fix help message for Func and BoolFunc flags #430

* have '.Type()' for boolfuncValue return "boolfunc" (dedicated value,
  which now makes it distinct from funcValue)
* hide extra "(default )" by stating that "" should be treated as
  a zero value for a boolFlag
  note:
  - a boolfuncValue matches 'case boolFlag:', as it
    implements the boolFlag interface,
  - treating "" as a value which shouldn't trigger a "(default )"
    for a regular Bool flag does not look like a breaking change
* hide extra "[=something]" for boolfuncValue
* set default placeholder name for "boolfunc" and "func" flag types

1 files changed, 30 insertions, 0 deletions

diff --git a/func_test.go b/func_test.go
index 9be74fa..d492b48 100644
--- a/func_test.go
+++ b/func_test.go
@@ -151,3 +151,33 @@ func TestFuncCompat(t *testing.T) {
 		}
 	})
 }
+
+func TestFuncUsage(t *testing.T) {
+	t.Run("regular func flag", func(t *testing.T) {
+		// regular func flag:
+		// expect to see '--flag1 value' followed by the usageMessage, and no mention of a default value
+		fset := NewFlagSet("unittest", ContinueOnError)
+		fset.Func("flag1", "usage message", func(s string) error { return nil })
+		usage := fset.FlagUsagesWrapped(80)
+
+		usage = strings.TrimSpace(usage)
+		expected := "--flag1 value   usage message"
+		if usage != expected {
+			t.Fatalf("unexpected generated usage message\n  expected: %s\n       got: %s", expected, usage)
+		}
+	})
+
+	t.Run("func flag with placeholder name", func(t *testing.T) {
+		// func flag, with a placeholder name:
+		// if usageMesage contains a placeholder, expect that name; still expect no mention of a default value
+		fset := NewFlagSet("unittest", ContinueOnError)
+		fset.Func("flag2", "usage message with `name` placeholder", func(s string) error { return nil })
+		usage := fset.FlagUsagesWrapped(80)
+
+		usage = strings.TrimSpace(usage)
+		expected := "--flag2 name   usage message with name placeholder"
+		if usage != expected {
+			t.Fatalf("unexpected generated usage message\n  expected: %s\n       got: %s", expected, usage)
+		}
+	})
+}