Improve E0308 error message wording again
Hello again,
I recently did this PR: #70242
I felt the error message could be further improved, so I made [a post on the Rust community forum](https://users.rust-lang.org/t/looking-for-feedback-on-an-improved-error-message-for-e0308/40004) to ask for feedback.
(Also, there were some comments on my original PR that I took into consideration as well.)
This PR is my attempt to take all the feedback into account and propose a better and simplified error message that should still be accurate. Its main benefit is having simpler grammar, and hopefully being easier to read and understand.
Thanks to everyone who commented and gave feedback, and thank you for taking a look at this PR.
Reading from the return place is fine
Const eval thinks that reading from local `_0` is UB, but it isn't. `_0` is just a normal local like any other, and codegen handles it that way too. The only special thing is that the `Return` terminator will read from it.
I've hit these errors while working on an NRVO pass that can merge other locals with `_0` in https://github.com/rust-lang/rust/pull/71003.
r? @oli-obk
proc_macro::is_available()
This PR adds `proc_macro::is_available() -> bool` to determine whether proc_macro has been made accessible to the currently running program.
The proc_macro crate is only intended for use inside the implementation of procedural macros. All the functions in the crate panic if invoked from outside of a procedural macro, such as from a build script or unit test or ordinary Rust binary.
Unfortunately those panics made it impossible for libraries that are designed to support both macro and non-macro use cases (e.g. Syn) to be used from binaries that are compiled with panic=abort. In panic=unwind mode we're able to attempt a proc macro call inside catch_unwind and use libproc_macro's result if it succeeds, otherwise fall back to a non-macro alternative implementation. But in panic=abort there was no way to determine which implementation needs to be used.
r? @eddyb
attn: @petrochenkov @adetaylor
ref: https://github.com/dtolnay/cxx/issues/130
Lint must_use on mem::replace
This adds a hint on `mem::replace`, "if you don't need the old value,
you can just assign the new value directly". This is in similar spirit
to the `must_use` on `ManuallyDrop::take`.
Added detailed error code explanation for issue E0696 in Rust compiler.
Added proper error explanation for issue E0696 in the Rust compiler.
Error Code E0696
Sub Part of Issue #61137
r? @GuillaumeGomez
Exhaustively match on `{Statement,Terminator}Kind` during const checking
This adds a pre-monomorphization error for inline assembly in a const context as well.
r? @oli-obk
Clarify unused_doc_comments note on macro invocations
The previous error message used to say:
<pre>
/// doc
^^^^^^^ rustdoc does not generate documentation for <b>macros</b>
</pre>
Obviously we do generate documentation for macros, such as https://docs.rs/bitflags/1.2.1/bitflags/macro.bitflags.html. It's only macro invocations that don't get their own docs. This PR updates the message to say "rustdoc does not generate documentation for <b>macro invocations</b>".
I observe that prior to #69084 this used to say "rustdoc does not generate documentation for **macro expansions**", as implemented originally in #57882. I don't have a preference between those but I made the commit before looking up the history.
r? @Manishearth
attn: @yaahc @euclio
Detect mistyped associated consts in `Instance::resolve`.
*Based on #71049 to prevent redundant/misleading downstream errors.*
Fixes#70942 by refusing to resolve an associated `const` if it doesn't have the same type in the `impl` that it does in the `trait` (which we assume had errored, and `delay_span_bug` guards against bugs).
Suggest `-> impl Trait` and `-> Box<dyn Trait>` on fn that doesn't return
During development, a function could have a return type set that is a
bare trait object by accident. We already suggest using either a boxed
trait object or `impl Trait` if the return paths will allow it. We now
do so too when there are *no* return paths or they all resolve to `!`.
We still don't handle cases where the trait object is *not* the entirety
of the return type gracefully.
Closes#38376.
Check that main/start is not async
* Add new error code E0752
* Add span to hir::IsAsync::Yes
* Emit an error if main or the start function is marked as async
* Add two regression tests
This PR fixes#68523.
When the return type is `!Sized` we look for all the returned
expressions in the body to fetch their types and provide a reasonable
suggestion. The tail expression of the body is normally evaluated after
checking whether the return type is `Sized`. Changing the order of the
evaluation produces undesirable knock down effects, so we detect the
specific case that newcomers are likely to encounter ,returning a single
bare trait object, and only in that case we evaluate the tail
expression's type so that the suggestion will be accurate.
During development, a function could have a return type set that is a
bare trait object by accident. We already suggest using either a boxed
trait object or `impl Trait` if the return paths will allow it. We now
do so too when there are *no* return paths or they all resolve to `!`.
We still don't handle cases where the trait object is *not* the entirety
of the return type gracefully.
* Add new error code E0752
* Add span to hir::IsAsync::Yes
* Emit an error if main or the start function is marked as async
* Add two regression tests
Fix formatting errors and bless test outputs
* move tests to ui/async-await
fix test error text
remove span from IsAsync
Deprecate the asm! macro in favor of llvm_asm!
Since we will be changing the syntax of `asm!` soon, deprecate it and encourage people to use `llvm_asm!` instead (which preserves the old syntax). This will avoid breakage when `asm!` is changed.
RFC: https://github.com/rust-lang/rfcs/pull/2843
Make `needs_drop` less pessimistic on generators
Generators only have non-trivial drop logic when they may store (in upvars or across yields) a type that does.
This prevents generation of some unnecessary MIR in simple generators. There might be some impact on compile times, but this is probably limited in real-world applications.
~~This builds off of https://github.com/rust-lang/rust/pull/69814 since that contains some fixes that are made relevant by *this* PR (see https://github.com/rust-lang/rust/pull/69814#issuecomment-599147269).~~ (this has been merged)
Maintain chain of derived obligations
When evaluating the derived obligations from super traits, maintain a
reference to the original obligation in order to give more actionable
context in the output.
Continuation (and built on) #69745, subset of #69709.
r? @eddyb
When evaluating the derived obligations from super traits, maintain a
reference to the original obligation in order to give more actionable
context in the output.
miri-unleashed: test that we detect heap allocations
This removes the second-to-last use of `IS_SUPPORTED_IN_MIRI = false`.
r? @ecstatic-morse @oli-obk
