Auto merge of #55433 - kennytm:rollup, r=kennytm

Rollup of 11 pull requests

Successful merges:

 - #55148 (Implement FromStr for PathBuf)
 - #55185 (path suggestions in Rust 2018 should point out the change in semantics)
 - #55191 (Fix sub-variant doc display)
 - #55199 (Impl items have generics)
 - #55244 (Don't rerun MIR passes when inlining)
 - #55252 (Add MaybeUninit::new)
 - #55257 (Allow extern statics with an extern type)
 - #55389 (Remove unnecessary mut in iterator.find_map documentation example, R…)
 - #55406 (Update string.rs)
 - #55412 (Fix an ICE in the min_const_fn analysis)
 - #55421 (Add ManuallyDrop::take)

Author: bors

src/liballoc/string.rs

@@ -413,7 +413,7 @@ impl String {
     ///
     /// // These are all done without reallocating...
     /// let cap = s.capacity();
-    /// for i in 0..10 {
+    /// for _ in 0..10 {
     ///     s.push('a');
     /// }
     ///

src/libcore/iter/iterator.rs

@@ -1857,7 +1857,7 @@ pub trait Iterator {
     /// ```
     /// let a = ["lol", "NaN", "2", "5"];
     ///
-    /// let mut first_number = a.iter().find_map(|s| s.parse().ok());
+    /// let first_number = a.iter().find_map(|s| s.parse().ok());
     ///
     /// assert_eq!(first_number, Some(2));
     /// ```

src/libcore/lib.rs

@@ -82,6 +82,7 @@
 #![feature(const_fn)]
 #![feature(const_int_ops)]
 #![feature(const_fn_union)]
+#![feature(const_manually_drop_new)]
 #![feature(custom_attribute)]
 #![feature(doc_cfg)]
 #![feature(doc_spotlight)]

src/libcore/mem.rs

@@ -973,6 +973,26 @@ impl<T> ManuallyDrop<T> {
     pub fn into_inner(slot: ManuallyDrop<T>) -> T {
         slot.value
     }
+
+    /// Takes the contained value out.
+    ///
+    /// This method is primarily intended for moving out values in drop.
+    /// Instead of using [`ManuallyDrop::drop`] to manually drop the value,
+    /// you can use this method to take the value and use it however desired.
+    /// `Drop` will be invoked on the returned value following normal end-of-scope rules.
+    ///
+    /// If you have ownership of the container, you can use [`ManuallyDrop::into_inner`] instead.
+    ///
+    /// # Safety
+    ///
+    /// This function semantically moves out the contained value without preventing further usage.
+    /// It is up to the user of this method to ensure that this container is not used again.
+    #[must_use = "if you don't need the value, you can use `ManuallyDrop::drop` instead"]
+    #[unstable(feature = "manually_drop_take", issue = "55422")]
+    #[inline]
+    pub unsafe fn take(slot: &mut ManuallyDrop<T>) -> T {
+        ManuallyDrop::into_inner(ptr::read(slot))
+    }
 }
 
 impl<T: ?Sized> ManuallyDrop<T> {
@@ -1021,6 +1041,15 @@ pub union MaybeUninit<T> {
 }
 
 impl<T> MaybeUninit<T> {
+    /// Create a new `MaybeUninit` initialized with the given value.
+    ///
+    /// Note that dropping a `MaybeUninit` will never call `T`'s drop code.
+    /// It is your responsibility to make sure `T` gets dropped if it got initialized.
+    #[unstable(feature = "maybe_uninit", issue = "53491")]
+    pub const fn new(val: T) -> MaybeUninit<T> {
+        MaybeUninit { value: ManuallyDrop::new(val) }
+    }
+
     /// Create a new `MaybeUninit` in an uninitialized state.
     ///
     /// Note that dropping a `MaybeUninit` will never call `T`'s drop code.

src/librustc/mir/mod.rs

@@ -69,13 +69,38 @@ impl<'tcx> HasLocalDecls<'tcx> for Mir<'tcx> {
     }
 }
 
+/// The various "big phases" that MIR goes through.
+///
+/// Warning: ordering of variants is significant
+#[derive(Copy, Clone, RustcEncodable, RustcDecodable, Debug, PartialEq, Eq, PartialOrd, Ord)]
+pub enum MirPhase {
+    Build = 0,
+    Const = 1,
+    Validated = 2,
+    Optimized = 3,
+}
+
+impl MirPhase {
+    /// Gets the index of the current MirPhase within the set of all MirPhases.
+    pub fn phase_index(&self) -> usize {
+        *self as usize
+    }
+}
+
 /// Lowered representation of a single function.
 #[derive(Clone, RustcEncodable, RustcDecodable, Debug)]
 pub struct Mir<'tcx> {
     /// List of basic blocks. References to basic block use a newtyped index type `BasicBlock`
     /// that indexes into this vector.
     basic_blocks: IndexVec<BasicBlock, BasicBlockData<'tcx>>,
 
+    /// Records how far through the "desugaring and optimization" process this particular
+    /// MIR has traversed. This is particularly useful when inlining, since in that context
+    /// we instantiate the promoted constants and add them to our promoted vector -- but those
+    /// promoted items have already been optimized, whereas ours have not. This field allows
+    /// us to see the difference and forego optimization on the inlined promoted items.
+    pub phase: MirPhase,
+
     /// List of source scopes; these are referenced by statements
     /// and used for debuginfo. Indexed by a `SourceScope`.
     pub source_scopes: IndexVec<SourceScope, SourceScopeData>,
@@ -151,6 +176,7 @@ impl<'tcx> Mir<'tcx> {
         );
 
