move Func, BoolFunc, tests as they require go1.21

Commit 69bc3bd5b37fa90e994be9acecf7430269591713 added support for Func()
and BoolFunc() to match stdlib. However, the Func method was added in
[go1.16.0], and BoolFunc in [go1.21.0], so running the tests on older
versions of Go would fail;

    docker run -it --rm -v ./:/pflag -w /pflag golang:1.21 sh -c 'go test -v ./...'
    # github.com/spf13/pflag [github.com/spf13/pflag.test]
    ./bool_func_test.go:86:28: cannot use stdFSet (type *flag.FlagSet) as type BoolFuncFlagSet in argument to runCase:
        *flag.FlagSet does not implement BoolFuncFlagSet (missing BoolFunc method)
    ./bool_func_test.go:113:21: undefined: io.Discard
    ./bool_func_test.go:116:28: cannot use stdFSet (type *flag.FlagSet) as type BoolFuncFlagSet in argument to runCase:
        *flag.FlagSet does not implement BoolFuncFlagSet (missing BoolFunc method)
    ./bool_func_test.go:139:7: undefined: errors.Is
    ./func_test.go:92:28: cannot use stdFSet (type *flag.FlagSet) as type FuncFlagSet in argument to runCase:
        *flag.FlagSet does not implement FuncFlagSet (missing Func method)
    ./func_test.go:119:21: undefined: io.Discard
    ./func_test.go:122:28: cannot use stdFSet (type *flag.FlagSet) as type FuncFlagSet in argument to runCase:
        *flag.FlagSet does not implement FuncFlagSet (missing Func method)
    ./func_test.go:145:7: undefined: errors.Is
    ./func_test.go:145:7: too many errors
    FAIL	github.com/spf13/pflag [build failed]

This patch moves the tests to a separate file that is not built for older
versions of Go.

[go1.16.0]: https://pkg.go.dev/[email protected]#Func
[go1.21.0]: https://pkg.go.dev/[email protected]#BoolFunc

