Keep wrapping after an unbreakable usage word

flag.go

@@ -696,15 +696,23 @@ func UnquoteUsage(flag *Flag) (name string, usage string) {
 // Splits the string `s` on whitespace into an initial substring up to
 // `i` runes in length and the remainder. Will go `slop` over `i` if
 // that encompasses the entire string (which allows the caller to
-// avoid short orphan words on the final line).
+// avoid short orphan words on the final line). If the next word is
+// wider than `i`, it is returned on its own and wrapping continues
+// after it.
 func wrapN(i, slop int, s string) (string, string) {
 	if i+slop > len(s) {
 		return s, ""
 	}
 
 	w := strings.LastIndexAny(s[:i], " \t\n")
 	if w <= 0 {
-		return s, ""
+		// No break in the first i bytes. Emit the over-wide word
+		// alone and keep wrapping whatever follows.
+		next := strings.IndexAny(s, " \t\n")
+		if next <= 0 {
+			return s, ""
+		}
+		return s[:next], s[next+1:]
 	}
 	nlPos := strings.LastIndex(s[:i], "\n")
 	if nlPos > 0 && nlPos < w {

printusage_test.go

@@ -72,3 +72,19 @@ func TestPrintUsage_2(t *testing.T) {
 		t.Errorf("Expected \n%s \nActual \n%s", expectedOutput2, res)
 	}
 }
+
+// A word wider than the description column must sit on its own line.
+// Wrapping has to resume for the words after it (#501).
+func TestFlagUsagesWrappedContinuesAfterUnbreakableWord(t *testing.T) {
+	f := NewFlagSet("example", ContinueOnError)
+	f.String("mount", "", "a mount specification e.g. 'type=bind,source=/opt,destination=/hostopt'. The rest of this description is never wrapped.")
+	got := f.FlagUsagesWrapped(60)
+	want := `      --mount string   a mount specification e.g.
+                       'type=bind,source=/opt,destination=/hostopt'.
+                       The rest of this description is
+                       never wrapped.
+`
+	if got != want {
+		t.Errorf("FlagUsagesWrapped(60)\nwant:\n%q\ngot:\n%q", want, got)
+	}
+}