regexp: change Expr() to String(); add HasOperator method to Regexp.

It reports whether a regular expression has operators
as opposed to matching literal text.

R=rsc, gri
CC=golang-dev
https://golang.org/cl/3731041

src/pkg/regexp/all_test.go

@@ -229,18 +229,21 @@ func TestReplaceAllFunc(t *testing.T) {
 	}
 }
 
-type QuoteMetaTest struct {
-	pattern, output string
+type MetaTest struct {
+	pattern, output, literal string
+	isLiteral                bool
 }
 
-var quoteMetaTests = []QuoteMetaTest{
-	{``, ``},
-	{`foo`, `foo`},
-	{`!@#$%^&*()_+-=[{]}\|,<.>/?~`, `!@#\$%\^&\*\(\)_\+-=\[{\]}\\\|,<\.>/\?~`},
+var metaTests = []MetaTest{
+	{``, ``, ``, true},
+	{`foo`, `foo`, `foo`, true},
+	{`foo\.\$`, `foo\\\.\\\$`, `foo.$`, true}, // has meta but no operator
+	{`foo.\$`, `foo\.\\\$`, `foo`, false},     // has escaped operators and real operators
+	{`!@#$%^&*()_+-=[{]}\|,<.>/?~`, `!@#\$%\^&\*\(\)_\+-=\[{\]}\\\|,<\.>/\?~`, `!@#`, false},
 }
 
 func TestQuoteMeta(t *testing.T) {
-	for _, tc := range quoteMetaTests {
+	for _, tc := range metaTests {
 		// Verify that QuoteMeta returns the expected string.
 		quoted := QuoteMeta(tc.pattern)
 		if quoted != tc.output {
@@ -269,14 +272,16 @@ func TestQuoteMeta(t *testing.T) {
 	}
 }
 
-func TestHasMeta(t *testing.T) {
-	for _, tc := range quoteMetaTests {
-		// HasMeta should be false if QuoteMeta returns the original string;
-		// true otherwise.
-		quoted := QuoteMeta(tc.pattern)
-		if HasMeta(tc.pattern) != (quoted != tc.pattern) {
-			t.Errorf("HasMeta(`%s`) = %t; want %t",
-				tc.pattern, HasMeta(tc.pattern), quoted != tc.pattern)
+func TestLiteralPrefix(t *testing.T) {
+	for _, tc := range metaTests {
+		// Literal method needs to scan the pattern.
+		re := MustCompile(tc.pattern)
+		str, complete := re.LiteralPrefix()
+		if complete != tc.isLiteral {
+			t.Errorf("LiteralPrefix(`%s`) = %t; want %t", tc.pattern, complete, tc.isLiteral)
+		}
+		if str != tc.literal {
+			t.Errorf("LiteralPrefix(`%s`) = `%s`; want `%s`", tc.pattern, str, tc.literal)
 		}
 	}
 }

src/pkg/regexp/find_test.go

@@ -120,8 +120,8 @@ func build(n int, x ...int) [][]int {
 func TestFind(t *testing.T) {
 	for _, test := range findTests {
 		re := MustCompile(test.pat)
-		if re.Expr() != test.pat {
-			t.Errorf("Expr() = `%s`; should be `%s`", re.Expr(), test.pat)
+		if re.String() != test.pat {
+			t.Errorf("String() = `%s`; should be `%s`", re.String(), test.pat)
 		}
 		result := re.Find([]byte(test.text))
 		switch {

src/pkg/regexp/regexp.go

@@ -599,8 +599,8 @@ Loop:
 	re.prefix = string(b)
 }
 
-// Expr returns the source text used to compile the regular expression.
-func (re *Regexp) Expr() string {
+// String returns the source text used to compile the regular expression.
+func (re *Regexp) String() string {
 	return re.expr
 }
 
@@ -849,6 +849,24 @@ func (re *Regexp) doExecute(str string, bytestr []byte, pos int) []int {
 	return final.match.m
 }
 
+// LiteralPrefix returns a literal string that must begin any match
+// of the regular expression re.  It returns the boolean true if the
+// literal string comprises the entire regular expression.
+func (re *Regexp) LiteralPrefix() (prefix string, complete bool) {
+	c := make([]int, len(re.inst)-2) // minus start and end.
+	// First instruction is start; skip that.
+	i := 0
+	for inst := re.inst[0].next; inst.kind != iEnd; inst = inst.next {
+		// stop if this is not a char
+		if inst.kind != iChar {
+			return string(c[:i]), false
+		}
+		c[i] = inst.char
+		i++
+	}
+	return string(c[:i]), true
+}
+
 // MatchString returns whether the Regexp matches the string s.
 // The return value is a boolean: true for match, false for no match.
 func (re *Regexp) MatchString(s string) bool { return len(re.doExecute(s, nil, 0)) > 0 }
@@ -1003,18 +1021,6 @@ func QuoteMeta(s string) string {
 	return string(b[0:j])
 }
 
-// HasMeta returns a boolean indicating whether the string contains
-// any regular expression metacharacters.
-func HasMeta(s string) bool {
-	// A byte loop is correct because all metacharacters are ASCII.
-	for i := 0; i < len(s); i++ {
-		if special(int(s[i])) {
-			return true
-		}
-	}
-	return false
-}
-
 // Find matches in slice b if b is non-nil, otherwise find matches in string s.
 func (re *Regexp) allMatches(s string, b []byte, n int, deliver func([]int)) {
 	var end int