Rollup of 14 pull requests

config.toml.example

@@ -243,19 +243,36 @@
 # =============================================================================
 [rust]
 
-# Indicates that the build should be optimized for debugging Rust. Note that
-# this is typically not what you want as it takes an incredibly large amount of
-# time to have a debug-mode rustc compile any code (notably libstd). If this
-# value is set to `true` it will affect a number of configuration options below
-# as well, if unconfigured.
-#debug = false
-
-# Whether or not to optimize the compiler and standard library
+# Whether or not to optimize the compiler and standard library.
+#
 # Note: the slowness of the non optimized compiler compiling itself usually
 #       outweighs the time gains in not doing optimizations, therefore a
-#       full bootstrap takes much more time with optimize set to false.
+#       full bootstrap takes much more time with `optimize` set to false.
 #optimize = true
 
+# Indicates that the build should be configured for debugging Rust. A
+# `debug`-enabled compiler and standard library will be somewhat
+# slower (due to e.g. checking of debug assertions) but should remain
+# usable.
+#
+# Note: If this value is set to `true`, it will affect a number of
+#       configuration options below as well, if they have been left
+#       unconfigured in this file.
+#
+# Note: changes to the `debug` setting do *not* affect `optimize`
+#       above. In theory, a "maximally debuggable" environment would
+#       set `optimize` to `false` above to assist the introspection
+#       facilities of debuggers like lldb and gdb. To recreate such an
+#       environment, explicitly set `optimize` to `false` and `debug`
+#       to `true`. In practice, everyone leaves `optimize` set to
+#       `true`, because an unoptimized rustc with debugging
+#       enabled becomes *unusably slow* (e.g. rust-lang/rust#24840
+#       reported a 25x slowdown) and bootstrapping the supposed
+#       "maximally debuggable" environment (notably libstd) takes
+#       hours to build.
+#
+#debug = false
+
 # Number of codegen units to use for each compiler invocation. A value of 0
 # means "the number of cores on this machine", and 1+ is passed through to the
 # compiler.

src/Cargo.lock

@@ -1269,7 +1269,7 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 
 [[package]]
 name = "minifier"
-version = "0.0.19"
+version = "0.0.20"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 dependencies = [
  "macro-utils 0.1.2 (registry+https://github.com/rust-lang/crates.io-index)",
@@ -2484,7 +2484,7 @@ dependencies = [
 name = "rustdoc"
 version = "0.0.0"
 dependencies = [
- "minifier 0.0.19 (registry+https://github.com/rust-lang/crates.io-index)",
+ "minifier 0.0.20 (registry+https://github.com/rust-lang/crates.io-index)",
  "parking_lot 0.6.4 (registry+https://github.com/rust-lang/crates.io-index)",
  "pulldown-cmark 0.1.2 (registry+https://github.com/rust-lang/crates.io-index)",
  "tempfile 3.0.3 (registry+https://github.com/rust-lang/crates.io-index)",
@@ -3289,7 +3289,7 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 "checksum memchr 2.0.2 (registry+https://github.com/rust-lang/crates.io-index)" = "a3b4142ab8738a78c51896f704f83c11df047ff1bda9a92a661aa6361552d93d"
 "checksum memmap 0.6.2 (registry+https://github.com/rust-lang/crates.io-index)" = "e2ffa2c986de11a9df78620c01eeaaf27d94d3ff02bf81bfcca953102dd0c6ff"
 "checksum memoffset 0.2.1 (registry+https://github.com/rust-lang/crates.io-index)" = "0f9dc261e2b62d7a622bf416ea3c5245cdd5d9a7fcc428c0d06804dfce1775b3"
-"checksum minifier 0.0.19 (registry+https://github.com/rust-lang/crates.io-index)" = "9908ed7c62f990c21ab41fdca53a864a3ada0da69d8729c4de727b397e27bc11"
+"checksum minifier 0.0.20 (registry+https://github.com/rust-lang/crates.io-index)" = "96c269bb45c39b333392b2b18ad71760b34ac65666591386b0e959ed58b3f474"
 "checksum miniz-sys 0.1.10 (registry+https://github.com/rust-lang/crates.io-index)" = "609ce024854aeb19a0ef7567d348aaa5a746b32fb72e336df7fcc16869d7e2b4"
 "checksum miow 0.3.3 (registry+https://github.com/rust-lang/crates.io-index)" = "396aa0f2003d7df8395cb93e09871561ccc3e785f0acb369170e8cc74ddf9226"
 "checksum new_debug_unreachable 1.0.1 (registry+https://github.com/rust-lang/crates.io-index)" = "0cdc457076c78ab54d5e0d6fa7c47981757f1e34dc39ff92787f217dede586c4"

