testing/regexp: use recover.

R=rsc
CC=golang-dev
http://codereview.appspot.com/816042

Committer: Rob Pike <r@golang.org>

1 files changed, 31 insertions, 58 deletions

diff --git a/src/pkg/testing/regexp.go b/src/pkg/testing/regexp.go
index cd37699ce..78d801d51 100644
--- a/src/pkg/testing/regexp.go
+++ b/src/pkg/testing/regexp.go
@@ -34,13 +34,13 @@ var debug = false
 // Error codes returned by failures to parse an expression.
 var (
 	ErrInternal            = "internal error"
-	ErrUnmatchedLpar       = "unmatched ''"
-	ErrUnmatchedRpar       = "unmatched ''"
+	ErrUnmatchedLpar       = "unmatched '('"
+	ErrUnmatchedRpar       = "unmatched ')'"
 	ErrUnmatchedLbkt       = "unmatched '['"
 	ErrUnmatchedRbkt       = "unmatched ']'"
 	ErrBadRange            = "bad range in character class"
 	ErrExtraneousBackslash = "extraneous backslash"
-	ErrBadClosure          = "repeated closure **, ++, etc."
+	ErrBadClosure          = "repeated closure (**, ++, etc.)"
 	ErrBareClosure         = "closure applies to nothing"
 	ErrBadBackslash        = "illegal backslash escape"
 )
@@ -267,12 +267,15 @@ func (re *Regexp) add(i instr) instr {
 
 type parser struct {
 	re    *Regexp
-	error string
 	nlpar int // number of unclosed lpars
 	pos   int
 	ch    int
 }
 
+func (p *parser) error(err string) {
+	panic(err)
+}
+
 const endOfFile = -1
 
 func (p *parser) c() int { return p.ch }
@@ -326,8 +329,7 @@ func (p *parser) charClass() instr {
 		switch c := p.c(); c {
 		case ']', endOfFile:
 			if left >= 0 {
-				p.error = ErrBadRange
-				return nil
+				p.error(ErrBadRange)
 			}
 			// Is it [^\n]?
 			if cc.negate && len(cc.ranges) == 2 &&
@@ -339,21 +341,18 @@ func (p *parser) charClass() instr {
 			p.re.add(cc)
 			return cc
 		case '-': // do this before backslash processing
-			p.error = ErrBadRange
-			return nil
+			p.error(ErrBadRange)
 		case '\\':
 			c = p.nextc()
 			switch {
 			case c == endOfFile:
-				p.error = ErrExtraneousBackslash
-				return nil
+				p.error(ErrExtraneousBackslash)
 			case c == 'n':
 				c = '\n'
 			case specialcclass(c):
 			// c is as delivered
 			default:
-				p.error = ErrBadBackslash
-				return nil
+				p.error(ErrBadBackslash)
 			}
 			fallthrough
 		default:
@@ -370,8 +369,7 @@ func (p *parser) charClass() instr {
 				cc.addRange(left, c)
 				left = -1
 			default:
-				p.error = ErrBadRange
-				return nil
+				p.error(ErrBadRange)
 			}
 		}
 	}
@@ -379,28 +377,19 @@ func (p *parser) charClass() instr {
 }
 
