godoc: slightly smarter synopsis extraction

Ignore synopses that start with
"Copyright", "All rights", and "Author".

R=rsc
CC=golang-dev
https://golang.org/cl/6218047

src/pkg/go/doc/synopsis.go

@@ -4,7 +4,10 @@
 
 package doc
 
-import "unicode"
+import (
+	"strings"
+	"unicode"
+)
 
 // firstSentenceLen returns the length of the first sentence in s.
 // The sentence ends after the first period followed by space and
@@ -24,17 +27,12 @@ func firstSentenceLen(s string) int {
 	return len(s)
 }
 
-// Synopsis returns a cleaned version of the first sentence in s.
-// That sentence ends after the first period followed by space and
-// not preceded by exactly one uppercase letter. The result string
-// has no \n, \r, or \t characters and uses only single spaces between
-// words.
-//
-func Synopsis(s string) string {
-	n := firstSentenceLen(s)
+// clean replaces each sequence of space, \n, \r, or \t characters
+// with a single space and removes any trailing and leading spaces.
+func clean(s string) string {
 	var b []byte
 	p := byte(' ')
-	for i := 0; i < n; i++ {
+	for i := 0; i < len(s); i++ {
 		q := s[i]
 		if q == '\n' || q == '\r' || q == '\t' {
 			q = ' '
@@ -50,3 +48,26 @@ func Synopsis(s string) string {
 	}
 	return string(b)
 }
+
+// Synopsis returns a cleaned version of the first sentence in s.
+// That sentence ends after the first period followed by space and
+// not preceded by exactly one uppercase letter. The result string
+// has no \n, \r, or \t characters and uses only single spaces between
+// words. If s starts with any of the IllegalPrefixes, the result
+// is the empty string.
+//
+func Synopsis(s string) string {
+	s = clean(s[0:firstSentenceLen(s)])
+	for _, prefix := range IllegalPrefixes {
+		if strings.HasPrefix(strings.ToLower(s), prefix) {
+			return ""
+		}
+	}
+	return s
+}
+
+var IllegalPrefixes = []string{
+	"copyright",
+	"all rights",
+	"author",
+}

src/pkg/go/doc/synopsis_test.go

@@ -28,6 +28,11 @@ var tests = []struct {
 	{"P. Q.   ", 8, "P. Q."},
 	{"Package Καλημέρα κόσμε.", 36, "Package Καλημέρα κόσμε."},
 	{"Package こんにちは 世界\n", 31, "Package こんにちは 世界"},
+	{"Package foo does bar.", 21, "Package foo does bar."},
+	{"Copyright 2012 Google, Inc. Package foo does bar.", 27, ""},
+	{"All Rights reserved. Package foo does bar.", 20, ""},
+	{"All rights reserved. Package foo does bar.", 20, ""},
+	{"Authors: foo@bar.com. Package foo does bar.", 21, ""},
 }
 
 func TestSynopsis(t *testing.T) {