Fixes#67007
Currently, a 'borrowed data escapes' error does not mention
the specific lifetime involved (except indirectly through a suggestion
about adding a lifetime bound). We now explain the specific lifetime
relationship that failed to hold, which improves otherwise vague
error messages.
Don't suggest replacing region with 'static in NLL
Fixes#73159
This is similar to #69350 - if the user didn't initially
write out a 'static lifetime, adding 'static in response to
a lifetime error is usually the wrong thing to do.
Fixes#73159
This is similar to #69350 - if the user didn't initially
write out a 'static lifetime, adding 'static in response to
a lifetime error is usually the wrong thing to do.
Don't anonymize bound region names during typeck
Once this anonymization has performed, we have no
way of recovering the original names during NLL
borrow checking. Keeping the original names allows
error messages in full NLL mode to contain the original
bound region names.
As a result, the typeck results may contain types that
differ only in the names used for their bound regions. However,
anonimization of bound regions does not guarantee that
all distinct types are unqual (e.g. not subtypes of each other).
For example, `for<'a> fn(&'a u32, &'a u32)` and
`for<'b, 'c> fn(&'b u32, &'c u32)` are subtypes of each other,
as explained here:
63cc2bb3d0/compiler/rustc_infer/src/infer/nll_relate/mod.rs (L682-L690)
Therefore, any code handling types with higher-ranked regions already
needs to handle the case where two distinct `Ty`s are 'actually'
equal.
Use larger span for adjustment THIR expressions
Currently, we use a relatively 'small' span for THIR
expressions generated by an 'adjustment' (e.g. an autoderef,
autoborrow, unsizing). As a result, if a borrow generated
by an adustment ends up causing a borrowcheck error, for example:
```rust
let mut my_var = String::new();
let my_ref = &my_var
my_var.push('a');
my_ref;
```
then the span for the mutable borrow may end up referring
to only the base expression (e.g. `my_var`), rather than
the method call which triggered the mutable borrow
(e.g. `my_var.push('a')`)
Due to a quirk of the MIR borrowck implementation,
this doesn't always get exposed in migration mode,
but it does in many cases.
This commit makes THIR building consistently use 'larger'
spans for adjustment expressions. These spans are recoded
when we first create the adjustment during typecheck. For
example, an autoref adjustment triggered by a method call
will record the span of the entire method call.
The intent of this change it make it clearer to users
when it's the specific way in which a variable is
used (for example, in a method call) that produdes
a borrowcheck error. For example, an error message
claiming that a 'mutable borrow occurs here' might
be confusing if it just points at a usage of a variable
(e.g. `my_var`), when no `&mut` is in sight. Pointing
at the entire expression should help to emphasize
that the method call itself is responsible for
the mutable borrow.
In several cases, this makes the `#![feature(nll)]` diagnostic
output match up exactly with the default (migration mode) output.
As a result, several `.nll.stderr` files end up getting removed
entirely.
Once this anonymization has performed, we have no
way of recovering the original names during NLL
borrow checking. Keeping the original names allows
error messages in full NLL mode to contain the original
bound region names.
As a result, the typeck results may contain types that
differ only in the names used for their bound regions. However,
anonimization of bound regions does not guarantee that
all distinct types are unqual (e.g. not subtypes of each other).
For example, `for<'a> fn(&'a u32, &'a u32)` and
`for<'b, 'c> fn(&'b u32, &'c u32)` are subtypes of each other,
as explained here:
63cc2bb3d0/compiler/rustc_infer/src/infer/nll_relate/mod.rs (L682-L690)
Therefore, any code handling types with higher-ranked regions already
needs to handle the case where two distinct `Ty`s are 'actually'
equal.
Currently, we use a relatively 'small' span for THIR
expressions generated by an 'adjustment' (e.g. an autoderef,
autoborrow, unsizing). As a result, if a borrow generated
by an adustment ends up causing a borrowcheck error, for example:
```rust
let mut my_var = String::new();
let my_ref = &my_var
my_var.push('a');
my_ref;
```
then the span for the mutable borrow may end up referring
to only the base expression (e.g. `my_var`), rather than
the method call which triggered the mutable borrow
(e.g. `my_var.push('a')`)
Due to a quirk of the MIR borrowck implementation,
this doesn't always get exposed in migration mode,
but it does in many cases.
