[bug]: Invalid flags after payinvoice's pay_req are being ignored

[arturgontijo]

Background

Flags after lncli payinvoice [command options] pay_req are being ignored.

Your environment

• version of lnd: lnd-darwin-arm64-v0.18.4-beta
• which operating system (uname -a on *Nix): Darwin 24.2.0
• version of btcd, bitcoind, or other backend: bitcoind@v28.0.0
• any other relevant environment details

Steps to reproduce

These fail as expected:

lncli -n=signet payinvoice --last_hop=123 lntbs60030...hj32cppyeeac
>>> [lncli] invalid vertex string length of 3, want 66

lncli -n=signet payinvoice lntbs60030...hj32cppyeeac --last_hop=123
>>> [lncli] invalid vertex string length of 3, want 66

lncli -n=signet payinvoice --last_hop_non_existing=123 lntbs60030...hj32cppyeeac
>>> [lncli] flag provided but not defined: -last_hop_non_existing

But this doesn't:

lncli -n=signet payinvoice lntbs60030...hj32cppyeeac --last_hop_non_existing=123
>>> Payment hash: ...
Description: ...
Amount (in satoshis): 1
Fee limit (in satoshis): 300
Destination: ...
Confirm payment (yes/no): no
[lncli] payment not confirmed

Expected behaviour

Shouldn't we do the same check as we do for sendpayment here?

lncli -n=signet sendpayment --last_hop=123 --pay_req=lntbs60030...hj32cppyeeac
>>> [lncli] invalid vertex string length of 3, want 66

lncli -n=signet sendpayment --pay_req=lntbs60030...hj32cppyeeac --last_hop=123
>>> [lncli] invalid vertex string length of 3, want 66

lncli -n=signet sendpayment --last_hop_non_existing=123 --pay_req=lntbs60030...hj32cppyeeac
>>> [lncli] flag provided but not defined: -last_hop_non_existing

lncli -n=signet sendpayment --pay_req=lntbs60030...hj32cppyeeac --last_hop_non_existing=123
>>> [lncli] flag provided but not defined: -last_hop_non_existing

I think we should output the same error for payinvoice, eg:

lncli -n=signet payinvoice lntbs60030...hj32cppyeeac --last_hop_non_existing=123
>>> [lncli] flag provided but not defined: -last_hop_non_existing

If that makes sense, I can try to implement that check.