Unexported types causing TypeScript errors 4023 and 7056

What version of Ajv are you using? Does the issue happen if you use the latest version?

8.6.2

TypeScript version

4.3.5

TypeScript config

tsconfig.build.json is a tsconfig intended for building an NPM package. We use this successfully across many projects and with AJV 7.x. It extends a base tsconfig that successfully compiles, presumably because its rootDir is . (project root including node_modules). There’s no scope for changing this config in our org as a workaround for this particular issue.

{
  "extends": "./tsconfig.json",
  "compilerOptions": {
    "rootDir": "src",
    "outDir": "./lib"
  }
}

The tsconfig.json that this extends (compiles successfully):

{
  "include": [
    "src/**/*"
  ],
  "exclude": [
    "lib/**/*"
  ],
  "compilerOptions": {
    "target": "ES2019",
    "module": "commonjs",
    "rootDir": ".",
    "strict": true,
    "typeRoots": [
      "./node_modules/@types",
      "./src"
    ],
    "declaration": true,
    "types": [
      "node"
    ],
    "allowSyntheticDefaultImports": true,
    "esModuleInterop": true,
    "forceConsistentCasingInFileNames": true,
    "importHelpers": true,
    "lib": ["ES2019"],
    "noImplicitAny": true,
    "strictNullChecks": true,
    "alwaysStrict": true,
    "noUnusedLocals": true,
    "noUnusedParameters": true,
    "noImplicitReturns": true,
    "resolveJsonModule": true,
    "stripInternal": true
  }
}

Your code

This is comparable to a function that we’ve successfully used in AJV 7.x:

import type { JSONSchemaType } from 'ajv'

export const willICompile = <T>(schema: JSONSchemaType<T>): boolean =>
  schema ? false : false

TypeScript error output

src/validation/test.ts:3:14 - error TS4023: Exported variable 'willICompile' has or is using name 'NumberKeywords' from external module "...projectRoot/node_modules/ajv/dist/types/json-schema" but cannot be named.

3 export const willICompile = <T>(schema: JSONSchemaType<T>): boolean =>
               ~~~~~~~~~~~~

src/validation/test.ts:3:14 - error TS4023: Exported variable 'willICompile' has or is using name 'StringKeywords' from external module "...projectRoot/node_modules/ajv/dist/types/json-schema" but cannot be named.

3 export const willICompile = <T>(schema: JSONSchemaType<T>): boolean =>
               ~~~~~~~~~~~~

src/validation/test.ts:3:14 - error TS7056: The inferred type of this node exceeds the maximum length the compiler will serialize. An explicit type annotation is needed.

3 export const willICompile = <T>(schema: JSONSchemaType<T>): boolean =>
               ~~~~~~~~~~~~

What results did you expect?

I would expect this code to compile.

Various internally used types aren’t exported from the root of the ajv package. My working theory is that when an exported type uses one of these unexported types and the root dir does not include node_modules, we get a 4023 and/or a 7056 error.

We did not experience these errors with equivalent code and the same tsconfig in AJV 7.x.

Incidentally we also had the ability to declare something as a partial schema but this is also no longer possible due to unexported types.

Are you going to resolve the issue?

Could be a rabbit hole with no guarantee any PR would be accepted. Though not ideal I may have to roll my own versions of some types in types/json-schema.ts.

[erikbrinkman]

I get different results from you. neither tsconfig.json nor tsconfig.build.json compile (same errors for each), with the same ajv and typescript versions, which leads me to dismiss the roodDir hypothesis.

I was able to address it by doing what typescript asked:

interface WillICompile {
  <T>(schema: JSONSchemaType<T>): boolean;
}

export const willICompile: WillICompile = (schema) =>schema ? false : false

compiled just fine for me.

JSONSchemaType is right at the border of what typescript is willing to accept in terms of complexity, and I think the step up from 7 to 8 pushed it more towards that direction. My current hypothesis is that JSONSchemaType is just too complex. Potentially typescript was trying to simply the export by referencing NumberKeywords and StringKeywords which it can’t do because they’re internal, and that led to all of the errors. That hypothesis leads to investigating the third error: TS7056, but I’ve only found a handful of cases, and they all seem to reference “complicated” inferred types.

Given that I’m inclined to think it’s good practice manually annotate exported objects anyway, the above fix seems like good practice. From ajv side the fix would be to make JSONSchemaType simpler. I’m generally in favor of a breaking rewrite of that type, but JSONSchema is quite complicated, so even that is not super trivial.

[mgdigital]

We do need to be careful using stripInternal - I might look into api-extractor. But I don’t think that’s related to this issue.