Lexer silently accepts non-decimal integer literals without digits

[nsvke]

Summary

While refactoring the non-decimal integer literal parsing logic in the lexer, I noticed that gccrs does not enforce the presence of valid digits after a base prefix (0x, 0b, 0o). It silently accepts the empty prefix as a valid literal and evaluates it to 0.

Reproducer

I tried this code:

fn main() {
    let _a: u32 = 0x;
    let _b: i32 = 0b;
    let _c: usize = 0o;
}

Actual behavior

gccrs compiles the above code without emitting any errors. The lexer produces a valid token with the value 0 because the internal string parsing loop naturally terminates, and the empty string is evaluated as 0 by the underlying conversion logic.

Expected behavior

error[E0768]: no valid digits found for number
 --> src/main.rs:2:19
  |
2 |     let _a: u32 = 0x;
  |                   ^^

error[E0768]: no valid digits found for number
 --> src/main.rs:3:19
  |
3 |     let _b: i32 = 0b;
  |                   ^^

error[E0768]: no valid digits found for number
 --> src/main.rs:4:21
  |
4 |     let _c: usize = 0o;
  |                     ^^

For more information about this error, try `rustc --explain E0768`.
error: could not compile `t` (bin "t") due to 3 previous errors

GCC Version

commit-hash: 0c1834c