// Copyright 2006 The RE2 Authors. All Rights Reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
// Rewrite POSIX and other features in re
// to use simple extended regular expression features.
// Also sort and simplify character classes.
#include "util/util.h"
#include "re2/regexp.h"
#include "re2/walker-inl.h"
namespace re2 {
// Parses the regexp src and then simplifies it and sets *dst to the
// string representation of the simplified form. Returns true on success.
// Returns false and sets *error (if error != NULL) on error.
bool Regexp::SimplifyRegexp(const StringPiece& src, ParseFlags flags,
string* dst,
RegexpStatus* status) {
Regexp* re = Parse(src, flags, status);
if (re == NULL)
return false;
Regexp* sre = re->Simplify();
re->Decref();
if (sre == NULL) {
// Should not happen, since Simplify never fails.
LOG(ERROR) << "Simplify failed on " << src;
if (status) {
status->set_code(kRegexpInternalError);
status->set_error_arg(src);
}
return false;
}
*dst = sre->ToString();
sre->Decref();
return true;
}
// Assuming the simple_ flags on the children are accurate,
// is this Regexp* simple?
bool Regexp::ComputeSimple() {
Regexp** subs;
switch (op_) {
case kRegexpNoMatch:
case kRegexpEmptyMatch:
case kRegexpLiteral:
case kRegexpLiteralString:
case kRegexpBeginLine:
case kRegexpEndLine:
case kRegexpBeginText:
case kRegexpWordBoundary:
case kRegexpNoWordBoundary:
case kRegexpEndText:
case kRegexpAnyChar:
case kRegexpAnyByte:
case kRegexpHaveMatch:
return true;
case kRegexpConcat:
case kRegexpAlternate:
// These are simple as long as the subpieces are simple.
subs = sub();
for (int i = 0; i < nsub_; i++)
if (!subs[i]->simple_)
return false;
return true;
case kRegexpCharClass:
// Simple as long as the char class is not empty, not full.
if (ccb_ != NULL)
return !ccb_->empty() && !ccb_->full();
return !cc_->empty() && !cc_->full();
case kRegexpCapture:
subs = sub();
return subs[0]->simple_;
case kRegexpStar:
case kRegexpPlus:
case kRegexpQuest:
subs = sub();
if (!subs[0]->simple_)
return false;
switch (subs[0]->op_) {
case kRegexpStar:
case kRegexpPlus:
case kRegexpQuest:
case kRegexpEmptyMatch:
case kRegexpNoMatch:
return false;
default:
break;
}
return true;
case kRegexpRepeat:
return false;
}
LOG(DFATAL) << "Case not handled in ComputeSimple: " << op_;
return false;
}
// Walker subclass used by Simplify.
// The simplify walk is purely post-recursive: given the simplified children,
// PostVisit creates the simplified result.
// The child_args are simplified Regexp*s.
class SimplifyWalker : public Regexp::Walker<Regexp*> {
public:
SimplifyWalker() {}
virtual Regexp* PreVisit(Regexp* re, Regexp* parent_arg, bool* stop);
virtual Regexp* PostVisit(Regexp* re,
Regexp* parent_arg,
Regexp* pre_arg,
Regexp** child_args, int nchild_args);
virtual Regexp* Copy(Regexp* re);
virtual Regexp* ShortVisit(Regexp* re, Regexp* parent_arg);
private:
// These functions are declared inside SimplifyWalker so that
// they can edit the private fields of the Regexps they construct.
// Creates a concatenation of two Regexp, consuming refs to re1 and re2.
// Caller must Decref return value when done with it.
static Regexp* Concat2(Regexp* re1, Regexp* re2, Regexp::ParseFlags flags);
// Simplifies the expression re{min,max} in terms of *, +, and ?.
// Returns a new regexp. Does not edit re. Does not consume reference to re.
// Caller must Decref return value when done with it.
static Regexp* SimplifyRepeat(Regexp* re, int min, int max,
Regexp::ParseFlags parse_flags);
// Simplifies a character class by expanding any named classes
// into rune ranges. Does not edit re. Does not consume ref to re.