src/bootstrap/config.rs

@@ -628,6 +628,9 @@ impl Config {
         let default = false;
         config.llvm_assertions = llvm_assertions.unwrap_or(default);
 
+        let default = true;
+        config.rust_optimize = optimize.unwrap_or(default);
+
         let default = match &config.channel[..] {
             "stable" | "beta" | "nightly" => true,
             _ => false,
@@ -640,7 +643,6 @@ impl Config {
         config.debug_jemalloc = debug_jemalloc.unwrap_or(default);
         config.rust_debuginfo = debuginfo.unwrap_or(default);
         config.rust_debug_assertions = debug_assertions.unwrap_or(default);
-        config.rust_optimize = optimize.unwrap_or(!default);
 
         let default = config.channel == "dev";
         config.ignore_git = ignore_git.unwrap_or(default);

src/doc/rustc/src/lints/listing/warn-by-default.md

@@ -279,7 +279,7 @@ warning: functions generic over types must be mangled
 1 |   #[no_mangle]
   |   ------------ help: remove this attribute
 2 | / fn foo<T>(t: T) {
-3 | |     
+3 | |
 4 | | }
   | |_^
   |
@@ -513,7 +513,7 @@ This will produce:
 warning: borrow of packed field requires unsafe function or block (error E0133)
   --> src/main.rs:11:13
    |
-11 |     let y = &x.data.0; 
+11 |     let y = &x.data.0;
    |             ^^^^^^^^^
    |
    = note: #[warn(safe_packed_borrows)] on by default
@@ -874,7 +874,7 @@ fn main() {
 This will produce:
 
 ```text
-warning: unused `std::result::Result` which must be used
+warning: unused `std::result::Result` that must be used
  --> src/main.rs:6:5
   |
 6 |     returns_result();

src/liballoc/vec.rs

@@ -120,11 +120,17 @@ use raw_vec::RawVec;
 /// assert_eq!(vec, [1, 2, 3, 4]);
 /// ```
 ///
-/// It can also initialize each element of a `Vec<T>` with a given value:
+/// It can also initialize each element of a `Vec<T>` with a given value.
+/// This may be more efficient than performing allocation and initialization
+/// in separate steps, especially when initializing a vector of zeros:
 ///
 /// ```
 /// let vec = vec![0; 5];
 /// assert_eq!(vec, [0, 0, 0, 0, 0]);
+///
+/// // The following is equivalent, but potentially slower:
+/// let mut vec1 = Vec::with_capacity(5);
+/// vec1.resize(5, 0);
 /// ```
 ///
 /// Use a `Vec<T>` as an efficient stack:

src/libcore/iter/mod.rs

@@ -253,7 +253,7 @@
 //! using it. The compiler will warn us about this kind of behavior:
 //!
 //! ```text
-//! warning: unused result which must be used: iterator adaptors are lazy and
+//! warning: unused result that must be used: iterator adaptors are lazy and
 //! do nothing unless consumed
 //! ```
 //!

src/libcore/option.rs

@@ -867,8 +867,6 @@ impl<T> Option<T> {
     /// # Examples
     ///
     /// ```
-    /// #![feature(option_replace)]
-    ///
     /// let mut x = Some(2);
     /// let old = x.replace(5);
     /// assert_eq!(x, Some(5));
@@ -880,7 +878,7 @@ impl<T> Option<T> {
     /// assert_eq!(old, None);
     /// ```
     #[inline]
-    #[unstable(feature = "option_replace", issue = "51998")]
+    #[stable(feature = "option_replace", since = "1.31.0")]
     pub fn replace(&mut self, value: T) -> Option<T> {
         mem::replace(self, Some(value))
     }

src/libcore/tests/lib.rs

@@ -39,7 +39,6 @@
 #![feature(reverse_bits)]
 #![feature(inner_deref)]
 #![feature(slice_internals)]
-#![feature(option_replace)]
 #![feature(slice_partition_dedup)]
 #![feature(copy_within)]
 

src/librustc_driver/lib.rs

@@ -21,7 +21,6 @@
 #![feature(box_syntax)]
 #![cfg_attr(unix, feature(libc))]
 #![feature(nll)]
-#![feature(option_replace)]
 #![feature(quote)]
 #![feature(rustc_diagnostic_macros)]
 #![feature(slice_sort_by_cached_key)]

src/librustc_lint/unused.rs

