Auto merge of rust-lang#139126 - jhpratt:rollup-tdceqkd, r=jhpratt

Rollup of 5 pull requests

Successful merges:

 - rust-lang#137836 (Set `target_vendor = "openwrt"` on `mips64-openwrt-linux-musl`)
 - rust-lang#138206 ([AIX] Ignore linting on repr(C) structs with repr(packed) or repr(align(n)))
 - rust-lang#139044 (bootstrap: Avoid cloning `change-id` list)
 - rust-lang#139092 (Move `fd` into `std::sys`)
 - rust-lang#139111 (Properly document FakeReads)

r? `@ghost`
`@rustbot` modify labels: rollup

Author: bors

compiler/rustc_lint/src/types.rs

@@ -1634,6 +1634,9 @@ impl ImproperCTypesDefinitions {
             return true;
         } else if let Adt(adt_def, _) = ty.kind()
             && adt_def.is_struct()
+            && adt_def.repr().c()
+            && !adt_def.repr().packed()
+            && adt_def.repr().align.is_none()
         {
             let struct_variant = adt_def.variant(VariantIdx::ZERO);
             // Within a nested struct, all fields are examined to correctly
@@ -1655,8 +1658,11 @@ impl ImproperCTypesDefinitions {
         item: &'tcx hir::Item<'tcx>,
     ) {
         let adt_def = cx.tcx.adt_def(item.owner_id.to_def_id());
+        // repr(C) structs also with packed or aligned representation
+        // should be ignored.
         if adt_def.repr().c()
             && !adt_def.repr().packed()
+            && adt_def.repr().align.is_none()
             && cx.tcx.sess.target.os == "aix"
             && !adt_def.all_fields().next().is_none()
         {

compiler/rustc_middle/src/mir/syntax.rs

@@ -334,14 +334,19 @@ pub enum StatementKind<'tcx> {
     /// See [`Rvalue`] documentation for details on each of those.
     Assign(Box<(Place<'tcx>, Rvalue<'tcx>)>),
 
-    /// This represents all the reading that a pattern match may do (e.g., inspecting constants and
-    /// discriminant values), and the kind of pattern it comes from. This is in order to adapt
-    /// potential error messages to these specific patterns.
+    /// When executed at runtime, this is a nop.
     ///
-    /// Note that this also is emitted for regular `let` bindings to ensure that locals that are
-    /// never accessed still get some sanity checks for, e.g., `let x: ! = ..;`
+    /// During static analysis, a fake read:
+    /// - requires that the value being read is initialized (or, in the case
+    ///   of closures, that it was fully initialized at some point in the past)
+    /// - constitutes a use of a value for the purposes of NLL (i.e. if the
+    ///   value being fake-read is a reference, the lifetime of that reference
+    ///   will be extended to cover the `FakeRead`)
+    /// - but, unlike an actual read, does *not* invalidate any exclusive
+    ///   borrows.
     ///
-    /// When executed at runtime this is a nop.
+    /// See [`FakeReadCause`] for more details on the situations in which a
+    /// `FakeRead` is emitted.
     ///
     /// Disallowed after drop elaboration.
     FakeRead(Box<(FakeReadCause, Place<'tcx>)>),
@@ -518,28 +523,59 @@ pub enum RetagKind {
 /// The `FakeReadCause` describes the type of pattern why a FakeRead statement exists.
 #[derive(Copy, Clone, TyEncodable, TyDecodable, Debug, Hash, HashStable, PartialEq)]
 pub enum FakeReadCause {
-    /// Inject a fake read of the borrowed input at the end of each guards
-    /// code.
+    /// A fake read injected into a match guard to ensure that the discriminants
+    /// that are being matched on aren't modified while the match guard is being
+    /// evaluated.
+    ///
+    /// At the beginning of each match guard, a [fake borrow][FakeBorrowKind] is
+    /// inserted for each discriminant accessed in the entire `match` statement.
+    ///
+    /// Then, at the end of the match guard, a `FakeRead(ForMatchGuard)` is
+    /// inserted to keep the fake borrows alive until that point.
     ///
     /// This should ensure that you cannot change the variant for an enum while
     /// you are in the midst of matching on it.
     ForMatchGuard,
 
