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fix(downgrader): give null its own anyOf branch for several types in 3.0 #78

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Merged
dinwwwh merged 1 commit into from
Oct 24, 2026
Merged

fix(downgrader): give null its own anyOf branch for several types in 3.0 #78

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2 changes: 1 addition & 1 deletion packages/downgrader/README.md
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Original file line number Diff line number Diff line change
Expand Up @@ -179,7 +179,7 @@ Accepts the default OAS dialect, which adds `discriminator`, `xml`, `externalDoc
| 3.1 | In 3.0 |
| ----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |
| [`type`][js-type] with `"null"` | `nullable: true` beside the other type. `type: "null"` alone becomes `type: "string", nullable: true, enum: [null]`, since 3.0 allows `nullable` only beside `type`, and code generators drop a bare `enum: [null]`. |
| [`type`][js-type] with several types | `anyOf` with one branch per type, which takes `items` for `"array"`. |
| [`type`][js-type] with several types | `anyOf` with one branch per type, which takes `items` for `"array"`. `"null"` gets its own branch, written as for `type: "null"` alone, since code generators ignore `nullable` inside an `anyOf` branch. |
| [`const`][js-const] | `enum` with its one value, and the `type` of that value when it has none, since code generators drop or leave untyped a bare `enum`. `const: null` becomes the same schema as `type: "null"`. |
| Numeric [`exclusiveMinimum`][js-exclusive-minimum] and [`exclusiveMaximum`][js-exclusive-maximum] | `minimum` or `maximum` with a boolean `exclusiveMinimum` or `exclusiveMaximum`, unless `minimum` or `maximum` is stricter. |
| [`examples`][js-examples] | The first entry fills `example` when that is missing. |
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27 changes: 13 additions & 14 deletions packages/downgrader/src/v3.1-to-v3.0.ts
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Expand Up @@ -440,14 +440,11 @@ function convertType(out: Record<string, unknown>, type: unknown): void {
out.nullable = true
}
} else if (rest.length > 1) {
addAnyOf(
out,
rest.map((item) => ({
type: item,
...(item === 'array' && { items: out.items ?? {} }),
...(nullable && { nullable: true }),
})),
)
// Code generators ignore `nullable` inside an `anyOf` branch, so null gets its own.
addAnyOf(out, [
...rest.map((item) => ({ type: item, ...(item === 'array' && { items: out.items ?? {} }) })),
...(nullable ? [onlyNull()] : []),
])
delete out.items
} else if (nullable) {
// 3.0 has no null type, so only null may match, and an `enum` without it matches nothing.
Expand All @@ -459,6 +456,12 @@ function convertType(out: Record<string, unknown>, type: unknown): void {
}
}

// Only null matches it. 3.0 admits null only through `nullable`, which
// needs a `type` beside it, and code generators drop a bare `enum: [null]`.
function onlyNull(): Record<string, unknown> {
return { type: 'string', nullable: true, enum: [null] }
}

function isOnlyNull(values: unknown): boolean {
return Array.isArray(values) && values.length === 1 && values[0] === null
}
Expand Down Expand Up @@ -538,14 +541,10 @@ function finishSchema(
out.nullable = true
loose = true
}
// Only null matches it. 3.0 admits null only through `nullable`, which
// needs a `type` beside it, and code generators drop a bare `enum: [null]`.
// `enum` is set again to follow them.
// Only null matches it. `enum` is set again to follow `type` and `nullable`.
if (out.type === undefined && isOnlyNull(out.enum)) {
delete out.enum
out.type = 'string'
out.nullable = true
out.enum = [null]
Object.assign(out, onlyNull())
}
// Code generators drop or leave untyped an `enum` with no `type`, as a
// `const` becomes, so it gets the type of its value.
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5 changes: 3 additions & 2 deletions packages/downgrader/tests/v3.1-to-v3.0.test.ts
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Expand Up @@ -431,8 +431,9 @@ describe('downgradeSchemaV31ToV30', () => {
).toEqual({
maxLength: 3,
anyOf: [
{ type: 'array', items: { type: 'number' }, nullable: true },
{ type: 'string', nullable: true },
{ type: 'array', items: { type: 'number' } },
{ type: 'string' },
{ type: 'string', nullable: true, enum: [null] },
],
})
})
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