fix(golang): cast string-enum fields in MySQL copyfrom encoder

mysqltsv.AppendValue uses a strict type-switch and rejects
string-derived enum types (e.g. ExperienceLocationsType) with
"can't encode type X to TSV". Detect string enums in the
go-sql-driver-mysql copyfrom template and emit
AppendString(string(field)) instead.

Fixes #4324

Signed-off-by: SAY-5 <saiasish.cnp@gmail.com>

Author: SAY-5

internal/codegen/golang/gen.go

@@ -218,6 +218,7 @@ func generate(req *plugin.GenerateRequest, options *opts.Options, enums []Enum,
 		"imports":    i.Imports,
 		"hasImports": i.HasImports,
 		"hasPrefix":  strings.HasPrefix,
+		"hasSuffix":  strings.HasSuffix,
 
 		// These methods are Go specific, they do not belong in the codegen package
 		// (as that is language independent)

internal/codegen/golang/templates/go-sql-driver-mysql/copyfromCopy.tmpl

@@ -7,13 +7,20 @@ func convertRowsFor{{.MethodName}}(w *io.PipeWriter, {{.Arg.SlicePair}}) {
 	e := mysqltsv.NewEncoder(w, {{ len .Arg.CopyFromMySQLFields }}, nil)
 	for _, row := range {{.Arg.Name}} {
 {{- with $arg := .Arg }}
+{{- $enums := $.Enums }}
 {{- range $arg.CopyFromMySQLFields}}
-{{- if eq .Type "string"}}
-	e.AppendString({{if $arg.Struct}}row.{{.Name}}{{else}}row{{end}})
-{{- else if or (eq .Type "[]byte") (eq .Type "json.RawMessage")}}
-	e.AppendBytes({{if $arg.Struct}}row.{{.Name}}{{else}}row{{end}})
+{{- $expr := "row" }}{{ if $arg.Struct }}{{ $expr = print "row." .Name }}{{ end }}
+{{- $fieldType := .Type }}
+{{- $isStringEnum := false }}
+{{- range $enums }}{{ if or (eq $fieldType .Name) (hasSuffix $fieldType (print "." .Name)) }}{{ $isStringEnum = true }}{{ end }}{{ end }}
+{{- if eq $fieldType "string"}}
+	e.AppendString({{$expr}})
+{{- else if or (eq $fieldType "[]byte") (eq $fieldType "json.RawMessage")}}
+	e.AppendBytes({{$expr}})
+{{- else if $isStringEnum }}
+	e.AppendString(string({{$expr}}))
 {{- else}}
-	e.AppendValue({{if $arg.Struct}}row.{{.Name}}{{else}}row{{end}})
+	e.AppendValue({{$expr}})
 {{- end}}
 {{- end}}
 {{- end}}

internal/endtoend/testdata/copyfrom_mysql_enum/mysql/go/copyfrom.go

@@ -0,0 +1,3 @@
+-- name: UpsertExperienceLocations :copyfrom
+REPLACE INTO experience_locations (location_id, type)
+VALUES (?, ?);

internal/endtoend/testdata/copyfrom_mysql_enum/mysql/go/db.go

@@ -0,0 +1,4 @@
+CREATE TABLE experience_locations (
+    location_id varchar(512) NOT NULL,
+    type ENUM('start_point', 'pickup_point', 'redemption_point', 'end_point') NOT NULL
+);

internal/endtoend/testdata/copyfrom_mysql_enum/mysql/go/models.go

@@ -0,0 +1,14 @@
+{
+  "version": "1",
+  "packages": [
+    {
+      "path": "go",
+      "sql_package": "database/sql",
+      "sql_driver": "github.com/go-sql-driver/mysql",
+      "engine": "mysql",
+      "name": "querytest",
+      "schema": "schema.sql",
+      "queries": "query.sql"
+    }
+  ]
+}