// Caller must Decref return value when done with it.
static Regexp* SimplifyCharClass(Regexp* re);
DISALLOW_EVIL_CONSTRUCTORS(SimplifyWalker);
};
// Simplifies a regular expression, returning a new regexp.
// The new regexp uses traditional Unix egrep features only,
// plus the Perl (?:) non-capturing parentheses.
// Otherwise, no POSIX or Perl additions. The new regexp
// captures exactly the same subexpressions (with the same indices)
// as the original.
// Does not edit current object.
// Caller must Decref() return value when done with it.
Regexp* Regexp::Simplify() {
if (simple_)
return Incref();
SimplifyWalker w;
return w.Walk(this, NULL);
}
#define Simplify DontCallSimplify // Avoid accidental recursion
Regexp* SimplifyWalker::Copy(Regexp* re) {
return re->Incref();
}
Regexp* SimplifyWalker::ShortVisit(Regexp* re, Regexp* parent_arg) {
// This should never be called, since we use Walk and not
// WalkExponential.
LOG(DFATAL) << "SimplifyWalker::ShortVisit called";
return re->Incref();
}
Regexp* SimplifyWalker::PreVisit(Regexp* re, Regexp* parent_arg, bool* stop) {
if (re->simple_) {
*stop = true;
return re->Incref();
}
return NULL;
}
Regexp* SimplifyWalker::PostVisit(Regexp* re,
Regexp* parent_arg,
Regexp* pre_arg,
Regexp** child_args,
int nchild_args) {
switch (re->op()) {
case kRegexpNoMatch:
case kRegexpEmptyMatch:
case kRegexpLiteral:
case kRegexpLiteralString:
case kRegexpBeginLine:
case kRegexpEndLine:
case kRegexpBeginText:
case kRegexpWordBoundary:
case kRegexpNoWordBoundary:
case kRegexpEndText:
case kRegexpAnyChar:
case kRegexpAnyByte:
case kRegexpHaveMatch:
// All these are always simple.
re->simple_ = true;
return re->Incref();
case kRegexpConcat:
case kRegexpAlternate: {
// These are simple as long as the subpieces are simple.
// Two passes to avoid allocation in the common case.
bool changed = false;
Regexp** subs = re->sub();
for (int i = 0; i < re->nsub_; i++) {
Regexp* sub = subs[i];
Regexp* newsub = child_args[i];
if (newsub != sub) {
changed = true;
break;
}
}
if (!changed) {
for (int i = 0; i < re->nsub_; i++) {
Regexp* newsub = child_args[i];
newsub->Decref();
}
re->simple_ = true;
return re->Incref();
}
Regexp* nre = new Regexp(re->op(), re->parse_flags());
nre->AllocSub(re->nsub_);
Regexp** nre_subs = nre->sub();
for (int i = 0; i <re->nsub_; i++)
nre_subs[i] = child_args[i];
nre->simple_ = true;
return nre;
}
case kRegexpCapture: {
Regexp* newsub = child_args[0];
if (newsub == re->sub()[0]) {
newsub->Decref();
re->simple_ = true;
return re->Incref();
}
Regexp* nre = new Regexp(kRegexpCapture, re->parse_flags());
nre->AllocSub(1);
nre->sub()[0] = newsub;
nre->cap_ = re->cap_;
nre->simple_ = true;
return nre;
}
case kRegexpStar:
case kRegexpPlus:
case kRegexpQuest: {
Regexp* newsub = child_args[0];
// Special case: repeat the empty string as much as
// you want, but it's still the empty string.
if (newsub->op() == kRegexpEmptyMatch)
return newsub;
// These are simple as long as the subpiece is simple.
if (newsub == re->sub()[0]) {
newsub->Decref();
re->simple_ = true;
return re->Incref();
}
// These are also idempotent if flags are constant.
