Fix evaluating trivial drop glue in constants
```rust
struct A;
impl Drop for A {
fn drop(&mut self) {}
}
const FOO: Option<A> = None;
const BAR: () = (FOO, ()).1;
```
was erroring with
```
error: any use of this value will cause an error
--> src/lib.rs:9:1
|
9 | const BAR: () = (FOO, ()).1;
| ^^^^^^^^^^^^^^^^^^^^^^^^^^-^
| |
| calling non-const function `std::ptr::real_drop_in_place::<(std::option::Option<A>, ())> - shim(Some((std::option::Option<A>, ())))`
|
= note: #[deny(const_err)] on by default
error: aborting due to previous error
```
before this PR. According to godbolt this last compiled successfully in 1.27
Remove unnecessary dummy span checks
The emitter already verifies wether a given span note or span label
can be emitted to the output. If it can't, because it is a dummy
span, it will be either elided for labels or emitted as an unspanned
note/help when applicable.
The emitter already verifies wether a given span note or span label
can be emitted to the output. If it can't, because it is a dummy
span, it will be either elided for labels or emitted as an unspanned
note/help when applicable.
Stabilize `let` bindings and destructuring in constants and const fn
r? @Centril
This PR stabilizes the following features in constants and `const` functions:
* irrefutable destructuring patterns (e.g. `const fn foo((x, y): (u8, u8)) { ... }`)
* `let` bindings (e.g. `let x = 1;`)
* mutable `let` bindings (e.g. `let mut x = 1;`)
* assignment (e.g. `x = y`) and assignment operator (e.g. `x += y`) expressions, even where the assignment target is a projection (e.g. a struct field or index operation like `x[3] = 42`)
* expression statements (e.g. `3;`)
This PR does explicitly *not* stabilize:
* mutable references (i.e. `&mut T`)
* dereferencing mutable references
* refutable patterns (e.g. `Some(x)`)
* operations on `UnsafeCell` types (as that would need raw pointers and mutable references and such, not because it is explicitly forbidden. We can't explicitly forbid it as such values are OK as long as they aren't mutated.)
* We are not stabilizing `let` bindings in constants that use `&&` and `||` short circuiting operations. These are treated as `&` and `|` inside `const` and `static` items right now. If we stopped treating them as `&` and `|` after stabilizing `let` bindings, we'd break code like `let mut x = false; false && { x = true; false };`. So to use `let` bindings in constants you need to change `&&` and `||` to `&` and `|` respectively.
Update migrate warning wording.
This PR modifies the wording of the warning for backwards-incompatible changes in migrate mode. The warning messages are changed to be lowercase and not include line-breaks in order to be consistent with other compiler diagnostics.
This commit modifies the wording of the warning for
backwards-incompatible changes in migrate mode. The warning messages are
changed to be lowercase and not include line-breaks in order to be
consistent with other compiler diagnostics.
Fix various aspects around `let` bindings inside const functions
* forbid `let` bindings in const contexts that use short circuiting operators
* harden analysis code against derefs of mutable references
Initially this PR was about stabilizing `let` bindings, but too many flaws were exposed that need some more testing on nightly
