Auto merge of #60351 - Centril:rollup-5xv3tka, r=Centril

Rollup of 4 pull requests

Successful merges:

 - #60022 (Document `Item` type in `std::env::SplitPaths` iterator.)
 - #60270 (rustc: Flag metadata compatible with multiple CGUs)
 - #60325 (Document ast::ExprKind::Type)
 - #60347 (Remove `-Z two-phase-borrows` and `-Z two-phase-beyond-autoref`)

Failed merges:

r? @ghost

src/librustc/session/config.rs

@@ -155,13 +155,12 @@ pub enum OutputType {
 impl OutputType {
     fn is_compatible_with_codegen_units_and_single_output_file(&self) -> bool {
         match *self {
-            OutputType::Exe | OutputType::DepInfo => true,
+            OutputType::Exe | OutputType::DepInfo | OutputType::Metadata => true,
             OutputType::Bitcode
             | OutputType::Assembly
             | OutputType::LlvmAssembly
             | OutputType::Mir
-            | OutputType::Object
-            | OutputType::Metadata => false,
+            | OutputType::Object => false,
         }
     }
 
@@ -1216,10 +1215,6 @@ fn parse_merge_functions(slot: &mut Option<MergeFunctions>, v: Option<&str>) ->
         "make unnamed regions display as '# (where # is some non-ident unique id)"),
     borrowck: Option<String> = (None, parse_opt_string, [UNTRACKED],
         "select which borrowck is used (`ast`, `mir`, `migrate`, or `compare`)"),
-    two_phase_borrows: bool = (false, parse_bool, [UNTRACKED],
-        "use two-phase reserved/active distinction for `&mut` borrows in MIR borrowck"),
-    two_phase_beyond_autoref: bool = (false, parse_bool, [UNTRACKED],
-        "when using two-phase-borrows, allow two phases even for non-autoref `&mut` borrows"),
     time_passes: bool = (false, parse_bool, [UNTRACKED],
         "measure time of each rustc pass"),
     time: bool = (false, parse_bool, [UNTRACKED],

src/librustc_mir/borrow_check/borrow_set.rs

@@ -1,5 +1,6 @@
 use crate::borrow_check::place_ext::PlaceExt;
 use crate::borrow_check::nll::ToRegionVid;
+use crate::borrow_check::path_utils::allow_two_phase_borrow;
 use crate::dataflow::indexes::BorrowIndex;
 use crate::dataflow::move_paths::MoveData;
 use rustc::mir::traversal;
@@ -299,13 +300,6 @@ fn visit_statement(
 }
 
 impl<'a, 'gcx, 'tcx> GatherBorrows<'a, 'gcx, 'tcx> {
-    /// Returns `true` if the borrow represented by `kind` is
-    /// allowed to be split into separate Reservation and
-    /// Activation phases.
-    fn allow_two_phase_borrow(&self, kind: mir::BorrowKind) -> bool {
-        kind.allows_two_phase_borrow()
-            || self.tcx.sess.opts.debugging_opts.two_phase_beyond_autoref
-    }
 
     /// If this is a two-phase borrow, then we will record it
     /// as "pending" until we find the activating use.
@@ -321,7 +315,7 @@ fn insert_as_pending_if_two_phase(
             start_location, assigned_place, borrow_index,
         );
 
-        if !self.allow_two_phase_borrow(kind) {
+        if !allow_two_phase_borrow(&self.tcx, kind) {
             debug!("  -> {:?}", start_location);
             return;
         }

src/librustc_mir/borrow_check/path_utils.rs

@@ -12,11 +12,10 @@
 /// allowed to be split into separate Reservation and
 /// Activation phases.
 pub(super) fn allow_two_phase_borrow<'a, 'tcx, 'gcx: 'tcx>(
-    tcx: &TyCtxt<'a, 'gcx, 'tcx>,
+    _tcx: &TyCtxt<'a, 'gcx, 'tcx>,
     kind: BorrowKind
 ) -> bool {
     kind.allows_two_phase_borrow()
-        || tcx.sess.opts.debugging_opts.two_phase_beyond_autoref
 }
 
 /// Control for the path borrow checking code

src/libstd/env.rs

@@ -359,9 +359,12 @@ fn _remove_var(k: &OsStr) {
 /// An iterator that splits an environment variable into paths according to
 /// platform-specific conventions.
 ///
+/// The iterator element type is [`PathBuf`].
+///
 /// This structure is created by the [`std::env::split_paths`] function. See its
 /// documentation for more.
 ///
+/// [`PathBuf`]: ../../std/path/struct.PathBuf.html
 /// [`std::env::split_paths`]: fn.split_paths.html
 #[stable(feature = "env", since = "1.0.0")]
 pub struct SplitPaths<'a> { inner: os_imp::SplitPaths<'a> }
@@ -369,7 +372,8 @@ pub struct SplitPaths<'a> { inner: os_imp::SplitPaths<'a> }
 /// Parses input according to platform conventions for the `PATH`
 /// environment variable.
 ///
-/// Returns an iterator over the paths contained in `unparsed`.
+/// Returns an iterator over the paths contained in `unparsed`. The iterator
+/// element type is [`PathBuf`].
 ///
 /// # Examples
 ///
@@ -386,6 +390,8 @@ pub struct SplitPaths<'a> { inner: os_imp::SplitPaths<'a> }
 ///     None => println!("{} is not defined in the environment.", key)
 /// }
 /// ```
+///
+/// [`PathBuf`]: ../../std/path/struct.PathBuf.html
 #[stable(feature = "env", since = "1.0.0")]
 pub fn split_paths<T: AsRef<OsStr> + ?Sized>(unparsed: &T) -> SplitPaths<'_> {
     SplitPaths { inner: os_imp::split_paths(unparsed.as_ref()) }

src/libsyntax/ast.rs

@@ -1137,6 +1137,7 @@ pub enum ExprKind {
     Lit(Lit),
     /// A cast (e.g., `foo as f64`).
     Cast(P<Expr>, P<Ty>),
+    /// A type ascription (e.g., `42: usize`).
     Type(P<Expr>, P<Ty>),
     /// An `if` block, with an optional `else` block.
     ///