Auto merge of #63471 - Mark-Simulacrum:rollup-m756lnx, r=Mark-Simulacrum

Rollup of 8 pull requests

Successful merges:

 - #61969 (Add #[repr(transparent)] for several types)
 - #63346 (Lint on some incorrect uses of mem::zeroed / mem::uninitialized)
 - #63433 (Miri shouldn't look at types)
 - #63440 (rename RUST_CTFE_BACKTRACE to RUSTC_CTFE_BACKTRACE)
 - #63441 (Derive Debug for CrateInfo)
 - #63442 (Add an example to show how to insert item to a sorted vec)
 - #63453 (rustdoc: general cleanup)
 - #63464 (Copy ty::Instance instead of passing by reference)

Failed merges:

r? @ghost

Cargo.lock

@@ -3252,7 +3252,6 @@ name = "rustdoc"
 version = "0.0.0"
 dependencies = [
  "minifier 0.0.33 (registry+https://github.com/rust-lang/crates.io-index)",
- "parking_lot 0.7.1 (registry+https://github.com/rust-lang/crates.io-index)",
  "pulldown-cmark 0.5.3 (registry+https://github.com/rust-lang/crates.io-index)",
  "rustc-rayon 0.2.0 (registry+https://github.com/rust-lang/crates.io-index)",
  "tempfile 3.0.5 (registry+https://github.com/rust-lang/crates.io-index)",

src/libcore/mem/maybe_uninit.rs

@@ -13,6 +13,7 @@ use crate::mem::ManuallyDrop;
 /// ever gets used to access memory:
 ///
 /// ```rust,no_run
+/// # #![allow(invalid_value)]
 /// use std::mem::{self, MaybeUninit};
 ///
 /// let x: &i32 = unsafe { mem::zeroed() }; // undefined behavior!
@@ -27,6 +28,7 @@ use crate::mem::ManuallyDrop;
 /// always be `true` or `false`. Hence, creating an uninitialized `bool` is undefined behavior:
 ///
 /// ```rust,no_run
+/// # #![allow(invalid_value)]
 /// use std::mem::{self, MaybeUninit};
 ///
 /// let b: bool = unsafe { mem::uninitialized() }; // undefined behavior!
@@ -40,6 +42,7 @@ use crate::mem::ManuallyDrop;
 /// which otherwise can hold any *fixed* bit pattern:
 ///
 /// ```rust,no_run
+/// # #![allow(invalid_value)]
 /// use std::mem::{self, MaybeUninit};
 ///
 /// let x: i32 = unsafe { mem::uninitialized() }; // undefined behavior!

src/libcore/mem/mod.rs

@@ -445,7 +445,8 @@ pub const fn needs_drop<T>() -> bool {
 ///
 /// *Incorrect* usage of this function: initializing a reference with zero.
 ///
-/// ```no_run
+/// ```rust,no_run
+/// # #![allow(invalid_value)]
 /// use std::mem;
 ///
 /// let _x: &i32 = unsafe { mem::zeroed() }; // Undefined behavior!

src/libcore/slice/mod.rs

@@ -1364,6 +1364,17 @@ impl<T> [T] {
     /// let r = s.binary_search(&1);
     /// assert!(match r { Ok(1..=4) => true, _ => false, });
     /// ```
+    ///
+    /// If you want to insert an item to a sorted vector, while maintaining
+    /// sort order:
+    ///
+    /// ```
+    /// let mut s = vec![0, 1, 1, 1, 1, 2, 3, 5, 8, 13, 21, 34, 55];
+    /// let num = 42;
+    /// let idx = s.binary_search(&num).unwrap_or_else(|x| x);
+    /// s.insert(idx, num);
+    /// assert_eq!(s, [0, 1, 1, 1, 1, 2, 3, 5, 8, 13, 21, 34, 42, 55]);
+    /// ```
     #[stable(feature = "rust1", since = "1.0.0")]
     pub fn binary_search(&self, x: &T) -> Result<usize, usize>
         where T: Ord

