Microsoft/TypeScript

Better display representation for intersection types

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#7,705 opened on Mar 27, 2016

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 (7 comments) (3 reactions) (0 assignees)TypeScript (48,455 stars) (6,726 forks)batch import
Effort: DifficultHelp WantedSuggestion

Description

I'm not sure if this has been discussed before, but join types are mostly unreadable. I think the type should be prettified somehow before being displayed to the user.

TypeScript Version:

1.8

Code

type T1 = {};
type T2 = {test: number};
type J = T1 & T2;

Expected behavior:

var x: J;
typeof x; // {test: number}

Actual behavior:

var x: J;
typeof x; // {} & {test: number}

Contributor guide

Tech stack
typescript
Domain
developer experience
Issue type
feature
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.
1-2 days
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
stale
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
mostly clear
Prerequisites
Understand intersection typesFamiliarity with TypeScript source codeKnowledge of type printerSetup dev environment
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
40
Research direction
Read the issue discussion to understand the desired behavior. Explore the TypeScript compiler source code, particularly files related to type printing (e.g., src/compiler/checker.ts). Identify where intersection types are currently formatted and consider adding simplification logic to flatten and merge intersection members. Also review existing test suites for type formatting to ensure no regressions.