microsoft / microsoft/TypeScript

fourslash test breaks when setting "@lib"

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Description

TypeScript Version: master

Code

/// <reference path="fourslash.ts" />

// @lib: es2015

////function f(x: number[]) { return x.length; }

verify.noErrors();

Expected behavior:

No error.

Actual behavior:

Error: At line 1, col 0: Found an error: /tests/cases/fourslash/quickInfoBar.ts@35: Property 'length' does not exist on type '{}'.

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First steps

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  2. Comment on the issue to say you are picking it up — it saves two people doing the same work.
  3. Fork the repository and make your change on a branch.
  4. Open a pull request that references the issue number.

Research direction

Start with the fourslash test that sets // @lib: es2015 and the reported tests/cases/fourslash/quickInfoBar.ts location. Reproduce the case and trace why x is treated as {} when checking x.length. Done means the shown test passes with no error.

Written by the indexing model from the issue text.

Assessment

Tech stack
typescript
Domain
compilers, testing
Issue type
Bug
Difficulty
3/5
Estimated time
1-2 days
Activity status
Stale
Clarity
Mostly clear
Newbie friendliness
45/100

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