src/librustc/middle/cstore.rs

@@ -87,7 +87,7 @@ pub enum LinkagePreference {
     RequireStatic,
 }
 
-#[derive(Copy, Clone, PartialEq, Eq, PartialOrd, Ord, Hash,
+#[derive(Copy, Clone, Debug, PartialEq, Eq, PartialOrd, Ord, Hash,
          RustcEncodable, RustcDecodable, HashStable)]
 pub enum NativeLibraryKind {
     /// native static library (.a archive)
@@ -100,7 +100,7 @@ pub enum NativeLibraryKind {
     NativeUnknown,
 }
 
-#[derive(Clone, RustcEncodable, RustcDecodable, HashStable)]
+#[derive(Clone, Debug, RustcEncodable, RustcDecodable, HashStable)]
 pub struct NativeLibrary {
     pub kind: NativeLibraryKind,
     pub name: Option<Symbol>,

src/librustc/mir/interpret/error.rs

@@ -217,7 +217,7 @@ fn print_backtrace(backtrace: &mut Backtrace) {
 
 impl<'tcx> From<InterpError<'tcx>> for InterpErrorInfo<'tcx> {
     fn from(kind: InterpError<'tcx>) -> Self {
-        let backtrace = match env::var("RUST_CTFE_BACKTRACE") {
+        let backtrace = match env::var("RUSTC_CTFE_BACKTRACE") {
             // Matching `RUST_BACKTRACE` -- we treat "0" the same as "not present".
             Ok(ref val) if val != "0" => {
                 let mut backtrace = Backtrace::new_unresolved();

src/librustc/ty/layout.rs

@@ -2518,7 +2518,7 @@ where
         + HasTyCtxt<'tcx>
         + HasParamEnv<'tcx>,
 {
-    fn of_instance(cx: &C, instance: &ty::Instance<'tcx>) -> Self;
+    fn of_instance(cx: &C, instance: ty::Instance<'tcx>) -> Self;
     fn new(cx: &C, sig: ty::FnSig<'tcx>, extra_args: &[Ty<'tcx>]) -> Self;
     fn new_vtable(cx: &C, sig: ty::FnSig<'tcx>, extra_args: &[Ty<'tcx>]) -> Self;
     fn new_internal(
@@ -2538,7 +2538,7 @@ where
         + HasTyCtxt<'tcx>
         + HasParamEnv<'tcx>,
 {
-    fn of_instance(cx: &C, instance: &ty::Instance<'tcx>) -> Self {
+    fn of_instance(cx: &C, instance: ty::Instance<'tcx>) -> Self {
         let sig = instance.fn_sig(cx.tcx());
         let sig = cx
             .tcx()

src/librustc/ty/mod.rs

@@ -1842,7 +1842,8 @@ pub struct VariantDef {
     pub ctor_kind: CtorKind,
     /// Flags of the variant (e.g. is field list non-exhaustive)?
     flags: VariantFlags,
-    /// Recovered?
+    /// Variant is obtained as part of recovering from a syntactic error.
+    /// May be incomplete or bogus.
     pub recovered: bool,
 }
 
@@ -1949,7 +1950,7 @@ pub struct FieldDef {
 pub struct AdtDef {
     /// `DefId` of the struct, enum or union item.
     pub did: DefId,
-    /// Variants of the ADT. If this is a struct or enum, then there will be a single variant.
+    /// Variants of the ADT. If this is a struct or union, then there will be a single variant.
     pub variants: IndexVec<self::layout::VariantIdx, VariantDef>,
     /// Flags of the ADT (e.g. is this a struct? is this non-exhaustive?)
     flags: AdtFlags,
@@ -2565,6 +2566,8 @@ impl<'tcx> AdtDef {
 }
 
 impl<'tcx> FieldDef {
+    /// Returns the type of this field. The `subst` is typically obtained
+    /// via the second field of `TyKind::AdtDef`.
     pub fn ty(&self, tcx: TyCtxt<'tcx>, subst: SubstsRef<'tcx>) -> Ty<'tcx> {
         tcx.type_of(self.did).subst(tcx, subst)
     }

src/librustc/ty/sty.rs

@@ -171,6 +171,7 @@ pub enum TyKind<'tcx> {
     Never,
 
     /// A tuple type. For example, `(i32, bool)`.
+    /// Use `TyS::tuple_fields` to iterate over the field types.
     Tuple(SubstsRef<'tcx>),
 
