Auto merge of #62253 - Centril:rollup-115uuuq, r=Centril

Rollup of 8 pull requests

Successful merges:

 - #62062 (Use a more efficient iteration order for forward dataflow)
 - #62063 (Use a more efficient iteration order for backward dataflow)
 - #62224 (rustdoc: remove unused derives and variants)
 - #62228 (Extend the #[must_use] lint to boxed types)
 - #62235 (Extend the `#[must_use]` lint to arrays)
 - #62239 (Fix a typo)
 - #62241 (Always parse 'async unsafe fn' + properly ban in 2015)
 - #62248 (before_exec actually will only get deprecated with 1.37)

Failed merges:

r? @ghost

RELEASES.md

@@ -309,9 +309,9 @@ Misc
 
 Compatibility Notes
 -------------------
-- [`Command::before_exec` is now deprecated in favor of the
-  unsafe method `Command::pre_exec`.][58059]
-- [Use of `ATOMIC_{BOOL, ISIZE, USIZE}_INIT` is now deprecated.][57425] As you
+- [`Command::before_exec` is being replaced by the unsafe method
+  `Command::pre_exec`][58059] and will be deprecated with Rust 1.37.0.
+- [Use of `ATOMIC_{BOOL, ISIZE, USIZE}_INIT` is now deprecated][57425] as you
   can now use `const` functions in `static` variables.
 
 [58370]: https://github.com/rust-lang/rust/pull/58370/

src/libcore/char/methods.rs

@@ -337,16 +337,16 @@ impl char {
     /// ```
     /// // as chars
     /// let eastern = '東';
-    /// let capitol = '京';
+    /// let capital = '京';
     ///
     /// // both can be represented as three bytes
     /// assert_eq!(3, eastern.len_utf8());
-    /// assert_eq!(3, capitol.len_utf8());
+    /// assert_eq!(3, capital.len_utf8());
     ///
     /// // as a &str, these two are encoded in UTF-8
     /// let tokyo = "東京";
     ///
-    /// let len = eastern.len_utf8() + capitol.len_utf8();
+    /// let len = eastern.len_utf8() + capital.len_utf8();
     ///
     /// // we can see that they take six bytes total...
     /// assert_eq!(6, tokyo.len());

src/librustc_lint/unused.rs

@@ -48,7 +48,7 @@ impl<'a, 'tcx> LateLintPass<'a, 'tcx> for UnusedResults {
         }
 
         let ty = cx.tables.expr_ty(&expr);
-        let type_permits_lack_of_use = check_must_use_ty(cx, ty, &expr, s.span, "");
+        let type_permits_lack_of_use = check_must_use_ty(cx, ty, &expr, s.span, "", "", false);
 
         let mut fn_warned = false;
         let mut op_warned = false;
@@ -133,23 +133,39 @@ impl<'a, 'tcx> LateLintPass<'a, 'tcx> for UnusedResults {
             ty: Ty<'tcx>,
             expr: &hir::Expr,
             span: Span,
-            descr_post_path: &str,
+            descr_pre: &str,
+            descr_post: &str,
+            plural: bool,
         ) -> bool {
             if ty.is_unit() || cx.tcx.is_ty_uninhabited_from(
                 cx.tcx.hir().get_module_parent(expr.hir_id), ty)
             {
                 return true;
             }
 
+            let plural_suffix = if plural { "s" } else { "" };
+
             match ty.sty {
-                ty::Adt(def, _) => check_must_use_def(cx, def.did, span, "", descr_post_path),
+                ty::Adt(..) if ty.is_box() => {
+                    let boxed_ty = ty.boxed_ty();
+                    let descr_pre = &format!("{}boxed ", descr_pre);
+                    check_must_use_ty(cx, boxed_ty, expr, span, descr_pre, descr_post, plural)
+                }
+                ty::Adt(def, _) => {
+                    check_must_use_def(cx, def.did, span, descr_pre, descr_post)
+                }
                 ty::Opaque(def, _) => {
                     let mut has_emitted = false;
                     for (predicate, _) in &cx.tcx.predicates_of(def).predicates {
                         if let ty::Predicate::Trait(ref poly_trait_predicate) = predicate {
                             let trait_ref = poly_trait_predicate.skip_binder().trait_ref;
                             let def_id = trait_ref.def_id;
-                            if check_must_use_def(cx, def_id, span, "implementer of ", "") {
+                            let descr_pre = &format!(
+                                "{}implementer{} of ",
+                                descr_pre,
+                                plural_suffix,
+                            );
+                            if check_must_use_def(cx, def_id, span, descr_pre, descr_post) {
                                 has_emitted = true;
                                 break;
                             }
@@ -162,7 +178,12 @@ impl<'a, 'tcx> LateLintPass<'a, 'tcx> for UnusedResults {
                     for predicate in binder.skip_binder().iter() {
                         if let ty::ExistentialPredicate::Trait(ref trait_ref) = predicate {
                             let def_id = trait_ref.def_id;
-                            if check_must_use_def(cx, def_id, span, "", " trait object") {
+                            let descr_post = &format!(
+                                " trait object{}{}",
+                                plural_suffix,
+                                descr_post,
+                            );
+                            if check_must_use_def(cx, def_id, span, descr_pre, descr_post) {
                                 has_emitted = true;
                                 break;
                             }
@@ -179,14 +200,27 @@ impl<'a, 'tcx> LateLintPass<'a, 'tcx> for UnusedResults {
                         vec![]
                     };
                     for (i, ty) in tys.iter().map(|k| k.expect_ty()).enumerate() {
-                        let descr_post_path = &format!(" in tuple element {}", i);
+                        let descr_post = &format!(" in tuple element {}", i);
                         let span = *spans.get(i).unwrap_or(&span);
-                        if check_must_use_ty(cx, ty, expr, span, descr_post_path) {
+                        if check_must_use_ty(cx, ty, expr, span, descr_pre, descr_post, plural) {
                             has_emitted = true;
                         }
                     }
                     has_emitted
                 }
+                ty::Array(ty, len) => match len.assert_usize(cx.tcx) {
+                    // If the array is definitely non-empty, we can do `#[must_use]` checking.
+                    Some(n) if n != 0 => {
+                        let descr_pre = &format!(
+                            "{}array{} of ",
+                            descr_pre,
+                            plural_suffix,
+                        );
+                        check_must_use_ty(cx, ty, expr, span, descr_pre, descr_post, true)
+                    }
+                    // Otherwise, we don't lint, to avoid false positives.
+                    _ => false,
+                }
                 _ => false,
             }
         }

