Make transmuting from fn item types to pointer-sized types a hard error.
Closes#19925 by removing the future compatibility lint and the associated workarounds.
This is a `[breaking-change]` if you `transmute` from a function item without casting first.
For more information on how to fix your code, see https://github.com/rust-lang/rust/issues/19925.
Deny (by default) transmuting from fn item types to pointer-sized types.
This sets the #19925 lint (transmute from zero-sized fn item type) to `deny` by default.
Technically a `[breaking-change]`, but will not affect dependent crates because of `--cap-lints`.
This is a [breaking-change]: according to RFC #1445, constants used as
patterns must be of a type that *derives* `Eq`. If you encounter a
problem, you are most likely using a constant in an expression where the
type of the constant is some struct that does not currently implement
`Eq`. Something like the following:
```rust
struct SomeType { ... }
const SOME_CONST: SomeType = ...;
match foo {
SOME_CONST => ...
}
```
The easiest and most future compatible fix is to annotate the type in
question with `#[derive(Eq)]` (note that merely *implementing* `Eq` is
not enough, it must be *derived*):
```rust
struct SomeType { ... }
const SOME_CONST: SomeType = ...;
match foo {
SOME_CONST => ...
}
```
Another good option is to rewrite the match arm to use an `if`
condition (this is also particularly good for floating point types,
which implement `PartialEq` but not `Eq`):
```rust
match foo {
c if c == SOME_CONST => ...
}
```
Finally, a third alternative is to tag the type with
`#[structural_match]`; but this is not recommended, as the attribute is
never expected to be stabilized. Please see RFC #1445 for more details.
This adds back the raw_pointer_derive lint as a 'removed' lint, so that its removal does not cause errors (#30346) but warnings.
In the process I discovered regressions in the code for renamed and removed lints, which didn't appear to have any tests. The addition of a second lint pass (ast vs. hir) meant that attributes were being inspected twice, renamed and removed warnings printed twice. I restructured the code so these tests are only done once and added tests. Unfortunately it makes the patch more complicated for the needed beta backport.
r? @nikomatsakis
[breaking-change] for lint authors
You must now implement LateLintPass or EarlyLintPass as well as LintPass and use either register_late_lint_pass or register_early_lint_pass, rather than register_lint_pass.
