…EFS.

Signed-off-by: Yuki Okushi <jtitor@2k36.org>

… r=thomcc

Add assertion that `transmute_copy`'s U is not larger than T

This is called out as a safety requirement in the docs, but because knowing this can be done at compile time and constant folded (just like the `align_of` branch is removed), we can just panic here.

I've looked at the asm (using `cargo-asm`) of a function that both is correct and incorrect, and the panic is completely removed, or is unconditional, without needing build-std.

I don't expect this to cause much breakage in the wild. I scanned through https://miri.saethlin.dev/ub for issues that would look like this (error: Undefined Behavior: memory access failed: alloc1768 has size 1, so pointer to 8 bytes starting at offset 0 is out-of-bounds), but couldn't find any.

That doesn't rule out it happening in crates tested that fail earlier for some other reason, though, but it indicates that doing this is rare, if it happens at all. A crater run for this would need to be build and test, since this is a runtime thing.

Also added a few more transmute_copy tests.

…and-map, r=nagisa

Remove the unused StableSet and StableMap types from rustc_data_structures.

The current implementation is not "stable" in the same sense that `HashStable` and `StableHasher` are stable, i.e. across compilation sessions. So, in my opinion, it's better to remove those types (which are basically unused anyway) than to give the wrong impression that these are safe for incr. comp.

I plan to provide new "stable" collection types soon that can be used to replace `FxHashMap` and `FxHashSet` in query results (see [draft](michaelwoerister@69d03ac)). It's unsound that `HashMap` and `HashSet` implement `HashStable` (see rust-lang#98890 for a recent P-critical bug caused by this) -- so we should make some progress there.

add missing null ptr check in alloc example

`alloc` can return null on OOM, if I understood correctly. So we should never just deref a pointer we get from `alloc`.

…rrors

Add regression test for rust-lang#95230

Closes rust-lang#95230
r? `@compiler-errors`

Signed-off-by: Yuki Okushi <jtitor@2k36.org>