     /// The projection of an associated type. For example,
@@ -1723,8 +1724,8 @@ impl<'tcx> TyS<'tcx> {
                     })
                 })
             }
-            ty::Tuple(tys) => tys.iter().any(|ty| {
-                ty.expect_ty().conservative_is_privately_uninhabited(tcx)
+            ty::Tuple(..) => self.tuple_fields().any(|ty| {
+                ty.conservative_is_privately_uninhabited(tcx)
             }),
             ty::Array(ty, len) => {
                 match len.try_eval_usize(tcx, ParamEnv::empty()) {
@@ -2103,6 +2104,15 @@ impl<'tcx> TyS<'tcx> {
         }
     }
 
+    /// Iterates over tuple fields.
+    /// Panics when called on anything but a tuple.
+    pub fn tuple_fields(&self) -> impl DoubleEndedIterator<Item=Ty<'tcx>> {
+        match self.sty {
+            Tuple(substs) => substs.iter().map(|field| field.expect_ty()),
+            _ => bug!("tuple_fields called on non-tuple"),
+        }
+    }
+
     /// If the type contains variants, returns the valid range of variant indices.
     /// FIXME This requires the optimized MIR in the case of generators.
     #[inline]

src/librustc/ty/util.rs

@@ -845,15 +845,15 @@ impl<'tcx> ty::TyS<'tcx> {
             ty: Ty<'tcx>,
         ) -> Representability {
             match ty.sty {
-                Tuple(ref ts) => {
+                Tuple(..) => {
                     // Find non representable
-                    fold_repr(ts.iter().map(|ty| {
+                    fold_repr(ty.tuple_fields().map(|ty| {
                         is_type_structurally_recursive(
                             tcx,
                             sp,
                             seen,
                             representable_cache,
-                            ty.expect_ty(),
+                            ty,
                         )
                     }))
                 }
@@ -1095,7 +1095,7 @@ fn needs_drop_raw<'tcx>(tcx: TyCtxt<'tcx>, query: ty::ParamEnvAnd<'tcx, Ty<'tcx>
         // state transformation pass
         ty::Generator(..) => true,
 
-        ty::Tuple(ref tys) => tys.iter().map(|k| k.expect_ty()).any(needs_drop),
+        ty::Tuple(..) => ty.tuple_fields().any(needs_drop),
 
         // unions don't have destructors because of the child types,
         // only if they manually implement `Drop` (handled above).

src/librustc/ty/walk.rs

@@ -119,8 +119,8 @@ fn push_subtypes<'tcx>(stack: &mut TypeWalkerStack<'tcx>, parent_ty: Ty<'tcx>) {
         ty::GeneratorWitness(ts) => {
             stack.extend(ts.skip_binder().iter().cloned().rev());
         }
-        ty::Tuple(ts) => {
-            stack.extend(ts.iter().map(|k| k.expect_ty()).rev());
+        ty::Tuple(..) => {
+            stack.extend(parent_ty.tuple_fields().rev());
         }
         ty::FnDef(_, substs) => {
             stack.extend(substs.types().rev());

src/librustc_codegen_ssa/lib.rs

@@ -128,6 +128,7 @@ bitflags::bitflags! {
 }
 
 /// Misc info we load from metadata to persist beyond the tcx.
+#[derive(Debug)]
 pub struct CrateInfo {
     pub panic_runtime: Option<CrateNum>,
     pub compiler_builtins: Option<CrateNum>,

