chore(gnolang): revamp switch fallthrough

[tbruyelle]

Description

Found out there's an other TODO CHALLENGE switch fallthrough in pre-process, which makes me realize the proper way of dealing with jump statements like fallthrough.

In the initial version, a new attribute ATTR_SWITCH_CLAUSE_IDX was introduced to store the clause index, but it appears this kind of thing should be handled in the pre-process step.

As a result the attribute is removed and replaced with some code in pre-process step, that stores the clause index in node.BodyIndex, only in case we're dealing with a fallthrough.

How has this been tested?

The tests remain unchanged, which proves this still works as expected.

$ go test ./tests -v -run `/switch'

[moul]

Could you write a unit test to verify that the change to the codebase is working as expected and providing the desired outcome?

[tbruyelle]

Could you write a unit test to verify that the change to the codebase is working as expected and providing the desired outcome?

The tests I relied on for this change were written in the previous PR #504, they use the tests/files/switch*.gno files. Do you want me to add a test specifically for this package ?

[moul]

Ideally, a test should be conducted to demonstrate the change, such as something that was not functioning properly before. If no new tests can be found, let's use the existing ones.

[tbruyelle]

Ideally, a test should be conducted to demonstrate the change, such as something that was not functioning properly before. If no new tests can be found, let's use the existing ones.

Well, the change doesn't add, remove or fix anything. It's just an other way of dealing with fallthrough, but a way that looks more compliant with the existing code. Namely, goto, continue and break use the preprocess step to register the label position, so it seemed normal to me for fallthrough to act this way, instead of using node attributes.

Maybe I should have prefix the change with refac instead of chore, but it doesn't look like a refac for me, since I'm not convinced it brings any performance or clarity improvement. It just looks more compliant, but maybe I'm wrong ?