Text between Unicode escapes within an identifier is skipped #61043

🔎 Search Terms

• Unicode escape sequences
• extended Unicode escapes
• variables, constants, property names, JSX identifiers, JSX attribute names…
• regular expression group names, RegExp identifiers
• bundling & transpilation

🕗 Version & Regression Information

• This is the behavior since Support extended unicode escapes in identifiers, per es6 spec #32725 lands

⏯ Playground Link

https://www.typescriptlang.org/play/?#code/MYewdgzgLgBAhgHQK4G8BsAmAvsZ6AsWApjALwz4YDcAUHAEbAAmRVMA9OzAKIBOvIXgC4YAYThgwIWADMAlmCYwwcALYkA5A2ZENAOhgAROUoCeIJDHUSYWvJhz3CugPx16LNpxgA5EDCJ+QRpQSFg8AHY0LDheewBOGPoAGxJySloAN1i5BlSvLj4BYTEJKVkFJRV1W2zeXJTdA2MzCysiGw1I6NiEpNSNN0yG-I4uPwCg3hogA

💻 Code

const a\u{62}c\u{64}e = 42;
abcde; // Error: Cannot find name 'abcde'. Did you mean 'a\u{62}c\u{64}e'?
abde; // No error
const \u{76}ar\u{69}able = 42;
variable; // Error: Cannot find name 'variable'. Did you mean '\u{76}ar\u{69}able'?
viable; // No error

🙁 Actual behavior

abde and viable are recognised but not abcde and variable.

🙂 Expected behavior

abcde and variable are recognised but not abde and viable.

Additional information about the issue

Precisely, text between a 4-digit or extended Unicode escape and an extended Unicode escape is ignored.
(This is not the case for text between a 4-digit or extended Unicode escape and a 4-digit Unicode escape.)
This happens with all kinds of identifiers, not just variable names, due to the missing line result += text.substring(start, pos);. This issue is opened just for trackability and is fixed in #61042.