`--enum-field-as-literal=all` + `--use-type-alias` inlines property-referenced enum schemas instead of emitting a named Literal alias

[vdusek]

Describe the bug

With --enum-field-as-literal=all + --use-type-alias on a Pydantic v2 OpenAPI spec, named enum schemas in components.schemas only become a top-level TypeAliasType("Name", Literal[...]) if they are referenced from at least one operation parameter. Enums referenced only from another schema's properties are inlined at every reference site, with the original name reduced to a Field(title="<Name>") hint.

This contradicts the resolution claimed for #1285 in PR #2505, which describes the combination as producing a named alias for any enum schema regardless of how it is referenced.

To reproduce

EnumFromParam is referenced from a query parameter; EnumFromProperty is referenced from a schema property.

Example schema:

{
  "openapi": "3.0.3",
  "info": { "title": "repro", "version": "0.0.1" },
  "paths": {
    "/things": {
      "get": {
        "parameters": [
          {
            "name": "ownership",
            "in": "query",
            "schema": { "$ref": "#/components/schemas/EnumFromParam" }
          }
        ],
        "responses": {
          "200": {
            "description": "ok",
            "content": {
              "application/json": {
                "schema": { "$ref": "#/components/schemas/Thing" }
              }
            }
          }
        }
      }
    }
  },
  "components": {
    "schemas": {
      "EnumFromParam":    { "type": "string", "enum": ["a", "b"] },
      "EnumFromProperty": { "type": "string", "enum": ["x", "y"] },
      "Thing": {
        "type": "object",
        "properties": {
          "kind": { "$ref": "#/components/schemas/EnumFromProperty" }
        }
      }
    }
  }
}

Used command line:

$ datamodel-codegen \
    --input repro.json \
    --input-file-type openapi \
    --output out.py \
    --target-python-version 3.11 \
    --output-model-type pydantic_v2.BaseModel \
    --use-annotated \
    --use-union-operator \
    --enum-field-as-literal all \
    --use-type-alias

Observed output:

EnumFromParam = TypeAliasType("EnumFromParam", Literal['a', 'b'])

class Thing(BaseModel):
    kind: Annotated[Literal['x', 'y'] | None, Field(title='EnumFromProperty')] = None

Expected behavior

Both named enum schemas should produce a top-level alias, identically — not just the parameter-referenced one:

EnumFromParam = TypeAliasType("EnumFromParam", Literal['a', 'b'])
EnumFromProperty = TypeAliasType("EnumFromProperty", Literal['x', 'y'])

class Thing(BaseModel):
    kind: EnumFromProperty | None = None

Version

• OS: Fedora Linux 43
• Python version: 3.11
• datamodel-code-generator version: 0.56.0

Additional context

Variations that don't change the behavior: --collapse-root-models on/off, --reuse-model, removing --use-schema-description, stripping title/description from the enum schema. --enum-field-as-literal=one instead of all falls back to class Name(StrEnum): ... for every named enum.

Without a stable named alias, the enum's value list is duplicated at every reference site (painful for large enums — e.g. an ErrorType with hundreds of members) and downstream code can't import the name to reuse in its own annotations. The Field(title=...) hint is documentation-only.

Two possible fixes:

1. Make --enum-field-as-literal=all + --use-type-alias emit a named alias for every enum schema in components.schemas, regardless of how it is referenced.
2. Or add a dedicated flag (e.g. --enum-as-literal-alias) that emits Name: TypeAlias = Literal[...] for named enum schemas only, independently of --use-type-alias.

Related: #1285, #2505 (original request and the PR that was supposed to cover this), #3009, #3092 (related bugs blocking adjacent workarounds).

[coderabbitai]

🔗 Related PRs

#2677 - Support enum-field-as-literal in GraphQL parser [merged]
#2824 - Fix propertyNames constraint ignored when using $ref to enum definition [merged]
#2853 - Fix reuse-model generating type aliases instead of class inheritance [merged]
#2999 - Fix extra underscore on enum members like replace with --capitalise-enum-members [merged]
#3012 - Skip default_factory wrapping for non-callable type aliases [merged]

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[koxudaxi]

Thanks for the detailed report.

I checked the current main branch and could not reproduce the issue anymore: with the provided OpenAPI schema and options, both EnumFromParam and EnumFromProperty are generated as named TypeAliasType(..., Literal[...]) aliases.

I opened PR #3124 to add a regression test covering the property-referenced enum case, so this behavior stays protected.

[vdusek]

Closing as this is no longer an issue in v0.57.0, thanks.