diff --git a/.palantir/go-version b/.palantir/go-version
index 952a187d..06e64096 100644
--- a/.palantir/go-version
+++ b/.palantir/go-version
@@ -1 +1 @@
-go1.20.7
\ No newline at end of file
+go1.21.1
\ No newline at end of file
diff --git a/generated_src/internal/amalgomated_flag/example_func_test.go b/generated_src/internal/amalgomated_flag/example_func_test.go
index 7c30c5e7..ac9f9858 100644
--- a/generated_src/internal/amalgomated_flag/example_func_test.go
+++ b/generated_src/internal/amalgomated_flag/example_func_test.go
@@ -39,3 +39,19 @@ func ExampleFunc() {
 	//     	IP address to parse
 	// {ip: <nil>, loopback: false}
 }
+
+func ExampleBoolFunc() {
+	fs := flag.NewFlagSet("ExampleBoolFunc", flag.ContinueOnError)
+	fs.SetOutput(os.Stdout)
+
+	fs.BoolFunc("log", "logs a dummy message", func(s string) error {
+		fmt.Println("dummy message:", s)
+		return nil
+	})
+	fs.Parse([]string{"-log"})
+	fs.Parse([]string{"-log=0"})
+
+	// Output:
+	// dummy message: true
+	// dummy message: 0
+}
diff --git a/generated_src/internal/amalgomated_flag/flag.go b/generated_src/internal/amalgomated_flag/flag.go
index ef3cf29c..9d3e8d32 100644
--- a/generated_src/internal/amalgomated_flag/flag.go
+++ b/generated_src/internal/amalgomated_flag/flag.go
@@ -89,6 +89,7 @@ import (
 	"io"
 	"os"
 	"reflect"
+	"runtime"
 	"sort"
 	"strconv"
 	"strings"
@@ -337,6 +338,15 @@ func (f funcValue) Set(s string) error { return f(s) }
 
 func (f funcValue) String() string { return "" }
 
+// -- boolFunc Value
+type boolFuncValue func(string) error
+
+func (f boolFuncValue) Set(s string) error { return f(s) }
+
+func (f boolFuncValue) String() string { return "" }
+
+func (f boolFuncValue) IsBoolFlag() bool { return true }
+
 // Value is the interface to the dynamic value stored in a flag.
 // (The default value is represented as a string.)
 //
@@ -390,7 +400,8 @@ type FlagSet struct {
 	formal        map[string]*Flag
 	args          []string // arguments after flags
 	errorHandling ErrorHandling
-	output        io.Writer // nil means stderr; use Output() accessor
+	output        io.Writer         // nil means stderr; use Output() accessor
+	undef         map[string]string // flags which didn't exist at the time of Set
 }
 
 // A Flag represents the state of a flag.
@@ -481,8 +492,29 @@ func Lookup(name string) *Flag {
 
 // Set sets the value of the named flag.
 func (f *FlagSet) Set(name, value string) error {
+	return f.set(name, value)
+}
+func (f *FlagSet) set(name, value string) error {
 	flag, ok := f.formal[name]
 	if !ok {
+		// Remember that a flag that isn't defined is being set.
+		// We return an error in this case, but in addition if
+		// subsequently that flag is defined, we want to panic
+		// at the definition point.
+		// This is a problem which occurs if both the definition
+		// and the Set call are in init code and for whatever
+		// reason the init code changes evaluation order.
+		// See issue 57411.
+		_, file, line, ok := runtime.Caller(2)
+		if !ok {
+			file = "?"
+			line = 0
+		}
+		if f.undef == nil {
+			f.undef = map[string]string{}
+		}
+		f.undef[name] = fmt.Sprintf("%s:%d", file, line)
+
 		return fmt.Errorf("no such flag -%v", name)
 	}
 	err := flag.Value.Set(value)
@@ -498,7 +530,7 @@ func (f *FlagSet) Set(name, value string) error {
 
 // Set sets the value of the named command-line flag.
 func Set(name, value string) error {
-	return CommandLine.Set(name, value)
+	return CommandLine.set(name, value)
 }
 
 // isZeroValue determines whether the string represents the zero
@@ -955,6 +987,20 @@ func Func(name, usage string, fn func(string) error) {
 	CommandLine.Func(name, usage, fn)
 }
 