This commit makes THIR building consistently use 'larger'
spans for adjustment expressions
The intent of this change it make it clearer to users
when it's the specific way in which a variable is
used (for example, in a method call) that produdes
a borrowcheck error. For example, an error message
claiming that a 'mutable borrow occurs here' might
be confusing if it just points at a usage of a variable
(e.g. `my_var`), when no `&mut` is in sight. Pointing
at the entire expression should help to emphasize
that the method call itself is responsible for
the mutable borrow.
In several cases, this makes the `#![feature(nll)]` diagnostic
output match up exactly with the default (migration mode) output.
As a result, several `.nll.stderr` files end up getting removed
entirely.
Add `ConstraintCategory::Usage` for handling aggregate construction
In some cases, we emit borrowcheck diagnostics pointing
at a particular field expression in a struct expression
(e.g. `MyStruct { field: my_expr }`). However, this
behavior currently relies on us choosing the
`ConstraintCategory::Boring` with the 'correct' span.
When adding additional variants to `ConstraintCategory`,
(or changing existing usages away from `ConstraintCategory::Boring`),
the current behavior can easily get broken, since a non-boring
constraint will get chosen over a boring one.
To make the diagnostic output less fragile, this commit
adds a `ConstraintCategory::Usage` variant. We use this variant
for the temporary assignments created for each field of
an aggregate we are constructing.
Using this new variant, we can emit a message mentioning
"this usage", emphasizing the fact that the error message
is related to the specific use site (in the struct expression).
This is preparation for additional work on improving NLL error messages
(see #57374)
Propagate coercion cause into `try_coerce`
Currently, `coerce_inner` discards its `ObligationCause`
when calling `try_coerce`. This interfers with other
diagnostc improvements I'm working on, since we will lose
the original span by the time the actual coercion occurs.
Additionally, we now use the span of the trailing expression
(rather than the span of the entire function) when performing
a coercion in `check_return_expr`. This currently has no visible
effect on any of the unit tests, but will unblock future
diagnostic improvements.
Currently, `coerce_inner` discards its `ObligationCause`
when calling `try_coerce`. This interfers with other
diagnostc improvements I'm working on, since we will lose
the original span by the time the actual coercion occurs.
Additionally, we now use the span of the trailing expression
(rather than the span of the entire function) when performing
a coercion in `check_return_expr`. This currently has no visible
effect on any of the unit tests, but will unblock future
diagnostic improvements.
In some cases, we emit borrowcheck diagnostics pointing
at a particular field expression in a struct expression
(e.g. `MyStruct { field: my_expr }`). However, this
behavior currently relies on us choosing the
`ConstraintCategory::Boring` with the 'correct' span.
When adding additional variants to `ConstraintCategory`,
(or changing existing usages away from `ConstraintCategory::Boring`),
the current behavior can easily get broken, since a non-boring
constraint will get chosen over a boring one.
To make the diagnostic output less fragile, this commit
adds a `ConstraintCategory::Usage` variant. We use this variant
for the temporary assignments created for each field of
an aggregate we are constructing.
Using this new variant, we can emit a message mentioning
"this usage", emphasizing the fact that the error message
is related to the specific use site (in the struct expression).
This is preparation for additional work on improving NLL error messages
(see #57374)
Previously, we would set up the source lines for `match` expressions so
that the code generated to perform the test of the scrutinee was matched
to the line of the arm that required the test and then jump from the arm
block to the "next" block was matched to all of the lines in the `match`
expression.
While that makes sense, it has the side effect of causing strange
stepping behavior in debuggers.
I've changed the source information so that all of the generated tests
are sourced to `match {scrutinee}` and the jumps are sourced to the last
line of the block they are inside. This resolves the weird stepping
behavior in all debuggers and resolves some instances of "ambiguous
symbol" errors in WinDbg preventing the user from setting breakpoints at
`match` expressions.
