…d a long lost assertion

This reverts part of commit 9712fa4.

Co-Authored-By: Ralf Jung <[email protected]>

This commit modifies the use of `subst_and_normalize_erasing_regions` on
parts of the MIR bodies returned from `instance_mir`, so that
`InstanceDef::CloneShim` and `InstanceDef::DropGlue` (where there is a
type) do not perform substitutions. This avoids double substitutions and
enables polymorphic `InstanceDef`s.

Signed-off-by: David Wood <[email protected]>

Fixes rust-lang#55099

The minimized reproducer in issue rust-lang#55099 now compiles successfully.
This commit adds a regression test for it.

patch is required to avoid compiler errors by building src/libpanic_unwind/hermit.rs

As discussed on reddit, this commit addresses two issues with the
documentation of `mem::forget()`:

* The documentation of `mem::forget()` can confuse the reader because of the
  discrepancy between usage examples that show correct usage and the
  accompanying text which speaks of the possibility of double-free.  The
  text that says "if the panic occurs before `mem::forget` was called"
  refers to a variant of the second example that was never shown, modified
  to use `mem::forget` instead of `ManuallyDrop`.  Ideally the documentation
  should show both variants, so it's clear what it's talking about.

  Also, the double free could be fixed just by placing `mem::forget(v)`
  before the construction of `s`.  Since the lifetimes of `s` and `v`
  wouldn't overlap, there would be no point where panic could cause a double
  free.  This could be mentioned, and contrasted against the more robust fix
  of using `ManuallyDrop`.

* This sentence seems unjustified: "For some types, operations such as
  passing ownership (to a funcion like `mem::forget`) requires them to
  actually be fully owned right now [...]".  Unlike C++, Rust has no move
  constructors, its moves are (possibly elided) bitwise copies.  Even if you
  pass an invalid object to `mem::forget`, no harm should come to pass
  because `mem::forget` consumes the object and exists solely to prevent
  drop, so there no one left to observe the invalid state state.

…m::forget.

As pointed out by Ralf Jung, dangling references and boxes are
undefined behavior as per
https://doc.rust-lang.org/reference/behavior-considered-undefined.html
and the Miri checker.

Co-Authored-By: Ralf Jung <[email protected]>

Co-Authored-By: lzutao <[email protected]>

Clarify the relationship between `forget()` and `ManuallyDrop`.

As discussed on reddit, this commit addresses two issues with the
documentation of `mem::forget()`:

* The documentation of `mem::forget()` can confuse the reader because of the
  discrepancy between usage examples that show correct usage and the
  accompanying text which speaks of the possibility of double-free.  The
  text that says "if the panic occurs before `mem::forget` was called"
  refers to a variant of the second example that was never shown, modified
  to use `mem::forget` instead of `ManuallyDrop`.  Ideally the documentation
  should show both variants, so it's clear what it's talking about.

  Also, the double free could be fixed just by placing `mem::forget(v)`
  before the construction of `s`.  Since the lifetimes of `s` and `v`
  wouldn't overlap, there would be no point where panic could cause a double
  free.  This could be mentioned, and contrasted against the more robust fix
  of using `ManuallyDrop`.

* This sentence seems unjustified: "For some types, operations such as
  passing ownership (to a funcion like `mem::forget`) requires them to
  actually be fully owned right now [...]".  Unlike C++, Rust has no move
  constructors, its moves are (possibly elided) bitwise copies.  Even if you
  pass an invalid object to `mem::forget`, no harm should come to pass
  because `mem::forget` consumes the object and exists solely to prevent
  drop, so there no one left to observe the invalid state state.

…lfJung

Compute the correct layout for variants of uninhabited enums

r? @eddyb
cc @RalfJung

fixes rust-lang#69191
cc rust-lang#69763

codegen/mir: support polymorphic `InstanceDef`s

cc rust-lang#69925

This PR modifies the use of `subst_and_normalize_erasing_regions` on parts of the MIR bodies returned from `instance_mir`, so that `InstanceDef::CloneShim` and `InstanceDef::DropGlue` (where there is a type) do not perform substitutions. This avoids double substitutions and enables polymorphic `InstanceDef`s.

r? @eddyb
cc @nikomatsakis

…an-DPC

Clean up E0437 explanation

r? @Dylan-DPC

…ikomatsakis

Add regression test for TAIT lifetime inference (issue rust-lang#55099)

Fixes rust-lang#55099

The minimized reproducer in issue rust-lang#55099 now compiles successfully.
This commit adds a regression test for it.

…atsakis

remove unused imports

patch is required to avoid compiler errors by building src/libpanic_unwind/hermit.rs

doc: Add quote to .init_array

The current formatting is not good without quotes:
![without-quote](https://i.imgur.com/RkIm4cr.png)

…an-DPC

Clean up e0438 explanation

r? @Dylan-DPC

…rk-Simulacrum

triagebot.toml: accept cleanup-crew

r? @Mark-Simulacrum