Auto merge of #63341 - Centril:rollup-hkhxahb, r=Centril

Rollup of 9 pull requests

Successful merges:

 - #63034 (Fix generator size regressions due to optimization)
 - #63035 (Use MaybeUninit to produce more correct layouts)
 - #63163 (add a pair of whitespace after remove parentheses)
 - #63294 (tests for async/await drop order)
 - #63307 (don't ignore mir_dump folder)
 - #63308 (PlaceRef's base is already a reference)
 - #63310 (Tests around moving parts of structs and tuples across await points)
 - #63314 (doc: the content has since been moved to the guide)
 - #63333 (Remove unnecessary features from compiler error code list)

Failed merges:

r? @ghost

Author: bors

.gitignore

@@ -52,7 +52,6 @@ config.mk
 config.stamp
 keywords.md
 lexer.ml
-mir_dump
 Session.vim
 src/etc/dl
 tmp.*.rs

src/README.md

@@ -5,10 +5,7 @@ This directory contains the source code of the rust project, including:
 
 For more information on how various parts of the compiler work, see the [rustc guide].
 
-There is also useful content in the following READMEs, which are gradually being moved over to the guide:
-- https://github.com/rust-lang/rust/tree/master/src/librustc/ty/query
-- https://github.com/rust-lang/rust/tree/master/src/librustc/dep_graph
-- https://github.com/rust-lang/rust/tree/master/src/librustc/infer/higher_ranked
-- https://github.com/rust-lang/rust/tree/master/src/librustc/infer/lexical_region_resolve
+There is also useful content in this README:
+https://github.com/rust-lang/rust/tree/master/src/librustc/infer/lexical_region_resolve.
 
 [rustc guide]: https://rust-lang.github.io/rustc-guide/about-this-guide.html

src/libcore/mem/maybe_uninit.rs

@@ -209,6 +209,8 @@ use crate::mem::ManuallyDrop;
 /// guarantee may evolve.
 #[allow(missing_debug_implementations)]
 #[stable(feature = "maybe_uninit", since = "1.36.0")]
+// Lang item so we can wrap other types in it. This is useful for generators.
+#[cfg_attr(not(bootstrap), lang = "maybe_uninit")]
 #[derive(Copy)]
 #[repr(transparent)]
 pub union MaybeUninit<T> {

src/librustc/middle/lang_items.rs

@@ -365,6 +365,8 @@ language_item_table! {
 
     ManuallyDropItem,            "manually_drop",      manually_drop,           Target::Struct;
 
+    MaybeUninitLangItem,         "maybe_uninit",       maybe_uninit,            Target::Union;
+
     DebugTraitLangItem,          "debug_trait",        debug_trait,             Target::Trait;
 
     // Align offset for stride != 1, must not panic.

src/librustc/ty/context.rs

@@ -2347,18 +2347,17 @@ impl<'tcx> TyCtxt<'tcx> {
         self.mk_ty(Foreign(def_id))
     }
 
-    pub fn mk_box(self, ty: Ty<'tcx>) -> Ty<'tcx> {
-        let def_id = self.require_lang_item(lang_items::OwnedBoxLangItem);
-        let adt_def = self.adt_def(def_id);
-        let substs = InternalSubsts::for_item(self, def_id, |param, substs| {
+    fn mk_generic_adt(self, wrapper_def_id: DefId, ty_param: Ty<'tcx>) -> Ty<'tcx> {
+        let adt_def = self.adt_def(wrapper_def_id);
+        let substs = InternalSubsts::for_item(self, wrapper_def_id, |param, substs| {
             match param.kind {
                 GenericParamDefKind::Lifetime |
                 GenericParamDefKind::Const => {
                     bug!()
                 }
                 GenericParamDefKind::Type { has_default, .. } => {
                     if param.index == 0 {
-                        ty.into()
+                        ty_param.into()
                     } else {
                         assert!(has_default);
                         self.type_of(param.def_id).subst(self, substs).into()
@@ -2369,6 +2368,18 @@ impl<'tcx> TyCtxt<'tcx> {
         self.mk_ty(Adt(adt_def, substs))
     }
 
+    #[inline]
+    pub fn mk_box(self, ty: Ty<'tcx>) -> Ty<'tcx> {
+        let def_id = self.require_lang_item(lang_items::OwnedBoxLangItem);
+        self.mk_generic_adt(def_id, ty)
+    }
+
+    #[inline]
+    pub fn mk_maybe_uninit(self, ty: Ty<'tcx>) -> Ty<'tcx> {
+        let def_id = self.require_lang_item(lang_items::MaybeUninitLangItem);
+        self.mk_generic_adt(def_id, ty)
+    }
+
     #[inline]
     pub fn mk_ptr(self, tm: TypeAndMut<'tcx>) -> Ty<'tcx> {
         self.mk_ty(RawPtr(tm))

src/librustc/ty/layout.rs

@@ -1368,6 +1368,27 @@ impl<'tcx> LayoutCx<'tcx, TyCtxt<'tcx>> {
             }
         }
 
