🐛Deepmerge-ts now making typescript build hang / not responding

[fatihaziz]

Bug Report

It's started since last week, when I try to compile my typescript,
tsc
something wrong happen, it never done. something is stuck.

I tried to reinstall all node_modules, clean NPM cache, lastly I uninstall my node and change to version 16.14.2
none of them works...

then today, I try to install all my dependencies one by one and see if the tsc running / atleast throwing error.
when it comes to remove deepmerge-ts. it works, my tsc throwing error module not found.

having dependency to deepmerge-ts:

after removing

I tried with all version deepmerge-ts@3, @2, and @1, none of them work...

deepmerge-ts is awesome library that I need for my project, I hope it can be solved.

Expected behavior

Won't affect to tsc compiler behavior

Actual behavior

It make tsc compiler stuck

Steps to reproduce

1. npm i deepmerge-ts
2. npm run build or tsc
3. getting stuck

System Environtment

• OS: Windows 11
• NodeJS: 16.14.2, 14.17.6
• Typescript: 4.4.2, 4.4.4, 4.6.3
• npm: 6, 8.5

Files:

tsconfig.json:

{
	"compileOnSave": true,
	"compilerOptions": {
		"composite": true,
		"baseUrl": "./",
		"outDir": "./lib",
		"declaration": true,
		"declarationDir": "./@types",
		"declarationMap": true,
		"target": "ES6",
		"module": "CommonJS",
		"lib": [
			"ES6",
			"ES2018",
			"ESNext",
			"DOM"
		],
		"strict": true,
		"strictPropertyInitialization": false,
		"noImplicitAny": false,
		"noImplicitThis": false,
		"pretty": true,
		"sourceMap": true,
		"allowJs": true,
		"noEmit": false,
		"moduleResolution": "node",
		"allowSyntheticDefaultImports": true,
		"forceConsistentCasingInFileNames": true,
		"esModuleInterop": true,
		"experimentalDecorators": true,
		"emitDecoratorMetadata": true,
		"useUnknownInCatchVariables": false,
		"removeComments": true,
		"typeRoots": [
			"src/@types",
			"node_modules/@types"
		]
	},
	"include": [
		"src/**/*.ts"
	],
	"exclude": [
		"dist",
		"lib",
		"node_modules",
		"tests",
		"*deprecated*",
		"*ignore*"
	]
}

[fatihaziz]

I forked the repo, https://github.com/fatihaziz/deepmerge-ts-es6/compare/main...fix/ts-issue-es6
and now somehow its working fine, no more hang or not responding.

but, I still don't know the reason behind it, why the tsc compiler become not responding...

Could I upload this into npm?

[RebeccaStevens]

Give me a bit and I'll see if I can resolve this.
Would you be able to provide a minimal repo that reproduces the issue?

[fatihaziz]

this is the minimal repo: here

[RebeccaStevens]

Just started looking into this now.
I haven't found the exact cause of the problem yet but the issue goes away it you use "skipLibCheck": true in your project's tsconfig.json

[fatihaziz]

If we set the skipLibCheck: true typescript compiler will ignore descrepancy from the dependencies types.

Typescript server won't bother checking the types error from modules anymore. Which we won't like to do.

I think the problem is from the v04 types generated by rollup. But i never use rollup before, so i dont know what the purpose of it.

[RebeccaStevens]

What I've found so far it that it seems to be this type declaration that is causing the hang.

