Proposal: automatically highlight diff in ex_unit when match operator is used

[Artur Plysyuk]

Hi,

Current behavour:

[]  = all_enqueued(queue: :default)

#  raises ** (MatchError)

assert []  = all_enqueued(queue: :default)

# formatted as match (=) failed

Actually, the proposal is to kinda implicitly add assert to expressions which have match operator, so in case of errors output is automatically formatted like the expression is written with assert.

[José Valim]

I would prefer to not change the semantics of the code, because it can lead to subtle behavior: for example, what if the match is inside one of the monad libraries that already override what = means?

You can say we could detect those cases, but it is not trivial to differentiate from a macro that transform = from another one that wouldn’t (such as the if/2) macro.

In other words, macros that traverse ASTs and change the semantics of the code should not be encouraged, so I don’t think we should go ahead with this.

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