+        // Count the number of variants in use. If only one of them, then it is
+        // impossible to overlap any locals in our layout. In this case it's
+        // always better to make the remaining locals ineligible, so we can
+        // lay them out with the other locals in the prefix and eliminate
+        // unnecessary padding bytes.
+        {
+            let mut used_variants = BitSet::new_empty(info.variant_fields.len());
+            for assignment in &assignments {
+                match assignment {
+                    Assigned(idx) => { used_variants.insert(*idx); }
+                    _ => {}
+                }
+            }
+            if used_variants.count() < 2 {
+                for assignment in assignments.iter_mut() {
+                    *assignment = Ineligible(None);
+                }
+                ineligible_locals.insert_all();
+            }
+        }
+
         // Write down the order of our locals that will be promoted to the prefix.
         {
             let mut idx = 0u32;
@@ -1406,24 +1427,21 @@ impl<'tcx> LayoutCx<'tcx, TyCtxt<'tcx>> {
             Abi::Scalar(s) => s.clone(),
             _ => bug!(),
         };
-        // FIXME(eddyb) wrap each promoted type in `MaybeUninit` so that they
-        // don't poison the `largest_niche` or `abi` fields of `prefix`.
         let promoted_layouts = ineligible_locals.iter()
             .map(|local| subst_field(info.field_tys[local]))
+            .map(|ty| tcx.mk_maybe_uninit(ty))
             .map(|ty| self.layout_of(ty));
         let prefix_layouts = substs.prefix_tys(def_id, tcx)
             .map(|ty| self.layout_of(ty))
             .chain(iter::once(Ok(discr_layout)))
             .chain(promoted_layouts)
             .collect::<Result<Vec<_>, _>>()?;
-        let mut prefix = self.univariant_uninterned(
+        let prefix = self.univariant_uninterned(
             ty,
             &prefix_layouts,
             &ReprOptions::default(),
             StructKind::AlwaysSized,
         )?;
-        // FIXME(eddyb) need `MaybeUninit` around promoted types (see above).
-        prefix.largest_niche = None;
 
         let (prefix_size, prefix_align) = (prefix.size, prefix.align);
 

src/librustc_lint/unused.rs

@@ -15,7 +15,7 @@ use syntax::print::pprust;
 use syntax::symbol::{kw, sym};
 use syntax::symbol::Symbol;
 use syntax::util::parser;
-use syntax_pos::Span;
+use syntax_pos::{Span, BytePos};
 
 use rustc::hir;
 
@@ -353,31 +353,46 @@ declare_lint! {
 declare_lint_pass!(UnusedParens => [UNUSED_PARENS]);
 
 impl UnusedParens {
+
+    fn is_expr_parens_necessary(inner: &ast::Expr, followed_by_block: bool) -> bool {
+        followed_by_block && match inner.node {
+            ast::ExprKind::Ret(_) | ast::ExprKind::Break(..) => true,
+            _ => parser::contains_exterior_struct_lit(&inner),
+        }
+    }
+
     fn check_unused_parens_expr(&self,
-                                cx: &EarlyContext<'_>,
-                                value: &ast::Expr,
-                                msg: &str,
-                                followed_by_block: bool) {
+                                     cx: &EarlyContext<'_>,
+                                     value: &ast::Expr,
+                                     msg: &str,
+                                     followed_by_block: bool,
+                                     left_pos: Option<BytePos>,
+                                     right_pos: Option<BytePos>) {
         match value.node {
             ast::ExprKind::Paren(ref inner) => {
-                let necessary = followed_by_block && match inner.node {
-                    ast::ExprKind::Ret(_) | ast::ExprKind::Break(..) => true,
-                    _ => parser::contains_exterior_struct_lit(&inner),
-                };
-                if !necessary {
+                if !Self::is_expr_parens_necessary(inner, followed_by_block) {
                     let expr_text = if let Ok(snippet) = cx.sess().source_map()
                         .span_to_snippet(value.span) {
                             snippet
                         } else {
                             pprust::expr_to_string(value)
                         };
-                    Self::remove_outer_parens(cx, value.span, &expr_text, msg);
+                    let keep_space = (
+                        left_pos.map(|s| s >= value.span.lo()).unwrap_or(false),
+                        right_pos.map(|s| s <= value.span.hi()).unwrap_or(false),
+                    );
+                    Self::remove_outer_parens(cx, value.span, &expr_text, msg, keep_space);
                 }
             }
             ast::ExprKind::Let(_, ref expr) => {
                 // FIXME(#60336): Properly handle `let true = (false && true)`
                 // actually needing the parenthesis.
-                self.check_unused_parens_expr(cx, expr, "`let` head expression", followed_by_block);
+                self.check_unused_parens_expr(
+                    cx, expr,
+                    "`let` head expression",
+                    followed_by_block,
+                    None, None
+                );
             }
             _ => {}
         }
@@ -394,11 +409,15 @@ impl UnusedParens {
                 } else {
                     pprust::pat_to_string(value)
                 };
-            Self::remove_outer_parens(cx, value.span, &pattern_text, msg);
+            Self::remove_outer_parens(cx, value.span, &pattern_text, msg, (false, false));
         }
     }
 
