Use enumer to generate String() methods for most enums (#25705)

We have many hand-written String() methods (and similar) for enums.
These require more maintenance and are more error-prone than using
automatically generated methods. In addition, the auto-generated
versions can be more efficient.

Here, we switch to using https://github.com/loggerhead/enumer, itself
a fork of https://github.com/diegostamigni/enumer, no longer maintained,
and a fork of the mostly standard tool
https://pkg.go.dev/golang.org/x/tools/cmd/stringer.
We use this fork of enumer for Go 1.20+ compatibility and because
we require the `-transform` flag to be able to generate
constants that match our current code base.

Some enums were not targeted for this change:

sdk/database/dbplugin/v5/credentialtype_enumer.go

@@ -0,0 +1,50 @@
+// Code generated by "enumer -type=CredentialType -trimprefix=CredentialType -transform=snake"; DO NOT EDIT.
+
+package dbplugin
+
+import (
+	"fmt"
+)
+
+const _CredentialTypeName = "passwordrsa_private_keyclient_certificate"
+
+var _CredentialTypeIndex = [...]uint8{0, 8, 23, 41}
+
+func (i CredentialType) String() string {
+	if i < 0 || i >= CredentialType(len(_CredentialTypeIndex)-1) {
+		return fmt.Sprintf("CredentialType(%d)", i)
+	}
+	return _CredentialTypeName[_CredentialTypeIndex[i]:_CredentialTypeIndex[i+1]]
+}
+
+var _CredentialTypeValues = []CredentialType{0, 1, 2}
+
+var _CredentialTypeNameToValueMap = map[string]CredentialType{
+	_CredentialTypeName[0:8]:   0,
+	_CredentialTypeName[8:23]:  1,
+	_CredentialTypeName[23:41]: 2,
+}
+
+// CredentialTypeString retrieves an enum value from the enum constants string name.
+// Throws an error if the param is not part of the enum.
+func CredentialTypeString(s string) (CredentialType, error) {
+	if val, ok := _CredentialTypeNameToValueMap[s]; ok {
+		return val, nil
+	}
+	return 0, fmt.Errorf("%s does not belong to CredentialType values", s)
+}
+
+// CredentialTypeValues returns all values of the enum
+func CredentialTypeValues() []CredentialType {
+	return _CredentialTypeValues
+}
+
+// IsACredentialType returns "true" if the value is listed in the enum definition. "false" otherwise
+func (i CredentialType) IsACredentialType() bool {
+	for _, v := range _CredentialTypeValues {
+		if i == v {
+			return true
+		}
+	}
+	return false
+}

sdk/database/dbplugin/v5/database.go

@@ -144,6 +144,8 @@ type NewUserResponse struct {
 	Username string
 }
 
+//go:generate enumer -type=CredentialType -trimprefix=CredentialType -transform=snake
+
 // CredentialType is a type of database credential.
 type CredentialType int
 
@@ -153,19 +155,6 @@ const (
 	CredentialTypeClientCertificate
 )
 
-func (k CredentialType) String() string {
-	switch k {
-	case CredentialTypePassword:
-		return "password"
-	case CredentialTypeRSAPrivateKey:
-		return "rsa_private_key"
-	case CredentialTypeClientCertificate:
-		return "client_certificate"
-	default:
-		return "unknown"
-	}
-}
-
 // ///////////////////////////////////////////////////////
 // UpdateUser()
 // ///////////////////////////////////////////////////////