 func (p *parser) term() (start, end instr) {
-	// term() is the leaf of the recursion, so it's sufficient to pick off the
-	// error state here for early exit.
-	// The other functions (closure(), concatenation() etc.) assume
-	// it's safe to recur to here.
-	if p.error != "" {
-		return
-	}
 	switch c := p.c(); c {
 	case '|', endOfFile:
 		return nil, nil
 	case '*', '+':
-		p.error = ErrBareClosure
+		p.error(ErrBareClosure)
 		return
 	case ')':
 		if p.nlpar == 0 {
-			p.error = ErrUnmatchedRpar
-			return
+			p.error(ErrUnmatchedRpar)
 		}
 		return nil, nil
 	case ']':
-		p.error = ErrUnmatchedRbkt
-		return
+		p.error(ErrUnmatchedRbkt)
 	case '^':
 		p.nextc()
 		start = p.re.add(new(_Bot))
@@ -416,12 +405,8 @@ func (p *parser) term() (start, end instr) {
 	case '[':
 		p.nextc()
 		start = p.charClass()
-		if p.error != "" {
-			return
-		}
 		if p.c() != ']' {
-			p.error = ErrUnmatchedLbkt
-			return
+			p.error(ErrUnmatchedLbkt)
 		}
 		p.nextc()
 		return start, start
@@ -432,8 +417,7 @@ func (p *parser) term() (start, end instr) {
 		nbra := p.re.nbra
 		start, end = p.regexp()
 		if p.c() != ')' {
-			p.error = ErrUnmatchedLpar
-			return
+			p.error(ErrUnmatchedLpar)
 		}
 		p.nlpar--
 		p.nextc()
@@ -445,8 +429,7 @@ func (p *parser) term() (start, end instr) {
 		ebra.n = nbra
 		if start == nil {
 			if end == nil {
-				p.error = ErrInternal
-				return
+				p.error(ErrInternal)
 			}
 			start = ebra
 		} else {
@@ -458,15 +441,14 @@ func (p *parser) term() (start, end instr) {
 		c = p.nextc()
 		switch {
 		case c == endOfFile:
-			p.error = ErrExtraneousBackslash
+			p.error(ErrExtraneousBackslash)
 			return
 		case c == 'n':
 			c = '\n'
 		case special(c):
 		// c is as delivered
 		default:
-			p.error = ErrBadBackslash
-			return
+			p.error(ErrBadBackslash)
 		}
 		fallthrough
 	default:
@@ -480,7 +462,7 @@ func (p *parser) term() (start, end instr) {
 
 func (p *parser) closure() (start, end instr) {
 	start, end = p.term()
-	if start == nil || p.error != "" {
+	if start == nil {
 		return
 	}
 	switch p.c() {
@@ -515,7 +497,7 @@ func (p *parser) closure() (start, end instr) {
 	}
 	switch p.nextc() {
 	case '*', '+', '?':
-		p.error = ErrBadClosure
+		p.error(ErrBadClosure)
 	}
 	return
 }
@@ -523,9 +505,6 @@ func (p *parser) closure() (start, end instr) {
 func (p *parser) concatenation() (start, end instr) {
 	for {
 		nstart, nend := p.closure()
-		if p.error != "" {
-			return
-		}
 		switch {
 		case nstart == nil: // end of this concatenation
 			if start == nil { // this is the empty string
@@ -545,9 +524,6 @@ func (p *parser) concatenation() (start, end instr) {
 
 func (p *parser) regexp() (start, end instr) {
 	start, end = p.concatenation()
-	if p.error != "" {
-		return
-	}
 	for {
 		switch p.c() {
 		default:
@@ -555,9 +531,6 @@ func (p *parser) regexp() (start, end instr) {
 		case '|':
 			p.nextc()
 			nstart, nend := p.concatenation()
-			if p.error != "" {
-				return
-			}
 			alt := new(_Alt)
 			p.re.add(alt)
 			alt.left = start
@@ -593,31 +566,31 @@ func (re *Regexp) eliminateNops() {
 	}
 }
 
-func (re *Regexp) doParse() string {
+func (re *Regexp) doParse() {
 	p := newParser(re)
 	start := new(_Start)
 	re.add(start)
 	s, e := p.regexp()
-	if p.error != "" {
-		return p.error
-	}
 	start.setNext(s)
 	re.start = start
 	e.setNext(re.add(new(_End)))
 	re.eliminateNops()
-	return p.error
 }
 
 // CompileRegexp parses a regular expression and returns, if successful, a Regexp
 // object that can be used to match against text.
 func CompileRegexp(str string) (regexp *Regexp, error string) {
 	regexp = new(Regexp)
+	// doParse will panic if there is a parse error.
+	defer func() {
+		if e := recover(); e != nil {
+			regexp = nil
+			error = e.(string) // Will re-panic if error was not a string, e.g. nil-pointer exception
+		}
+	}()
 	regexp.expr = str
 	regexp.inst = make([]instr, 0, 20)
-	error = regexp.doParse()
-	if error != "" {
-		regexp = nil
-	}
+	regexp.doParse()
 	return
 }