Rollup of 2 pull requests

library/core/src/mem/maybe_uninit.rs

@@ -253,6 +253,89 @@ use crate::{fmt, intrinsics, ptr, slice};
 ///     std::process::exit(*code); // UB! Accessing uninitialized memory.
 /// }
 /// ```
+///
+/// # Validity
+///
+/// `MaybeUninit<T>` has no validity requirements –- any sequence of [bytes] of
+/// the appropriate length, initialized or uninitialized, are a valid
+/// representation.
+///
+/// Moving or copying a value of type `MaybeUninit<T>` (i.e., performing a
+/// "typed copy") will exactly preserve the contents, including the
+/// [provenance], of all non-padding bytes of type `T` in the value's
+/// representation.
+///
+/// Therefore `MaybeUninit` can be used to perform a round trip of a value from
+/// type `T` to type `MaybeUninit<U>` then back to type `T`, while preserving
+/// the original value, if two conditions are met. One, type `U` must have the
+/// same size as type `T`. Two, for all byte offsets where type `U` has padding,
+/// the corresponding bytes in the representation of the value must be
+/// uninitialized.
+///
+/// For example, due to the fact that the type `[u8; size_of::<T>]` has no
+/// padding, the following is sound for any type `T` and will return the
+/// original value:
+///
+/// ```rust,no_run
+/// # use core::mem::{MaybeUninit, transmute};
+/// # struct T;
+/// fn identity(t: T) -> T {
+///     unsafe {
+///         let u: MaybeUninit<[u8; size_of::<T>()]> = transmute(t);
+///         transmute(u) // OK.
+///     }
+/// }
+/// ```
+///
+/// Note: Copying a value that contains references may implicitly reborrow them
+/// causing the provenance of the returned value to differ from that of the
+/// original. This applies equally to the trivial identity function:
+///
+/// ```rust,no_run
+/// fn trivial_identity<T>(t: T) -> T { t }
+/// ```
+///
+/// Note: Moving or copying a value whose representation has initialized bytes
+/// at byte offsets where the type has padding may lose the value of those
+/// bytes, so while the original value will be preserved, the original
+/// *representation* of that value as bytes may not be. Again, this applies
+/// equally to `trivial_identity`.
+///
+/// Note: Performing this round trip when type `U` has padding at byte offsets
+/// where the representation of the original value has initialized bytes may
+/// produce undefined behavior or a different value. For example, the following
+/// is unsound since `T` requires all bytes to be initialized:
+///
+/// ```rust,no_run
+/// # use core::mem::{MaybeUninit, transmute};
+/// #[repr(C)] struct T([u8; 4]);
+/// #[repr(C)] struct U(u8, u16);
+/// fn unsound_identity(t: T) -> T {
+///     unsafe {
+///         let u: MaybeUninit<U> = transmute(t);
+///         transmute(u) // UB.
+///     }
+/// }
+/// ```
+///
+/// Conversely, the following is sound since `T` allows uninitialized bytes in
+/// the representation of a value, but the round trip may alter the value:
+///
+/// ```rust,no_run
+/// # use core::mem::{MaybeUninit, transmute};
+/// #[repr(C)] struct T(MaybeUninit<[u8; 4]>);
+/// #[repr(C)] struct U(u8, u16);
+/// fn non_identity(t: T) -> T {
+///     unsafe {
+///         // May lose an initialized byte.
+///         let u: MaybeUninit<U> = transmute(t);
+///         transmute(u)
+///     }
+/// }
+/// ```
+///
+/// [bytes]: ../../reference/memory-model.html#bytes
+/// [provenance]: crate::ptr#provenance
 #[stable(feature = "maybe_uninit", since = "1.36.0")]
 // Lang item so we can wrap other types in it. This is useful for coroutines.
 #[lang = "maybe_uninit"]

src/tools/tidy/src/alphabetical.rs

@@ -24,7 +24,7 @@ use std::fmt::Display;
 use std::iter::Peekable;
 use std::path::Path;
 
