Microsoft/TypeScript

Missing IntelliSense suggestions in a partial mapped generic argument

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#47,518 opened on Jan 19, 2022

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 (1 comment) (1 reaction) (0 assignees)TypeScript (6,726 forks)batch import
Domain: LS: Completion ListsExperience EnhancementHelp WantedSuggestion

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Description

Bug Report

The issue I'm facing is missing IntelliSense suggestions inside the inline object argument of a function which accepts a generic extending the partial of a mapped type. (Wow, that sentence was a doozy, no worries code sample below)

🔎 Search Terms

IntelliSense, Generic, Partial, Optional , Mapped, Function, Parameter, Argument, Object

🕗 Version & Regression Information

I'm using 4.5.4 Seems to be working in 4.3.5 on the playground.

⏯ Playground Link

Playground link with relevant code

💻 Code

type Original = {
    prop1: true,
    prop2: string
}

type Mapped = {[Prop in keyof Original as `get${Capitalize<string & Prop>}`]: Original[Prop]};

declare function foo<T extends Partial<Mapped>>(options: T): void;

foo({
/* cursor */
});

🙁 Actual behavior

  1. No (relevant) suggestion on CTRL + SPACE
  2. Suggestion on typing correct prefix ("get") of either parameter
  3. After setting said parameter correctly neither CTRL + SPACE nor typing gives another suggestion

🙂 Expected behavior

CTRL + SPACE (hopefully) would always give suggestion for allowed/fitting/legal properties

Contributor guide

Research direction
Look at the language service's completion provider for generic function arguments. Investigate how the constraint `Partial<Mapped>` is resolved and why suggestions are not shown for the initial empty object. Check the behavior in older versions (4.3.5) and see what changed.
Tech stack
typescript
Domain
compilersdeveloper experience
Issue type
Bug
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
4
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
Half day
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
Active
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
Clear
Prerequisites
TypeScriptGit
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
40