[BUG] Type instantiation is excessively deep and possibly infinite on latest TypeScript 4.5

There is a new issue that appeared in TypeScript 4.5.0-dev.20211001 and exists until now.

To reproduce the error:

npm init -y
npm add zod
npm add -D typescript@next
echo 'import { z } from "zod";' > main.ts
echo '{"compilerOptions":{"lib":["es2020"]},"include":["main.ts"]}' > tsconfig.json
npx tsc -p .

TypeScript output:

node_modules/zod/lib/helpers/partialUtil.d.ts:4:29 - error TS2589: Type instantiation is excessively deep and possibly infinite.

4         [k in keyof Shape]: ZodOptional<DeepPartial<Shape[k]>>;
                              ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~


Found 1 error.

It affects the latest Zod (3.10.1), and also any other 3.x version. The issue appeared in https://github.com/microsoft/TypeScript/pull/41821 (producing a memory error), and later a check was added in https://github.com/microsoft/TypeScript/pull/46326 to prevent the infinite loop and give a meaningful message.

This is the same issue as #689 except that now we have an error message.

Demo code: https://github.com/mmvsk/zod-issue-715

[colinhacks]

Great minimal repro of the problem. I’m pretty sure we’re the only people who will every be affected by it 😛

[maxmvsk]

My thoughts exactly 😃))

I posted this as a TS issue: https://github.com/microsoft/TypeScript/issues/46500

And indeed, it’s confirmed:

Yeah, that isn’t right. The issue here is that we bypass caching of relations for small unions and intersections, but that bypass also causes us to loose a check for deeply nested types that would have stopped the recursion. It used to not matter, but after #41821 it does. We need to revise our logic such that we can bypass caching but still check for deep nesting.