Ability to patch/overwrite missing/wrong declarations

Search Terms

correct wrong declaration, fix declaration, overwrite module declaration, fix module type

Suggestion

Sometimes we encounter an npm module with missing declarations and incorrect declarations in its types file. Wish we have this ability patch/correct its declaration for temporary using before PR a patch and have it's released.

Current behavior & Workaround

Consider this situation, module moduleWithIssues indeed exports itemExistedWithoutDeclaration but its declaration file doesn't contain it, and has a incorrect declaration itemWithWrongDeclaration

import {
    foo, bar,
    itemExistedWithoutDeclaration,   // report 'itemExistedWithoutDeclaration' doesn't exist
    itemWithWrongDeclaration
} from 'moduleWithIssues'

// 'itemWithWrongDeclaration' is number type but declared as string, TS report type error
console.log(Math.abs(itemWithWrongDeclaration))

At present, I found a workaround is adding a local module declaration for itemExistedWithoutDeclaration and assert itemWithWrongDeclaration as its correct declaration

import { foo, bar, itemExistedWithoutDeclaration, itemWithWrongDeclaration } from 'moduleWithIssues'

declare module 'moduleWithIssues' {
  const itemExistedWithoutDeclaration: number
}

const itemCorrected: number = itemWithWrongDeclaration as any

It works in *.ts file but not in *.d.ts file. An idea patching solution should be re-declare some items of moduleWithIssues in a *.d.ts file in the project. like below:

// interfaceInProject.d.ts
declare module 'moduleWithIssues' {
  const itemExistedWithoutDeclaration: number
  const itemWithWrongDeclaration: number
}

unfortunately this patch module will shadow original module declaration of moduleWithIssues package.

import { foo, bar, itemExistedWithoutDeclaration, itemWithWrongDeclaration } from 'moduleWithIssues'

foo and bar are reported non-existent.

Checklist

My suggestion meets these guidelines:

• This wouldn't be a breaking change in existing TypeScript / JavaScript code
• This wouldn't change the runtime behavior of existing JavaScript code
• This could be implemented without emitting different JS based on the types of the expressions
• This isn't a runtime feature (e.g. new expression-level syntax)

Start with the moduleWithIssues examples in a .ts file and an interfaceInProject.d.ts file, comparing the current workaround with the shadowing behavior described. Investigate how module declarations are merged and determine whether missing and corrected exports can coexist with the package declaration. Done means the local declaration preserves foo and bar while adding or overriding the specified items.