(Without this commit, you still get an error (a very similar one, at
that), but it complains about use of forward declaration, which is
confusing since people do not necessarily think of `Self` as being
declared at all.)
Update: incorporate review feedback.
Inline `{min,max}_value` even in debug builds
I think it is worth to inline `{min,max}_value` even in debug builds.
See this godbolt link: https://godbolt.org/z/-COkVS
Rollup of 7 pull requests
Successful merges:
- #63678 (Improve HRTB error span when -Zno-leak-check is used)
- #64931 (Reword E0392 slightly)
- #64959 (syntax: improve parameter without type suggestions)
- #64975 (Implement Clone::clone_from for LinkedList)
- #64993 (BacktraceStatus: add Eq impl)
- #64998 (Filter out RLS output directories on tidy runs)
- #65010 (Compare `primary` with maximum of `children`s' line num instead of dropping it)
Failed merges:
r? @ghost
BacktraceStatus: add Eq impl
See discussion on #53487.
---
Is adding `Copy` too ambitious? It's a "status", so I don't forsee any non-POD data that might go in there, but it would restrict future variants more than `Eq` does.
Cc: @withoutboats @abonander
Implement Clone::clone_from for LinkedList
See #28481. This represents a substantial speedup when the list sizes are comparable, and shouldn't ever be significantly worse. Technically split_off is doing an unnecessary search, but the code is hopefully cleaner as a result. I'm happy to rework anything that needs to be changed as well!
syntax: improve parameter without type suggestions
Fixes#64252.
This PR improves the suggestions provided when function parameters
do not have types:
- A new suggestion is added for arbitrary self types, which suggests
adding `self: ` before the type.
- Existing suggestions are now provided when a `<` is found where a `:`
was expected (previously only `,` and `)` or trait items), this gives
suggestions in the case where the unnamed parameter type is generic
in a free function.
- The suggestion that a type name be provided (e.g. `fn foo(HashMap<u32>)`
-> `fn foo(HashMap: TypeName<u32>)`) will no longer occur when a `<` was
found instead of `:`.
- The ident will not be used for recovery when a `<` was found instead
of `:`.
r? @Centril
cc @estebank @yoshuawuyts
Reword E0392 slightly
Make it clearer that a type or lifetime argument not being used can be
fixed by referencing it in a struct's fields, not just using `PhathomData`.
CC #53589.
Improve HRTB error span when -Zno-leak-check is used
As described in #57374, NLL currently produces unhelpful higher-ranked
trait bound (HRTB) errors when '-Zno-leak-check' is enabled.
This PR tackles one half of this issue - making the error message point
at the proper span. The error message itself is still the very generic
"higher-ranked subtype error", but this can be improved in a follow-up
PR.
The root cause of the bad spans lies in how NLL attempts to compute the
'blamed' region, for which it will retrieve a span for.
Consider the following code, which (correctly) does not compile:
```rust
let my_val: u8 = 25;
let a: &u8 = &my_val;
let b = a;
let c = b;
let d: &'static u8 = c;
```
This will cause NLL to generate the following subtype constraints:
d :< c
c :< b
b <: a
Since normal Rust lifetimes are covariant, this results in the following
region constraints (I'm using 'd to denote the lifetime of 'd',
'c to denote the lifetime of 'c, etc.):
'c: 'd
'b: 'c
'a: 'b
From this, we can derive that 'a: 'd holds, which implies that 'a: 'static
must hold. However, this is not the case, since 'a refers to 'my_val',
which does not outlive the current function.
When NLL attempts to infer regions for this code, it will see that the
region 'a has grown 'too large' - it will be inferred to outlive
'static, despite the fact that is not declared as outliving 'static
We can find the region responsible, 'd, by starting at the *end* of
the 'constraint chain' we generated above. This works because for normal
(non-higher-ranked) lifetimes, we generally build up a 'chain' of
lifetime constraints *away* from the original variable/lifetime.
That is, our original lifetime 'a is required to outlive progressively
more regions. If it ends up living for too long, we can look at the
'end' of this chain to determine the 'most recent' usage that caused
the lifetime to grow too large.
However, this logic does not work correctly when higher-ranked trait
bounds (HRTBs) come into play. This is because HRTBs have
*contravariance* with respect to their bound regions. For example,
this code snippet compiles:
```rust
let a: for<'a> fn(&'a ()) = |_| {};
let b: fn(&'static ()) = a;
```
Here, we require that 'a' is a subtype of 'b'. Because of
contravariance, we end up with the region constraint 'static: 'a,
*not* 'a: 'static
This means that our 'constraint chains' grow in the opposite direction
of 'normal lifetime' constraint chains. As we introduce subtypes, our
lifetime ends up being outlived by other lifetimes, rather than
outliving other lifetimes. Therefore, starting at the end of the
'constraint chain' will cause us to 'blame' a lifetime close to the original
definition of a variable, instead of close to where the bad lifetime
constraint is introduced.
This PR improves how we select the region to blame for 'too large'
universal lifetimes, when bound lifetimes are involved. If the region
we're checking is a 'placeholder' region (e.g. the region 'a' in
for<'a>, or the implicit region in fn(&())), we start traversing the
constraint chain from the beginning, rather than the end.
There are two (maybe more) different ways we generate region constraints for NLL:
requirements generated from trait queries, and requirements generated
from MIR subtype constraints. While the former always use explicit
placeholder regions, the latter is more tricky. In order to implement
contravariance for HRTBs, TypeRelating replaces placeholder regions with
existential regions. This requires us to keep track of whether or not an
existential region was originally a placeholder region. When we look for
a region to blame, we check if our starting region is either a
placeholder region or is an existential region created from a
placeholder region. If so, we start iterating from the beginning of the
constraint chain, rather than the end.
