Point at return type always when type mismatch against it
Before this, the diagnostic errors would only point at the return type
when changing it would be a possible solution to a type error. Add a
label to the return type without a suggestion to change in order to make
the source of the expected type obvious.
Follow up to #42850, fixes#25133, fixes#41897.
In preparation for incremental compilation this commit refactors the lint
handling infrastructure in the compiler to be more "eager" and overall more
incremental-friendly. Many passes of the compiler can emit lints at various
points but before this commit all lints were buffered in a table to be emitted
at the very end of compilation. This commit changes these lints to be emitted
immediately during compilation using pre-calculated lint level-related data
structures.
Linting today is split into two phases, one set of "early" lints run on the
`syntax::ast` and a "late" set of lints run on the HIR. This commit moves the
"early" lints to running as late as possible in compilation, just before HIR
lowering. This notably means that we're catching resolve-related lints just
before HIR lowering. The early linting remains a pass very similar to how it was
before, maintaining context of the current lint level as it walks the tree.
Post-HIR, however, linting is structured as a method on the `TyCtxt` which
transitively executes a query to calculate lint levels. Each request to lint on
a `TyCtxt` will query the entire crate's 'lint level data structure' and then go
from there about whether the lint should be emitted or not.
The query depends on the entire HIR crate but should be very quick to calculate
(just a quick walk of the HIR) and the red-green system should notice that the
lint level data structure rarely changes, and should hopefully preserve
incrementality.
Overall this resulted in a pretty big change to the test suite now that lints
are emitted much earlier in compilation (on-demand vs only at the end). This in
turn necessitated the addition of many `#![allow(warnings)]` directives
throughout the compile-fail test suite and a number of updates to the UI test
suite.
It's more pleasing to use the inner-attribute syntax (`#!` rather than
`#`) in the error message, as that is how `feature` attributes in
particular will be declared (as they apply to the entire crate).
We don't want to guarantee that `Instant::now() != Instant::now()` is
always true since that depends on the speed of the processor and the
resolution of the clock.
#[must_use] for functions
This implements [RFC 1940](https://github.com/rust-lang/rfcs/pull/1940).
The RFC and discussion thereof seem to suggest that tagging `PartialEq::eq` and friends as `#[must_use]` would automatically lint for unused comparisons, but it doesn't work out that way (at least the way I've implemented it): unused `.eq` method calls get linted, but not `==` expressions. (The lint operates on the HIR, which sees binary operations as their own thing, even if they ultimately just call `.eq` _&c._.)
What do _you_ think??
Resolves#43302.
Add an overflow check in the Iter::next() impl for Range<_> to help with vectorization.
This helps with vectorization in some cases, such as (0..u16::MAX).collect::<Vec<u16>>(),
as LLVM is able to change the loop condition to use equality instead of less than and should help with #43124. (See also my [last comment](https://github.com/rust-lang/rust/issues/43124#issuecomment-319098625) there.) This PR makes collect on ranges of u16, i16, i8, and u8 **significantly** faster (at least on x86-64 and i686), and pretty close, though not quite equivalent to a [manual unsafe implementation](https://is.gd/nkoecB). 32 ( and 64-bit values on x86-64) bit values were already vectorized without this change, and they still are. This PR doesn't seem to help with 64-bit values on i686, as they still don't vectorize well compared to doing a manual loop.
I'm a bit unsure if this was the best way of implementing this, I tried to do it with as little changes as possible and avoided changing the step trait and the behavior in RangeFrom (I'll leave that for others like #43127 to discuss wider changes to the trait). I tried simply changing the comparison to `self.start != self.end` though that made the compiler segfault when compiling stage0, so I went with this method instead for now.
As for `next_back()`, reverse ranges seem to optimise properly already.
Mark it with the `unreachable` feature and put it into the `mem` module.
This is a pretty straight-forward API that can already be simulated in
stable Rust by using `transmute` to create an uninhabited enum that can
be matched.
Update the list of confusable characters
Also reorder and space the list to make it clearer for futures updates
and to come closer to the original list.
This was tedious but somewhat rewarding!
Thanks @est31 for the instructions.
Fixes#43629.
r? @est31
The spans previously encoded only span the first token after the opening
brace, up to the closing brace of inline `mod` declarations. Thus, when
examining exports from an external crate, the spans don't include the
header of inline `mod` declarations.
make `for_all_relevant_impls` O(1) again
A change in #41911 had made `for_all_relevant_impls` do a linear scan over
all impls, instead of using an HashMap. Use an HashMap again to avoid
quadratic blowup when there is a large number of structs with impls.
I think this fixes#43141 completely, but I want better measurements in
order to be sure. As a perf patch, please don't roll this up.
r? @eddyb
beta-nominating because regression
