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Rollup of 9 pull requests #82785

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rylev and others added 28 commits March 3, 2021 11:23
 ### Overview

    This commit begins the implementation work for RFC 2945. For more
    information, see the rendered RFC [1] and tracking issue [2].

    A boolean `unwind` payload is added to the `C`, `System`, `Stdcall`,
    and `Thiscall` variants, marking whether unwinding across FFI
    boundaries is acceptable. The cases where each of these variants'
    `unwind` member is true correspond with the `C-unwind`,
    `system-unwind`, `stdcall-unwind`, and `thiscall-unwind` ABI strings
    introduced in RFC 2945 [3].

 ### Feature Gate and Unstable Book

    This commit adds a `c_unwind` feature gate for the new ABI strings.
    Tests for this feature gate are included in `src/test/ui/c-unwind/`,
    which ensure that this feature gate works correctly for each of the
    new ABIs.

    A new language features entry in the unstable book is added as well.

 ### Further Work To Be Done

    This commit does not proceed to implement the new unwinding ABIs,
    and is intentionally scoped specifically to *defining* the ABIs and
    their feature flag.

 ### One Note on Test Churn

    This will lead to some test churn, in re-blessing hash tests, as the
    deleted comment in `src/librustc_target/spec/abi.rs` mentioned,
    because we can no longer guarantee the ordering of the `Abi`
    variants.

    While this is a downside, this decision was made bearing in mind
    that RFC 2945 states the following, in the "Other `unwind` Strings"
    section [3]:

    >  More unwind variants of existing ABI strings may be introduced,
    >  with the same semantics, without an additional RFC.

    Adding a new variant for each of these cases, rather than specifying
    a payload for a given ABI, would quickly become untenable, and make
    working with the `Abi` enum prone to mistakes.

    This approach encodes the unwinding information *into* a given ABI,
    to account for the future possibility of other `-unwind` ABI
    strings.

 ### Ignore Directives

    `ignore-*` directives are used in two of our `*-unwind` ABI test
    cases.

    Specifically, the `stdcall-unwind` and `thiscall-unwind` test cases
    ignore architectures that do not support `stdcall` and
    `thiscall`, respectively.

    These directives are cribbed from
    `src/test/ui/c-variadic/variadic-ffi-1.rs` for `stdcall`, and
    `src/test/ui/extern/extern-thiscall.rs` for `thiscall`.

    This would otherwise fail on some targets, see:
    rust-lang-ci@fcf697f

 ### Footnotes

[1]: https://github.com/rust-lang/rfcs/blob/master/text/2945-c-unwind-abi.md
[2]: rust-lang#74990
[3]: https://github.com/rust-lang/rfcs/blob/master/text/2945-c-unwind-abi.md#other-unwind-abi-strings
 ### Changes

    This commit implements unwind ABI's, specified in RFC 2945.

    We adjust the `rustc_middle::ty::layout::fn_can_unwind` function,
    used to compute whether or not a `FnAbi` object represents a
    function that should be able to unwind when `panic=unwind` is in
    use.

    Changes are also made to
    `rustc_mir_build::build::should_abort_on_panic` so that the
    function ABI is used to determind whether it should abort, assuming
    that the `panic=unwind` strategy is being used, and no explicit
    unwind attribute was provided.

 ### Tests

    Unit tests, checking that the behavior is correct for `C-unwind`,
    `stdcall-unwind`, `system-unwind`, and `thiscall-unwind`, are
    included. These alternative `unwind` ABI strings are specified in
    RFC 2945, in the "_Other `unwind` ABI strings_" section.

    Additionally, a test case is included to assert that the LLVM IR
    generated for an external function defined with the `C-unwind` ABI
    will be appropriately labeled with the `nounwind` LLVM attribute
    when the `panic=abort` compilation flag is used.

 ### Ignore Directives

    This commit uses `ignore-*` directives in two of our `*-unwind` ABI
    test cases.

    Specifically, the `stdcall-unwind` and `thiscall-unwind` test cases
    ignore architectures that do not support `stdcall` and `thiscall`,
    respectively.

    These directives are cribbed from
    `src/test/ui/c-variadic/variadic-ffi-1.rs` for `stdcall`, and
    `src/test/ui/extern/extern-thiscall.rs` for `thiscall`.
 ### Integration Tests

    This commit introduces some new fixtures to the `run-make-fulldeps`
    test suite.

