A flag with a non-zero default value will now show the default in the help

.golangci.yml

@@ -21,10 +21,12 @@ linters:
     - lll # Auto formatters do this and what they can't do I don't care about
     - maintidx # This is just the inverse of complexity... which is cyclop
     - nestif # cyclop does this
+    - nlreturn # Similar to wsl, I think best left to judgement
     - nonamedreturns # Named returns are often helpful, it's naked returns that are the issue
     - paralleltest # I've never had Go tests take longer than a few seconds, it's fine
     - varnamelen # Lots of false positives of things that are fine
     - wrapcheck # Not every error must be wrapped
+    - wsl # Very aggressive, some of this I like but tend to do anyway
 
 issues:
   exclude-rules:

internal/flag/flag.go

@@ -103,6 +103,12 @@
 
 	*p = value
 
+	// If the default value is not the zero value for the type, it is treated as
+	// significant and shown to the user
+	if !isZero(value) {
+		usage += fmt.Sprintf(" [default: %v]", value)
+	}
+
 	flag := Flag[T]{
 		value: p,
 		name:  name,
@@ -625,3 +631,29 @@
 		return strconv.FormatFloat(float64(in), 'g', -1, bits)
 	}
 }
+
+// isZero reports whether value is the zero value for it's type.
+func isZero[T Flaggable](value T) bool {
+	switch typ := any(value).(type) {
+	case int, int8, int16, int32, int64, uint, uint8, uint16, uint32, uint64, uintptr, float32, float64:
+		return typ == 0
+	case Count:
+		return typ == Count(0)
+	case string:
+		return typ == ""
+	case bool:
+		return !typ
+	case []byte:
+		return typ == nil
+	case time.Time:
+		var zero time.Time
+		return typ.Equal(zero)
+	case time.Duration:
+		var zero time.Duration
+		return typ == zero
+	case net.IP:
+		return typ == nil
+	default:
+		return false
+	}
+}

internal/flag/set.go

@@ -13,10 +13,6 @@ import (
 
 // Set is a set of command line flags.
 type Set struct {
-	// Note: flags and shorthands are different "views" to the same *Entry, the Entry
-	// is not duplicated, it's just two maps to the same pointer so we can look up
-	// using either
-
 	flags      map[string]Value // The actual stored flags, can lookup by name
 	shorthands map[rune]Value   // The flags by shorthand
 	args       []string         // Arguments minus flags or flag values

option.go

@@ -451,10 +451,15 @@ func Allow(validator ArgValidator) Option {
 	return option(f)
 }
 
-// Flag is an [Option] that adds a flag to a [Command], storing its value in a variable.
+// Flag is an [Option] that adds a flag to a [Command], storing its value in a variable via it's
+// pointer 'p'.
 //
 // The variable is set when the flag is parsed during command execution. The value provided
-// in the call to [Flag] is used as the default value.
+// by the 'value' argument to [Flag] is used as the default value, which will be used if the
+// flag value was not given via the command line.
+//
+// If the default value is not the zero value for the type T, the flags usage message will
+// show the default value in the commands help text.
 //
 // To add a long flag only (e.g. --delete with no -d option), pass [NoShortHand] for "short".
 //

testdata/snapshots/TestHelp/with_subcommands_and_flags.snap.txt

@@ -9,7 +9,7 @@ Commands:
   sub2  Do another thing
 
 Options:
-  N/A  --count    int   Count something
+  N/A  --count    int   Count something [default: -1]
   -d   --delete   bool  Delete something
   -h   --help     bool  Show help for test
   -V   --version  bool  Show version info for test