Signed-off-by: Sebastiaan van Stijn <[email protected]>

4 files changed, 212 insertions, 194 deletions

diff --git a/bool_func_go1.21_test.go b/bool_func_go1.21_test.go
new file mode 100644
index 0000000..5b1bd55
--- /dev/null
+++ b/bool_func_go1.21_test.go
@@ -0,0 +1,110 @@
+//go:build go1.21
+// +build go1.21
+
+package pflag
+
+import (
+	"errors"
+	"flag"
+	"io"
+	"strings"
+	"testing"
+)
+
+func TestBoolFuncCompat(t *testing.T) {
+	// compare behavior with the stdlib 'flag' package
+	type BoolFuncFlagSet interface {
+		BoolFunc(name string, usage string, fn func(string) error)
+		Parse([]string) error
+	}
+
+	unitTestErr := errors.New("unit test error")
+	runCase := func(f BoolFuncFlagSet, name string, args []string) (values []string, err error) {
+		fn := func(s string) error {
+			values = append(values, s)
+			if s == "err" {
+				return unitTestErr
+			}
+			return nil
+		}
+		f.BoolFunc(name, "Callback function", fn)
+
+		err = f.Parse(args)
+		return values, err
+	}
+
+	t.Run("regular parsing", func(t *testing.T) {
+		flagName := "bflag"
+		args := []string{"--bflag", "--bflag=false", "--bflag=1", "--bflag=bar", "--bflag="}
+
+		// It turns out that, even though the function is called "BoolFunc",
+		// the standard flag package does not try to parse the value assigned to
+		// that cli flag as a boolean. The string provided on the command line is
+		// passed as is to the callback.
+		//   e.g: with "--bflag=not_a_bool" on the command line, the FlagSet does not
+		// generate an error stating "invalid boolean value", and `fn` will be called
+		// with "not_a_bool" as an argument.
+
+		stdFSet := flag.NewFlagSet("std test", flag.ContinueOnError)
+		stdValues, err := runCase(stdFSet, flagName, args)
+		if err != nil {
+			t.Fatalf("std flag: expected no error, got %v", err)
+		}
+		expected := []string{"true", "false", "1", "bar", ""}
+		if !cmpLists(expected, stdValues) {
+			t.Fatalf("std flag: expected %v, got %v", expected, stdValues)
+		}
+
+		fset := NewFlagSet("pflag test", ContinueOnError)
+		pflagValues, err := runCase(fset, flagName, args)
+		if err != nil {
+			t.Fatalf("pflag: expected no error, got %v", err)
+		}
+		if !cmpLists(stdValues, pflagValues) {
+			t.Fatalf("pflag: expected %v, got %v", stdValues, pflagValues)
+		}
+	})
+
+	t.Run("error triggered by callback", func(t *testing.T) {
+		flagName := "bflag"
+		args := []string{"--bflag", "--bflag=err", "--bflag=after"}
+
+		// test behavior of standard flag.Fset with an error triggered by the callback:
+		// (note: as can be seen in 'runCase()', if the callback sees "err" as a value
+		//  for the bool flag, it will return an error)
+		stdFSet := flag.NewFlagSet("std test", flag.ContinueOnError)
+		stdFSet.SetOutput(io.Discard) // suppress output
+
+		// run test case with standard flag.Fset
+		stdValues, err := runCase(stdFSet, flagName, args)
+
+		// double check the standard behavior:
+		// - .Parse() should return an error, which contains the error message
+		if err == nil {
+			t.Fatalf("std flag: expected an error triggered by callback, got no error instead")
+		}
+		if !strings.HasSuffix(err.Error(), unitTestErr.Error()) {
+			t.Fatalf("std flag: expected unittest error, got unexpected error value: %T %v", err, err)
+		}
+		// - the function should have been called twice, with the first two values,
+		//   the final "=after" should not be recorded
+		expected := []string{"true", "err"}
+		if !cmpLists(expected, stdValues) {
+			t.Fatalf("std flag: expected %v, got %v", expected, stdValues)
+		}
+
+		// now run the test case on a pflag FlagSet:
+		fset := NewFlagSet("pflag test", ContinueOnError)
+		pflagValues, err := runCase(fset, flagName, args)
+
+		// check that there is a similar error (note: pflag will _wrap_ the error, while the stdlib
+		// currently keeps the original message but creates a flat errors.Error)
+		if !errors.Is(err, unitTestErr) {
+			t.Fatalf("pflag: got unexpected error value: %T %v", err, err)
+		}
+		// the callback should be called the same number of times, with the same values:
+		if !cmpLists(stdValues, pflagValues) {
+			t.Fatalf("pflag: expected %v, got %v", stdValues, pflagValues)
+		}
+	})
+}
diff --git a/bool_func_test.go b/bool_func_test.go
index c16be83..765c9c0 100644
--- a/bool_func_test.go
+++ b/bool_func_test.go
@@ -1,9 +1,6 @@
 package pflag
 
 import (
-	"errors"
-	"flag"
-	"io"
 	"strings"
 	"testing"
 )
@@ -48,104 +45,6 @@ func TestBoolFuncP(t *testing.T) {
 	}
 }
 
