[NLL] Suggest let binding
Closes#49821
Also adds an alternative to `explain_why_borrow_contains_point` that allows changing error messages based on the reason that will be given. This will also be useful for #51026, #51169 and maybe further changes to does not live long enough messages.
dead-code lint: say "constructed" for structs
Respectively.
This is a sequel to November 2017's #46103 / 1a9dc2e9. It had been
reported (more than once—at least #19140, #44083, and #44565) that the
"never used" language was confusing for enum variants that were "used"
as match patterns, so the wording was changed to say never "constructed"
specifically for enum variants. More recently, the same issue was raised
for structs (#52325). It seems consistent to say "constructed" here,
too, for the same reasons.
~~While we're here, we can also use more specific word "called" for unused
functions and methods. (We declined to do this in #46103, but the
rationale given in the commit message doesn't actually make sense.)~~
This resolves#52325.
(Presumably the place that borrow_check ends up reporting for the
error about is no longer the root `Local` itself, and thus the note
diagnostic here stops firing.)
NLL: sort diagnostics by span
Sorting the output diagnostics by span is a long planned revision to the NLL diagnostics that we hope will yield a less surprising user experience in some case.
Once we got them buffered, it was trivial to implement. (The hard part is skimming the resulting changes to the diagnostics to make sure nothing broke... Note that I largely rubber-stamped the `#[rustc_regions]` output change.)
Fix#51167
Don't match on region kinds when reporting NLL errors
First half (by number of tests affected) of the changes to "does not live long enough".
Now that lexical MIR borrowck is gone, region kinds are always ReVar, so matching on them to change errors does nothing.
Changes "borrowed value only lives until here" to "`x` is dropped here while still borrowed".
r? @pnkfelix cc @nikomatsakis
Do not suggest using `to_owned()` on `&str += &str`
- Don't provide incorrect suggestion for `&str += &str` (fix#52410)
- On `&str + String` suggest `&str.to_owned() + &String` as a single suggestion
This is a sequel to November 2017's #46103 / 1a9dc2e9. It had been
reported (more than once—at least #19140, #44083, and #44565) that the
"never used" language was confusing for enum variants that were "used"
as match patterns, so the wording was changed to say never
"constructed" specifically for enum variants. More recently, the same
issue was raised for structs (#52325). It seems consistent to say
"constructed" here, too, for the same reasons.
We considered using more specific word "called" for unused functions
and methods (while we declined to do this in #46103, the rationale
given in the commit message doesn't actually make sense), but it turns
out that Cargo's test suite expects the "never used" message, and
maybe we don't care enough even to make a Cargo PR over such a petty
and subjective wording change.
This resolves#52325.
When encountering an unexisting method for a given trait where an
associated function has the same name, suggest using the appropriate
syntax, instead of using `help` text.
When only one candidate is found, do not call it "candidate #1", just
call it "the candidate".
This PR improves the span of eager resolution type errors referring to indexing and field access to use the base span rather than the whole expression.
Also a note "Type must be known at this point." is added to where we at some point in the past emitted the "type must be known at this context" error, so that early failures can be differentiated and will hopefully be less surprising.
Fixes#50692 (or at least does the best we can for the moment)
r? @estebank
This commit only applies the flag to the one test case,
ui/span/dropck_vec_cycle_checked.rs, that absolutely needs it. Without
the flag, that test takes an unknown amount of time (greater than 1
minute) to compile. But its possible that other tests would also
benefit from the flag, and we may want to make it the default (after
evaluating its impact on other tests).
In terms of its known impact on other tests, I have only evaluated the
ui tests, and the *only* ui test I have found that the flag impacts
(running under NLL mode, of course), is src/test/ui/nll/issue-31567.rs
In particular:
```
% ./build/x86_64-unknown-linux-gnu/stage1/bin/rustc ../src/test/ui/nll/issue-31567.rs
error[E0597]: `*v.0` does not live long enough
--> ../src/test/ui/nll/issue-31567.rs:22:26
|
22 | let s_inner: &'a S = &*v.0; //~ ERROR `*v.0` does not live long enough
| ^^^^^ borrowed value does not live long enough
23 | &s_inner.0
24 | }
| - borrowed value only lives until here
|
note: borrowed value must be valid for the lifetime 'a as defined on the function body at 21:1...
--> ../src/test/ui/nll/issue-31567.rs:21:1
|
21 | fn get_dangling<'a>(v: VecWrapper<'a>) -> &'a u32 {
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
error: aborting due to previous error
For more information about this error, try `rustc --explain E0597`.
% ./build/x86_64-unknown-linux-gnu/stage1/bin/rustc ../src/test/ui/nll/issue-31567.rs -Z nll-subminimal-causes
error[E0597]: `*v.0` does not live long enough
--> ../src/test/ui/nll/issue-31567.rs:22:26
|
22 | let s_inner: &'a S = &*v.0; //~ ERROR `*v.0` does not live long enough
| ^^^^^ borrowed value does not live long enough
23 | &s_inner.0
24 | }
| -
| |
| borrowed value only lives until here
| borrow later used here, when `v` is dropped
error: aborting due to previous error
For more information about this error, try `rustc --explain E0597`.
%
```
NOTE: I was careful to make each change in a manner that preserves the
existing diagnostic output (usually by ensuring that no lines were
added or removed). This means that the resulting source files are not
as nice to read as they were at the start. But we will have to review
these cases by hand anyway as follow-up work, so cleanup could
reasonably happen then (or not at all).
Stabilize the copy_closures and clone_closures features
In addition to the `Fn*` family of traits, closures now implement `Copy` (and similarly `Clone`) if all of the captures do.
Tracking issue: https://github.com/rust-lang/rust/issues/44490