+// BoolFunc defines a flag with the specified name and usage string without requiring values.
+// Each time the flag is seen, fn is called with the value of the flag.
+// If fn returns a non-nil error, it will be treated as a flag value parsing error.
+func (f *FlagSet) BoolFunc(name, usage string, fn func(string) error) {
+	f.Var(boolFuncValue(fn), name, usage)
+}
+
+// BoolFunc defines a flag with the specified name and usage string without requiring values.
+// Each time the flag is seen, fn is called with the value of the flag.
+// If fn returns a non-nil error, it will be treated as a flag value parsing error.
+func BoolFunc(name, usage string, fn func(string) error) {
+	CommandLine.BoolFunc(name, usage, fn)
+}
+
 // Var defines a flag with the specified name and usage string. The type and
 // value of the flag are represented by the first argument, of type Value, which
 // typically holds a user-defined implementation of Value. For instance, the
@@ -981,6 +1027,9 @@ func (f *FlagSet) Var(value Value, name string, usage string) {
 		}
 		panic(msg) // Happens only if flags are declared with identical names
 	}
+	if pos := f.undef[name]; pos != "" {
+		panic(fmt.Sprintf("flag %s set at %s before being defined", name, pos))
+	}
 	if f.formal == nil {
 		f.formal = make(map[string]*Flag)
 	}
diff --git a/generated_src/internal/amalgomated_flag/flag_test.go b/generated_src/internal/amalgomated_flag/flag_test.go
index 17551684..57c88f00 100644
--- a/generated_src/internal/amalgomated_flag/flag_test.go
+++ b/generated_src/internal/amalgomated_flag/flag_test.go
@@ -12,6 +12,7 @@ import (
 	"io"
 	"os"
 	"os/exec"
+	"regexp"
 	"runtime"
 	"sort"
 	"strconv"
@@ -38,6 +39,7 @@ func TestEverything(t *testing.T) {
 	Float64("test_float64", 0, "float64 value")
 	Duration("test_duration", 0, "time.Duration value")
 	Func("test_func", "func value", func(string) error { return nil })
+	BoolFunc("test_boolfunc", "func", func(string) error { return nil })
 
 	m := make(map[string]*Flag)
 	desired := "0"
@@ -54,6 +56,8 @@ func TestEverything(t *testing.T) {
 				ok = true
 			case f.Name == "test_func" && f.Value.String() == "":
 				ok = true
+			case f.Name == "test_boolfunc" && f.Value.String() == "":
+				ok = true
 			}
 			if !ok {
 				t.Error("Visit: bad value", f.Value.String(), "for", f.Name)
@@ -61,7 +65,7 @@ func TestEverything(t *testing.T) {
 		}
 	}
 	VisitAll(visitor)
-	if len(m) != 9 {
+	if len(m) != 10 {
 		t.Error("VisitAll misses some flags")
 		for k, v := range m {
 			t.Log(k, *v)
@@ -85,9 +89,10 @@ func TestEverything(t *testing.T) {
 	Set("test_float64", "1")
 	Set("test_duration", "1s")
 	Set("test_func", "1")
+	Set("test_boolfunc", "")
 	desired = "1"
 	Visit(visitor)
-	if len(m) != 9 {
+	if len(m) != 10 {
 		t.Error("Visit fails after set")
 		for k, v := range m {
 			t.Log(k, *v)
@@ -722,7 +727,7 @@ func mustPanic(t *testing.T, testName string, expected string, f func()) {
 		case nil:
 			t.Errorf("%s\n: expected panic(%q), but did not panic", testName, expected)
 		case string:
-			if msg != expected {
+			if ok, _ := regexp.MatchString(expected, msg); !ok {
 				t.Errorf("%s\n: expected panic(%q), but got panic(%q)", testName, expected, msg)
 			}
 		default:
@@ -797,3 +802,57 @@ func TestRedefinedFlags(t *testing.T) {
 		}
 	}
 }
+
+func TestUserDefinedBoolFunc(t *testing.T) {
+	flags := NewFlagSet("test", ContinueOnError)
+	flags.SetOutput(io.Discard)
+	var ss []string
+	flags.BoolFunc("v", "usage", func(s string) error {
+		ss = append(ss, s)
+		return nil
+	})
+	if err := flags.Parse([]string{"-v", "", "-v", "1", "-v=2"}); err != nil {
+		t.Error(err)
+	}
+	if len(ss) != 1 {
+		t.Fatalf("got %d args; want 1 arg", len(ss))
+	}
+	want := "[true]"
+	if got := fmt.Sprint(ss); got != want {
+		t.Errorf("got %q; want %q", got, want)
+	}
+	// test usage
+	var buf strings.Builder
+	flags.SetOutput(&buf)
+	flags.Parse([]string{"-h"})
+	if usage := buf.String(); !strings.Contains(usage, "usage") {
+		t.Errorf("usage string not included: %q", usage)
+	}
+	// test BoolFunc error
+	flags = NewFlagSet("test", ContinueOnError)
+	flags.SetOutput(io.Discard)
+	flags.BoolFunc("v", "usage", func(s string) error {
+		return fmt.Errorf("test error")
+	})
+	// flag not set, so no error
+	if err := flags.Parse(nil); err != nil {
+		t.Error(err)
+	}
+	// flag set, expect error
+	if err := flags.Parse([]string{"-v", ""}); err == nil {
+		t.Error("got err == nil; want err != nil")
+	} else if errMsg := err.Error(); !strings.Contains(errMsg, "test error") {
+		t.Errorf(`got %q; error should contain "test error"`, errMsg)
+	}
+}
+
+func TestDefineAfterSet(t *testing.T) {
+	flags := NewFlagSet("test", ContinueOnError)
+	// Set by itself doesn't panic.
+	flags.Set("myFlag", "value")
+
+	// Define-after-set panics.
+	mustPanic(t, "DefineAfterSet", "flag myFlag set at .*/flag_test.go:.* before being defined", func() {
+		_ = flags.String("myFlag", "default", "usage")
+	})
+}
diff --git a/go.mod b/go.mod
index 8d03c767..cb871d52 100644
--- a/go.mod
+++ b/go.mod
@@ -1,6 +1,6 @@
 module github.com/palantir/godel-okgo-asset-ineffassign
 
