fix(codegen): emit single-value Literals for discriminator fields#10
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Pydantic 2.12+ requires a discriminated-union member's discriminator field
to be typed as `Literal[...]`. datamodel-codegen was emitting it as a
single-value `StrEnum` (e.g. `kind: Kind` where `Kind(StrEnum)` had one
entry), which causes Pydantic to refuse to build the union with:
PydanticUserError: Model 'X' needs field 'kind' to be of type `Literal`
This affects any sealed hierarchy on the API side that currently has only
one variant (and trips immediately when an oneOf is exposed before the
second variant lands, e.g. `AuditMetadata` introduced in mono PR #283).
Fix:
- scripts/typegen.sh: pass `--enum-field-as-literal one` and
`--use-one-literal-as-default` to datamodel-codegen.
- Single-value enums now render as `kind: Literal["..."] = "..."`,
which both satisfies the discriminator requirement and lets callers
omit the obvious value.
- Regenerate src/devhelm/_generated.py (net -310/+78 lines: most of
the noisy single-value StrEnum classes collapse into inline Literals).
- Update one negative test (`TestConfirmationPolicyNegative.test_missing_type`)
to reflect the new defaulting behaviour and document the rollback
when a second variant is added.
No public-API changes for callers that already passed the discriminator
explicitly. Branch name matches the mono PR so the spec-evolution harness
on devhelmhq/mono#283 picks it up automatically.
Made-with: Cursor
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Summary
datamodel-codegenwas emitting single-value enums asStrEnumclasses (kind: KindwhereKind(StrEnum)had one entry). Pydantic 2.12+ rejects this when the parent is a discriminated union:PydanticUserError: Model 'X' needs field 'kind' to be of type Literal.--enum-field-as-literal oneand--use-one-literal-as-defaulttoscripts/typegen.shso single-value enums collapse tokind: Literal["..."] = "...". This both satisfies the discriminator requirement and removes redundant ceremony for callers._generated.py(-310/+78 lines: noisy single-value enum classes collapse into inline literals).Context
This is the SDK-side fix paired with devhelmhq/mono#283, which introduces a sealed
AuditMetadatahierarchy on the API side that currently has only one variant (MemberRoleChangedMetadata). Without this fix, the spec-evolution harness on the mono PR fails immediately onimport devhelm._generated.The mono PR's harness clones surface repos by branch-name match (
PR_BRANCH→chore/end-1098-chunk1-typed-internals), so this branch will be paired automatically.Why default the discriminator?
For a single-variant union there is exactly one valid discriminator value. Forcing callers to repeat it (
kind="member_role_changed") is busywork — they already chose the model class. When a second variant is added to the spec, the codegen will drop the default automatically and we'll flip the negative test back. The test comment documents this.Test plan
uv run pytest -q→ 707 passed (was: 706 passed + 1 failed before regen)uv run mypy src/→ no issuesuv run ruff check .→ cleanPydanticUserErrorduring regen)Made with Cursor