1 files changed, 78 insertions, 0 deletions
diff --git a/src/go/doc/synopsis.go b/src/go/doc/synopsis.go
new file mode 100644
index 0000000..3c9e7e9
--- /dev/null
+++ b/src/go/doc/synopsis.go
@@ -0,0 +1,78 @@
+// Copyright 2012 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 doc
+
+import (
+	"go/doc/comment"
+	"strings"
+	"unicode"
+)
+
+// firstSentence returns the first sentence in s.
+// The sentence ends after the first period followed by space and
+// not preceded by exactly one uppercase letter.
+func firstSentence(s string) string {
+	var ppp, pp, p rune
+	for i, q := range s {
+		if q == '\n' || q == '\r' || q == '\t' {
+			q = ' '
+		}
+		if q == ' ' && p == '.' && (!unicode.IsUpper(pp) || unicode.IsUpper(ppp)) {
+			return s[:i]
+		}
+		if p == '。' || p == '．' {
+			return s[:i]
+		}
+		ppp, pp, p = pp, p, q
+	}
+	return s
+}
+
+// Synopsis returns a cleaned version of the first sentence in text.
+//
+// Deprecated: New programs should use [Package.Synopsis] instead,
+// which handles links in text properly.
+func Synopsis(text string) string {
+	var p Package
+	return p.Synopsis(text)
+}
+
+// IllegalPrefixes is a list of lower-case prefixes that identify
+// a comment as not being a doc comment.
+// This helps to avoid misinterpreting the common mistake
+// of a copyright notice immediately before a package statement
+// as being a doc comment.
+var IllegalPrefixes = []string{
+	"copyright",
+	"all rights",
+	"author",
+}
+
+// Synopsis returns a cleaned version of the first sentence in text.
+// That sentence ends after the first period followed by space and not
+// preceded by exactly one uppercase letter, or at the first paragraph break.
+// The result string has no \n, \r, or \t characters and uses only single
+// spaces between words. If text starts with any of the IllegalPrefixes,
+// the result is the empty string.
+func (p *Package) Synopsis(text string) string {
+	text = firstSentence(text)
+	lower := strings.ToLower(text)
+	for _, prefix := range IllegalPrefixes {
+		if strings.HasPrefix(lower, prefix) {
+			return ""
+		}
+	}
+	pr := p.Printer()
+	pr.TextWidth = -1
+	d := p.Parser().Parse(text)
+	if len(d.Content) == 0 {
+		return ""
+	}
+	if _, ok := d.Content[0].(*comment.Paragraph); !ok {
+		return ""
+	}
+	d.Content = d.Content[:1] // might be blank lines, code blocks, etc in “first sentence”
+	return strings.TrimSpace(string(pr.Text(d)))
+}