@@ -59,15 +59,17 @@ impl<'a, 'tcx> LateLintPass<'a, 'tcx> for UnusedResults {
         }
 
         let t = cx.tables.expr_ty(&expr);
-        let ty_warned = match t.sty {
-            ty::Tuple(ref tys) if tys.is_empty() => return,
-            ty::Never => return,
+        // FIXME(varkor): replace with `t.is_unit() || t.conservative_is_uninhabited()`.
+        let type_permits_no_use = match t.sty {
+            ty::Tuple(ref tys) if tys.is_empty() => true,
+            ty::Never => true,
             ty::Adt(def, _) => {
                 if def.variants.is_empty() {
-                    return;
+                    true
+                } else {
+                    check_must_use(cx, def.did, s.span, "")
                 }
-                check_must_use(cx, def.did, s.span, "")
-            },
+            }
             _ => false,
         };
 
@@ -95,7 +97,12 @@ impl<'a, 'tcx> LateLintPass<'a, 'tcx> for UnusedResults {
         if let Some(def) = maybe_def {
             let def_id = def.def_id();
             fn_warned = check_must_use(cx, def_id, s.span, "return value of ");
+        } else if type_permits_no_use {
+            // We don't warn about unused unit or uninhabited types.
+            // (See https://github.com/rust-lang/rust/issues/43806 for details.)
+            return;
         }
+
         let must_use_op = match expr.node {
             // Hardcoding operators here seemed more expedient than the
             // refactoring that would be needed to look up the `#[must_use]`
@@ -135,18 +142,18 @@ impl<'a, 'tcx> LateLintPass<'a, 'tcx> for UnusedResults {
 
         if let Some(must_use_op) = must_use_op {
             cx.span_lint(UNUSED_MUST_USE, expr.span,
-                         &format!("unused {} which must be used", must_use_op));
+                         &format!("unused {} that must be used", must_use_op));
             op_warned = true;
         }
 
-        if !(ty_warned || fn_warned || op_warned) {
+        if !(type_permits_no_use || fn_warned || op_warned) {
             cx.span_lint(UNUSED_RESULTS, s.span, "unused result");
         }
 
         fn check_must_use(cx: &LateContext, def_id: DefId, sp: Span, describe_path: &str) -> bool {
             for attr in cx.tcx.get_attrs(def_id).iter() {
                 if attr.check_name("must_use") {
-                    let msg = format!("unused {}`{}` which must be used",
+                    let msg = format!("unused {}`{}` that must be used",
                                           describe_path, cx.tcx.item_path_str(def_id));
                     let mut err = cx.struct_span_lint(UNUSED_MUST_USE, sp, &msg);
                     // check for #[must_use = "..."]
@@ -233,7 +240,7 @@ impl<'a, 'tcx> LateLintPass<'a, 'tcx> for UnusedAttributes {
                 .find(|&&(builtin, ty, _)| name == builtin && ty == AttributeType::CrateLevel)
                 .is_some();
 
-            // Has a plugin registered this attribute as one which must be used at
+            // Has a plugin registered this attribute as one that must be used at
             // the crate level?
             let plugin_crate = plugin_attributes.iter()
                 .find(|&&(ref x, t)| name == &**x && AttributeType::CrateLevel == t)

src/librustc_mir/borrow_check/mutability_errors.rs

@@ -218,6 +218,38 @@ impl<'a, 'gcx, 'tcx> MirBorrowckCtxt<'a, 'gcx, 'tcx> {
         debug!("report_mutability_error: act={:?}, acted_on={:?}", act, acted_on);
 
         match the_place_err {
+            // Suggest making an existing shared borrow in a struct definition a mutable borrow.
+            //
+            // This is applicable when we have a deref of a field access to a deref of a local -
+            // something like `*((*_1).0`. The local that we get will be a reference to the
