https://github.com/rust-lang/rfcs/pull/221
The current terminology of "task failure" often causes problems when
writing or speaking about code. You often want to talk about the
possibility of an operation that returns a Result "failing", but cannot
because of the ambiguity with task failure. Instead, you have to speak
of "the failing case" or "when the operation does not succeed" or other
circumlocutions.
Likewise, we use a "Failure" header in rustdoc to describe when
operations may fail the task, but it would often be helpful to separate
out a section describing the "Err-producing" case.
We have been steadily moving away from task failure and toward Result as
an error-handling mechanism, so we should optimize our terminology
accordingly: Result-producing functions should be easy to describe.
To update your code, rename any call to `fail!` to `panic!` instead.
Assuming you have not created your own macro named `panic!`, this
will work on UNIX based systems:
grep -lZR 'fail!' . | xargs -0 -l sed -i -e 's/fail!/panic!/g'
You can of course also do this by hand.
[breaking-change]
Similar to the stability attributes, a type annotated with `#[must_use =
"informative snippet"]` will print the normal warning message along with
"informative snippet". This allows the type author to provide some
guidance about why the type should be used.
I attempted to implement the lint in two steps. My first attempt was a
default-warn lint about *all* unused results. While this attempt did indeed find
many possible bugs, I felt that the false-positive rate was too high to be
turned on by default for all of Rust.
My second attempt was to make unused-result a default-allow lint, but allow
certain types to opt-in to the notion of "you must use this". For example, the
Result type is now flagged with #[must_use]. This lint about "must use" types is
warn by default (it's different from unused-result).
The unused_must_use lint had a 100% hit rate in the compiler, but there's not
that many places that return Result right now. I believe that this lint is a
crucial step towards moving away from conditions for I/O (because all I/O will
return Result by default). I'm worried that this lint is a little too specific
to Result itself, but I believe that the false positive rate for the
unused_result lint is too high to make it useful when turned on by default.
