crstrings: add Indent

Add a function that indents a multi-line string.

Author: RaduBerinde

crstrings/utils.go

@@ -97,3 +97,23 @@ func Lines(s string) []string {
 	}
 	return strings.Split(s, "\n")
 }
+
+// Indent prepends a string to every line of the given string.
+//
+// If the string ends in a newline, the resulting string also ends in a newline.
+func Indent(prepend, str string) string {
+	lines := strings.Split(str, "\n")
+	var b strings.Builder
+	b.Grow(len(str) + len(lines)*len(prepend))
+	for i, l := range lines {
+		if i > 0 {
+			b.WriteString("\n")
+		}
+		// Make sure we don't add an extra prepend after a trailing newline.
+		if i < len(lines)-1 || l != "" {
+			b.WriteString(prepend)
+			b.WriteString(l)
+		}
+	}
+	return b.String()
+}

crstrings/utils_test.go

@@ -76,3 +76,18 @@ func TestLines(t *testing.T) {
 	require.Equal(t, `[]`, fmt.Sprintf("%q", Lines("")))
 	require.Equal(t, `[]`, fmt.Sprintf("%q", Lines("\n")))
 }
+
+func TestIndent(t *testing.T) {
+	testCases := [][2]string{
+		{"", ""},
+		{"foo", "--foo"},
+		{"foo\n", "--foo\n"},
+		{"foo\n\n", "--foo\n--\n"},
+		{"foo\nbar", "--foo\n--bar"},
+		{"foo\nbar\n", "--foo\n--bar\n"},
+		{"foo\n\nbar\n", "--foo\n--\n--bar\n"},
+	}
+	for _, tc := range testCases {
+		require.Equal(t, tc[1], Indent("--", tc[0]))
+	}
+}