[FRAME] Enum `UpgradeCheckSelect` should be a bit flag

[ggwpez]

This enum could also get a new variant for the new DecodeState check. Then it becomes impractical to not use a bit flag:

pub enum UpgradeCheckSelect {
	None,
	All,
	PreAndPost,
	TryState,
}

(Easy issue good for newcomers.)

[chungquantin]

@ggwpez I have added this PR to resolve the issue. However, I think this PR will need a further consideration: #3719

However, I have a question: What is the purpose of implementing TryDecodeEntireStorage on UpgradeCheckSelect? As my understanding, the trait is used for Decode the entire data under the given storage type (from TryDecodeEntireStorage doc). Hence, I simply decode and accumulate all enum field values using information provided. If you could help me to provide more context, it would be clearer!

[ggwpez]

Thanks for picking this up @chungquantin!

However, I have a question: What is the purpose of implementing TryDecodeEntireStorage on UpgradeCheckSelect?

This is not what i meant - TryDecodeEntireStorage should not be implemented on that, but instead used to select whether that check is enabled in this function:

polkadot-sdk/substrate/frame/executive/src/lib.rs

Line 434 in eefd5fe

pub fn try_runtime_upgrade(checks: UpgradeCheckSelect) -> Result<Weight, TryRuntimeError> {

You see that it uses checks.any() here instead of something like checks.should_check_state():

polkadot-sdk/substrate/frame/executive/src/lib.rs

Line 452 in eefd5fe

if checks.any() {

We want to use a bitflag for UpgradeCheckSelect here to selectively enable/disable specific checks, instead of an all-or-nothing approach (how it currently is).