Numeric string key is being converted to a number in declaration file

[tinytim84]

Bug Report

When TS converts a specific type into a static type in a d.ts file, it's converting numeric string keys into a number, e.g. '1' becomes 1. It seems similar to the issue described here, but my value is being re-mapped with generics and mapped types, so it seems like it's a more complicated version of this. The .d.ts tab in the playground link shows what is happening.

🔎 Search Terms

numeric string key converted to number

🕗 Version & Regression Information

TS 4.7.4

⏯ Playground Link

Playground link with relevant code

💻 Code

It's an issue with compilation, the playground link above shows it.

🙁 Actual behavior

Conversion of a specific type with mapped keys to a static type is resulting in string numeric keys being converted to numbers. e.g. '0', '1', getting converted to 1,2.

🙂 Expected behavior

Keys to remain as strings and not be converted to a number.

[fredericoo]

I’m facing this in 4.9.4. Am I missing something?