Implement special-cased projection error message for some common traits #98863
Conversation
rustbot
added
the
T-compiler
|
r? @estebank (rust-highfive has picked a reviewer for you, use r? to override) |
rust-highfive
added
the
S-waiting-on-review
|
☔ The latest upstream changes (presumably #98482) made this pull request unmergeable. Please resolve the merge conflicts. |
compiler-errors
force-pushed
the
projection-msg
branch
from
98197f5
to
a1dcb95
Compare
| )) | ||
| } else if Some(trait_def_id) == self.tcx.get_diagnostic_item(sym::Iterator) { | ||
| Some(format!( | ||
| "expected `{self_ty}` to be an iterator of `{expected_ty}`, but it actually returns items of `{normalized_ty}`" |
There was a problem hiding this comment.
I'm less enthusiastic about the wording "expected foo to be an iterator of i32 but it actually returns items of u32", because it feels we're mixing up concepts here. We could use "yields items of u32" instead, but yield isn't a keyword people will know from Rust (yet).
What about "expected foo to be an iterator over items of type i32 but it is an iterator over items of type u32"?
There was a problem hiding this comment.
I think "yield" is okay here since it doesn't necessarily imply connection to the yield kw, but I can just use "over".
There was a problem hiding this comment.
What do you think of
expected `foo` to be an iterator that yields `i32` but it yields `u32`
| )) | ||
| } else if Some(trait_def_id) == self.tcx.lang_items().future_trait() { | ||
| Some(format!( | ||
| "expected `{self_ty}` to be a future that yields `{expected_ty}`, but it actually yields `{normalized_ty}`" |
There was a problem hiding this comment.
Maybe the same about using "yields" to talk about the Future::Output? What about "...to be a future that resolves to ty, but it resolves to ty".
Let's also drop the "actually". It doesn't add as much to the messaging, I feel.
|
I can apply these messaging changes, the ones I wrote originally were just kinda there to demonstrate the concept. @rustbot author |
rustbot
added
S-waiting-on-author
compiler-errors
force-pushed
the
projection-msg
branch
from
a1dcb95
to
3fdf3cb
Compare
|
@rustbot ready Adjusted the wording, what do you think now? Open to more changes if needed. |
rustbot
added
S-waiting-on-review
| @@ -22,19 22,22 @@ LL | where | |||
| LL | F: for<'r> T0<'r, (<Self as Ty<'r>>::V,), O = <B as Ty<'r>>::V>, | |||
| | ^^^^^^^^^^^^^^^^^^^^ required by this bound in `T1::m` | |||
|
|
|||
| error[E0271]: type mismatch resolving `for<'r> <[closure@$DIR/issue-62203-hrtb-ice.rs:42:17: 42:20] as FnOnce<((&'r u8,),)>>::Output == Unit3` | |||
| error[E0271]: expected `[closure@$DIR/issue-62203-hrtb-ice.rs:42:16: 42:19]` to be a closure that returns `Unit3`, but it returns `Unit4` | |||
There was a problem hiding this comment.
Not for this PR: I would love to instead say "expected the closure to return Unit3..." and have a span label pointing at the closure, but we need to improve that in general.
| @@ -1,7 1,7 @@ | |||
| error[E0271]: type mismatch resolving `<fn() -> impl Sized {hi} as FnOnce<()>>::Output == Box<u8>` | |||
| --> $DIR/issue-98608.rs:4:39 | |||
| error[E0271]: expected `fn() -> impl Sized {hi}` to be a fn item that returns `Box<u8>`, but it returns `impl Sized` | |||
There was a problem hiding this comment.
Similarly here, we could refer to the function by name
expected `hi` to return `Box<u8>`, but it returns `impl Sized`
|
@bors r |
bors
added
S-waiting-on-bors
|
☀️ Test successful - checks-actions |
|
Finished benchmarking commit (f03ce30): comparison url. Instruction countThis benchmark run did not return any relevant results for this metric. Max RSS (memory usage)Results
CyclesThis benchmark run did not return any relevant results for this metric. If you disagree with this performance assessment, please file an issue in rust-lang/rustc-perf. @rustbot label: -perf-regression Footnotes |
Not sure what the best phrasing is, but I feel like these are more clear than the plain
<Type as Iterator>::Output == Typemessages.If this is actually a good idea, are there any other traits this could benefit?