-func TestBoolFuncCompat(t *testing.T) {
-	// compare behavior with the stdlib 'flag' package
-	type BoolFuncFlagSet interface {
-		BoolFunc(name string, usage string, fn func(string) error)
-		Parse([]string) error
-	}
-
-	unitTestErr := errors.New("unit test error")
-	runCase := func(f BoolFuncFlagSet, name string, args []string) (values []string, err error) {
-		fn := func(s string) error {
-			values = append(values, s)
-			if s == "err" {
-				return unitTestErr
-			}
-			return nil
-		}
-		f.BoolFunc(name, "Callback function", fn)
-
-		err = f.Parse(args)
-		return values, err
-	}
-
-	t.Run("regular parsing", func(t *testing.T) {
-		flagName := "bflag"
-		args := []string{"--bflag", "--bflag=false", "--bflag=1", "--bflag=bar", "--bflag="}
-
-		// It turns out that, even though the function is called "BoolFunc",
-		// the standard flag package does not try to parse the value assigned to
-		// that cli flag as a boolean. The string provided on the command line is
-		// passed as is to the callback.
-		//   e.g: with "--bflag=not_a_bool" on the command line, the FlagSet does not
-		// generate an error stating "invalid boolean value", and `fn` will be called
-		// with "not_a_bool" as an argument.
-
-		stdFSet := flag.NewFlagSet("std test", flag.ContinueOnError)
-		stdValues, err := runCase(stdFSet, flagName, args)
-		if err != nil {
-			t.Fatalf("std flag: expected no error, got %v", err)
-		}
-		expected := []string{"true", "false", "1", "bar", ""}
-		if !cmpLists(expected, stdValues) {
-			t.Fatalf("std flag: expected %v, got %v", expected, stdValues)
-		}
-
-		fset := NewFlagSet("pflag test", ContinueOnError)
-		pflagValues, err := runCase(fset, flagName, args)
-		if err != nil {
-			t.Fatalf("pflag: expected no error, got %v", err)
-		}
-		if !cmpLists(stdValues, pflagValues) {
-			t.Fatalf("pflag: expected %v, got %v", stdValues, pflagValues)
-		}
-	})
-
-	t.Run("error triggered by callback", func(t *testing.T) {
-		flagName := "bflag"
-		args := []string{"--bflag", "--bflag=err", "--bflag=after"}
-
-		// test behavior of standard flag.Fset with an error triggered by the callback:
-		// (note: as can be seen in 'runCase()', if the callback sees "err" as a value
-		//  for the bool flag, it will return an error)
-		stdFSet := flag.NewFlagSet("std test", flag.ContinueOnError)
-		stdFSet.SetOutput(io.Discard) // suppress output
-
-		// run test case with standard flag.Fset
-		stdValues, err := runCase(stdFSet, flagName, args)
-
-		// double check the standard behavior:
-		// - .Parse() should return an error, which contains the error message
-		if err == nil {
-			t.Fatalf("std flag: expected an error triggered by callback, got no error instead")
-		}
-		if !strings.HasSuffix(err.Error(), unitTestErr.Error()) {
-			t.Fatalf("std flag: expected unittest error, got unexpected error value: %T %v", err, err)
-		}
-		// - the function should have been called twice, with the first two values,
-		//   the final "=after" should not be recorded
-		expected := []string{"true", "err"}
-		if !cmpLists(expected, stdValues) {
-			t.Fatalf("std flag: expected %v, got %v", expected, stdValues)
-		}
-
-		// now run the test case on a pflag FlagSet:
-		fset := NewFlagSet("pflag test", ContinueOnError)
-		pflagValues, err := runCase(fset, flagName, args)
-
-		// check that there is a similar error (note: pflag will _wrap_ the error, while the stdlib
-		// currently keeps the original message but creates a flat errors.Error)
-		if !errors.Is(err, unitTestErr) {
-			t.Fatalf("pflag: got unexpected error value: %T %v", err, err)
-		}
-		// the callback should be called the same number of times, with the same values:
-		if !cmpLists(stdValues, pflagValues) {
-			t.Fatalf("pflag: expected %v, got %v", stdValues, pflagValues)
-		}
-	})
-}
-
