p2sh – Unable to push script bytes into a Script builder

The issue is with the push_slice API in recent versions of rust-bitcoin (≥ 0.30).

ScriptBuf::builder().push_slice (and Builder::push_slice) now requires T: AsRef for safety—it enforces Bitcoin’s push-data limits at compile time where possible and prevents oversized pushes. &[u8] (what redeem_script.as_bytes() returns) no longer satisfies that bound directly.

Fix

Convert the redeem script bytes to PushBytesBuf (the owned version) using TryFrom:

use bitcoin::script::{Builder, PushBytesBuf, ScriptBuf}; // or the full path: bitcoin::blockdata::script::*

// ... your redeem_script construction (this part is already correct) ...
let redeem_script = Script::builder()
    .push_opcode(OP_PUSHNUM_1)
    .push_key(&pubkey1)
    .push_opcode(OP_PUSHNUM_1)
    .push_opcode(OP_CHECKMULTISIG)
    .into_script();

// Build the scriptSig for the P2SH spend (1-of-1 multisig redeem script)
let mut script_sig = Builder::new()
    .push_opcode(OP_0)                          // dummy 0 for CHECKMULTISIG
    .push_slice(&signature1.serialize())        // signature (already a valid push)
    .push_slice(
        PushBytesBuf::try_from(redeem_script.as_bytes())
            .expect("redeem script too large to push")  // will never fail for normal multisig
    )
    .into_script();

tx.input[0].script_sig = script_sig;  // or however you're attaching it

Why this works

PushBytesBuf::try_from(&[u8]) (or &PushBytes::try_from(&[u8]) if you prefer a reference) validates the length and gives you a type that implements AsRef.
For a 1-of-1 P2MS redeem script the size is tiny (~36 bytes), so the expect/unwrap is safe. In production you can handle the PushBytesError if you want to be extra defensive.
The resulting script_sig will be a valid P2SH unlocking script: <0> (all pushes).

Alternative one-liners (if you prefer)

.push_slice(PushBytesBuf::from(redeem_script.as_bytes()))  // panics on >4 GiB (impossible)

.push_slice(redeem_script.as_bytes().try_into().unwrap())

(using the TryInto impl that PushBytesBuf provides).

This is the idiomatic way in current rust-bitcoin. Your redeem script builder and overall P2SH flow look correct—only the final push needed the type adjustment.