        * c-unwind-abi-catch-panic: Exercise unwinding a panic. This
          catches a panic across an FFI boundary and downcasts it into
          an integer.

        * c-unwind-abi-catch-lib-panic: This is similar to the previous
         `*catch-panic` test, however in this case the Rust code that
         panics resides in a separate crate.

 ### Add `rust_eh_personality` to `#[no_std]` alloc tests

    This commit addresses some test failures that now occur in the
    following two tests:

        * no_std-alloc-error-handler-custom.rs
        * no_std-alloc-error-handler-default.rs

    Each test now defines a `rust_eh_personality` extern function, in
    the same manner as shown in the "Writing an executable without
    stdlib" section of the `lang_items` documentation here:
    https://doc.rust-lang.org/unstable-book/language-features/lang-items.html#writing-an-executable-without-stdlib

    Without this change, these tests would fail to compile due to a
    linking error explaining that there was an "undefined reference
    to `rust_eh_personality'."

 ### Updated hash

    * update 32-bit hash in `impl1` test

 ### Panics

    This commit uses `panic!` macro invocations that return a string,
    rather than using an integer as a panic payload.

    Doing so avoids the following warnings that were observed during
    rollup for the `*-msvc-1` targets:

    ```
    warning: panic message is not a string literal
      --> panic.rs:10:16
       |
    10 |         panic!(x); // That is too big!
       |                ^
       |
       = note: `#[warn(non_fmt_panic)]` on by default
       = note: this is no longer accepted in Rust 2021
    help: add a "{}" format string to Display the message
       |
    10 |         panic!("{}", x); // That is too big!
       |                ^^^^^
    help: or use std::panic::panic_any instead
       |
    10 |         std::panic::panic_any(x); // That is too big!
       |         ^^^^^^^^^^^^^^^^^^^^^

    warning: 1 warning emitted
    ```

    See: https://github.com/rust-lang-ci/rust/runs/1992118428

    As these errors imply, panicking without a format string will be
    disallowed in Rust 2021, per rust-lang#78500.
 ### Add debug assertion to check `AbiDatas` ordering

    This makes a small alteration to `Abi::index`, so that we include a
    debug assertion to check that the index we are returning corresponds
    with the same abi in our data array.

    This will help prevent ordering bugs in the future, which can
    manifest in rather strange errors.

 ### Using exhaustive ABI matches

    This slightly modifies the changes from our previous commits,
    favoring exhaustive matches in place of `_ => ...` fall-through
    arms.

    This should help with maintenance in the future, when additional
    ABI's are added, or when existing ABI's are modified.

 ### List all `-unwind` ABI's in unstable book

    This updates the `c-unwind` page in the unstable book to list _all_
    of the other ABI strings that are introduced by this feature gate.

    Now, all of the ABI's specified by RFC 2945 are shown.

Co-authored-by: Amanieu d'Antras <[email protected]>
Co-authored-by: Niko Matsakis <[email protected]>
Due to a rebase, some edits were needed in the mod file.
- Remove most of the information about passes. Passes are deprecated.
- Add `--document-private-items`; it was missing before.
- Update `--output-format json`; it was very outdated.
- Note that `--input-format` is deprecated.
- Move deprecated options to the very end.
- Move `passes.html` to the end of the table of contents. Ideally it
  would be removed altogether, but that causes mdbook not to generate the
  docs.
…atsakis

Inherit `#[stable(..)]` annotations in enum variants and fields from its item

Lint changes for rust-lang#65515. The stdlib will have to be updated once this lands in beta and that version is promoted in master.
…d-abi, r=Amanieu

Implement RFC 2945: "C-unwind" ABI

## Implement RFC 2945: "C-unwind" ABI

This branch implements [RFC 2945]. The tracking issue for this RFC is rust-lang#74990.

The feature gate for the issue is `#![feature(c_unwind)]`.

This RFC was created as part of the ffi-unwind project group tracked at rust-lang/lang-team#19.

### Changes

Further details will be provided in commit messages, but a high-level overview
of the changes follows:

* A boolean `unwind` payload is added to the `C`, `System`, `Stdcall`,
and `Thiscall` variants, marking whether unwinding across FFI boundaries is
acceptable. The cases where each of these variants' `unwind` member is true
correspond with the `C-unwind`, `system-unwind`, `stdcall-unwind`, and
`thiscall-unwind` ABI strings introduced in RFC 2945 [3].