src/librustc_codegen_ssa/mir/block.rs

@@ -337,7 +337,7 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
             }
             _ => {
                 (bx.get_fn(drop_fn),
-                 FnType::of_instance(&bx, &drop_fn))
+                 FnType::of_instance(&bx, drop_fn))
             }
         };
         helper.do_call(self, &mut bx, fn_ty, drop_fn, args,
@@ -435,7 +435,7 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
         // Obtain the panic entry point.
         let def_id = common::langcall(bx.tcx(), Some(span), "", lang_item);
         let instance = ty::Instance::mono(bx.tcx(), def_id);
-        let fn_ty = FnType::of_instance(&bx, &instance);
+        let fn_ty = FnType::of_instance(&bx, instance);
         let llfn = bx.get_fn(instance);
 
         // Codegen the actual panic invoke/call.
@@ -552,7 +552,7 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
                 let def_id =
                     common::langcall(bx.tcx(), Some(span), "", lang_items::PanicFnLangItem);
                 let instance = ty::Instance::mono(bx.tcx(), def_id);
-                let fn_ty = FnType::of_instance(&bx, &instance);
+                let fn_ty = FnType::of_instance(&bx, instance);
                 let llfn = bx.get_fn(instance);
 
                 // Codegen the actual panic invoke/call.

src/librustc_lint/builtin.rs

@@ -23,7 +23,7 @@
 
 use rustc::hir::def::{Res, DefKind};
 use rustc::hir::def_id::{DefId, LOCAL_CRATE};
-use rustc::ty::{self, Ty, TyCtxt};
+use rustc::ty::{self, Ty, TyCtxt, layout::VariantIdx};
 use rustc::{lint, util};
 use hir::Node;
 use util::nodemap::HirIdSet;
@@ -1862,3 +1862,92 @@ impl EarlyLintPass for IncompleteFeatures {
             });
     }
 }
+
+declare_lint! {
+    pub INVALID_VALUE,
+    Warn,
+    "an invalid value is being created (such as a NULL reference)"
+}
+
+declare_lint_pass!(InvalidValue => [INVALID_VALUE]);
+
+impl<'a, 'tcx> LateLintPass<'a, 'tcx> for InvalidValue {
+    fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, expr: &hir::Expr) {
+
+        const ZEROED_PATH: &[Symbol] = &[sym::core, sym::mem, sym::zeroed];
+        const UININIT_PATH: &[Symbol] = &[sym::core, sym::mem, sym::uninitialized];
+
+        /// Return `false` only if we are sure this type does *not*
+        /// allow zero initialization.
+        fn ty_maybe_allows_zero_init<'tcx>(tcx: TyCtxt<'tcx>, ty: Ty<'tcx>) -> bool {
+            use rustc::ty::TyKind::*;
+            match ty.sty {
+                // Primitive types that don't like 0 as a value.
+                Ref(..) | FnPtr(..) | Never => false,
+                Adt(..) if ty.is_box() => false,
+                // Recurse for some compound types.
+                Adt(adt_def, substs) if !adt_def.is_union() => {
+                    match adt_def.variants.len() {
+                        0 => false, // Uninhabited enum!
+                        1 => {
+                            // Struct, or enum with exactly one variant.
+                            // Proceed recursively, check all fields.
+                            let variant = &adt_def.variants[VariantIdx::from_u32(0)];
+                            variant.fields.iter().all(|field| {
+                                ty_maybe_allows_zero_init(
+                                    tcx,
+                                    field.ty(tcx, substs),
+                                )
+                            })
+                        }
+                        _ => true, // Conservative fallback for multi-variant enum.
+                    }
+                }
+                Tuple(..) => {
+                    // Proceed recursively, check all fields.
+                    ty.tuple_fields().all(|field| ty_maybe_allows_zero_init(tcx, field))
+                }
+                // FIXME: Would be nice to also warn for `NonNull`/`NonZero*`.
+                // FIXME: *Only for `mem::uninitialized`*, we could also warn for `bool`,
+                //        `char`, and any multivariant enum.
+                // Conservative fallback.
+                _ => true,
+            }
+        }
+
+        if let hir::ExprKind::Call(ref path_expr, ref _args) = expr.node {
+            if let hir::ExprKind::Path(ref qpath) = path_expr.node {
+                if let Some(def_id) = cx.tables.qpath_res(qpath, path_expr.hir_id).opt_def_id() {
+                    if cx.match_def_path(def_id, &ZEROED_PATH) ||
+                        cx.match_def_path(def_id, &UININIT_PATH)
+                    {
+                        // This conjures an instance of a type out of nothing,
+                        // using zeroed or uninitialized memory.
+                        // We are extremely conservative with what we warn about.
+                        let conjured_ty = cx.tables.expr_ty(expr);
+
+                        if !ty_maybe_allows_zero_init(cx.tcx, conjured_ty) {
+                            cx.struct_span_lint(
+                                INVALID_VALUE,
+                                expr.span,
+                                &format!(
+                                    "the type `{}` does not permit {}",
+                                    conjured_ty,
+                                    if cx.match_def_path(def_id, &ZEROED_PATH) {
+                                        "zero-initialization"
+                                    } else {
+                                        "being left uninitialized"
+                                    }
+                                ),
+                            )
+                            .note("this means that this code causes undefined behavior \
+                                when executed")
+                            .help("use `MaybeUninit` instead")
+                            .emit();
+                        }
+                    }
+                }
+            }
+        }
+    }
+}