Matthew's work on improving NLL's "higher-ranked subtype error"s
This PR rebases `@matthewjasper's` [branch](https://github.com/matthewjasper/rust/tree/nll-hrtb-errors) which has great work to fix the obscure higher-ranked subtype errors that are tracked in #57374.
These are a blocker to turning full NLLs on, and doing some internal cleanups to remove some of the old region code.
The goal is so `@nikomatsakis` can take a look at this early, and I'll then do my best to help do the changes and followup work to land this work, and move closer to turning off the migration mode.
I've only updated the branch and made it compile, removed a warning or two.
r? `@nikomatsakis`
(Here's the [zulip topic to discuss this](https://rust-lang.zulipchat.com/#narrow/stream/122657-t-compiler.2Fwg-nll/topic/.2357374.3A.20improving.20higher-ranked.20subtype.20errors.20via.20.2386700) that Niko wanted)
Update `polonius-engine` to 0.13.0
This PR updates the use of `polonius-engine` to the recently released 0.13.0:
- this version renamed a lot of relations to match the current terminology
- "illegal subset relationships errors" (AKA "subset errors" or "universal region errors" in rustc parlance) have been implemented in all variants, and therefore the `Hybrid` variant can be the rustc default once again
- some of the blessed expectations were updated: new tests have been added since the last time I updated the tests, diagnostics have changed, etc.
In particular:
- a few tests had trivial expectations changes such as basic diagnostics changes for the migrate-mode and full NLLs
- others were recursion and lengths limits which emits a file, and under the polonius compare-mode, the folder has a different name
- a few tests were ignored in the NLL compare-mode for reasons that obviously also apply to Polonius
- some diagnostics were unified so that older expectations no longer made sense: the NLL and Polonius outputs were identical.
- in a few cases Polonius gets a chance to emit more errors than NLLs
A few tests in the compare-mode still are super slow and trigger the 60s warning, or OOM rustc during fact generation, and I've detailed these [on Zulip](https://rust-lang.zulipchat.com/#narrow/stream/186049-t-compiler.2Fwg-polonius/topic/Challenges.20for.20move.2Finit.2C.20liveness.2C.20and.20.60Location.3A.3AAll.60):
- `src/test/ui/numbers-arithmetic/saturating-float-casts.rs` -> OOM during rustc fact generation
- `src/test/ui/numbers-arithmetic/num-wrapping.rs`
- `src/test/ui/issues/issue-72933-match-stack-overflow.rs`
- `src/test/ui/issues/issue-74564-if-expr-stack-overflow.rs`
- `src/test/ui/repr/repr-no-niche.rs`
In addition, 2 tests don't currently pass and I didn't want to bless them now: they deal with HRTBs and miss errors that NLLs emit. We're currently trying to see if we need chalk to deal with HRTB errors (as we thought we would have to) but during the recent sprint, we discovered that we may be able to detect some of these errors in a way that resembles subset errors:
- `ui/hrtb/hrtb-just-for-static.rs` -> 3 errors in NLL, 2 in polonius: a missing error about HRTB + needing to outlive 'static
- `ui/issues/issue-26217.rs` -> missing HRTB that makes the test compile instead of emitting an error
We'll keep talking about this at the next sprint as well.
cc `@rust-lang/wg-polonius` r? `@nikomatsakis`
* On suggestions that include deletions, use a diff inspired output format
* When suggesting addition, use `+` as underline
* Color highlight modified span
Replace associated item bound vars with placeholders when projecting
Fixes#76407Fixes#76826
Similar, but more limited, to #85499. This allows us to handle things like `for<'a> <T as Trait>::Assoc<'a>` but not `for<'a> <T as Trait<'a>>::Assoc`, unblocking GATs.
r? `@nikomatsakis`
This is step 2 towards fixing #77548.
In the codegen and codegen-units test suites, the `//` comment markers
were kept in order not to affect any source locations. This is because
these tests cannot be automatically `--bless`ed.
Add lint for 2229 migrations
Implements the first for RFC 2229 where we make the decision to migrate a root variable based on if the type of the variable needs Drop and if the root variable would be moved into the closure when the feature isn't enabled.
r? `@nikomatsakis`
