Sometimes an obligation depends on a later one, so we can't just process them in order like it was done previously.

This is not a problem in our test suite, but there may be ICEs out there and it will definitely be a problem with lazy TAIT.

The issue here is that the logic used to determine which CGU to put the
dead function stubs in doesn't handle cases where a module is never
assigned to a CGU.

The partitioning logic also caused issues in rust-lang#85461 where inline
functions were duplicated into multiple CGUs resulting in duplicate
symbols.

This commit fixes the issue by removing the complex logic used to assign
dead code stubs to CGUs and replaces it with a much simplier model: we
pick one CGU to hold all the dead code stubs. We pick a CGU which has
exported items which increases the likelihood the linker won't throw
away our dead functions and we pick the smallest to minimize the impact
on compilation times for crates with very large CGUs.

Fixes rust-lang#86177
Fixes rust-lang#85718
Fixes rust-lang#79622

Because MIPSr6 has many differences with previous MIPSr2 arch, the previous rlib metadata stripping code in `rustc_codegen_ssa` is only for MIPSr2/r3/r5 (which share the same elf e_flags).
This commit fixed this problem. It makes `rustc_codegen_ssa` happy when compiling rustc for MIPSr6 target or hosts.

Use "(associated) function" terminology instead of "method".

Co-authored-by: Daniel Henry-Mantilla <[email protected]>

It's already a (fat) reference.
Double referencing it creates lifetime issues for its methods that want to return iterators.

This adds the old, pre 90639 `is_implemented` that previously only was
true if the implementation of the item was from the given impl block and
not from the trait default.

As discussed in
rust-lang#92142 (comment),
tests that contain multiple files order their results differently on
Windows and Linux which the test runner currently can't handle
correctly. For now, ignore the "bin" part of the test and only include
the unused library dependency which is what the test really cares about
anyway.

This test checks that `#[rustc_must_implement_one_of]` is gated behind
`#![feature(rustc_attrs)]`.

Make rlib metadata strip works with MIPSr6 architecture

Because MIPSr6 has many differences with previous MIPSr2 arch, the previous rlib metadata stripping code in `rustc_codegen_ssa` is only for MIPSr2/r3/r5 (which share the same elf e_flags).

This commit fixed this problem. It makes `rustc_codegen_ssa` happy when compiling rustc for MIPSr6 target or hosts.

e_flags REF: https://github.com/llvm/llvm-project/blob/e356027016c6365b3d8924f54c33e2c63d931492/llvm/include/llvm/BinaryFormat/ELF.h#L562

…imulacrum

`std::path::absolute`

Implements rust-lang#59117 by adding a `std::path::absolute` function that creates an absolute path without reading the filesystem. This is intended to be a drop-in replacement for [`std::fs::canonicalize`](https://doc.rust-lang.org/std/fs/fn.canonicalize.html) in cases where it isn't necessary to resolve symlinks. It can be used on paths that don't exist or where resolving symlinks is unwanted. It can also be used to avoid circumstances where `canonicalize` might otherwise fail.

On Windows this is a wrapper around [`GetFullPathNameW`](https://docs.microsoft.com/en-us/windows/win32/api/fileapi/nf-fileapi-getfullpathnamew). On Unix it partially implements the POSIX [pathname resolution](https://pubs.opengroup.org/onlinepubs/9699919799/basedefs/V1_chap04.html#tag_04_13) specification, stopping just short of actually resolving symlinks.

… r=GuillaumeGomez

rustdoc: do not emit tuple variant fields if none are documented

Fixes rust-lang#90824.

Before:

![2021-12-15T22:26:41](https://user-images.githubusercontent.com/1372438/146302871-4d265433-b9aa-4e53-adfb-e7cb92107180.png)

After:

![2021-12-15T22:27:01](https://user-images.githubusercontent.com/1372438/146302872-e39eda3d-2fb2-4fb9-aae7-2008e4e1b4dd.png)

Add `std::error::Report` type

This is a continuation of rust-lang#90174, split into a separate PR since I cannot push to `````@seanchen1991````` 's fork

…he_fold, r=nikomatsakis

Welcome opaque types into the fold

r? `@nikomatsakis` because idk who else to bug on the type_op changes

The commits have explanations in them. The TLDR is that

* 5c46002 stops the "recurse and replace" scheme that replaces opaque types with their canonical inference var by just doing that ahead of time
* bdeeb07 does not affect anything on master afaict, but since opaque types generate obligations when instantiated, and lazy TAIT instantiates opaque types *everywhere*, we need to properly handle obligations here instead of just hoping no problematic obligations ever come up.

