Validate git protocol config before setting it

internal/config/config_type.go

@@ -5,6 +5,7 @@ import (
 	"errors"
 	"fmt"
 	"sort"
+	"strings"
 
 	"github.com/cli/cli/internal/ghinstance"
 	"gopkg.in/yaml.v3"
@@ -16,6 +17,10 @@ const (
 	PromptsEnabled     = "enabled"
 )
 
+var configValues = map[string][]string{
+	"git_protocol": {"ssh", "https"},
+}
+
 // This interface describes interacting with some persistent configuration for gh.
 type Config interface {
 	Get(string, string) (string, error)
@@ -271,7 +276,30 @@ func (c *fileConfig) GetWithSource(hostname, key string) (string, string, error)
 	return value, defaultSource, nil
 }
 
+func validConfigValues(key string) []string {
+	return configValues[key]
+}
+
+func validateConfigEntry(key, value string) error {
+	validValues := validConfigValues(key)
+
+	if len(validValues) == 0 {
+		return nil
+	}
+
+	for _, v := range validValues {
+		if v == value {
+			return nil
+		}
+	}
+
+	return fmt.Errorf("invalid value. Possible values for \"%s\" are: %s", key, strings.Join(validValues, ", "))
+}
+
 func (c *fileConfig) Set(hostname, key, value string) error {
+	if err := validateConfigEntry(key, value); err != nil {
+		return err
+	}
 	if hostname == "" {
 		return c.SetStringValue(key, value)
 	} else {

internal/config/config_type_test.go

@@ -28,6 +28,7 @@ func Test_fileConfig_Set(t *testing.T) {
 example.com:
     editor: vim
 `, hostsBuf.String())
+	assert.EqualError(t, c.Set("github.com", "git_protocol", "sshpps"), "invalid value. Possible values for \"git_protocol\" are: ssh, https")
 }
 
 func Test_defaultConfig(t *testing.T) {
@@ -68,3 +69,17 @@ func Test_defaultConfig(t *testing.T) {
 	expansion, _ := aliases.Get("co")
 	assert.Equal(t, expansion, "pr checkout")
 }
+
+func Test_validateConfigEntry(t *testing.T) {
+	err := validateConfigEntry("git_protocol", "sshpps")
+	assert.EqualError(t, err, "invalid value. Possible values for \"git_protocol\" are: ssh, https")
+
+	err = validateConfigEntry("git_protocol", "ssh")
+	assert.Nil(t, err)
+
+	err = validateConfigEntry("editor", "vim")
+	assert.Nil(t, err)
+
+	err = validateConfigEntry("got", "123")
+	assert.Nil(t, err)
+}