-go 1.20
+go 1.21
 
 require (
 	github.com/gordonklaus/ineffassign v0.0.0-20210914165742-4cc7213b9bc8
diff --git a/go.sum b/go.sum
index 82453455..15b4629b 100644
--- a/go.sum
+++ b/go.sum
@@ -21,6 +21,7 @@ github.com/golang/snappy v0.0.3 h1:fHPg5GQYlCeLIPB9BZqMVR5nR9A+IM5zcgeTdjMYmLA=
 github.com/golang/snappy v0.0.3/go.mod h1:/XxbfmMg8lxefKM7IXC3fBNl/7bRcc72aCRzEWrmP2Q=
 github.com/google/go-cmp v0.3.0/go.mod h1:8QqcDgzrUqlUb/G2PQTWiueGozuR1884gddMywk6iLU=
 github.com/google/go-cmp v0.5.6 h1:BKbKCqvP6I+rmFHt06ZmyQtvB8xAkWdhFyr0ZUNZcxQ=
+github.com/google/go-cmp v0.5.6/go.mod h1:v8dTdLbMG2kIc/vJvl+f65V22dbkXbowE6jgT/gNBxE=
 github.com/gordonklaus/ineffassign v0.0.0-20210914165742-4cc7213b9bc8 h1:PVRE9d4AQKmbelZ7emNig1+NT27DUmKZn5qXxfio54U=
 github.com/gordonklaus/ineffassign v0.0.0-20210914165742-4cc7213b9bc8/go.mod h1:Qcp2HIAYhR7mNUVSIxZww3Guk4it82ghYcEXIAk+QT0=
 github.com/inconshreveable/mousetrap v1.1.0 h1:wN+x4NVGpMsO7ErUn/mUI3vEoE6Jt13X2s0bqwp9tc8=
@@ -33,6 +34,7 @@ github.com/klauspost/pgzip v1.2.1 h1:oIPZROsWuPHpOdMVWLuJZXwgjhrW8r1yEX8UqMyeNHM
 github.com/klauspost/pgzip v1.2.1/go.mod h1:Ch1tH69qFZu15pkjo5kYi6mth2Zzwzt50oCQKQE9RUs=
 github.com/kr/pretty v0.1.0/go.mod h1:dAy3ld7l9f0ibDNOQOHHMYYIIbhfbHSm3C4ZsoJORNo=
 github.com/kr/pretty v0.2.0 h1:s5hAObm+yFO5uHYt5dYjxi2rXrsnmRpJx4OYvIWUaQs=
+github.com/kr/pretty v0.2.0/go.mod h1:ipq/a2n7PKx3OHsz4KJII5eveXtPO4qwEXGdVfWzfnI=
 github.com/kr/pty v1.1.1/go.mod h1:pFQYn66WHrOpPYNljwOMqo10TkYh1fy3cYio2l3bCsQ=
 github.com/kr/text v0.1.0 h1:45sCR5RtlFHMR4UwH9sdQ5TC8v0qDQCHnXt+kaKSTVE=
 github.com/kr/text v0.1.0/go.mod h1:4Jbv+DJW3UT/LiOwJeYQe1efqtUx/iVham/4vfdArNI=
@@ -69,6 +71,7 @@ github.com/palantir/pkg v1.1.0/go.mod h1:KC9srP/9ssWRxBxFCIqhUGC4Jt7OJkWRz0Iqehu
 github.com/palantir/pkg/cobracli v1.2.0 h1:hANp5fUB5cX90SVri97Apz4xB3BqnZw0gP2jMQ34G8Y=
 github.com/palantir/pkg/cobracli v1.2.0/go.mod h1:8poQy1FM1lISezW7Czmhmj7I0xEVpuYpv/ywgsAzv0Y=
 github.com/palantir/pkg/gittest v1.2.0 h1:RPINGtLh+Mlt+o1M/nRQlTPrt4CP5tJOSMgeB5vxerM=