-use crate::diagnostics::{CheckId, DiagCtx, RunningCheck};
+use crate::diagnostics::{CheckId, RunningCheck, TidyCtx};
 use crate::walk::{filter_dirs, walk};
 
 #[cfg(test)]
@@ -130,8 +130,8 @@ fn check_lines<'a>(
     }
 }
 
-pub fn check(path: &Path, diag_ctx: DiagCtx) {
-    let mut check = diag_ctx.start_check(CheckId::new("alphabetical").path(path));
+pub fn check(path: &Path, tidy_ctx: TidyCtx) {
+    let mut check = tidy_ctx.start_check(CheckId::new("alphabetical").path(path));
 
     let skip =
         |path: &_, _is_dir| filter_dirs(path) || path.ends_with("tidy/src/alphabetical/tests.rs");

src/tools/tidy/src/alphabetical/tests.rs

@@ -1,12 +1,12 @@
 use std::path::Path;
 
 use crate::alphabetical::check_lines;
-use crate::diagnostics::DiagCtx;
+use crate::diagnostics::{TidyCtx, TidyFlags};
 
 #[track_caller]
 fn test(lines: &str, name: &str, expected_msg: &str, expected_bad: bool) {
-    let diag_ctx = DiagCtx::new(Path::new("/"), false);
-    let mut check = diag_ctx.start_check("alphabetical-test");
+    let tidy_ctx = TidyCtx::new(Path::new("/"), false, TidyFlags::default());
+    let mut check = tidy_ctx.start_check("alphabetical-test");
     check_lines(&name, lines.lines().enumerate(), &mut check);
 
     assert_eq!(expected_bad, check.is_bad());

src/tools/tidy/src/bins.rs

@@ -12,13 +12,13 @@ pub use os_impl::*;
 mod os_impl {
     use std::path::Path;
 
-    use crate::diagnostics::DiagCtx;
+    use crate::diagnostics::TidyCtx;
 
     pub fn check_filesystem_support(_sources: &[&Path], _output: &Path) -> bool {
         return false;
     }
 
-    pub fn check(_path: &Path, _diag_ctx: DiagCtx) {}
+    pub fn check(_path: &Path, _tidy_ctx: TidyCtx) {}
 }
 
 #[cfg(unix)]
@@ -38,7 +38,7 @@ mod os_impl {
 
     use FilesystemSupport::*;
 
-    use crate::diagnostics::DiagCtx;
+    use crate::diagnostics::TidyCtx;
 
     fn is_executable(path: &Path) -> std::io::Result<bool> {
         Ok(path.metadata()?.mode() & 0o111 != 0)
@@ -110,8 +110,8 @@ mod os_impl {
     }
 
     #[cfg(unix)]
-    pub fn check(path: &Path, diag_ctx: DiagCtx) {
-        let mut check = diag_ctx.start_check("bins");
+    pub fn check(path: &Path, tidy_ctx: TidyCtx) {
+        let mut check = tidy_ctx.start_check("bins");
 
         use std::ffi::OsStr;
 

src/tools/tidy/src/debug_artifacts.rs

@@ -2,13 +2,13 @@
 
 use std::path::Path;
 
-use crate::diagnostics::{CheckId, DiagCtx};
+use crate::diagnostics::{CheckId, TidyCtx};
 use crate::walk::{filter_dirs, filter_not_rust, walk};
 
 const GRAPHVIZ_POSTFLOW_MSG: &str = "`borrowck_graphviz_postflow` attribute in test";
 
-pub fn check(test_dir: &Path, diag_ctx: DiagCtx) {
-    let mut check = diag_ctx.start_check(CheckId::new("debug_artifacts").path(test_dir));
+pub fn check(test_dir: &Path, tidy_ctx: TidyCtx) {
+    let mut check = tidy_ctx.start_check(CheckId::new("debug_artifacts").path(test_dir));
 
     walk(
         test_dir,

src/tools/tidy/src/deps.rs

@@ -9,7 +9,7 @@ use build_helper::ci::CiEnv;
 use cargo_metadata::semver::Version;
 use cargo_metadata::{Metadata, Package, PackageId};
 
