Generic class in a reference cycle measured invariant in 7.1: `Link<Sub>` no longer assignable to `Link<EntityBase>` (@sap-cloud-sdk/odata-common)
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評估
- 難度
- 4/5
- 預估耗時
- 3-5 天
- 新手友好度
- 46/100
- Issue 類型
- 缺陷
- 描述清晰度
- 描述清楚
- 活躍度
- 活躍
- 技術堆疊
- go, typescript
研究方向
Start by comparing TypeScript 7.0.2 and 7.1 behavior with the supplied minimal reproduction and strict tsconfig; the issue identifies variance computation and a possible connection to microsoft/typescript-go#4820. Trace the reported Link → EntityApi → RequestBuilder → Selectable reference cycle and inspect the variance elaboration path. Done means the reproduction compiles as it did on 7.0.2 while preserving the reported assignability behavior.
由索引模型根據 Issue 內容生成。
描述
🔎 Search Terms
variance circularity, circular variance class, variance computed invariant, subclass type argument not assignable, @sap-cloud-sdk Link not assignable, 7.1 variance regression
🕗 Version & Regression Information
- This changed between versions 7.0.2 (gitHead 2bd066d8) and 7.1.0-beta (gitHead 3e923636)
- passes on 7.0.2, fails on 7.1.0-beta, 7.1.0-dev.20261022.1, 7.1.0-dev.20261027.1 and 7.1.0-dev.20261028.1
- same result with
--singleThreaded
⏯ Playground Link
n/a - needs the @sap-cloud-sdk/odata-common package
💻 Code
// repro.ts - @sap-cloud-sdk/[email protected], node 24.18
import type { DefaultDeSerializers, EntityApi, EntityBase, Link } from '@sap-cloud-sdk/odata-common';
type D = DefaultDeSerializers;
declare class Sub extends EntityBase { readonly _oDataVersion: 'v2'; id: string }
declare const l: Link<Sub, D, EntityApi<EntityBase, D>>;
export const l2: Link<EntityBase, D, EntityApi<EntityBase, D>> = l;
// tsconfig.json
{
"compilerOptions": { "strict": true, "noEmit": true, "module": "nodenext", "target": "es2022", "skipLibCheck": true },
"files": ["repro.ts"]
}
npm i @sap-cloud-sdk/[email protected] && tsc -p .
🙁 Actual behavior
repro.ts(6,14): error TS2322: Type 'Link<Sub, DefaultDeSerializers, EntityApi<EntityBase, DefaultDeSerializers>>' is not assignable to type 'Link<EntityBase, DefaultDeSerializers, EntityApi<EntityBase, DefaultDeSerializers>>'.
Property 'id' is missing in type 'EntityBase' but required in type 'Sub'.
🙂 Expected behavior
no error, like 7.0.2. Link only uses EntityT in covariant positions (readonly _entity: EntityT, readonly _entityApi: EntityApi<EntityT, DeSerializersT>), and EntityApi<Sub, D> is assignable to EntityApi<EntityBase, D> on 7.1 too
Additional information about the issue
copying Link and Selectable from the package into local files makes the same assignment pass on 7.1, so it seems to need the package's own reference cycle Link -> EntityApi<E> -> RequestBuilder<E> -> select(Selectable<E>) -> Link: the elaboration goes straight from Link to EntityBase vs Sub, as if Link's variance for EntityT was measured invariant without falling back to a structural check
possibly related: microsoft/typescript-go#4820 "Order variance computation by associated type symbol" (merged 2026-08-05) is in 7.1 (its port d20f192a in this repo is an ancestor of all four 7.1 gitHeads above) and not in 7.0.2 (2bd066d8 branches from typescript-go main at 52168999, 2026-07-08)
in a real service this breaks every SAP Cloud SDK call that passes a generated entity's request builder or link where the SDK takes the EntityBase form (new ODataBatchRequestBuilder(...), new BatchChangeSet(...), .select(SomeApi.schema.TO_X.select(...)), .filter(SomeApi.schema.TO_X.filter(...))): 41 errors in 26 files, all of them TS2345/TS2769 that 7.0.2 accepts
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