-    /// `let x: !; match x {}` doesn't generate any read of x so we need to
-    /// generate a read of x to check that it is initialized and safe.
+    /// Fake read of the scrutinee of a `match` or destructuring `let`
+    /// (i.e. `let` with non-trivial pattern).
+    ///
+    /// In `match x { ... }`, we generate a `FakeRead(ForMatchedPlace, x)`
+    /// and insert it into the `otherwise_block` (which is supposed to be
+    /// unreachable for irrefutable pattern-matches like `match` or `let`).
+    ///
+    /// This is necessary because `let x: !; match x {}` doesn't generate any
+    /// actual read of x, so we need to generate a `FakeRead` to check that it
+    /// is initialized.
     ///
-    /// If a closure pattern matches a Place starting with an Upvar, then we introduce a
-    /// FakeRead for that Place outside the closure, in such a case this option would be
-    /// Some(closure_def_id).
-    /// Otherwise, the value of the optional LocalDefId will be None.
+    /// If the `FakeRead(ForMatchedPlace)` is being performed with a closure
+    /// that doesn't capture the required upvars, the `FakeRead` within the
+    /// closure is omitted entirely.
+    ///
+    /// To make sure that this is still sound, if a closure matches against
+    /// a Place starting with an Upvar, we hoist the `FakeRead` to the
+    /// definition point of the closure.
+    ///
+    /// If the `FakeRead` comes from being hoisted out of a closure like this,
+    /// we record the `LocalDefId` of the closure. Otherwise, the `Option` will be `None`.
     //
     // We can use LocalDefId here since fake read statements are removed
     // before codegen in the `CleanupNonCodegenStatements` pass.
     ForMatchedPlace(Option<LocalDefId>),
 
-    /// A fake read of the RefWithinGuard version of a bind-by-value variable
-    /// in a match guard to ensure that its value hasn't change by the time
-    /// we create the OutsideGuard version.
+    /// A fake read injected into a match guard to ensure that the places
+    /// bound by the pattern are immutable for the duration of the match guard.
+    ///
+    /// Within a match guard, references are created for each place that the
+    /// pattern creates a binding for — this is known as the `RefWithinGuard`
+    /// version of the variables. To make sure that the references stay
+    /// alive until the end of the match guard, and properly prevent the
+    /// places in question from being modified, a `FakeRead(ForGuardBinding)`
+    /// is inserted at the end of the match guard.
+    ///
+    /// For details on how these references are created, see the extensive
+    /// documentation on `bind_matched_candidate_for_guard` in
+    /// `rustc_mir_build`.
     ForGuardBinding,
 
     /// Officially, the semantics of
@@ -552,22 +588,42 @@ pub enum FakeReadCause {
     /// However, if we see the simple pattern `let var = <expr>`, we optimize this to
     /// evaluate `<expr>` directly into the variable `var`. This is mostly unobservable,
     /// but in some cases it can affect the borrow checker, as in #53695.
-    /// Therefore, we insert a "fake read" here to ensure that we get
-    /// appropriate errors.
     ///
-    /// If a closure pattern matches a Place starting with an Upvar, then we introduce a
-    /// FakeRead for that Place outside the closure, in such a case this option would be
-    /// Some(closure_def_id).
-    /// Otherwise, the value of the optional DefId will be None.
+    /// Therefore, we insert a `FakeRead(ForLet)` immediately after each `let`
+    /// with a trivial pattern.
+    ///
+    /// FIXME: `ExprUseVisitor` has an entirely different opinion on what `FakeRead(ForLet)`
+    /// is supposed to mean. If it was accurate to what MIR lowering does,
+    /// would it even make sense to hoist these out of closures like
+    /// `ForMatchedPlace`?
     ForLet(Option<LocalDefId>),
 
-    /// If we have an index expression like
+    /// Currently, index expressions overloaded through the `Index` trait
+    /// get lowered differently than index expressions with builtin semantics
+    /// for arrays and slices — the latter will emit code to perform
+    /// bound checks, and then return a MIR place that will only perform the
+    /// indexing "for real" when it gets incorporated into an instruction.
+    ///
+    /// This is observable in the fact that the following compiles:
+    ///
+    /// ```
+    /// fn f(x: &mut [&mut [u32]], i: usize) {
+    ///     x[i][x[i].len() - 1] += 1;
+    /// }
+    /// ```
+    ///
+    /// However, we need to be careful to not let the user invalidate the
+    /// bound check with an expression like
+    ///
+    /// `(*x)[1][{ x = y; 4}]`
     ///
-    /// (*x)[1][{ x = y; 4}]
+    /// Here, the first bounds check would be invalidated when we evaluate the
+    /// second index expression. To make sure that this doesn't happen, we
+    /// create a fake borrow of `x` and hold it while we evaluate the second
+    /// index.
     ///
-    /// then the first bounds check is invalidated when we evaluate the second
-    /// index expression. Thus we create a fake borrow of `x` across the second
-    /// indexer, which will cause a borrow check error.
+    /// This borrow is kept alive by a `FakeRead(ForIndex)` at the end of its
+    /// scope.
     ForIndex,
 }
 

compiler/rustc_target/src/spec/targets/mips64_openwrt_linux_musl.rs

@@ -23,6 +23,7 @@ pub(crate) fn target() -> Target {
         data_layout: "E-m:e-i8:8:32-i16:16:32-i64:64-i128:128-n32:64-S128".into(),
         arch: "mips64".into(),
         options: TargetOptions {
+            vendor: "openwrt".into(),
             abi: "abi64".into(),
             endian: Endian::Big,
             mcount: "_mcount".into(),

library/std/src/sys/pal/hermit/fd.rs renamed to library/std/src/sys/fd/hermit.rs

@@ -1,8 +1,8 @@
 #![unstable(reason = "not public", issue = "none", feature = "fd")]
 
