also, ensure that callers are checked.

looks like some mix of #18653 and `projection_must_outlive`, but
that needs to be investigated further (crater run?)

By RFC1214:
Before calling a fn, we check that its argument and return types are WF. This check takes place after all higher-ranked lifetimes have been instantiated. Checking the argument types ensures that the implied bounds due to argument types are correct. Checking the return type ensures that the resulting type of the call is WF.

The previous code only checked the trait-ref, which was not enough
in several cases.

As this is a soundness fix, it is a [breaking-change].

Fixes #28609

As described in https://github.com/rust-lang/rfcs/pull/1298, the idea here is to make DefIds independent of changes to the content of other items. They are also *mostly* independent from ordering, so e.g. reordering two functions will change the defids, but it will not change the paths that they expand into (but this is not the case for some things, such as impls).

This is a major refactoring, so I did it in slices. The final commit is in some sense The Big One where most of the work is done. The earlier commits just pave the way by gradually refactoring accesses to the `node` field.

This is a [breaking-change] for plugin authors. The things you need to do to migrate your code are as follows:

1. For local def-ids, rather than do `def_id.node`, call `tcx.map.as_local_node_id(def_id)`.
2. To construct a local def-id, call `tcx.map.local_def_id(node_id)`.
3. Note that you cannot make def-ids for any node, but only for "definitions" -- which include all items, as well as a number of other things, but not e.g. arbitrary expressions.
4. You can get the path to a def-id by calling `tcx.def_path(def_id)`.

One thing that is NOT part of this PR, but which I plan do in a follow-up, is converting uses of the existing `with_path` API to use `def_path`, which is basically the same.

r? @EddyB (or @nrc)

have always been returning None anyway, since it was comparing node-ids
across crates incorrectly -- and remove the now unused map
`extern_const_variants`

paths, and construct paths for all definitions. Also, stop rewriting
DefIds for closures, and instead just load the closure data from
the original def-id, which may be in another crate.

of xxx_local.

were returned, either the trait or the *self type itself*, were not
particularly representative of what the Def is (a type parameter).
Rewrite paths to handle this case specially, just as they handle the
primitive case specifically. This entire `def_id` codepath is kind of a
mess.

they are being used as an opaque "position identifier"

Fixes #23057 
Fixes #27890
Fixes #28099
Fixes #28113

r? @pnkfelix 

Fixes #27890
Fixes #28099
Fixes #28113

@marchelzo pointed out on IRC that this doesn't have docs, so, let's
change that.

this simplifies the code while reducing the size of libcore.rlib by
3.3 MiB (~1M of which is bloat a separate patch of mine removes
too), while reducing rustc memory usage on small crates by 18MiB.

This also simplifies the code considerably.

I have measured a small, but possibly insignificant, bootstrap performance improvement, and the memory savings grow to about 30M for larger crates (but that is still less as a percentage).

r? @EddyB 

Turns out the symbol names are slightly different on 32-bit than on 64, so the
prefix needs to be tweaked just a bit!

This commit swaps the order of linking local native libraries and upstream
native libraries on the linker command line. Detail of bugs this can cause can
be found in #28595, and this change also invalidates the test case that was
added for #12446 which is now considered a bug because the downstream dependency
would need to declare that it depends on the native library somehow.

Closes #28595
[breaking-change]

This commit swaps the order of linking local native libraries and upstream
native libraries on the linker command line. Detail of bugs this can cause can
be found in #28595, and this change also invalidates the test case that was
added for #12446 which is now considered a bug because the downstream dependency
would need to declare that it depends on the native library somehow.

Closes #28595

This enables the Debug trait to work on syntax::ast::Stmt.

Closes #28709.

- Successful merges: #28753, #28760, #28764, #28770, #28771, #28772
- Failed merges: 

Fixes #28706 

I am pretty sure that this is accurate, bout would love a double check.

Fixes #28166

This is part of #28572, but doesn't complete it. Amongst other things,
this patch:

* Increases consistency in the way feature flags are used with other
  docs.
* Removes the ignores, which is nice: we actually had some syntax errors
  in the examples 😭.
* Mentions #![no_core]

Realistically, this document used to be in the order of least to most:
nothing, then adding core. But with the changes in RFC 1184, this is
backwards: it now shows stuff that uses core from the beginning. In the
future, I'd like to revamp this to go from 'most to least', but I'd like
to see the discussion in https://github.com/rust-lang/rust/issues/27701
goes before I write more.

@marchelzo pointed out on IRC that this doesn't have docs, so, let's
change that.

this simplifies the code while reducing the size of libcore.rlib by
3.3 MiB (~1M of which is bloat a separate patch of mine removes
too), while reducing rustc memory usage on small crates by 18MiB.

This also simplifies the code considerably.

Turns out the symbol names are slightly different on 32-bit than on 64, so the
prefix needs to be tweaked just a bit!