 func TestBoolFuncUsage(t *testing.T) {
 	t.Run("regular func flag", func(t *testing.T) {
 		// regular boolfunc flag:
diff --git a/func_go1.21_test.go b/func_go1.21_test.go
new file mode 100644
index 0000000..2d5ea31
--- /dev/null
+++ b/func_go1.21_test.go
@@ -0,0 +1,102 @@
+//go:build go1.21
+// +build go1.21
+
+package pflag
+
+import (
+	"errors"
+	"flag"
+	"io"
+	"strings"
+	"testing"
+)
+
+func TestFuncCompat(t *testing.T) {
+	// compare behavior with the stdlib 'flag' package
+	type FuncFlagSet interface {
+		Func(name string, usage string, fn func(string) error)
+		Parse([]string) error
+	}
+
+	unitTestErr := errors.New("unit test error")
+	runCase := func(f FuncFlagSet, name string, args []string) (values []string, err error) {
+		fn := func(s string) error {
+			values = append(values, s)
+			if s == "err" {
+				return unitTestErr
+			}
+			return nil
+		}
+		f.Func(name, "Callback function", fn)
+
+		err = f.Parse(args)
+		return values, err
+	}
+
+	t.Run("regular parsing", func(t *testing.T) {
+		flagName := "fnflag"
+		args := []string{"--fnflag=xx", "--fnflag", "yy", "--fnflag=zz"}
+
+		stdFSet := flag.NewFlagSet("std test", flag.ContinueOnError)
+		stdValues, err := runCase(stdFSet, flagName, args)
+		if err != nil {
+			t.Fatalf("std flag: expected no error, got %v", err)
+		}
+		expected := []string{"xx", "yy", "zz"}
+		if !cmpLists(expected, stdValues) {
+			t.Fatalf("std flag: expected %v, got %v", expected, stdValues)
+		}
+
+		fset := NewFlagSet("pflag test", ContinueOnError)
+		pflagValues, err := runCase(fset, flagName, args)
+		if err != nil {
+			t.Fatalf("pflag: expected no error, got %v", err)
+		}
+		if !cmpLists(stdValues, pflagValues) {
+			t.Fatalf("pflag: expected %v, got %v", stdValues, pflagValues)
+		}
+	})
+
+	t.Run("error triggered by callback", func(t *testing.T) {
+		flagName := "fnflag"
+		args := []string{"--fnflag", "before", "--fnflag", "err", "--fnflag", "after"}
+
+		// test behavior of standard flag.Fset with an error triggered by the callback:
+		// (note: as can be seen in 'runCase()', if the callback sees "err" as a value
+		//  for the flag, it will return an error)
+		stdFSet := flag.NewFlagSet("std test", flag.ContinueOnError)
+		stdFSet.SetOutput(io.Discard) // suppress output
+
+		// run test case with standard flag.Fset
+		stdValues, err := runCase(stdFSet, flagName, args)
+
+		// double check the standard behavior:
+		// - .Parse() should return an error, which contains the error message
+		if err == nil {
+			t.Fatalf("std flag: expected an error triggered by callback, got no error instead")
+		}
+		if !strings.HasSuffix(err.Error(), unitTestErr.Error()) {
+			t.Fatalf("std flag: expected unittest error, got unexpected error value: %T %v", err, err)
+		}
+		// - the function should have been called twice, with the first two values,
+		//   the final "=after" should not be recorded
+		expected := []string{"before", "err"}
+		if !cmpLists(expected, stdValues) {
+			t.Fatalf("std flag: expected %v, got %v", expected, stdValues)
+		}
+
+		// now run the test case on a pflag FlagSet:
+		fset := NewFlagSet("pflag test", ContinueOnError)
+		pflagValues, err := runCase(fset, flagName, args)
+
+		// check that there is a similar error (note: pflag will _wrap_ the error, while the stdlib
+		// currently keeps the original message but creates a flat errors.Error)
+		if !errors.Is(err, unitTestErr) {
+			t.Fatalf("pflag: got unexpected error value: %T %v", err, err)
+		}
+		// the callback should be called the same number of times, with the same values:
+		if !cmpLists(stdValues, pflagValues) {
+			t.Fatalf("pflag: expected %v, got %v", stdValues, pflagValues)
+		}
+	})
+}
diff --git a/func_test.go b/func_test.go
index d492b48..4badf93 100644
--- a/func_test.go
+++ b/func_test.go
@@ -1,9 +1,6 @@
 package pflag
 