-use crate::diagnostics::{DiagCtx, RunningCheck};
+use crate::diagnostics::{RunningCheck, TidyCtx};
 
 #[path = "../../../bootstrap/src/utils/proc_macro_deps.rs"]
 mod proc_macro_deps;
@@ -615,8 +615,9 @@ const PERMITTED_CRANELIFT_DEPENDENCIES: &[&str] = &[
 ///
 /// `root` is path to the directory with the root `Cargo.toml` (for the workspace). `cargo` is path
 /// to the cargo executable.
-pub fn check(root: &Path, cargo: &Path, bless: bool, diag_ctx: DiagCtx) {
-    let mut check = diag_ctx.start_check("deps");
+pub fn check(root: &Path, cargo: &Path, tidy_ctx: TidyCtx) {
+    let mut check = tidy_ctx.start_check("deps");
+    let bless = tidy_ctx.is_bless_enabled();
 
     let mut checked_runtime_licenses = false;
 

src/tools/tidy/src/diagnostics.rs

@@ -5,28 +5,59 @@ use std::sync::{Arc, Mutex};
 
 use termcolor::{Color, WriteColor};
 
+#[derive(Clone, Default)]
+///CLI flags used by tidy.
+pub struct TidyFlags {
+    ///Applies style and formatting changes during a tidy run.
+    bless: bool,
+}
+
+impl TidyFlags {
+    pub fn new(cfg_args: &[String]) -> Self {
+        let mut flags = Self::default();
+
+        for arg in cfg_args {
+            match arg.as_str() {
+                "--bless" => flags.bless = true,
+                _ => continue,
+            }
+        }
+        flags
+    }
+}
+
 /// Collects diagnostics from all tidy steps, and contains shared information
 /// that determines how should message and logs be presented.
 ///
 /// Since checks are executed in parallel, the context is internally synchronized, to avoid
 /// all checks to lock it explicitly.
 #[derive(Clone)]
-pub struct DiagCtx(Arc<Mutex<DiagCtxInner>>);
+pub struct TidyCtx {
+    tidy_flags: TidyFlags,
+    diag_ctx: Arc<Mutex<DiagCtxInner>>,
+}
+
+impl TidyCtx {
+    pub fn new(root_path: &Path, verbose: bool, tidy_flags: TidyFlags) -> Self {
+        Self {
+            diag_ctx: Arc::new(Mutex::new(DiagCtxInner {
+                running_checks: Default::default(),
+                finished_checks: Default::default(),
+                root_path: root_path.to_path_buf(),
+                verbose,
+            })),
+            tidy_flags,
+        }
+    }
 
-impl DiagCtx {
-    pub fn new(root_path: &Path, verbose: bool) -> Self {
-        Self(Arc::new(Mutex::new(DiagCtxInner {
-            running_checks: Default::default(),
-            finished_checks: Default::default(),
-            root_path: root_path.to_path_buf(),
-            verbose,
-        })))
+    pub fn is_bless_enabled(&self) -> bool {
+        self.tidy_flags.bless
     }
 
     pub fn start_check<Id: Into<CheckId>>(&self, id: Id) -> RunningCheck {
         let mut id = id.into();
 
-        let mut ctx = self.0.lock().unwrap();
+        let mut ctx = self.diag_ctx.lock().unwrap();
 
