name: tokens-no-whitespace internalName: TokensNoWhitespace timeline:

• date: 2026-01-30 release: 2.95.0 cls: [4782] message: Introduced as parser error.

The grammar has several bugs around token boundaries, where two adjacent literals are not always required to have whitespace between them: 0a, 0.00.0 or foo"1"2. This results in the following unexpected behaviors in the language:

• In lists, adjacent tokens will be parsed as several distinct elements, but outside of lists they will be parsed as a function application.
• Because leading zeroes in floating point literals are not allowed, 00012.3 unexpectedly parses as 12 0.3.
• Nix does not have hexadecimal number literal notation, but a user naively typing 0x10 will not receive a parser error (because it validly parses as 0 x10 instead).

Because the parser cannot be fixed without introducing breaking changes to the language, all token sequences with known confusing semantics are deprecated with a parse error. To fix this, insert whitespace between tokens to properly separate them.