+            // struct we've got a field access of (it must be a reference since there's a deref
+            // after the field access).
+            Place::Projection(box Projection {
+                base: Place::Projection(box Projection {
+                    base: Place::Projection(box Projection {
+                        base,
+                        elem: ProjectionElem::Deref,
+                    }),
+                    elem: ProjectionElem::Field(field, _),
+                }),
+                elem: ProjectionElem::Deref,
+            }) => {
+                err.span_label(span, format!("cannot {ACT}", ACT = act));
+
+                if let Some((span, message)) = annotate_struct_field(
+                    self.infcx.tcx,
+                    base.ty(self.mir, self.infcx.tcx).to_ty(self.infcx.tcx),
+                    field,
+                ) {
+                    err.span_suggestion_with_applicability(
+                        span,
+                        "consider changing this to be mutable",
+                        message,
+                        Applicability::MaybeIncorrect,
+                    );
+                }
+            },
+
             // Suggest removing a `&mut` from the use of a mutable reference.
             Place::Local(local)
                 if {
@@ -592,3 +624,54 @@ fn suggest_ampmut<'cx, 'gcx, 'tcx>(
 fn is_closure_or_generator(ty: ty::Ty) -> bool {
     ty.is_closure() || ty.is_generator()
 }
+
+/// Add a suggestion to a struct definition given a field access to a local.
+/// This function expects the local to be a reference to a struct in order to produce a suggestion.
+///
+/// ```text
+/// LL |     s: &'a String
+///    |        ---------- use `&'a mut String` here to make mutable
+/// ```
+fn annotate_struct_field(
+    tcx: TyCtxt<'cx, 'gcx, 'tcx>,
+    ty: ty::Ty<'tcx>,
+    field: &mir::Field,
+) -> Option<(Span, String)> {
+    // Expect our local to be a reference to a struct of some kind.
+    if let ty::TyKind::Ref(_, ty, _) = ty.sty {
+        if let ty::TyKind::Adt(def, _) = ty.sty {
+            let field = def.all_fields().nth(field.index())?;
+            // Use the HIR types to construct the diagnostic message.
+            let node_id = tcx.hir.as_local_node_id(field.did)?;
+            let node = tcx.hir.find(node_id)?;
+            // Now we're dealing with the actual struct that we're going to suggest a change to,
+            // we can expect a field that is an immutable reference to a type.
+            if let hir::Node::Field(field) = node {
+                if let hir::TyKind::Rptr(lifetime, hir::MutTy {
+                    mutbl: hir::Mutability::MutImmutable,
+                    ref ty
+                }) = field.ty.node {
+                    // Get the snippets in two parts - the named lifetime (if there is one) and
+                    // type being referenced, that way we can reconstruct the snippet without loss
+                    // of detail.
+                    let type_snippet = tcx.sess.source_map().span_to_snippet(ty.span).ok()?;
+                    let lifetime_snippet = if !lifetime.is_elided() {
+                        format!("{} ", tcx.sess.source_map().span_to_snippet(lifetime.span).ok()?)
+                    } else {
+                        String::new()
+                    };
+
+                    return Some((
+                        field.ty.span,
+                        format!(
+                            "&{}mut {}",
+                            lifetime_snippet, &*type_snippet,
+                        ),
+                    ));
+                }
+            }
+        }
+    }
+
+    None
+}