         // Shorten path for shorter diagnostics
         id.path = match id.path {
@@ -38,14 +69,14 @@ impl DiagCtx {
         RunningCheck {
             id,
             bad: false,
-            ctx: self.0.clone(),
+            ctx: self.diag_ctx.clone(),
             #[cfg(test)]
             errors: vec![],
         }
     }
 
     pub fn into_failed_checks(self) -> Vec<FinishedCheck> {
-        let ctx = Arc::into_inner(self.0).unwrap().into_inner().unwrap();
+        let ctx = Arc::into_inner(self.diag_ctx).unwrap().into_inner().unwrap();
         assert!(ctx.running_checks.is_empty(), "Some checks are still running");
         ctx.finished_checks.into_iter().filter(|c| c.bad).collect()
     }
@@ -151,7 +182,7 @@ impl RunningCheck {
     /// Useful if you want to run some functions from tidy without configuring
     /// diagnostics.
     pub fn new_noop() -> Self {
-        let ctx = DiagCtx::new(Path::new(""), false);
+        let ctx = TidyCtx::new(Path::new(""), false, TidyFlags::default());
         ctx.start_check("noop")
     }
 

src/tools/tidy/src/edition.rs

@@ -2,11 +2,11 @@
 
 use std::path::Path;
 
-use crate::diagnostics::{CheckId, DiagCtx};
+use crate::diagnostics::{CheckId, TidyCtx};
 use crate::walk::{filter_dirs, walk};
 
-pub fn check(path: &Path, diag_ctx: DiagCtx) {
-    let mut check = diag_ctx.start_check(CheckId::new("edition").path(path));
+pub fn check(path: &Path, tidy_ctx: TidyCtx) {
+    let mut check = tidy_ctx.start_check(CheckId::new("edition").path(path));
     walk(path, |path, _is_dir| filter_dirs(path), &mut |entry, contents| {
         let file = entry.path();
         let filename = file.file_name().unwrap();

src/tools/tidy/src/error_codes.rs

@@ -22,7 +22,7 @@ use std::path::Path;
 
 use regex::Regex;
 
-use crate::diagnostics::{DiagCtx, RunningCheck};
+use crate::diagnostics::{RunningCheck, TidyCtx};
 use crate::walk::{filter_dirs, walk, walk_many};
 
 const ERROR_CODES_PATH: &str = "compiler/rustc_error_codes/src/lib.rs";
@@ -36,8 +36,8 @@ const IGNORE_DOCTEST_CHECK: &[&str] = &["E0464", "E0570", "E0601", "E0602", "E07
 const IGNORE_UI_TEST_CHECK: &[&str] =
     &["E0461", "E0465", "E0514", "E0554", "E0640", "E0717", "E0729"];
 
-pub fn check(root_path: &Path, search_paths: &[&Path], ci_info: &crate::CiInfo, diag_ctx: DiagCtx) {
-    let mut check = diag_ctx.start_check("error_codes");
+pub fn check(root_path: &Path, search_paths: &[&Path], ci_info: &crate::CiInfo, tidy_ctx: TidyCtx) {
+    let mut check = tidy_ctx.start_check("error_codes");
 
     // Check that no error code explanation was removed.
     check_removed_error_code_explanation(ci_info, &mut check);

src/tools/tidy/src/extdeps.rs

@@ -4,7 +4,7 @@ use std::fs;
 use std::path::Path;
 
 use crate::deps::WorkspaceInfo;
-use crate::diagnostics::DiagCtx;
+use crate::diagnostics::TidyCtx;
 
 /// List of allowed sources for packages.
 const ALLOWED_SOURCES: &[&str] = &[
@@ -15,8 +15,8 @@ const ALLOWED_SOURCES: &[&str] = &[
 
 /// Checks for external package sources. `root` is the path to the directory that contains the
 /// workspace `Cargo.toml`.
-pub fn check(root: &Path, diag_ctx: DiagCtx) {
-    let mut check = diag_ctx.start_check("extdeps");
+pub fn check(root: &Path, tidy_ctx: TidyCtx) {
+    let mut check = tidy_ctx.start_check("extdeps");
 
     for &WorkspaceInfo { path, submodules, .. } in crate::deps::WORKSPACES {
         if crate::deps::has_missing_submodule(root, submodules) {