deepmerge-ts/dist/node/types/current/index.d.ts

Line 389 in 4b6b64d

declare function defaultMergeArrays<Ts extends ReadonlyArray<ReadonlyArray<unknown>>, MF extends DeepMergeMergeFunctionsURIs, M>(values: Ts): Ts extends readonly [infer Head, ...infer Rest] ? Head extends readonly unknown[] ? Rest extends readonly [readonly unknown[], ...(readonly unknown[])[]] ? Rest extends readonly [infer Head, ...infer Rest] ? Head extends readonly unknown[] ? Rest extends readonly [readonly unknown[], ...(readonly unknown[])[]] ? Rest extends readonly [infer Head, ...infer Rest] ? Head extends readonly unknown[] ? Rest extends readonly [readonly unknown[], ...(readonly unknown[])[]] ? Rest extends readonly [infer Head, ...infer Rest] ? Head extends readonly unknown[] ? Rest extends readonly [readonly unknown[], ...(readonly unknown[])[]] ? Rest extends readonly [infer Head, ...infer Rest] ? Head extends readonly unknown[] ? Rest extends readonly [readonly unknown[], ...(readonly unknown[])[]] ? Rest extends readonly [infer Head, ...infer Rest] ? Head extends readonly unknown[] ? Rest extends readonly [readonly unknown[], ...(readonly unknown[])[]] ? Rest extends readonly [infer Head, ...infer Rest] ? Head extends readonly unknown[] ? Rest extends readonly [readonly unknown[], ...(readonly unknown[])[]] ? Rest extends readonly [infer Head, ...infer Rest] ? Head extends readonly unknown[] ? Rest extends readonly [readonly unknown[], ...(readonly unknown[])[]] ? Rest extends readonly [infer Head, ...infer Rest] ? Head extends readonly unknown[] ? Rest extends readonly [readonly unknown[], ...(readonly unknown[])[]] ? Rest extends readonly [infer Head, ...infer Rest] ? Head extends readonly unknown[] ? Rest extends readonly [readonly unknown[], ...(readonly unknown[])[]] ? Rest extends readonly [infer Head, ...infer Rest] ? Head extends readonly unknown[] ? Rest extends readonly [readonly unknown[], ...(readonly unknown[])[]] ? any : [...Head, ...Head, ...Head, ...Head, ...Head, ...Head, ...Head, ...Head, ...Head, ...Head, ...Head] : never : never : [...Head, ...Head, ...Head, ...Head, ...Head, ...Head, ...Head, ...Head, ...Head, ...Head] : never : never : [...Head, ...Head, ...Head, ...Head, ...Head, ...Head, ...Head, ...Head, ...Head] : never : never : [...Head, ...Head, ...Head, ...Head, ...Head, ...Head, ...Head, ...Head] : never : never : [...Head, ...Head, ...Head, ...Head, ...Head, ...Head, ...Head] : never : never : [...Head, ...Head, ...Head, ...Head, ...Head, ...Head] : never : never : [...Head, ...Head, ...Head, ...Head, ...Head] : never : never : [...Head, ...Head, ...Head, ...Head] : never : never : [...Head, ...Head, ...Head] : never : never : [...Head, ...Head] : never : never : [...Head] : never : never;

I don't know why yet.

[fatihaziz]

Maybe its goes like this:

1. deepmerge-ts types which generated is occuring a loophole for typescript compiler.
2. No error when compiling on the deepmerge-ts side.
3. then, when it published. someone install it, and try to compile it, the typescript will fall into the loophole.
   And the compiler stuck.

Its weird and mindblowing for me since how types can make the compiler fall into indefinitely loophole.

This is indicated by my laptop performance when i try to compile it, the fan speed rise up higher than usually.
Which it rarely happen on normal build, that indicates there is some resource intensive task when compiling.
I try to make indefinitely while loop and run on browser and have same indication.

[RebeccaStevens]

I'm trying to debug tsc atm to see what is going on. It's possible this is an upstream problem with TypeScript itself.

[fatihaziz]

Alright, i will wait for the updates then.

[RebeccaStevens]

So I'm not sure exactly what is going on but I think it is to do with the type complexity.
The type shouldn't actually be that complex, it should be aliased.

[github-actions]

🎉 This issue has been resolved in version 4.0.3 🎉

The release is available on:

• npm package (@latest dist-tag)
• GitHub release

Your semantic-release bot 📦🚀