[XCM] don't ignore errors

[xlc]

I am debugging some XCM error and this is the log I got

 xcm::weight  TRACE: [22] WeightInfoBounds message: Xcm([WithdrawAsset(Assets([Asset { id: AssetId(Location { parents: 1, interior: Here }), fun: Fungible(100000000000) }])), BuyExecution { fees: Asset { id: AssetId(Location { parents: 1, interior: Here }), fun: Fungible(100000000000) }, weight_limit: Unlimited }, Transact { origin_kind: SovereignAccount, fallback_max_weight: Some(Weight { ref_time: 1500000000, proof_size: 10000 }), call: "0x3c0aed030000" }, RefundSurplus, DepositAsset { assets: Wild(AllCounted(1)), beneficiary: Location { parents: 0, interior: X1([Parachain(2000)]) } }])
        xcm::process-message  TRACE: [22] Failed to prepare message.

No idea what's wrong with my message. Seems like the error is dropped here

polkadot-sdk/polkadot/xcm/xcm-executor/src/lib.rs

Line 236 in bff1ae9

Err(_) => Err(message),

[bkchr]

CC @paritytech/xcm

[acatangiu]

@raymondkfcheung another leaky point part of #6119

[acatangiu]

maybe include this (and any other Err(_)) you find, with the work in #7730

[raymondkfcheung]

If we want to go with the approach in #7730, we may need to update the WeightBounds trait to return Result<Weight, XcmError> instead of Result<Weight, ()>, otherwise the error details will continue to be dropped.

In draft PR #8535, I took a different approach: using XcmError internally while keeping the trait signature unchanged. This preserves compatibility but still enables detailed debug logs.

Let me know which direction you’d prefer.

[raymondkfcheung]

Closing, addressed by #8535