Tolk: `stringHexToSlice(\"\")` is rejected as “not a constant string” (empty string mishandled)

[Gusarich]

Compile-time string builtins require a constant string literal. However, an empty string literal ("") is rejected as “not a constant string”, while a whitespace-only string (" ") is accepted and evaluated as an empty hex bitstring. This indicates the compiler is conflating “missing/non-constant string” with “empty string literal”.

Reproduction

Control: whitespace-only string compiles and produces an empty slice.

Create /tmp/tolk_stringHexToSlice_spaces_ok.tolk:

tolk 1.0

import "@stdlib/common.tolk";

fun onInternalMessage() { return 0; }

@method_id(100)
fun bitsCount(): int {
    var s: slice = stringHexToSlice("   "); // hex parser skips spaces -> empty slice
    return s.remainingBitsCount();
}

Compile + run:

./artifacts/tolk /tmp/tolk_stringHexToSlice_spaces_ok.tolk > /tmp/tolk_stringHexToSlice_spaces_ok.fif
./artifacts/fift -I artifacts/lib /tmp/tolk_stringHexToSlice_spaces_ok_runner.fif

Create /tmp/tolk_stringHexToSlice_spaces_ok_runner.fif:

"/tmp/tolk_stringHexToSlice_spaces_ok.fif" include <s constant code
100 code 1 runvmx abort"exitcode is not 0" .s cr { drop } depth 1- times

Observed output:

0

Failing case: empty string literal is rejected.

Create /tmp/tolk_stringHexToSlice_empty_rejects.tolk:

tolk 1.0

import "@stdlib/common.tolk";

fun onInternalMessage() { return 0; }

@method_id(100)
fun bitsCount(): int {
    var s: slice = stringHexToSlice("");
    return s.remainingBitsCount();
}

Compile:

./artifacts/tolk /tmp/tolk_stringHexToSlice_empty_rejects.tolk > /tmp/out.fif

Observed:

error: function `stringHexToSlice` requires a constant string, like `stringHexToSlice("some_str")`

Expected behavior

Empty string literals should be treated as valid constant strings. In particular, stringHexToSlice("") should compile and evaluate to the empty slice (the same result as stringHexToSlice(" ")).