if (re->op() == newsub->op() &&
re->parse_flags() == newsub->parse_flags())
return newsub;
Regexp* nre = new Regexp(re->op(), re->parse_flags());
nre->AllocSub(1);
nre->sub()[0] = newsub;
nre->simple_ = true;
return nre;
}
case kRegexpRepeat: {
Regexp* newsub = child_args[0];
// Special case: repeat the empty string as much as
// you want, but it's still the empty string.
if (newsub->op() == kRegexpEmptyMatch)
return newsub;
Regexp* nre = SimplifyRepeat(newsub, re->min_, re->max_,
re->parse_flags());
newsub->Decref();
nre->simple_ = true;
return nre;
}
case kRegexpCharClass: {
Regexp* nre = SimplifyCharClass(re);
nre->simple_ = true;
return nre;
}
}
LOG(ERROR) << "Simplify case not handled: " << re->op();
return re->Incref();
}
// Creates a concatenation of two Regexp, consuming refs to re1 and re2.
// Returns a new Regexp, handing the ref to the caller.
Regexp* SimplifyWalker::Concat2(Regexp* re1, Regexp* re2,
Regexp::ParseFlags parse_flags) {
Regexp* re = new Regexp(kRegexpConcat, parse_flags);
re->AllocSub(2);
Regexp** subs = re->sub();
subs[0] = re1;
subs[1] = re2;
return re;
}
// Simplifies the expression re{min,max} in terms of *, +, and ?.
// Returns a new regexp. Does not edit re. Does not consume reference to re.
// Caller must Decref return value when done with it.
// The result will *not* necessarily have the right capturing parens
// if you call ToString() and re-parse it: (x){2} becomes (x)(x),
// but in the Regexp* representation, both (x) are marked as $1.
Regexp* SimplifyWalker::SimplifyRepeat(Regexp* re, int min, int max,
Regexp::ParseFlags f) {
// x{n,} means at least n matches of x.
if (max == -1) {
// Special case: x{0,} is x*
if (min == 0)
return Regexp::Star(re->Incref(), f);
// Special case: x{1,} is x+
if (min == 1)
return Regexp::Plus(re->Incref(), f);
// General case: x{4,} is xxxx+
Regexp* nre = new Regexp(kRegexpConcat, f);
nre->AllocSub(min);
VLOG(1) << "Simplify " << min;
Regexp** nre_subs = nre->sub();
for (int i = 0; i < min-1; i++)
nre_subs[i] = re->Incref();
nre_subs[min-1] = Regexp::Plus(re->Incref(), f);
return nre;
}
// Special case: (x){0} matches only empty string.
if (min == 0 && max == 0)
return new Regexp(kRegexpEmptyMatch, f);
// Special case: x{1} is just x.
if (min == 1 && max == 1)
return re->Incref();
// 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. Capturing only on the last one.
Regexp* nre = NULL;
if (min > 0) {
nre = new Regexp(kRegexpConcat, f);
nre->AllocSub(min);
Regexp** nre_subs = nre->sub();
for (int i = 0; i < min; i++)
nre_subs[i] = re->Incref();
}
// Build and attach suffix: (x(x(x)?)?)?
if (max > min) {
Regexp* suf = Regexp::Quest(re->Incref(), f);
for (int i = min+1; i < max; i++)
suf = Regexp::Quest(Concat2(re->Incref(), suf, f), f);
if (nre == NULL)
nre = suf;
else
nre = Concat2(nre, suf, f);
}
if (nre == NULL) {
// Some degenerate case, like min > max, or min < max < 0.
// This shouldn't happen, because the parser rejects such regexps.
LOG(DFATAL) << "Malformed repeat " << re->ToString() << " " << min << " " << max;
return new Regexp(kRegexpNoMatch, f);
}
return nre;
}
// Simplifies a character class.
// Caller must Decref return value when done with it.
Regexp* SimplifyWalker::SimplifyCharClass(Regexp* re) {
CharClass* cc = re->cc();
// Special cases
if (cc->empty())
return new Regexp(kRegexpNoMatch, re->parse_flags());
if (cc->full())
return new Regexp(kRegexpAnyChar, re->parse_flags());
return re->Incref();
}
} // namespace re2