Rollup of 11 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",

RELEASES.md

@@ -90,7 +90,7 @@ Compatibility Notes
 
 Internal Only
 --------
-- [Improved default settings for bootstrapping in `x.py`.][73964] You can read details about this change in the ["Changes To `x.py` Defaults"](https://blog.rust-lang.org/inside-rust/2020/08/30/changes-to-x-py-defaults.html) post on the Inside Rust blog.
+- [Improved default settings for bootstrapping in `x.py`.][73964] You can read details about this change in the ["Changes to `x.py` defaults"](https://blog.rust-lang.org/inside-rust/2020/08/30/changes-to-x-py-defaults.html) post on the Inside Rust blog.
 
 [1.47.0-cfg]: https://docs.microsoft.com/en-us/windows/win32/secbp/control-flow-guard
 [75048]: https://github.com/rust-lang/rust/pull/75048/

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_error_codes/src/error_codes.rs

@@ -459,6 +459,7 @@ E0773: include_str!("./error_codes/E0773.md"),
 E0774: include_str!("./error_codes/E0774.md"),
 E0775: include_str!("./error_codes/E0775.md"),
 E0776: include_str!("./error_codes/E0776.md"),
+E0777: include_str!("./error_codes/E0777.md"),
 ;
 //  E0006, // merged with E0005
 //  E0008, // cannot bind by-move into a pattern guard

compiler/rustc_error_codes/src/error_codes/E0777.md

@@ -0,0 +1,19 @@
+A literal value was used inside `#[derive]`.
+
+Erroneous code example:
+
+```compile_fail,E0777
+#[derive("Clone")] // error!
+struct Foo;
+```
+
+Only paths to traits are allowed as argument inside `#[derive]`. You can find
+more information about the `#[derive]` attribute in the [Rust Book].
+
+
+```
+#[derive(Clone)] // ok!
+struct Foo;
+```
+
+[Rust Book]: https://doc.rust-lang.org/book/appendix-03-derivable-traits.html

compiler/rustc_expand/src/expand.rs

@@ -18,7 +18,7 @@ use rustc_ast_pretty::pprust;
 use rustc_attr::{self as attr, is_builtin_attr, HasAttrs};
 use rustc_data_structures::map_in_place::MapInPlace;
 use rustc_data_structures::stack::ensure_sufficient_stack;
-use rustc_errors::{Applicability, PResult};
+use rustc_errors::{struct_span_err, Applicability, PResult};
 use rustc_feature::Features;
 use rustc_parse::parser::Parser;
 use rustc_parse::validate_attr;
@@ -542,7 +542,7 @@ impl<'a, 'b> MacroExpander<'a, 'b> {
     fn error_derive_forbidden_on_non_adt(&self, derives: &[Path], item: &Annotatable) {
         let attr = self.cx.sess.find_by_name(item.attrs(), sym::derive);
         let span = attr.map_or(item.span(), |attr| attr.span);
-        let mut err = rustc_errors::struct_span_err!(
+        let mut err = struct_span_err!(
             self.cx.sess,
             span,
             E0774,

compiler/rustc_expand/src/proc_macro.rs

@@ -5,7 +5,8 @@ use rustc_ast::token;
 use rustc_ast::tokenstream::{TokenStream, TokenTree};
 use rustc_ast::{self as ast, *};
 use rustc_data_structures::sync::Lrc;
-use rustc_errors::{Applicability, ErrorReported};
+use rustc_errors::{struct_span_err, Applicability, ErrorReported};
+use rustc_lexer::is_ident;
 use rustc_parse::nt_to_tokenstream;
 use rustc_span::symbol::sym;
 use rustc_span::{Span, DUMMY_SP};
@@ -182,9 +183,22 @@ crate fn collect_derives(cx: &mut ExtCtxt<'_>, attrs: &mut Vec<ast::Attribute>)
             .filter_map(|nmi| match nmi {
                 NestedMetaItem::Literal(lit) => {
                     error_reported_filter_map = true;
-                    cx.struct_span_err(lit.span, "expected path to a trait, found literal")
-                        .help("for example, write `#[derive(Debug)]` for `Debug`")
-                        .emit();
+                    let mut err = struct_span_err!(
+                        cx.sess,
+                        lit.span,
+                        E0777,
+                        "expected path to a trait, found literal",
+                    );
+                    let token = lit.token.to_string();
+                    if token.starts_with('"')
+                        && token.len() > 2
+                        && is_ident(&token[1..token.len() - 1])
+                    {
+                        err.help(&format!("try using `#[derive({})]`", &token[1..token.len() - 1]));
+                    } else {
+                        err.help("for example, write `#[derive(Debug)]` for `Debug`");
+                    }
+                    err.emit();
                     None
                 }
                 NestedMetaItem::MetaItem(mi) => Some(mi),

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()
+                });
+            }
+        }
+    }
+}