fix: more safe work with mapped refs to use oneOf baseNames

Author: DDtKey

modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/RustClientCodegen.java

@@ -219,11 +219,13 @@ public CodegenModel fromModel(String name, Schema model) {
                 throw new RuntimeException("oneOf size does not match the model");
             }
 
-            Map<String, String> mappedNameByRef = Optional.ofNullable(model.getDiscriminator())
+            // Reverse mapped references to use as baseName for oneOF, but different keys may point to the same $ref.
+            // Thus, we group them by the value
+            Map<String, List<String>> mappedNamesByRef = Optional.ofNullable(model.getDiscriminator())
                     .map(Discriminator::getMapping)
-                    .map(mapping -> mapping.entrySet()
-                            .stream()
-                            .collect(Collectors.toMap(Map.Entry::getValue, Map.Entry::getKey))
+                    .map(mapping -> mapping.entrySet().stream()
+                            .collect(Collectors.groupingBy(Map.Entry::getValue,
+                                    Collectors.mapping(Map.Entry::getKey, Collectors.toList())))
                     )
                     .orElse(Collections.emptyMap());
 
@@ -234,8 +236,8 @@ public CodegenModel fromModel(String name, Schema model) {
                 if (aliasName != null) {
                     oneOf.setName(toModelName(aliasName));
                 }
-                if (oneOf.getRef() != null) {
-                    oneOf.setBaseName(mappedNameByRef.get(oneOf.getRef()));
+                if (oneOf.getRef() != null && !mappedNamesByRef.isEmpty()) {
+                    oneOf.setBaseName(mappedNamesByRef.get(oneOf.getRef()).removeFirst());
                 }
 
             }