This PR implements rust-lang/rfcs#1023. In the process it fixes#23086 and #23516. A few impls in libcore had to be updated, but the impact is generally pretty minimal. Most of the fallout is in the tests that probed the limits of today's coherence.
I tested and we were able to build the most popular crates along with iron (modulo errors around errors being sendable).
Fixes#23918.
This introduces no functional changes except for reducing a few unnecessary operations and variables. Vec has the behavior that, if you request space past the capacity with reserve(), it will round up to the nearest power of 2. What that effectively means is that after the first call to reserve(16), we are doubling our capacity every time. So using the DEFAULT_BUF_SIZE and doubling cap_size() here is meaningless and has no effect on the call to reserve().
Note that with #23842 implemented this will hopefully have a clearer API and less of a need for commenting. If #23842 is not implemented then the most clear implementation would be to call reserve_exact(buf.capacity()) at every step (and making sure that buf.capacity() is not zero at the beginning of the function of course).
Edit- functional change now introduced. We will now zero 16 bytes of the vector first, then double to 32, then 64, etc. until we read 64kB. This stops us from zeroing the entire vector when we double it, some of which may be wasted work. Reallocation still follows the doubling strategy, but the responsibility has been moved to vec.extend(), which calls reserve() and push_back().
While trying to implement parallel ECS processing, I stumbled upon the need to mutate `Arc` contents. The only existed method that allowed that was `make_unique`, but it has issues:
- it may clone the data as if nothing happened, where the program may just need to crash
- it forces `Clone` bound, which I don't have
The new `try_unique` allows accessing the contents mutably without `Clone` bound and error out if the pointer is not unique.
This PR solves #21559 by making sure that unreachable if-expressions are not further translated.
Could someone who knows their way around `trans` take a look at the changes in `controlflow.rs`? I'm not sure if any other code relies on any side-effects of translating unreachable things.
cc @nikomatsakis @nrc @eddyb
for `Box<FnBox()>`. I found the alias was still handy because it is
shorter than the fully written type.
This is a [breaking-change]: convert code using `Invoke` to use `FnBox`,
which is usually pretty straight-forward. Code using thunk mostly works
if you change `Thunk::new => Box::new` and `foo.invoke(arg)` to
`foo(arg)`.
local only if matches `FUNDAMENTAL(LocalType)`, where `FUNDAMENTAL`
includes `&T` and types marked as fundamental (which includes `Box`).
Also apply these tests to negative reasoning.
case where `None` was returned should never happen in practice; it
amounts to comparing regions from two unrelated hierarchies. (I was also
not able to make it happen.)
This means passing in e.g. a `Vec<u8>` or `String` will work as
intended, rather than deref-ing to `&mut [u8]` or `&mut str`.
[breaking-change]
Closes#23768
const_eval : add overflow-checking for {`+`, `-`, `*`, `/`, `<<`, `>>`}.
One tricky detail here: There is some duplication of labor between `rustc::middle::const_eval` and `rustc_trans::trans::consts`. It might be good to explore ways to try to factor out the common structure to the two passes (by abstracting over the particular value-representation used in the compile-time interpreter).
----
Update: Rebased atop #23841Fix#22531Fix#23030Fix#23221Fix#23235
The overflow-checking attempts to accommodate early evaluation where
we do not have type information yet.
Also, add fixme note about something that has been bothering me.
Add option-returning variants to `const_to_int`/`const_to_uint` that
never assert fail. (These will be used for overflow checking from
rustc_trans::trans::consts.)