-use super::hermit_abi;
 use crate::cmp;
 use crate::io::{self, BorrowedCursor, IoSlice, IoSliceMut, Read, SeekFrom};
+use crate::os::hermit::hermit_abi;
 use crate::os::hermit::io::{AsFd, AsRawFd, BorrowedFd, FromRawFd, IntoRawFd, OwnedFd, RawFd};
 use crate::sys::{cvt, unsupported};
 use crate::sys_common::{AsInner, FromInner, IntoInner};

library/std/src/sys/fd/mod.rs

@@ -0,0 +1,19 @@
+//! Platform-dependent file descriptor abstraction.
+
+#![forbid(unsafe_op_in_unsafe_fn)]
+
+cfg_if::cfg_if! {
+    if #[cfg(target_family = "unix")] {
+        mod unix;
+        pub use unix::*;
+    } else if #[cfg(target_os = "hermit")] {
+        mod hermit;
+        pub use hermit::*;
+    } else if #[cfg(all(target_vendor = "fortanix", target_env = "sgx"))] {
+        mod sgx;
+        pub use sgx::*;
+    } else if #[cfg(target_os = "wasi")] {
+        mod wasi;
+        pub use wasi::*;
+    }
+}

library/std/src/sys/pal/sgx/fd.rs renamed to library/std/src/sys/fd/sgx.rs

@@ -1,8 +1,8 @@
 use fortanix_sgx_abi::Fd;
 
-use super::abi::usercalls;
 use crate::io::{self, BorrowedCursor, IoSlice, IoSliceMut};
 use crate::mem::ManuallyDrop;
+use crate::sys::pal::abi::usercalls;
 use crate::sys::{AsInner, FromInner, IntoInner};
 
 #[derive(Debug)]

library/std/src/sys/pal/unix/fd.rs renamed to library/std/src/sys/fd/unix.rs

@@ -22,6 +22,10 @@ use crate::cmp;
 use crate::io::{self, BorrowedCursor, IoSlice, IoSliceMut, Read};
 use crate::os::unix::io::{AsFd, AsRawFd, BorrowedFd, FromRawFd, IntoRawFd, OwnedFd, RawFd};
 use crate::sys::cvt;
+#[cfg(all(target_os = "android", target_pointer_width = "64"))]
+use crate::sys::pal::weak::syscall;
+#[cfg(any(all(target_os = "android", target_pointer_width = "32"), target_vendor = "apple"))]
+use crate::sys::pal::weak::weak;
 use crate::sys_common::{AsInner, FromInner, IntoInner};
 
 #[derive(Debug)]
@@ -232,7 +236,7 @@ impl FileDesc {
     // implementation if `preadv` is not available.
     #[cfg(all(target_os = "android", target_pointer_width = "64"))]
     pub fn read_vectored_at(&self, bufs: &mut [IoSliceMut<'_>], offset: u64) -> io::Result<usize> {
-        super::weak::syscall!(
+        syscall!(
             fn preadv(
                 fd: libc::c_int,
                 iovec: *const libc::iovec,
@@ -257,7 +261,7 @@ impl FileDesc {
     // and its metadata from LLVM IR.
     #[no_sanitize(cfi)]
     pub fn read_vectored_at(&self, bufs: &mut [IoSliceMut<'_>], offset: u64) -> io::Result<usize> {
-        super::weak::weak!(
+        weak!(
             fn preadv64(
                 fd: libc::c_int,
                 iovec: *const libc::iovec,
@@ -293,7 +297,7 @@ impl FileDesc {
     // use "weak" linking.
     #[cfg(target_vendor = "apple")]
     pub fn read_vectored_at(&self, bufs: &mut [IoSliceMut<'_>], offset: u64) -> io::Result<usize> {
-        super::weak::weak!(
+        weak!(
             fn preadv(
                 fd: libc::c_int,
                 iovec: *const libc::iovec,
@@ -442,7 +446,7 @@ impl FileDesc {
     // implementation if `pwritev` is not available.
     #[cfg(all(target_os = "android", target_pointer_width = "64"))]
     pub fn write_vectored_at(&self, bufs: &[IoSlice<'_>], offset: u64) -> io::Result<usize> {
-        super::weak::syscall!(
+        syscall!(
             fn pwritev(
                 fd: libc::c_int,
                 iovec: *const libc::iovec,
@@ -464,7 +468,7 @@ impl FileDesc {
 