src/librustc_mir/dataflow/mod.rs

@@ -228,9 +228,25 @@ where
     BD: BitDenotation<'tcx>,
 {
     fn walk_cfg(&mut self, in_out: &mut BitSet<BD::Idx>) {
-        let mut dirty_queue: WorkQueue<mir::BasicBlock> =
-            WorkQueue::with_all(self.builder.body.basic_blocks().len());
         let body = self.builder.body;
+
+        // Initialize the dirty queue in reverse post-order. This makes it more likely that the
+        // entry state for each basic block will have the effects of its predecessors applied
+        // before it is processed. In fact, for CFGs without back edges, this guarantees that
+        // dataflow will converge in exactly `N` iterations, where `N` is the number of basic
+        // blocks.
+        let mut dirty_queue: WorkQueue<mir::BasicBlock> =
+            WorkQueue::with_none(body.basic_blocks().len());
+        for (bb, _) in traversal::reverse_postorder(body) {
+            dirty_queue.insert(bb);
+        }
+
+        // Add blocks which are not reachable from START_BLOCK to the work queue. These blocks will
+        // be processed after the ones added above.
+        for bb in body.basic_blocks().indices() {
+            dirty_queue.insert(bb);
+        }
+
         while let Some(bb) = dirty_queue.pop() {
             let (on_entry, trans) = self.builder.flow_state.sets.get_mut(bb.index());
             debug_assert!(in_out.words().len() == on_entry.words().len());

src/librustc_mir/util/liveness.rs

@@ -75,9 +75,24 @@ pub fn liveness_of_locals<'tcx>(
 
     let mut bits = LiveVarSet::new_empty(num_live_vars);
 
-    // queue of things that need to be re-processed, and a set containing
-    // the things currently in the queue
-    let mut dirty_queue: WorkQueue<BasicBlock> = WorkQueue::with_all(body.basic_blocks().len());
+    // The dirty queue contains the set of basic blocks whose entry sets have changed since they
+    // were last processed. At the start of the analysis, we initialize the queue in post-order to
+    // make it more likely that the entry set for a given basic block will have the effects of all
+    // its successors in the CFG applied before it is processed.
+    //
+    // FIXME(ecstaticmorse): Reverse post-order on the reverse CFG may generate a better iteration
+    // order when cycles are present, but the overhead of computing the reverse CFG may outweigh
+    // any benefits. Benchmark this and find out.
+    let mut dirty_queue: WorkQueue<BasicBlock> = WorkQueue::with_none(body.basic_blocks().len());
+    for (bb, _) in traversal::postorder(body) {
+        dirty_queue.insert(bb);
+    }
+
+    // Add blocks which are not reachable from START_BLOCK to the work queue. These blocks will
+    // be processed after the ones added above.
+    for bb in body.basic_blocks().indices() {
+        dirty_queue.insert(bb);
+    }
 
     let predecessors = body.predecessors();
 

src/librustc_passes/ast_validation.rs

@@ -837,13 +837,6 @@ impl<'a> Visitor<'a> for AstValidator<'a> {
                                  the relevant `fold_*()` method in `PlaceholderExpander`?");
     }
 
-    fn visit_fn_header(&mut self, header: &'a FnHeader) {
-        if header.asyncness.node.is_async() && self.session.rust_2015() {
-            struct_span_err!(self.session, header.asyncness.span, E0670,
-                             "`async fn` is not permitted in the 2015 edition").emit();
-        }
-    }
-
     fn visit_impl_item(&mut self, ii: &'a ImplItem) {
         match ii.node {
             ImplItemKind::Method(ref sig, _) => {

src/librustdoc/clean/cfg.rs

@@ -16,7 +16,7 @@ use syntax_pos::Span;
 
 use crate::html::escape::Escape;
 
-#[derive(Clone, RustcEncodable, RustcDecodable, Debug, PartialEq, Eq, Hash)]
+#[derive(Clone, Debug, PartialEq, Eq, Hash)]
 pub enum Cfg {
     /// Accepts all configurations.
     True,