* This commit adds a `c_unwind` feature gate for the new ABI strings.
Tests for this feature gate are included in `src/test/ui/c-unwind/`, which
ensure that this feature gate works correctly for each of the new ABIs.
A new language features entry in the unstable book is added as well.

* We adjust the `rustc_middle::ty::layout::fn_can_unwind` function,
used to compute whether or not a `FnAbi` object represents a function that
should be able to unwind when `panic=unwind` is in use.

* Changes are also made to
`rustc_mir_build::build::should_abort_on_panic` so that the function ABI is
used to determind whether it should abort, assuming that the `panic=unwind`
strategy is being used, and no explicit unwind attribute was provided.

[RFC 2945]: https://github.com/rust-lang/rfcs/blob/master/text/2945-c-unwind-abi.md
…c-hidden, r=jyn514

Don't warn for `missing_doc_examples` when item is #[doc(hidden)]

r? ``@jyn514``
Implement NOOP_METHOD_CALL lint

Implements the beginnings of rust-lang/lang-team#67 - a lint for detecting noop method calls (e.g, calling `<&T as Clone>::clone()` when `T: !Clone`).

This PR does not fully realize the vision and has a few limitations that need to be addressed either before merging or in subsequent PRs:
* [ ] No UFCS support
* [ ] The warning message is pretty plain
* [ ] Doesn't work for `ToOwned`

The implementation uses [`Instance::resolve`](https://doc.rust-lang.org/nightly/nightly-rustc/rustc_middle/ty/instance/struct.Instance.html#method.resolve) which is normally later in the compiler. It seems that there are some invariants that this function relies on that we try our best to respect. For instance, it expects substitutions to have happened, which haven't yet performed, but we check first for `needs_subst` to ensure we're dealing with a monomorphic type.

Thank you to `@davidtwco,` `@Aaron1011,` and `@wesleywiser` for helping me at various points through out this PR ❤️.
resolve: Reduce scope of `pub_use_of_private_extern_crate` deprecation lint

This lint was deny-by-default since July 2017, crater showed 7 uses on crates.io back then (rust-lang#42894 (comment)).

Unfortunately, the construction `pub use foo as bar` where `foo` is `extern crate foo;` was used by an older version `bitflags`, so turning it into an error causes too many regressions.
So, this PR reduces the scope of the lint instead of turning it into a hard error, and only turns some more rarely used components of it into errors.
…ramertj

Improved IO Bytes Size Hint

After trying to implement better `size_hint()` return values for `File` in [this PR](rust-lang#81044) and changing to implementing it for `BufReader` in [this PR](rust-lang#81052), I have arrived at this implementation that provides tighter bounds for the `Bytes` iterator of various readers including `BufReader`, `Empty`, and `Chain`.

Unfortunately, for `BufReader`, the size_hint only improves after calling `fill_buffer` due to it using the contents of the buffer for the hint. Nevertheless, the the tighter bounds  should result in better pre-allocation of space to handle the contents of the `Bytes` iterator.

Closes rust-lang#81052
… r=davidtwco

Add suggestion `.collect()` for iterators in iterators

Closes rust-lang#81584

```
error[E0515]: cannot return value referencing function parameter `y`
 --> main3.rs:4:38
  |
4 | ...                   .map(|y| y.iter().map(|x| x + 1))
  |                                -^^^^^^^^^^^^^^^^^^^^^^
  |                                |
  |                                returns a value referencing data owned by the current function
  |                                `y` is borrowed here
  |                                help: Maybe use `.collect()` to allocate the iterator
```

Added the suggestion: `help: Maybe use `.collect()` to allocate the iterator`
… r=GuillaumeGomez

Shorten html::render

The `mod.rs` for librustdoc's `html::render` was over 3,000 lines. This PR reduces it to around 2,300 by
1. Moving `Context` and associated `impl`s to a separate file
2. Moving the `print_item` function and its helpers to a separate file
3. Moving `write_shared` and `write_minify` to their own file

Related to issue rust-lang#60302.
Edit 1: `SharedContext` and related `impl`s is only 72 lines and so will not be moved.
Update rustdoc documentation

- Remove most of the information about passes. Passes are deprecated.
- Add `--document-private-items`; it was missing before.
- Update `--output-format json`; it was very outdated.
- Note that `--input-format` is deprecated.
- Move deprecated options to the very end.

Closes rust-lang#82675.

r? ``@Manishearth``
@rustbot rustbot added the rollup A PR which is a rollup label Mar 5, 2021
@m-ou-se m-ou-se closed this Mar 5, 2021
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