Microsoft/TypeScript

Intellisense stops working inside nested `Array.map`

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#51,823 opened on Dec 8, 2022

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 (0 comments) (2 reactions) (0 assignees)TypeScript (48,455 stars) (6,726 forks)batch import
Domain: LS: Completion ListsExperience EnhancementHelp WantedSuggestion

Description

Bug Report

🔎 Search Terms

Intellisense stops working inside Array.map

🕗 Version & Regression Information

  • Version 4.9.3

⏯ Playground Link

Playground link with relevant code

💻 Code

type Children = {
    name: string;
};

type Parent = {
    children: Children[];
};

let parents: Parent[] = [].map(() => ({ children: [].map(() => ({ /* Missing `name` property in intellisense */ })) }))

🙁 Actual behavior

Missing name property in intellisense image

🙂 Expected behavior

Have name property in intellisense

Note

I know I can put map<Children> to show intellisense, but using complex types like prisma, and with a lot of nested array, it wouldn't be very convenient to keep putting map<Type> (even worse if the type is in another file needs to be imported)

Contributor guide

Tech stack
typescriptjavascript
Domain
developer experiencetooling
Issue type
bug
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
5
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
over 1 week
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
fresh
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
mostly clear
Prerequisites
understanding of TypeScript type inferenceknowledge of Array.map and generics
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
20
Research direction
The bug is in TypeScript's type inference for nested Array.map calls. Likely involves the checker.ts file in src/compiler/ where type inference for callbacks is handled. Look for how contextual types are propagated through nested arrow functions. No linked PRs or comments exist, so investigation should start by reproducing the issue with the provided playground link and tracing the type inference logic.