src/librustc_lint/lib.rs

@@ -177,6 +177,7 @@ macro_rules! late_lint_mod_passes {
             UnreachablePub: UnreachablePub,
 
             ExplicitOutlivesRequirements: ExplicitOutlivesRequirements,
+            InvalidValue: InvalidValue,
         ]);
     )
 }

src/librustc_mir/interpret/eval_context.rs

@@ -385,15 +385,19 @@ impl<'mir, 'tcx, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
         local: mir::Local,
         layout: Option<TyLayout<'tcx>>,
     ) -> InterpResult<'tcx, TyLayout<'tcx>> {
-        match frame.locals[local].layout.get() {
+        // `const_prop` runs into this with an invalid (empty) frame, so we
+        // have to support that case (mostly by skipping all caching).
+        match frame.locals.get(local).and_then(|state| state.layout.get()) {
             None => {
                 let layout = crate::interpret::operand::from_known_layout(layout, || {
                     let local_ty = frame.body.local_decls[local].ty;
                     let local_ty = self.monomorphize_with_substs(local_ty, frame.instance.substs)?;
                     self.layout_of(local_ty)
                 })?;
-                // Layouts of locals are requested a lot, so we cache them.
-                frame.locals[local].layout.set(Some(layout));
+                if let Some(state) = frame.locals.get(local) {
+                    // Layouts of locals are requested a lot, so we cache them.
+                    state.layout.set(Some(layout));
+                }
                 Ok(layout)
             }
             Some(layout) => Ok(layout),

src/librustc_mir/interpret/snapshot.rs

@@ -304,7 +304,7 @@ impl_stable_hash_for!(enum crate::interpret::eval_context::StackPopCleanup {
 
 #[derive(Eq, PartialEq)]
 struct FrameSnapshot<'a, 'tcx> {
-    instance: &'a ty::Instance<'tcx>,
+    instance: ty::Instance<'tcx>,
     span: Span,
     return_to_block: &'a StackPopCleanup,
     return_place: Option<Place<(), AllocIdSnapshot<'a>>>,
@@ -344,7 +344,7 @@ impl<'a, 'mir, 'tcx, Ctx> Snapshot<'a, Ctx> for &'a Frame<'mir, 'tcx>
         } = self;
 
         FrameSnapshot {
-            instance,
+            instance: *instance,
             span: *span,
             return_to_block,
             block,