On Wed, Dec 09, 2020 at 10:25:37PM +0000, Andrew Chow via bitcoin-dev wrote:
> Hi All,
> 
> I would like to propose a new PSBT version that addresses a few 
> deficiencies in the current PSBT v0. As this will be backwards 
> incompatible, a new PSBT version will be used, v1.
> 
> The primary change is to truly have all input and output data for each 
> in their respective maps. Instead of having to parse an unsigned 
> transaction and lookup some data from there, and other data from the 
> correct map, all of the data for an input will be contained in its map. 
> Doing so also disallows PSBT_GLOBAL_UNSIGNED_TX in this new version. 
> Thus I propose that the following fields be added:
> 
> Global:
> * PSBT_GLOBAL_TX_VERSION = 0x02
>  ?? * Key: empty
>  ?? * Value: 32-bit little endian unsigned integer for the transaction 
> version number. Must be provided in PSBT v1 and omitted in v0.

All of these changes sound great. It would definitely make working with
PSBTs easier if all data was accessible in the same format, rather than
being split between the global unsigned tx and the main body.

One minor quibble is the version numbering -- you mention "v1" in this
post but set GLOBAL_TX_VERSION to 2. I think we should consistently use
2 everywhere; probably nobody thinks of the existing PSBT as "version 0".

-- 
Andrew Poelstra
Director of Research, Blockstream
Email: apoelstra at wpsoftware.net
Web:   https://www.wpsoftware.net/andrew

The sun is always shining in space
    -Justin Lewis-Webster