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Highlight parts of fn in type errors
When a type error arises between two fn items, fn pointers or tuples,
highlight only the differing parts of each.
Examples:
<img width="699" alt="" src="https://user-images.githubusercontent.com/1606434/69487597-ab561600-0e11-11ea-9b4e-d4fd9e91d5dc.png">
<img width="528" alt="" src="https://user-images.githubusercontent.com/1606434/69487207-9033d800-0e0a-11ea-93e3-8c4d002411a5.png">
<img width="468" alt="" src="https://user-images.githubusercontent.com/1606434/69487208-9033d800-0e0a-11ea-92e3-2b2cee120335.png">
<img width="775" alt="" src="https://user-images.githubusercontent.com/1606434/69487209-9033d800-0e0a-11ea-9e68-7f6ed5c8cb08.png">
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When a type error arises between two fn items, fn pointers or tuples,
highlight only the differing parts of each.
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This creates a new test directory, `ui/consts/control-flow` to hold
tests related to control flow in a const context. It also blesses all
existing tests with the new error messages, and adds new tests for the
`const_if_match` feature.
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Specific labels when referring to "expected" and "found" types
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Also remove `never_type` the feature-gate test.
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Add long error explanation for E0594
Part of #61137.
r? @Dylan-DPC
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Add outlives suggestions for some lifetime errors
This PR implements suggestion diagnostics for some lifetime mismatch errors. When the borrow checker finds that some lifetime 'a doesn't outlive some other lifetime 'b that it should outlive, then in addition to the current lifetime error, we also emit a suggestion for how to fix the problem by adding a bound:
- If a and b are normal named regions, suggest to add the bound `'a: 'b`
- If b is static, suggest to replace a with static
- If b also needs to outlive a, they must be the same, so suggest unifying them
We start with a simpler implementation that avoids diagnostic regression or implementation complexity:
- We only makes suggestions for lifetimes the user can already name (eg not closure regions or elided regions)
- For now, we only emit a help note, not an actually suggestion because it is significantly easier.
Finally, there is one hack: it seems that implicit regions in async fn are given the name '_ incorrectly. To avoid suggesting '_: 'x, we simply filter out such lifetimes by name.
For more info, see this internals thread:
https://internals.rust-lang.org/t/mechanical-suggestions-for-some-borrow-checker-errors/9049/3
TL;DR Make suggestions to add a `where 'a: 'b` constraint for some lifetime errors. Details are in the paper linked from the internals thread above.
r? @estebank
TODO
- [x] Clean up code
- [x] Only make idiomatic suggestions
- [x] don't suggest naming `&'a self`
- [x] rather than `'a: 'static`, suggest replacing `'a` with `'static`
- [x] rather than `'a: 'b, 'b: 'a`, suggest replacing `'a` with `'b` or vice versa
- [x] Performance (maybe need a perf run when this is closer to the finish line?)
- perf run was clean...
- EDIT: perf run seems to only check non-error performance... How do we check that error performance didn't regress?
- [x] Needs ui tests
- [x] Integrate the `help` message into the main lifetime `error`
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Add long error explanation for E0623
Part of #61137.
r? @Dylan-DPC
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This fixes some ordering problems around assignment expressions.
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An expression like `x[1][{ x = y; 2}]` would perform the bounds check
for the inner index operation before evaluating the outer index. This
would allow out of bounds memory accesses.
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Make the spacing between the code snippet and verbose structured
suggestions consistent with note and help messages.
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Fix most remaining Polonius test differences
This fixes most of the Polonius test differences and also avoids overflow in issue-38591.rs.
r? @nikomatsakis
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This fixes some test differences and also avoids overflow in
issue-38591.rs.
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Error explanation e0524
Part of https://github.com/rust-lang/rust/issues/61137
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Fix backticks in documentation
Fix a few typos in comments/documentation where backticks were doubled-up on one side.
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Polonius
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Stabilize `bind_by_move_pattern_guards` in Rust 1.39.0
Closes https://github.com/rust-lang/rust/issues/15287.
After stabilizing `#![feature(bind_by_move_pattern_guards)]`, you can now use bind-by-move bindings in patterns and take references to those bindings in `if` guards of `match` expressions. For example, the following now becomes legal:
```rust
fn main() {
let array: Box<[u8; 4]> = Box::new([1, 2, 3, 4]);
match array {
nums
// ---- `nums` is bound by move.
if nums.iter().sum::<u8>() == 10
// ^------ `.iter()` implicitly takes a reference to `nums`.
=> {
drop(nums);
// --------- Legal as `nums` was bound by move and so we have ownership.
}
_ => unreachable!(),
}
}
```
r? @matthewjasper
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Fixed grammar/style in some error messages
Factored out from hacking on rustc for work on the REPL.
r? @Centril
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It can return `Err` due to macros being expanded across crates or
files.
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Make use of possibly uninitialized data [E0381] a hard error
This is one of the behaviors we no longer allow in NLL. Since it can
lead to undefined behavior, I think it's definitely worth making it a
hard error without waiting to turn off migration mode (#58781).
Closes #60450.
My ulterior motive here is making it impossible to leave variables
partially initialized across a yield (see #60889, discussion at #63035), so
tests are included for that.
cc #54987
---
I'm not sure if bypassing the buffer is a good way of doing this. We could also make a `force_errors_buffer` or similar that gets recombined with all the errors as they are emitted. But this is simpler and seems fine to me.
r? @Centril
cc @cramertj @nikomatsakis @pnkfelix @RalfJung
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This is one of the behaviors we no longer allow in NLL. Since it can
lead to undefined behavior, I think it's definitely worth making it a
hard error without waiting to turn off migration mode (#58781).
Closes #60450.
My ulterior motive here is making it impossible to leave variables
partially initialized across a yield (see discussion at #63035), so
tests are included for that.
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Avoid ICE when referencing desugared local binding in borrow error
To avoid leaking the names of local bindings from expressions like for loops, #60984 explicitly ignored them, but an assertion that `LocalKind::Var` *must* have a name would trigger an ICE.
Before this change, the binding generated by desugaring the for loop would leak into the diagnostic (#63027):
```
error[E0515]: cannot return value referencing local variable `__next`
--> return-local-binding-from-desugaring.rs:LL:CC
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LL | for ref x in xs {
| ----- `__next` is borrowed here
...
LL | result
| ^^^^^^ returns a value referencing data owned by the current function
```
Ideally `LocalKind` would carry more information to more accurately explain the problem, but for now, in order to avoid the ICE (fix #63026), we accept `LocalKind::Var` without a name and produce the following output:
```
error[E0515]: cannot return value referencing local binding
--> $DIR/return-local-binding-from-desugaring.rs:30:5
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LL | for ref x in xs {
| -- local binding introduced here
...
LL | result
| ^^^^^^ returns a value referencing data owned by the current function
```
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Polonius
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