 import (
-	"errors"
-	"flag"
-	"io"
 	"strings"
 	"testing"
 )
@@ -62,96 +59,6 @@ func TestFuncP(t *testing.T) {
 	}
 }
 
-func TestFuncCompat(t *testing.T) {
-	// compare behavior with the stdlib 'flag' package
-	type FuncFlagSet interface {
-		Func(name string, usage string, fn func(string) error)
-		Parse([]string) error
-	}
-
-	unitTestErr := errors.New("unit test error")
-	runCase := func(f FuncFlagSet, name string, args []string) (values []string, err error) {
-		fn := func(s string) error {
-			values = append(values, s)
-			if s == "err" {
-				return unitTestErr
-			}
-			return nil
-		}
-		f.Func(name, "Callback function", fn)
-
-		err = f.Parse(args)
-		return values, err
-	}
-
-	t.Run("regular parsing", func(t *testing.T) {
-		flagName := "fnflag"
-		args := []string{"--fnflag=xx", "--fnflag", "yy", "--fnflag=zz"}
-
-		stdFSet := flag.NewFlagSet("std test", flag.ContinueOnError)
-		stdValues, err := runCase(stdFSet, flagName, args)
-		if err != nil {
-			t.Fatalf("std flag: expected no error, got %v", err)
-		}
-		expected := []string{"xx", "yy", "zz"}
-		if !cmpLists(expected, stdValues) {
-			t.Fatalf("std flag: expected %v, got %v", expected, stdValues)
-		}
-
-		fset := NewFlagSet("pflag test", ContinueOnError)
-		pflagValues, err := runCase(fset, flagName, args)
-		if err != nil {
-			t.Fatalf("pflag: expected no error, got %v", err)
-		}
-		if !cmpLists(stdValues, pflagValues) {
-			t.Fatalf("pflag: expected %v, got %v", stdValues, pflagValues)
-		}
-	})
-
-	t.Run("error triggered by callback", func(t *testing.T) {
-		flagName := "fnflag"
-		args := []string{"--fnflag", "before", "--fnflag", "err", "--fnflag", "after"}
-
-		// test behavior of standard flag.Fset with an error triggered by the callback:
-		// (note: as can be seen in 'runCase()', if the callback sees "err" as a value
-		//  for the flag, it will return an error)
-		stdFSet := flag.NewFlagSet("std test", flag.ContinueOnError)
-		stdFSet.SetOutput(io.Discard) // suppress output
-
-		// run test case with standard flag.Fset
-		stdValues, err := runCase(stdFSet, flagName, args)
-
-		// double check the standard behavior:
-		// - .Parse() should return an error, which contains the error message
-		if err == nil {
-			t.Fatalf("std flag: expected an error triggered by callback, got no error instead")
-		}
-		if !strings.HasSuffix(err.Error(), unitTestErr.Error()) {
-			t.Fatalf("std flag: expected unittest error, got unexpected error value: %T %v", err, err)
-		}
-		// - the function should have been called twice, with the first two values,
-		//   the final "=after" should not be recorded
-		expected := []string{"before", "err"}
-		if !cmpLists(expected, stdValues) {
-			t.Fatalf("std flag: expected %v, got %v", expected, stdValues)
-		}
-
-		// now run the test case on a pflag FlagSet:
-		fset := NewFlagSet("pflag test", ContinueOnError)
-		pflagValues, err := runCase(fset, flagName, args)
-
-		// check that there is a similar error (note: pflag will _wrap_ the error, while the stdlib
-		// currently keeps the original message but creates a flat errors.Error)
-		if !errors.Is(err, unitTestErr) {
-			t.Fatalf("pflag: got unexpected error value: %T %v", err, err)
-		}
-		// the callback should be called the same number of times, with the same values:
-		if !cmpLists(stdValues, pflagValues) {
-			t.Fatalf("pflag: expected %v, got %v", stdValues, pflagValues)
-		}
-	})
-}
-
 func TestFuncUsage(t *testing.T) {
 	t.Run("regular func flag", func(t *testing.T) {
 		// regular func flag: