+ {`[a-ma-ha-e]`, `[a-m]`},
+ {`[a-zA-Z0-9 -~]`, `[ -~]`},
+
+ // Empty character classes
+ {`[^[:cntrl:][:^cntrl:]]`, `[^\x00-\x{10FFFF}]`},
+
+ // Full character classes
+ {`[[:cntrl:][:^cntrl:]]`, `.`},
+
+ // Unicode case folding.
+ {`(?i)A`, `(?i:A)`},
+ {`(?i)a`, `(?i:a)`},
+ {`(?i)[A]`, `(?i:A)`},
+ {`(?i)[a]`, `(?i:A)`},
+ {`(?i)K`, `(?i:K)`},
+ {`(?i)k`, `(?i:k)`},
+ {`(?i)\x{212a}`, "(?i:\u212A)"},
+ {`(?i)[K]`, "[Kk\u212A]"},
+ {`(?i)[k]`, "[Kk\u212A]"},
+ {`(?i)[\x{212a}]`, "[Kk\u212A]"},
+ {`(?i)[a-z]`, "[A-Za-z\u017F\u212A]"},
+ {`(?i)[\x00-\x{FFFD}]`, "[\\x00-\uFFFD]"},
+ {`(?i)[\x00-\x{10FFFF}]`, `.`},
+
+ // Empty string as a regular expression.
+ // The empty string must be preserved inside parens in order
+ // to make submatches work right, so these tests are less
+ // interesting than they might otherwise be. String inserts
+ // explicit (?:) in place of non-parenthesized empty strings,
+ // to make them easier to spot for other parsers.
+ {`(a|b|)`, `([a-b]|(?:))`},
+ {`(|)`, `()`},
+ {`a()`, `a()`},
+ {`(()|())`, `(()|())`},
+ {`(a|)`, `(a|(?:))`},
+ {`ab()cd()`, `ab()cd()`},
+ {`()`, `()`},
+ {`()*`, `()*`},
+ {`()+`, `()+`},
+ {`()?`, `()?`},
+ {`(){0}`, `(?:)`},
+ {`(){1}`, `()`},
+ {`(){1,}`, `()+`},
+ {`(){0,2}`, `(?:()()?)?`},
+}
+
+func TestSimplify(t *testing.T) {
+ for _, tt := range simplifyTests {
+ re, err := Parse(tt.Regexp, MatchNL|Perl&^OneLine)
+ if err != nil {
+ t.Errorf("Parse(%#q) = error %v", tt.Regexp, err)
+ continue
+ }
+ s := re.Simplify().String()
+ if s != tt.Simple {
+ t.Errorf("Simplify(%#q) = %#q, want %#q", tt.Regexp, s, tt.Simple)
+ }
+ }
+}