     #[cfg(all(target_os = "android", target_pointer_width = "32"))]
     pub fn write_vectored_at(&self, bufs: &[IoSlice<'_>], offset: u64) -> io::Result<usize> {
-        super::weak::weak!(
+        weak!(
             fn pwritev64(
                 fd: libc::c_int,
                 iovec: *const libc::iovec,
@@ -500,7 +504,7 @@ impl FileDesc {
     // use "weak" linking.
     #[cfg(target_vendor = "apple")]
     pub fn write_vectored_at(&self, bufs: &[IoSlice<'_>], offset: u64) -> io::Result<usize> {
-        super::weak::weak!(
+        weak!(
             fn pwritev(
                 fd: libc::c_int,
                 iovec: *const libc::iovec,
@@ -669,6 +673,6 @@ impl IntoRawFd for FileDesc {
 
 impl FromRawFd for FileDesc {
     unsafe fn from_raw_fd(raw_fd: RawFd) -> Self {
-        Self(FromRawFd::from_raw_fd(raw_fd))
+        Self(unsafe { FromRawFd::from_raw_fd(raw_fd) })
     }
 }

library/std/src/sys/pal/unix/fd/tests.rs renamed to library/std/src/sys/fd/unix/tests.rs

@@ -1,6 +1,7 @@
 use core::mem::ManuallyDrop;
 
-use super::{FileDesc, IoSlice};
+use super::FileDesc;
+use crate::io::IoSlice;
 use crate::os::unix::io::FromRawFd;
 
 #[test]

library/std/src/sys/pal/wasi/fd.rs renamed to library/std/src/sys/fd/wasi.rs

@@ -1,11 +1,10 @@
-#![forbid(unsafe_op_in_unsafe_fn)]
-#![allow(dead_code)]
+#![expect(dead_code)]
 
-use super::err2io;
 use crate::io::{self, BorrowedCursor, IoSlice, IoSliceMut, SeekFrom};
 use crate::mem;
 use crate::net::Shutdown;
 use crate::os::wasi::io::{AsFd, AsRawFd, BorrowedFd, FromRawFd, IntoRawFd, OwnedFd, RawFd};
+use crate::sys::pal::err2io;
 use crate::sys_common::{AsInner, AsInnerMut, FromInner, IntoInner};
 
 #[derive(Debug)]

library/std/src/sys/fs/hermit.rs

@@ -9,8 +9,8 @@ use crate::os::hermit::io::{AsFd, AsRawFd, BorrowedFd, FromRawFd, IntoRawFd, Raw
 use crate::path::{Path, PathBuf};
 use crate::sync::Arc;
 use crate::sys::common::small_c_string::run_path_with_cstr;
+use crate::sys::fd::FileDesc;
 pub use crate::sys::fs::common::{copy, exists};
-use crate::sys::pal::fd::FileDesc;
 use crate::sys::time::SystemTime;
 use crate::sys::{cvt, unsupported};
 use crate::sys_common::{AsInner, AsInnerMut, FromInner, IntoInner};

library/std/src/sys/mod.rs

@@ -12,6 +12,7 @@ pub mod anonymous_pipe;
 pub mod backtrace;
 pub mod cmath;
 pub mod exit_guard;
+pub mod fd;
 pub mod fs;
 pub mod io;
 pub mod net;

library/std/src/sys/pal/hermit/mod.rs

@@ -20,7 +20,6 @@ use crate::os::raw::c_char;
 
 pub mod args;
 pub mod env;
-pub mod fd;
 pub mod futex;
 pub mod os;
 #[path = "../unsupported/pipe.rs"]

library/std/src/sys/pal/sgx/mod.rs

@@ -11,7 +11,6 @@ use crate::sync::atomic::{AtomicBool, Ordering};
 pub mod abi;
 pub mod args;
 pub mod env;
-pub mod fd;
 mod libunwind_integration;
 pub mod os;
 #[path = "../unsupported/pipe.rs"]

library/std/src/sys/pal/unix/linux/pidfd.rs

@@ -1,7 +1,7 @@
 use crate::io;
 use crate::os::fd::{AsRawFd, FromRawFd, RawFd};
 use crate::sys::cvt;
-use crate::sys::pal::unix::fd::FileDesc;
+use crate::sys::fd::FileDesc;
 use crate::sys::process::ExitStatus;
 use crate::sys_common::{AsInner, FromInner, IntoInner};
 

library/std/src/sys/pal/unix/mod.rs

@@ -8,7 +8,6 @@ pub mod weak;
 
 pub mod args;
 pub mod env;
-pub mod fd;
 #[cfg(target_os = "fuchsia")]
 pub mod fuchsia;
 pub mod futex;