Fix example in docs on documentation
debuginfo: Make names of types in debuginfo reliable and omit source locations from debug info type descriptions.

So far, type names generated for debuginfo where a bit sketchy. It was not clearly defined when a name should be fully qualified and when not, if region parameters should be shown or not, and other things like that.
This commit makes the debuginfo module responsible for creating type names instead of using ppaux::ty_to_str() and brings type names, as they show up in the DWARF information, in line with GCC and Clang:

* The name of the type being described is unqualified. It's path is defined by its position in the namespace hierarchy.
* Type arguments are always fully qualified, no matter if they would actually be in scope at the type definition location.

Care is also taken to reliably make type names consistent across crate boundaries. That is, the code now tries make the type name the same, regardless if the type is in the local crate or reconstructed from metadata. Otherwise LLVM will complain about violating the one-definition-rule when using link-time-optimization.

This commit also removes all source location information from type descriptions because these cannot be reconstructed for types instantiated from metadata. Again, with LTO enabled, this can lead to two versions of the debuginfo type description, one with and one without source location information, which then triggers the LLVM ODR assertion.
Fortunately, source location information about types is rarely used, so this has little impact. Once source location information is preserved in metadata (#1972) it can also be reenabled for type descriptions.
Fix rotate_{left, right} for multiple of bitsize rotation amounts

Add additional rotation tests
auto merge of #15324 : sneves/rust/master, r=alexcrichton

The current implementation of `rotate_left` and `rotate_right` are incorrect when the rotation amount is 0, or a multiple of the input's bitsize. When `n = 0`, the expression

    (self >> n) | (self << ($BITS - n))

results in a shift left by `$BITS` bits, which is undefined behavior (see https://github.com/rust-lang/rust/issues/10183), and currently results in a hardcoded `-1` value, instead of the original input value. Reducing `($BITS - n)` modulo `$BITS`, simplified to `(-n % $BITS)`, fixes this problem.
Improve code reuse between trans/_match.rs and check_match.rs

The specialization logic for patterns is really the same in both
exhaustiveness/reachability checking and codegen.
auto merge of #15078 : jakub-/rust/pattern-matching-refactor-vol-2, r=pnkfelix

I believe there's more commonality to be found there but maybe small steps are better. I'm also in the process of documenting what I can, I will see if I can add it to this PR.

It also seems to me that ideally some of this stuff (especially the pattern sanity check) could live as a separate compiler-agnostic module but I understand this may not be the right time (if not the worst) to start the process of modularising rustc.
auto merge of #15199 : michaelwoerister/rust/cross-crate-stability, r=luqmana

So far, type names generated for debuginfo where a bit sketchy. It was not clearly defined when a name should be fully qualified and when not, if region parameters should be shown or not, and other things like that.
This commit makes the debuginfo module responsible for creating type names instead of using `ppaux::ty_to_str()` and brings type names (as they show up in the DWARF information) in line with GCC and Clang:

* The name of the type being described is unqualified. It's path is defined by its position in the namespace hierarchy.
* Type arguments are always fully qualified, no matter if they would actually be in scope at the type definition location.

Care is also taken to make type names consistent across crate boundaries. That is, the code now tries make the type name the same, regardless if the type is in the local crate or reconstructed from metadata. Otherwise LLVM will complain about violating the one-definition-rule when using link-time-optimization.

This commit also removes all source location information from type descriptions because these cannot be reconstructed for types instantiated from metadata. Again, with LTO enabled, this can lead to two versions of the debuginfo type description, one with and one without source location information, which then triggers the LLVM ODR assertion.
Fortunately, source location information about types is rarely used, so this has little impact. Once source location information is preserved in metadata (#1972) it can also be re-enabled for type descriptions.

`RUSTFLAGS=-g make check` no works again for me locally, including the LTO test cases (note that I've taken care of #15156 by reverting the change in LLVM that @luqmana identified as the culprit for that issue).
auto merge of #15331 : Derecho/rust/master, r=alexcrichton

One of the examples in the docs on adding documentation to rust code has an error that will cause the function to run endlessly rather than return the desired result, should someone actually implement this for some reason. While the error does not hinder the explanation of documenting code, it does look better if it is corrected.
Rename set_broadast() to set_broadcast().