For following circuit:

include "../circomlib/circuits/sha256/sha256.circom";

template Sha256Wrap(nBits) {

    signal input bits[nBits];

    var bitPadding = 8 - nBits % 8;
    if (bitPadding == 8){
        bitPadding = 0;
    }

    var hashBits = nBits + bitPadding;
    component hasher = Sha256(hashBits);

    for (var i = 0; i < nBits; i++){
        hasher.in[i] <== bits[i];
    }
    assert(nBits == 5);
    for (var i = nBits; i < hashBits; i++){
        hasher.in[i] <== 0;
    }    
}

component main = Sha256Wrap(5);

The code generated by circom would not run correctly: for native backend, it halt forever before load input successfully and for WASM backend it simply prompt "Constraint doesn't match"

For some similar circuit, the natvie backend may also complain that some signal has been assigned before being used.

However, code would run well if we simply change the last 'nBits' into the value (5) it should be in this circuit:

assert(nBits == 5);
for (var i = 5; i < hashBits; i++){
hasher.in[i] <== 0;
}

such issue keeps until at least 0.5.45, the latest version when this issue has been put.

Num2Bits may fail if the input and n unmatch. It needs a 'enabled' https://github.com/Fluidex/circuits/blob/06c932546cb280e2ee53c55ad1078553ed2e85c3/src/lib/bitify.circom#L2

1. show progress: our fork of circom prints circuit compiling progress.

1. component without input signals can not has a child component without input signals

https://github.com/Fluidex/circuits/blob/06c932546cb280e2ee53c55ad1078553ed2e85c3/src/lib/hash_state.circom#L99

2. if a file has /* without */, the compiler will hang