-    fn remove_outer_parens(cx: &EarlyContext<'_>, span: Span, pattern: &str, msg: &str) {
+    fn remove_outer_parens(cx: &EarlyContext<'_>,
+                           span: Span,
+                           pattern: &str,
+                           msg: &str,
+                           keep_space: (bool, bool)) {
         let span_msg = format!("unnecessary parentheses around {}", msg);
         let mut err = cx.struct_span_lint(UNUSED_PARENS, span, &span_msg);
         let mut ate_left_paren = false;
@@ -424,11 +443,27 @@ impl UnusedParens {
                     },
                     _ => false,
                 }
-            }).to_owned();
+            });
+
+        let replace = {
+            let mut replace = if keep_space.0 {
+                let mut s = String::from(" ");
+                s.push_str(parens_removed);
+                s
+            } else {
+                String::from(parens_removed)
+            };
+
+            if keep_space.1 {
+                replace.push(' ');
+            }
+            replace
+        };
+
         err.span_suggestion_short(
             span,
             "remove these parentheses",
-            parens_removed,
+            replace,
             Applicability::MachineApplicable,
         );
         err.emit();
@@ -438,14 +473,35 @@ impl UnusedParens {
 impl EarlyLintPass for UnusedParens {
     fn check_expr(&mut self, cx: &EarlyContext<'_>, e: &ast::Expr) {
         use syntax::ast::ExprKind::*;
-        let (value, msg, followed_by_block) = match e.node {
-            If(ref cond, ..) => (cond, "`if` condition", true),
-            While(ref cond, ..) => (cond, "`while` condition", true),
-            ForLoop(_, ref cond, ..) => (cond, "`for` head expression", true),
-            Match(ref head, _) => (head, "`match` head expression", true),
-            Ret(Some(ref value)) => (value, "`return` value", false),
-            Assign(_, ref value) => (value, "assigned value", false),
-            AssignOp(.., ref value) => (value, "assigned value", false),
+        let (value, msg, followed_by_block, left_pos, right_pos) = match e.node {
+            If(ref cond, ref block, ..) => {
+                let left = e.span.lo() + syntax_pos::BytePos(2);
+                let right = block.span.lo();
+                (cond, "`if` condition", true, Some(left), Some(right))
+            }
+
+            While(ref cond, ref block, ..) => {
+                let left = e.span.lo() + syntax_pos::BytePos(5);
+                let right = block.span.lo();
+                (cond, "`while` condition", true, Some(left), Some(right))
+            },
+
+            ForLoop(_, ref cond, ref block, ..) => {
+                (cond, "`for` head expression", true, None, Some(block.span.lo()))
+            }
+
+            Match(ref head, _) => {
+                let left = e.span.lo() + syntax_pos::BytePos(5);
+                (head, "`match` head expression", true, Some(left), None)
+            }
+
+            Ret(Some(ref value)) => {
+                let left = e.span.lo() + syntax_pos::BytePos(3);
+                (value, "`return` value", false, Some(left), None)
+            }
+
+            Assign(_, ref value) => (value, "assigned value", false, None, None),
+            AssignOp(.., ref value) => (value, "assigned value", false, None, None),
             // either function/method call, or something this lint doesn't care about
             ref call_or_other => {
                 let (args_to_check, call_kind) = match *call_or_other {
@@ -467,12 +523,12 @@ impl EarlyLintPass for UnusedParens {
                 }
                 let msg = format!("{} argument", call_kind);
                 for arg in args_to_check {
-                    self.check_unused_parens_expr(cx, arg, &msg, false);
+                    self.check_unused_parens_expr(cx, arg, &msg, false, None, None);
                 }
                 return;
             }
         };
-        self.check_unused_parens_expr(cx, &value, msg, followed_by_block);
+        self.check_unused_parens_expr(cx, &value, msg, followed_by_block, left_pos, right_pos);
     }
 
     fn check_pat(&mut self, cx: &EarlyContext<'_>, p: &ast::Pat) {
@@ -492,7 +548,7 @@ impl EarlyLintPass for UnusedParens {
     fn check_stmt(&mut self, cx: &EarlyContext<'_>, s: &ast::Stmt) {
         if let ast::StmtKind::Local(ref local) = s.node {
             if let Some(ref value) = local.init {
-                self.check_unused_parens_expr(cx, &value, "assigned value", false);
+                self.check_unused_parens_expr(cx, &value, "assigned value", false, None, None);
             }
         }
     }