strutil: add ElliptRight

2 files changed, 38 insertions, 0 deletions

diff --git a/strutil/strutil.go b/strutil/strutil.go
index 5564b5b170..e794ab27ff 100644
--- a/strutil/strutil.go
+++ b/strutil/strutil.go
@@ -27,6 +27,7 @@ import (
	"strings"
	"time"
	"unicode"
+	"unicode/utf8"
 )
 
 func init() {
@@ -182,3 +183,18 @@ func CommaSeparatedList(str string) []string {
	}
	return filtered
 }
+
+// ElliptRight returns a string that is at most n runes long,
+// replacing the last rune with an ellipsis if necessary. If N is less
+// than 1 it's treated as a 1.
+func ElliptRight(str string, n int) string {
+	if n < 1 {
+	n = 1
+	}
+	if utf8.RuneCountInString(str) <= n {
+	return str
+	}
+
+	// this is expensive; look into a cheaper way maybe sometime
+	return string([]rune(str)[:n-1]) + "…"
+}
diff --git a/strutil/strutil_test.go b/strutil/strutil_test.go
index bf7ae4d442..70d4aa7b3e 100644
--- a/strutil/strutil_test.go
+++ b/strutil/strutil_test.go
@@ -200,3 +200,25 @@ func (strutilSuite) TestCommaSeparatedList(c *check.C) {
	c.Check(strutil.CommaSeparatedList(test.in), check.DeepEquals, test.out, check.Commentf("%q", test.in))
	}
 }
+
+func (strutilSuite) TestElliptRight(c *check.C) {
+	type T struct {
+	in string
+	n int
+	out string
+	}
+	for _, t := range []T{
+	{"", 10, ""},
+	{"", -1, ""},
+	{"hello", 10, "hello"},
+	{"hello", 5, "hello"},
+	{"hello", 3, "he…"},
+	{"hello", 0, "…"},
+	{"héllo", 4, "hé…"},
+	{"héllo", 3, "he…"},
+	{"he🐧lo", 4, "he🐧…"},
+	{"he🐧lo", 3, "he…"},
+	} {
+	c.Check(strutil.ElliptRight(t.in, t.n), check.Equals, t.out, check.Commentf("%q[:%d] -> %q", t.in, t.n, t.out))
+	}
+}