         Mir {
+            phase: MirPhase::Build,
             basic_blocks,
             source_scopes,
             source_scope_local_data,
@@ -368,6 +394,7 @@ pub enum Safety {
 }
 
 impl_stable_hash_for!(struct Mir<'tcx> {
+    phase,
     basic_blocks,
     source_scopes,
     source_scope_local_data,
@@ -616,6 +643,13 @@ impl_stable_hash_for!(enum self::ImplicitSelfKind {
     None
 });
 
+impl_stable_hash_for!(enum self::MirPhase {
+    Build,
+    Const,
+    Validated,
+    Optimized,
+});
+
 mod binding_form_impl {
     use ich::StableHashingContext;
     use rustc_data_structures::stable_hasher::{HashStable, StableHasher, StableHasherResult};
@@ -2905,6 +2939,7 @@ pub enum ClosureOutlivesSubject<'tcx> {
 
 CloneTypeFoldableAndLiftImpls! {
     BlockTailInfo,
+    MirPhase,
     Mutability,
     SourceInfo,
     UpvarDecl,
@@ -2917,6 +2952,7 @@ CloneTypeFoldableAndLiftImpls! {
 
 BraceStructTypeFoldableImpl! {
     impl<'tcx> TypeFoldable<'tcx> for Mir<'tcx> {
+        phase,
         basic_blocks,
         source_scopes,
         source_scope_local_data,

src/librustc/util/ppaux.rs

@@ -251,25 +251,17 @@ impl PrintContext {
     fn parameterized<F: fmt::Write>(&mut self,
                                     f: &mut F,
                                     substs: &subst::Substs<'_>,
-                                    mut did: DefId,
+                                    did: DefId,
                                     projections: &[ty::ProjectionPredicate<'_>])
                                     -> fmt::Result {
         let key = ty::tls::with(|tcx| tcx.def_key(did));
-        let mut item_name = if let Some(name) = key.disambiguated_data.data.get_opt_name() {
-            Some(name)
-        } else {
-            did.index = key.parent.unwrap_or_else(
-                || bug!("finding type for {:?}, encountered def-id {:?} with no parent",
-                        did, did));
-            self.parameterized(f, substs, did, projections)?;
-            return write!(f, "::{}", key.disambiguated_data.data.as_interned_str());
-        };
 
         let verbose = self.is_verbose;
         let mut num_supplied_defaults = 0;
         let mut has_self = false;
         let mut own_counts: GenericParamCount = Default::default();
         let mut is_value_path = false;
+        let mut item_name = Some(key.disambiguated_data.data.as_interned_str());
         let fn_trait_kind = ty::tls::with(|tcx| {
             // Unfortunately, some kinds of items (e.g., closures) don't have
             // generics. So walk back up the find the closest parent that DOES
@@ -282,6 +274,7 @@ impl PrintContext {
                     DefPathData::AssocTypeInImpl(_) |
                     DefPathData::AssocExistentialInImpl(_) |
                     DefPathData::Trait(_) |
+                    DefPathData::Impl |
                     DefPathData::TypeNs(_) => {
                         break;
                     }
@@ -292,7 +285,6 @@ impl PrintContext {
                     }
                     DefPathData::CrateRoot |
                     DefPathData::Misc |
-                    DefPathData::Impl |
                     DefPathData::Module(_) |
                     DefPathData::MacroDef(_) |
                     DefPathData::ClosureExpr |

src/librustc_mir/const_eval.rs

@@ -612,6 +612,13 @@ pub fn const_eval_raw_provider<'a, 'tcx>(
             other => return other,
         }
     }
+    // the first trace is for replicating an ice
+    // There's no tracking issue, but the next two lines concatenated link to the discussion on
+    // zulip. It's not really possible to test this, because it doesn't show up in diagnostics
+    // or MIR.
+    // https://rust-lang.zulipchat.com/#narrow/stream/146212-t-compiler.2Fconst-eval/
+    // subject/anon_const_instance_printing/near/135980032
+    trace!("const eval: {}", key.value.instance);
     trace!("const eval: {:?}", key);
 
     let cid = key.value;

src/librustc_mir/dataflow/impls/borrows.rs

@@ -184,7 +184,6 @@ impl<'a, 'gcx, 'tcx> Borrows<'a, 'gcx, 'tcx> {
     }
 
     crate fn borrows(&self) -> &IndexVec<BorrowIndex, BorrowData<'tcx>> { &self.borrow_set.borrows }
-    pub fn scope_tree(&self) -> &Lrc<region::ScopeTree> { &self.scope_tree }
 
     pub fn location(&self, idx: BorrowIndex) -> &Location {
         &self.borrow_set.borrows[idx].reserve_location

src/librustc_mir/dataflow/mod.rs

@@ -724,20 +724,6 @@ impl<'a, 'tcx, D> DataflowAnalysis<'a, 'tcx, D> where D: BitDenotation
             }
         }
     }
-
-    pub fn new_from_sets(mir: &'a Mir<'tcx>,
-                         dead_unwinds: &'a BitSet<mir::BasicBlock>,
-                         sets: AllSets<D::Idx>,
-                         denotation: D) -> Self {
-        DataflowAnalysis {
-            mir,
-            dead_unwinds,
-            flow_state: DataflowState {
-                sets: sets,
-                operator: denotation,
-            }
-        }
-    }
 }
 
 impl<'a, 'tcx: 'a, D> DataflowAnalysis<'a, 'tcx, D> where D: BitDenotation