…ioning, r=tmandry

[code coverage] Fix missing dead code in modules that are never called

The issue here is that the logic used to determine which CGU to put the dead function stubs in doesn't handle cases where a module is never assigned to a CGU (which is what happens when all of the code in the module is dead).

The partitioning logic also caused issues in rust-lang#85461 where inline functions were duplicated into multiple CGUs resulting in duplicate symbols.

This commit fixes the issue by removing the complex logic used to assign dead code stubs to CGUs and replaces it with a much simpler model: we pick one CGU to hold all the dead code stubs. We pick a CGU which has exported items which increases the likelihood the linker won't throw away our dead functions and we pick the smallest to minimize the impact on compilation times for crates with very large CGUs.

Fixes rust-lang#91661
Fixes rust-lang#86177
Fixes rust-lang#85718
Fixes rust-lang#79622

r? `@tmandry`
cc `@richkadel`

This PR is not urgent so please don't let it interrupt your holidays! 🎄 🎁

…ne_of_attr, r=Aaron1011

Implement `#[rustc_must_implement_one_of]` attribute

This PR adds a new attribute — `#[rustc_must_implement_one_of]` that allows changing the "minimal complete definition" of a trait. It's similar to GHC's minimal `{-# MINIMAL #-}` pragma, though `#[rustc_must_implement_one_of]` is weaker atm.

Such attribute was long wanted. It can be, for example, used in `Read` trait to make transitions to recently added `read_buf` easier:
```rust
#[rustc_must_implement_one_of(read, read_buf)]
pub trait Read {
    fn read(&mut self, buf: &mut [u8]) -> Result<usize> {
        let mut buf = ReadBuf::new(buf);
        self.read_buf(&mut buf)?;
        Ok(buf.filled_len())
    }

    fn read_buf(&mut self, buf: &mut ReadBuf<'_>) -> Result<()> {
        default_read_buf(|b| self.read(b), buf)
    }
}

impl Read for Ty0 {}
//^ This will fail to compile even though all `Read` methods have default implementations

// Both of these will compile just fine
impl Read for Ty1 {
    fn read(&mut self, buf: &mut [u8]) -> Result<usize> { /* ... */ }
}
impl Read for Ty2 {
    fn read_buf(&mut self, buf: &mut ReadBuf<'_>) -> Result<()> { /* ... */ }
}
```

For now, this is implemented as an internal attribute to start experimenting on the design of this feature. In the future we may want to extend it:
- Allow arbitrary requirements like `a | (b & c)`
- Allow multiple requirements like
  - ```rust
    #[rustc_must_implement_one_of(a, b)]
    #[rustc_must_implement_one_of(c, d)]
    ```
- Make it appear in rustdoc documentation
- Change the syntax?
- Etc

Eventually, we should make an RFC and make this (or rather similar) attribute public.

---

I'm fairly new to compiler development and not at all sure if the implementation makes sense, but at least it passes tests :)

rustc_metadata: Stop passing `CrateMetadataRef` by reference (step 1)

It's already a (fat) reference.
Double referencing it creates lifetime issues for its methods that want to return iterators.

---
Extracted from rust-lang#92245 for a perf run.
The PR changes a lot of symbol names due to function signature changes, so it's hard to do differential profiling, let's spend some machine time instead.

…uillaumeGomez

rustdoc: Preserve rendering of macro_rules matchers when possible

Fixes rust-lang#92331. This approach restores the behavior prior to rust-lang#86282 **if** the matcher token held by the compiler **and** the matcher token found in the source code are identical TokenTrees. Thus rust-lang#86208 remains fixed, but without regressing formatting for the vast majority of macros which are not macro-generated.

Update cargo

6 commits in 358e79fe56fe374649275ca7aebaafd57ade0e8d..06b9d31743210b788b130c8a484c2838afa6fc27
2022-01-04 18:39:45 +0000 to 2022-01-11 23:47:29 +0000
- Port cargo to clap3 (rust-lang/cargo#10265)
- feat: support rustflags per profile (rust-lang/cargo#10217)
- Make bors ignore the PR template so it doesn't end up in merge messages (rust-lang/cargo#10267)
- Be resilient to most IO error and filesystem loop while walking dirs (rust-lang/cargo#10214)
- Remove the option to disable pipelining (rust-lang/cargo#10258)
- Always ask rustc for messages about artifacts, and always process them (rust-lang/cargo#10255)