Unfortunately, projection errors do not come with a nice set of
mismatched types. This is because the type equality check occurs
within a higher-ranked context. Therefore, only the type error
is reported. This is ugly but was always the situation.
I will introduce better errors for the lower-ranked case in
another commit.
Fixes the last known occurence of #31173
This is a spiritual succesor to #34268/8531d581, in which we replaced a
number of matches of None to the unit value with `if let` conditionals
where it was judged that this made for clearer/simpler code (as would be
recommended by Manishearth/rust-clippy's `single_match` lint). The same
rationale applies to matches of None to the empty block.
Casual grepping revealed some places in the codebase (some of which
antedated `if let`'s December 2014 stabilization in c200ae5a) where we
were using a match with a `None => ()` arm where (in the present
author's opinion) an `if let` conditional would be more readable. (Other
places where matching to the unit value did seem to better express the
intent were left alone.)
It's likely that we don't care about making such trivial,
non-functional, sheerly æsthetic changes.
But if we do, this is a patch.
Currently, when projecting out of a higher-ranked where-clause, we
instantiate all higher-ranked regions with lifetime variables. This is
unnecessary since the language rules ought to guarantee (modulo #32330)
that each of those higher-ranked regions is equated with some regions
from the input types. This routine figures out what those regions are
and just uses them. Also, since #32330 is not fully fixed, it detects
when we may have unconstrained variables and indicates that in its
return value.
We used to make region->region edges part of the verify set, but this
change stores them like other edges, as a full-fledged constraint.
Besides making the code somewhat cleaner, this allows them to be more
easily dropped as part of `pop_skolemized`. This change also refactors
the code a bit to remove some intermediate data structures that are no
longer particular useful (e.g., VarValue).
When we do a "HR subtype" check, we replace all late-bound regions (LBR)
in the subtype with fresh variables, and skolemize the late-bound
regions in the supertype. If those skolemized regions from the supertype
wind up being super-regions (directly or indirectly) of either
- another skolemized region; or,
- some region that pre-exists the HR subtype check
- e.g., a region variable that is not one of those created
to represent bound regions in the subtype
then the subtype check fails.
What will change when we fix#32330 is that some of the LBR in the
subtype may become early-bound. In that case, they would no longer be in
the "permitted set" of variables that can be related to a skolemized
type.
So the foundation for this warning is to collect variables that we found
to be related to a skolemized type. For each of them, we have a
`BoundRegion` which carries a `Issue32330` flag. We check whether any of
those flags indicate that this variable was created from a lifetime
that will change from late- to early-bound. If so, we issue a warning
indicating that the results of compilation may change.
This is imperfect, since there are other kinds of code that will not
compile once #32330 is fixed. However, it fixes the errors observed in
practice on crater runs.
This indicates whether this `BoundRegion` will change from late to early
bound when issue 32330 is fixed. It also indicates the function on
which the lifetime is declared.
Currently, we consider region subtyping a failure
if a skolemized lifetime is relatable to any
other lifetime in any way at all. But a more precise
formulation is to say that a skolemized lifetime:
- must not have any *incoming* edges in the region graph
- only has *outgoing* edges to nodes that are `'static`
To enforce the latter requirement, we add edges from `'static -> 'x` for
each lifetime '`x' reachable from a skolemized region.
We now have to add a new `pop_skolemized` routine to do cleanup.
Whereas before if there were *any* edges relating to a skolemized
region, we would return `Err` and hence rollback the transaction, we now
tolerate some edges and return `Ok`. Therefore, the `pop_skolemized`
routine runs and cleans up those edges.
Fix for old school error issues, improvements to new school
This PR:
* Fixes some old school error issues, specifically #33559, #33543, #33366
* Improves wording borrowck errors with match patterns
* De-emphasize multi-line spans, so we don't color the single source character when we're trying to say "span starts here"
* Rollup of #33392 (which should help fix#33390)
r? @nikomatsakis
Remove ExplicitSelf from HIR
`self` argument is already kept in the argument list and can be retrieved from there if necessary, so there's no need for the duplication.
The same changes can be applied to AST, I'll make them in the next breaking batch.
The first commit also improves parsing of method declarations and fixes https://github.com/rust-lang/rust/issues/33413.
r? @eddyb
Batch of improvements to errors for new error format
This is a batch of improvements to existing errors to help get the most out of the new error format.
* Added labels to primary spans (^^^) for a set of errors that didn't currently have them
* Highlight the source blue under the secondary notes for better readability
* Move some of the "Note:" into secondary spans+labels
* Fix span_label to take &mut instead, which makes it work the same as other methods in that set
Add rustc_on_unimplemented for Index implementation on slice
Reopening of #31071.
It also extends the possibility of `#[rustc_on_unimplemented]` by providing a small type filter in order to find the ones which corresponds the most.
r? @pnkfelix
fix DFS for region error reporting
This was causing terrible error reports, because the algorithm was incorrectly identifying the constraints.
r? @eddyb
