Rollup of 12 pull requests

Cargo.lock

@@ -1726,15 +1726,6 @@ dependencies = [
  "cfg-if",
 ]
 
-[[package]]
-name = "log_settings"
-version = "0.1.2"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "19af41f0565d7c19b2058153ad0b42d4d5ce89ec4dbf06ed6741114a8b63e7cd"
-dependencies = [
- "lazy_static",
-]
-
 [[package]]
 name = "lsp-codec"
 version = "0.1.2"
@@ -3523,6 +3514,7 @@ dependencies = [
  "rustc_target",
  "tracing",
  "tracing-subscriber",
+ "tracing-tree",
  "winapi 0.3.9",
 ]
 
@@ -3810,7 +3802,6 @@ version = "0.0.0"
 dependencies = [
  "either",
  "itertools 0.9.0",
- "log_settings",
  "polonius-engine",
  "regex",
  "rustc_apfloat",
@@ -5105,9 +5096,9 @@ dependencies = [
 
 [[package]]
 name = "tracing-tree"
-version = "0.1.5"
+version = "0.1.6"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "e1a3dc4774db3a6b2d66a4f8d8de670e874ec3ed55615860c994927419b32c5f"
+checksum = "43aac8afb493b08e1e1904956f7407c1e671b9c83b26a17e1bd83d6a3520e350"
 dependencies = [
  "ansi_term 0.12.1",
  "atty",

compiler/rustc_ast_passes/src/ast_validation.rs

@@ -537,7 +537,8 @@ impl<'a> AstValidator<'a> {
     fn check_c_varadic_type(&self, fk: FnKind<'a>) {
         match (fk.ctxt(), fk.header()) {
             (Some(FnCtxt::Foreign), _) => return,
-            (Some(FnCtxt::Free), Some(header)) => match header.ext {
+            (Some(FnCtxt::Free), Some(header))
+            | (Some(FnCtxt::Assoc(AssocCtxt::Impl)), Some(header)) => match header.ext {
                 Extern::Explicit(StrLit { symbol_unescaped: sym::C, .. }) | Extern::Implicit
                     if matches!(header.unsafety, Unsafe::Yes(_)) =>
                 {

compiler/rustc_codegen_llvm/src/intrinsic.rs

@@ -793,14 +793,18 @@ fn generic_simd_intrinsic(
         require_simd!(arg_tys[1], "argument");
         let v_len = arg_tys[1].simd_size(tcx);
         require!(
-            m_len == v_len,
+            // Allow masks for vectors with fewer than 8 elements to be
+            // represented with a u8 or i8.
+            m_len == v_len || (m_len == 8 && v_len < 8),
             "mismatched lengths: mask length `{}` != other vector length `{}`",
             m_len,
             v_len
         );
         let i1 = bx.type_i1();
-        let i1xn = bx.type_vector(i1, m_len);
-        let m_i1s = bx.bitcast(args[0].immediate(), i1xn);
+        let im = bx.type_ix(v_len);
+        let i1xn = bx.type_vector(i1, v_len);
+        let m_im = bx.trunc(args[0].immediate(), im);
+        let m_i1s = bx.bitcast(m_im, i1xn);
         return Ok(bx.select(m_i1s, args[1].immediate(), args[2].immediate()));
     }
 

compiler/rustc_driver/Cargo.toml

@@ -11,6 +11,7 @@ crate-type = ["dylib"]
 libc = "0.2"
 tracing = { version = "0.1.18" }
 tracing-subscriber = { version = "0.2.10", default-features = false, features = ["fmt", "env-filter", "smallvec", "parking_lot", "ansi"] }
+tracing-tree = "0.1.6"
 rustc_middle = { path = "../rustc_middle" }
 rustc_ast_pretty = { path = "../rustc_ast_pretty" }
 rustc_target = { path = "../rustc_target" }

compiler/rustc_driver/src/lib.rs

@@ -1251,11 +1251,21 @@ pub fn init_env_logger(env: &str) {
         Ok(s) if s.is_empty() => return,
         Ok(_) => {}
     }
-    let builder = tracing_subscriber::FmtSubscriber::builder();
-
-    let builder = builder.with_env_filter(tracing_subscriber::EnvFilter::from_env(env));
-
-    builder.init()
+    let filter = tracing_subscriber::EnvFilter::from_env(env);
+    let layer = tracing_tree::HierarchicalLayer::default()
+        .with_indent_lines(true)
+        .with_ansi(true)
+        .with_targets(true)
+        .with_thread_ids(true)
+        .with_thread_names(true)
+        .with_wraparound(10)
+        .with_verbose_exit(true)
+        .with_verbose_entry(true)
+        .with_indent_amount(2);
+
+    use tracing_subscriber::layer::SubscriberExt;
+    let subscriber = tracing_subscriber::Registry::default().with(filter).with(layer);
+    tracing::subscriber::set_global_default(subscriber).unwrap();
 }
 
 pub fn main() -> ! {

compiler/rustc_lint/src/lib.rs

@@ -53,6 +53,7 @@ mod non_ascii_idents;
 mod nonstandard_style;
 mod passes;
 mod redundant_semicolon;
+mod traits;
 mod types;
 mod unused;
 
