Added a failsafe validation for schemas about to be written to disk.

go/libraries/doltcore/schema/encoding/schema_marshaling.go

@@ -224,6 +224,13 @@ func (sd schemaData) decodeSchema() (schema.Schema, error) {
 
 // MarshalSchemaAsNomsValue takes a Schema and converts it to a types.Value
 func MarshalSchemaAsNomsValue(ctx context.Context, vrw types.ValueReadWriter, sch schema.Schema) (types.Value, error) {
+	// Anyone calling this is going to serialize this to disk, so it's our last line of defense against defective schemas.
+	// Business logic should catch errors before this point, but this is a failsafe.
+	err := schema.ValidateForInsert(sch.GetAllCols())
+	if err != nil {
+		return nil, err
+	}
+
 	sd, err := toSchemaData(sch)
 
 	if err != nil {