BIP 119: CHECKTEMPLATEVERIFY #875

I believe now is an appropriate time to apply for a BIP number/Draft Status for OP_CTV. A few elements will require updating before the BIP moves out of draft (e.g., the activation dates) but activation dates are a separate discussion from the technical considerations which are the focus of this BIP.

BTW I looked into the travis error -- it seems that the linter is reading a code block and failing because a C++ lambda looks like a improperly formatted markdown link.

I am happy to add a revert-able patch as below:

bool filter(const CTxIn& c) {
    return c.scriptSig != CScript();
}
uint256 GetStandardTemplateHash(const CTransaction& tx, const uint256& outputs_hash, const uint256& sequences_hash,
                                    const uint32_t input_index) {
        bool skip_scriptSigs = std::find_if(tx.vin.begin(), tx.vin.end(), filter) == tx.vin.end();
        return skip_scriptSigs ? GetStandardTemplateHashEmptyScript(tx, outputs_hash, sequences_hash, input_index) :
            GetStandardTemplateHashWithScript(tx, outputs_hash, sequences_hash, GetScriptSigsSHA256(tx), input_index);
    }

so that you don't have to muck around with a broken linter/supressions, but I think it's better to fix the linter longer term.

@JeremyRubin This is missing a backwards compatibility section. @kallewoof Can you look into a better fix for the linter issue?

Looking.

@luke-jr it was unclear to me that a backwards compatibility section was needed for this BIP, referencing BIP-65 and BIP-112 as examples. Neither covers the OP_NOP reinterpretation as being an incompatibility.

Regardless, I can push a section noting that there are no Backwards Incompatibilities.

• BIP 65 -- CLTV/CSV.

Added a backwards compatibility section; and rebased to pick up the linter fixes.

Use BIP 119

Thanks Luke! I've set the number & fixed links.

Hi @JeremyRubin, I was just going through the list of Draft BIPs, and trying to gauge which ones should be advanced to another Status. Would you agree that BIP119: CHECKTEMPLATEVERIFY should perhaps be advanced from Draft to Complete?

I think it's appropriate to be Complete.

The point of being Complete wrt CTV BIP is that there's historical discussions of what CTV can or cannot do, as an unchanged BIP artifact, spanning almost 7 years.

Previously, my preferred way to iterate when there was a substantive change during a feature BIP was to rename it. CheckOutputsHashVerify -> SecureTheBag -> CheckTemplateVerify are still 3 "independent" concepts from one another.

CTV I think would be unlikely to change at this point, and it serves historical discussion well to not change something like this, since it would confusingly invalidate much historical discussion.

So I'm favorable, but would want to think on it for a bit.