@@ -75,6 +76,7 @@ use internal::*;
 use non_ascii_idents::*;
 use nonstandard_style::*;
 use redundant_semicolon::*;
+use traits::*;
 use types::*;
 use unused::*;
 
@@ -157,6 +159,7 @@ macro_rules! late_lint_passes {
                 MissingDebugImplementations: MissingDebugImplementations::default(),
                 ArrayIntoIter: ArrayIntoIter,
                 ClashingExternDeclarations: ClashingExternDeclarations::new(),
+                DropTraitConstraints: DropTraitConstraints,
             ]
         );
     };

compiler/rustc_lint/src/traits.rs

@@ -0,0 +1,79 @@
+use crate::LateContext;
+use crate::LateLintPass;
+use crate::LintContext;
+use rustc_hir as hir;
+use rustc_span::symbol::sym;
+
+declare_lint! {
+    /// The `drop_bounds` lint checks for generics with `std::ops::Drop` as
+    /// bounds.
+    ///
+    /// ### Example
+    ///
+    /// ```rust
+    /// fn foo<T: Drop>() {}
+    /// ```
+    ///
+    /// {{produces}}
+    ///
+    /// ### Explanation
+    ///
+    /// `Drop` bounds do not really accomplish anything. A type may have
+    /// compiler-generated drop glue without implementing the `Drop` trait
+    /// itself. The `Drop` trait also only has one method, `Drop::drop`, and
+    /// that function is by fiat not callable in user code. So there is really
+    /// no use case for using `Drop` in trait bounds.
+    ///
+    /// The most likely use case of a drop bound is to distinguish between
+    /// types that have destructors and types that don't. Combined with
+    /// specialization, a naive coder would write an implementation that
+    /// assumed a type could be trivially dropped, then write a specialization
+    /// for `T: Drop` that actually calls the destructor. Except that doing so
+    /// is not correct; String, for example, doesn't actually implement Drop,
+    /// but because String contains a Vec, assuming it can be trivially dropped
+    /// will leak memory.
+    pub DROP_BOUNDS,
+    Warn,
+    "bounds of the form `T: Drop` are useless"
+}
+
+declare_lint_pass!(
+    /// Lint for bounds of the form `T: Drop`, which usually
+    /// indicate an attempt to emulate `std::mem::needs_drop`.
+    DropTraitConstraints => [DROP_BOUNDS]
+);
+
+impl<'tcx> LateLintPass<'tcx> for DropTraitConstraints {
+    fn check_item(&mut self, cx: &LateContext<'tcx>, item: &'tcx hir::Item<'tcx>) {
+        use rustc_middle::ty::PredicateAtom::*;
+
+        let def_id = cx.tcx.hir().local_def_id(item.hir_id);
+        let predicates = cx.tcx.explicit_predicates_of(def_id);
+        for &(predicate, span) in predicates.predicates {
+            let trait_predicate = match predicate.skip_binders() {
+                Trait(trait_predicate, _constness) => trait_predicate,
+                _ => continue,
+            };
+            let def_id = trait_predicate.trait_ref.def_id;
+            if cx.tcx.lang_items().drop_trait() == Some(def_id) {
+                // Explicitly allow `impl Drop`, a drop-guards-as-Voldemort-type pattern.
+                if trait_predicate.trait_ref.self_ty().is_impl_trait() {
+                    continue;
+                }
+                cx.struct_span_lint(DROP_BOUNDS, span, |lint| {
+                    let needs_drop = match cx.tcx.get_diagnostic_item(sym::needs_drop) {
+                        Some(needs_drop) => needs_drop,
+                        None => return,
+                    };
+                    let msg = format!(
+                        "bounds on `{}` are useless, consider instead \
+                         using `{}` to detect if a type has a destructor",
+                        predicate,
+                        cx.tcx.def_path_str(needs_drop)
+                    );
+                    lint.build(&msg).emit()
+                });
+            }
+        }
+    }
+}