From 760eb190baf688d40d128b7c0a4b2d11139ebed0 Mon Sep 17 00:00:00 2001
From: alliasgher <alliasgher123@gmail.com>
Date: Tue, 14 Apr 2026 03:39:33 +0500
Subject: [PATCH 1/2] flag: prevent BoolWithInverseFlag.String from panicking
 without a tab

When FlagStringer returns a string without a tab character,
strings.Index returns -1 and out[-1:] panics with
"slice bounds out of range [-1:]".

Guard against this by clamping the index to 0 when no tab is
found. In that case the entire FlagStringer output is used as
the suffix portion of the formatted string, matching the intent
of callers who use a custom stringer without the usual tab layout.

Fixes #2303

Signed-off-by: alliasgher <alliasgher123@gmail.com>
---
 flag_bool_with_inverse.go      |  8 ++++++++
 flag_bool_with_inverse_test.go | 23 +++++++++++++++++++++++
 2 files changed, 31 insertions(+)

diff --git a/flag_bool_with_inverse.go b/flag_bool_with_inverse.go
index 272dd98fec..680fe2c64e 100644
--- a/flag_bool_with_inverse.go
+++ b/flag_bool_with_inverse.go
@@ -179,6 +179,14 @@ func (bif *BoolWithInverseFlag) String() string {
 		prefix = "-"
 	}
 
+	// Guard against a FlagStringer that returns a string without a tab (e.g.
+	// a custom stringer or the default stringer when the flag does not
+	// implement DocGenerationFlag). In that case treat the entire output as
+	// the tab-delimited suffix so the slice never goes out of bounds.
+	if i < 0 {
+		i = 0
+	}
+
 	return fmt.Sprintf("%s[%s]%s%s", prefix, bif.inversePrefix(), bif.Name, out[i:])
 }
 
diff --git a/flag_bool_with_inverse_test.go b/flag_bool_with_inverse_test.go
index 981494586b..fbb7e43ff8 100644
--- a/flag_bool_with_inverse_test.go
+++ b/flag_bool_with_inverse_test.go
@@ -520,3 +520,26 @@ func TestBoolWithInverseFlag_SatisfiesVisibleFlagInterface(t *testing.T) {
 
 	_ = f.IsVisible()
 }
+
+// TestBoolWithInverseFlagStringNoPanicWithNoTabStringer is a regression test for
+// https://github.com/urfave/cli/issues/2303.
+// BoolWithInverseFlag.String() panicked with "slice bounds out of range [-1:]"
+// when the FlagStringer returned a string without a tab character.
+func TestBoolWithInverseFlagStringNoPanicWithNoTabStringer(t *testing.T) {
+	orig := FlagStringer
+	defer func() { FlagStringer = orig }()
+
+	FlagStringer = func(f Flag) string {
+		return "no tab here"
+	}
+
+	flag := &BoolWithInverseFlag{
+		Name: "verbose",
+	}
+
+	// Must not panic.
+	got := flag.String()
+	if !strings.Contains(got, "verbose") {
+		t.Errorf("expected String() to contain the flag name, got %q", got)
+	}
+}

From bb2e3ea0f522541c714f0b6f5e342e6dd9dd596e Mon Sep 17 00:00:00 2001
From: alliasgher <alliasgher123@gmail.com>
Date: Tue, 14 Apr 2026 03:41:30 +0500
Subject: [PATCH 2/2] errors: don't print an empty line for Exit with empty
 message

When HandleExitCoder received an ExitCoder whose Error() returned an
empty string (e.g. cli.Exit("", code)), it still called
fmt.Fprintln(ErrWriter, err) which wrote a bare newline to stderr.

Guard the print with a check on the error message so that an empty
message produces no output at all.

Fixes #2263

Signed-off-by: alliasgher <alliasgher123@gmail.com>
---
 errors.go      | 10 ++++++----
 errors_test.go | 25 +++++++++++++++++++++++++
 2 files changed, 31 insertions(+), 4 deletions(-)

diff --git a/errors.go b/errors.go
index f365a57990..ffd6471f23 100644
--- a/errors.go
+++ b/errors.go
@@ -150,10 +150,12 @@ func HandleExitCoder(err error) {
 	}
 
 	if exitErr, ok := err.(ExitCoder); ok {
-		if _, ok := exitErr.(ErrorFormatter); ok {
-			_, _ = fmt.Fprintf(ErrWriter, "%+v\n", err)
-		} else {
-			_, _ = fmt.Fprintln(ErrWriter, err)
+		if msg := err.Error(); msg != "" {
+			if _, ok := exitErr.(ErrorFormatter); ok {
+				_, _ = fmt.Fprintf(ErrWriter, "%+v\n", err)
+			} else {
+				_, _ = fmt.Fprintln(ErrWriter, err)
+			}
 		}
 		OsExiter(exitErr.ExitCode())
 		return
diff --git a/errors_test.go b/errors_test.go
index 35aaab54d4..6a497c58f5 100644
--- a/errors_test.go
+++ b/errors_test.go
@@ -232,3 +232,28 @@ func TestErrRequiredFlags_Error(t *testing.T) {
 	expectedMsg = "Required flag \"flag1\" not set"
 	assert.Equal(t, expectedMsg, err.Error())
 }
+
+// TestHandleExitCoder_EmptyMessage is a regression test for
+// https://github.com/urfave/cli/issues/2263.
+// HandleExitCoder must not print an empty line to ErrWriter when the ExitCoder
+// message is empty (e.g. cli.Exit("", code)).
+func TestHandleExitCoder_EmptyMessage(t *testing.T) {
+	called := false
+
+	OsExiter = func(rc int) {
+		if !called {
+			called = true
+		}
+	}
+	ErrWriter = &bytes.Buffer{}
+
+	defer func() {
+		OsExiter = fakeOsExiter
+		ErrWriter = fakeErrWriter
+	}()
+
+	HandleExitCoder(Exit("", 2))
+
+	assert.True(t, called)
+	assert.Empty(t, ErrWriter.(*bytes.Buffer).String(), "expected no output for empty-message exit")
+}