Unexpected "cannot find value in this scope" error when compiling `core/src/fmt/mod.rs`

Summary

Compiling libgrust/rustc-lib/core/src/fmt/mod.rs produces cannot find value ‘ZEROES’ in this scope [E0425] errors, which is unexpected as ZEROES was declared properly. The problematic code in question:

...
    for part in formatted.parts {
        match *part {
            flt2dec::Part::Zero(mut nzeroes) => {
                const ZEROES: &str = // 64 zeroes
                    "0000000000000000000000000000000000000000000000000000000000000000";
                while nzeroes > ZEROES.len() {
                    self.buf.write_str(ZEROES)?;
                    nzeroes -= ZEROES.len();
                }
                if nzeroes > 0 {
                    self.buf.write_str(&ZEROES[..nzeroes])?;
                }
            }
            flt2dec::Part::Num(mut v) => {
                let mut s = [0; 5];
                let len = part.len();
                for c in s[..len].iter_mut().rev() {
                    *c = b'0' + (v % 10) as u8;
                    v /= 10;
                }
                write_bytes(self.buf, &s[..len])?;
            }
            flt2dec::Part::Copy(buf) => {
                write_bytes(self.buf, buf)?;
            }
        }
    }
...

Reduced (note that there's no #![feature(no_core)] and #![no_core]):

fn main() -> i32 {
    let mut a = 0;
    for a in 0..10 {
        const zero: i32 = 0;
        a += zero;
    }
}

Reproducer

Compile PATH_TO_GCCRS/libgrust/rustc-lib/core/src/fmt/mod.rs with crab1.

Does the code make use of any (1.49) nightly feature ?

• Nightly

Godbolt link

No response

Actual behavior

cannot find value ‘ZEROES’ in this scope [E0425]

Expected behavior

No errors.

GCC Version

5c63b4c0d93d20efd014ccfd4250d82e27c3a23b

Start with the reduced Rust reproducer and the reported core/src/fmt/mod.rs case, then run them with crab1 to confirm the E0425 diagnostic. Trace how the compiler handles the const declaration inside the for loop and compare the result with the expected successful compilation. Done means both reproductions compile without the cannot-find-value error.