Because we're writing to a file, so `FileEncoder` is better because we
don't have to write all the data to memory first.

The suggestion given by `FIXME` to use `CompilerMetadata` for
`download_toolchain` in `bootstrap::download` can result in more
confusion. This is because `stamp_key` is not always a date; it
can also be a commit hash. Additionally, unlike in `download_beta_toolchain`,
in the `download_ci_rustc` function, `version` and `commit` values
are calculated separately.

Signed-off-by: ozkanonur <work@onurozkan.dev>

Round-trip encoding/decoding of many types is tested in
`compiler/rustc_serialize/tests/opaque.rs`. There is also a small amount
of encoding/decoding testing in three files in `tests/ui-fulldeps`.

There is no obvious reason why these three files are necessary. They
were originally added in 2014. Maybe it wasn't possible for a proc
macro to run in a unit test back then?

This commit just moves the testing from those three files into the unit
test.

It's only used in tests. Which is bad, because it means that
`FileEncoder` is used in the compiler but isn't used in tests!

`tests/opaque.rs` now tests encoding/decoding round-trips via file.
Because this is slower than memory, this commit also adjusts the
`u16`/`i16` tests so they are more like the `u32`/`i32` tests, i.e. they
don't test every possible value.

I don't like the current wording. It's obnoxious to be told by a bot
that a change I made intentionally is "probably unintentional"! I also
don't like describing unintentional changes as "Random", it's not the
right word.

This can be done by simply changing the `\??\` prefix to `\\?\` and then attempting to convert to a user path.

Currently it simply strips off the prefix which could lead to the wrong path being returned (e.g. if it's not a drive path or if the path contains trailing spaces, etc).

Correctly convert an NT path to a Win32 path in `read_link`

This can be done by simply changing the `\??\` prefix to `\\?\`.

Currently it strips off the prefix which could lead to the wrong path being returned (e.g. if it's not a drive path or if the path contains trailing spaces, etc).

r? libs

…, r=pietroalbini

Support loading version information from xz tarballs

This is intended to allow us to move recompression from xz (produced in CI) to gz after an initial manifest run, which produces a list of actually required artifacts. The rest are then deleted, which means that we can avoid recompressing them, saving a bunch of time.

This is essentially untested and more might be needed, will run a patched promote-release against try artifacts from this PR. If we do go ahead with this we'll either need to backport this patch to beta/stable, wait for it to propagate, or temporarily recompress to gzip but not xz tarballs (or similar).

r? `@pietroalbini`

…=oli-obk

Implement negative bounds for internal testing purposes

Implements partial support the `!` negative polarity on trait bounds. This is incomplete, but should allow us to at least be able to play with the feature.

Not even gonna consider them as a public-facing feature, but I'm implementing them because would've been nice to have in UI tests, for example in rust-lang#110671.

… r=oli-obk

Adjust obligation cause code for `find_and_report_unsatisfied_index_impl`

Makes the error message a bit easier to read.

…-errors

resolve: One more attempt to simplify `module_children`

If the next step is performed and `fn module_children_local` is merged with the `module_children` query, then it causes perf regressions, regardless of whether query result feeding is [used](https://perf.rust-lang.org/compare.html?start=43a78029b4f4d92978b8fde0a677ea300b113c41&end=2eb5bcc5068b9d92f74bcb1797da664865d6981d&stat=instructions:u) or [not](https://perf.rust-lang.org/compare.html?start=2fce2290865f012391b8f3e581c3852a248031fa&end=2a33d6cd99481d1712037a79e7d66a8aefadbf72&stat=instructions:u).

…, r=oli-obk

interpret: fail more gracefully on uninit unsized locals

r? `@oli-obk`

Fixes rust-lang#68538

…r=petrochenkov

Don't bail out early when checking invalid `repr` attr

Fixes rust-lang#111051

An invalid repr delays a bug. If there are other invalid attributes on the item, we emit a warning and exit without re-checking the repr here, so no error is emitted and the delayed bug ICEs

…r=albertlarsan68

remove pointless `FIXME` in `bootstrap::download`

The suggestion given by `FIXME` to use `CompilerMetadata` for `download_toolchain` in `bootstrap::download` can result in more confusion. This is because `stamp_key` is not always a date; it can also be a commit hash. Additionally, unlike in `download_beta_toolchain`, in the `download_ci_rustc` function, `version` and `commit` values are calculated separately.

Remove `MemEncoder`

`MemEncoder` only has one non-test use, and `FileEncoder` would be more appropriate there anyway.

r? ``@cjgillot``

Avoid ICEing miri on layout query cycles

Miri has special logic for catching panics during interpretation. Raising a fatal error in rustc uses unwinding to abort compilation. Thus miri ends up catching that fatal error and thinks it saw an ICE. While we should probably change that to ignore `Fatal` payloads, I think it's also neat to continue compilation after a layout query cycle 😆

Query cycles now (in addition to reporting an error just like before), return `Err(Cycle)` instead of raising a fatal error. This allows the interpreter to wind down via the regular error paths.

r? `@RalfJung` for a first round, feel free to reroll for the compiler team once the miri side looks good

…errors

Add some triagebot notifications for nnethercote.

r? ````@compiler-errors````