We force use of tal_wally_start/tal_wally_end around every wally
allocation, and with "end" make the caller choose where to reparent
everything.
This is particularly powerful where we allocate a tx or a psbt: we
want that tx or psbt to be the parent of the other allocations, so
this way we can reparent the tx or psbt, then reparent everything
else onto it.
Implementing psbt_finalize (which uses a behavior flag antipattern)
was tricky, so I ended up splitting that into 'psbt_finalize' and
'psbt_final_tx', which I think also makes the callers clearer.
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
`struct tx_parts` is just a txid and a bunch of inputs and outputs,
some of which may be NULL.
This is both a nod towards a future where we (or our peer) can combine
HTLCs or (in an eltoo world) commitments, although for the moment all
our tx_parts will be complete.
It also matches our plan to split `bitcoin_tx` into two types: this
`struct tx_parts` where we don't know input amounts etc, and `psbt`
where we do.
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
Rusty Russell
niftynei