+github.com/palantir/pkg/gittest v1.2.0/go.mod h1:z2eq/rEzUDmNR8rvJCb+/XZ7w9/nxRCAKvYjMYW/w/w=
 github.com/palantir/pkg/matcher v1.2.0 h1:h4IeYPSQGWIdi1Qh7QSzWATv0+2coTaaCiozYtPWBks=
 github.com/palantir/pkg/matcher v1.2.0/go.mod h1:JUH9L+Cmjv2U87y+1Ov5KKLmMbgHtESCTrPq5MyWeVM=
 github.com/palantir/pkg/pkgpath v1.2.0 h1:6JDFKFZZsiVBiek47OB7363oIAIjQNFkTsPoEtJpWzY=
@@ -110,6 +113,7 @@ golang.org/x/net v0.0.0-20210405180319-a5a99cb37ef4/go.mod h1:p54w0d4576C0XHj96b
 golang.org/x/sync v0.0.0-20190423024810-112230192c58/go.mod h1:RxMgew5VJxzue5/jJTE5uejpjVlOe/izrB70Jof72aM=
 golang.org/x/sync v0.0.0-20210220032951-036812b2e83c/go.mod h1:RxMgew5VJxzue5/jJTE5uejpjVlOe/izrB70Jof72aM=
 golang.org/x/sync v0.3.0 h1:ftCYgMx6zT/asHUrPw8BLLscYtGznsLAnjq5RH9P66E=
+golang.org/x/sync v0.3.0/go.mod h1:FU7BRWz2tNW+3quACPkgCx/L+uEAv1htQ0V83Z9Rj+Y=
 golang.org/x/sys v0.0.0-20190215142949-d0b11bdaac8a/go.mod h1:STP8DvDyc/dI5b8T5hshtkjS+E42TnysNCUPdjciGhY=
 golang.org/x/sys v0.0.0-20190222072716-a9d3bda3a223/go.mod h1:STP8DvDyc/dI5b8T5hshtkjS+E42TnysNCUPdjciGhY=
 golang.org/x/sys v0.0.0-20190412213103-97732733099d/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs=
@@ -137,6 +141,7 @@ golang.org/x/xerrors v0.0.0-20200804184101-5ec99f83aff1/go.mod h1:I/5z698sn9Ka8T
 gopkg.in/check.v1 v0.0.0-20161208181325-20d25e280405/go.mod h1:Co6ibVJAznAaIkqp8huTwlJQCZ016jof/cbN4VW5Yz0=
 gopkg.in/check.v1 v1.0.0-20180628173108-788fd7840127/go.mod h1:Co6ibVJAznAaIkqp8huTwlJQCZ016jof/cbN4VW5Yz0=
 gopkg.in/check.v1 v1.0.0-20190902080502-41f04d3bba15 h1:YR8cESwS4TdDjEe65xsg0ogRM/Nc3DYOhEAlW+xobZo=
+gopkg.in/check.v1 v1.0.0-20190902080502-41f04d3bba15/go.mod h1:Co6ibVJAznAaIkqp8huTwlJQCZ016jof/cbN4VW5Yz0=
 gopkg.in/errgo.v2 v2.1.0/go.mod h1:hNsd1EY+bozCKY1Ytp96fpM3vjJbqLJn88ws8XvfDNI=
 gopkg.in/yaml.v2 v2.2.2/go.mod h1:hI93XBmqTisBFMUTm0b8Fm+jr3Dg1NNxqwp+5A1VGuI=
 gopkg.in/yaml.v2 v2.4.0 h1:D8xgwECY7CYvx+Y2n4sBz93Jn9JRvxdiyyo8CTfuKaY=