Rebase resume argument projections during state transform
When remapping a resume argument with projections rebase them on top of
the new base.
The case where resume argument has projections is unusual, but might
arise with box syntax where the assignment is performed directly into
the box without an intermediate temporary.
Fixes#85635.
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.
When remapping a resume argument with projections rebase them on top of
the new base.
The case where resume argument has projections is unusual, but might
arise with box syntax where the assignment is performed directly into
the box without an intermediate temporary.
This PR has several interconnected pieces:
1. In some of the NLL region error code, we now pass
around an `ObligationCause`, instead of just a plain `Span`.
This gets forwarded into `fulfill_cx.register_predicate_obligation`
during error reporting.
2. The general InferCtxt error reporting code is extended to
handle `ObligationCauseCode::BindingObligation`
3. A new enum variant `ConstraintCategory::Predicate` is added.
We try to avoid using this as the 'best blame constraint' - instead,
we use it to enhance the `ObligationCause` of the `BlameConstraint`
that we do end up choosing.
As a result, several NLL error messages now contain the same
"the lifetime requirement is introduced here" message as non-NLL
errors.
Having an `ObligationCause` available will likely prove useful
for future improvements to NLL error messages.
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.
Improve error message for type mismatch in generator arguments
Fixes#88653. The code example given there is invalid because the `Generator` trait (unlike the `Fn` traits) does not take the generator arguments in tupled-up form (because there can only be one argument, from my understanding). Hence, the type error in the example in #88653 is correct, because the given generator takes a `bool` argument, whereas the function's return type talks about a generator with a `(bool,)` argument.
The error message is both confusing and wrong, though: It is wrong because it displays the wrong "expected signature", and it is confusing because both the "expected" and "found" notes point at the same span. With my changes, I get the following, more helpful output:
```
error[E0631]: type mismatch in generator arguments
--> test.rs:5:22
|
5 | fn foo(bar: bool) -> impl Generator<(bool,)> {
| ^^^^^^^^^^^^^^^^^^^^^^^ expected signature of `fn((bool,)) -> _`
6 | |bar| {
| ----- found signature of `fn(bool) -> _`
```
Don't mark `if_let_guard` as an incomplete feature
I don't think there is any reason for `if_let_guard` to be an incomplete feature, and I think the reason they were marked in the first place was simply because they weren't implemented at all.
r? `@pnkfelix`
cc tracking issue #51114
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)
* Always point at macros, including derive macros
* Point at non-local items that introduce a trait requirement
* On private associated item, point at definition
Fix expected/found order on impl trait projection mismatch error
fixes#68561
This PR adds a new `ObligationCauseCode` used when checking the concrete type of an impl trait satisfies its bounds, and checks for that cause code in the existing test to see if a projection's normalized type should be the "expected" or "found" type.
The second commit adds a `peel_derives` to that test, which appears to be necessary in some cases (see projection-mismatch-in-impl-where-clause.rs, which would still give expected/found in the wrong order otherwise). This caused some other changes in diagnostics not involving impl trait, but they look correct to me.
Do not ICE when evaluating locals' types of invalid `yield`
When a `yield` is outside of a generator, check its value regardless to
avoid an ICE while trying to get all locals' types in writeback.
Fix#78653.
