Auto merge of #54941 - pnkfelix:issue-21232-reject-partial-reinit, r=nikomatsakis

reject partial init and reinit of uninitialized data

Reject partial initialization of uninitialized structured types (i.e. structs and tuples) and also reject partial *reinitialization* of such types.

Fix #54986

Fix #54499

cc #21232

diff --combined src/librustc/mir/mod.rs
index 48b2ccbcf873749c3eac4175b0f9a566a97b8481,883a9d6497b0be59ef936723873ca019dde51986..9a0623ca539387c930d870092fa32fe40d268e99
--- 1/src/librustc/mir/mod.rs
--- 2/src/librustc/mir/mod.rs
+++ b/src/librustc/mir/mod.rs
@@@ -37,7 -37,7 +37,7 @@@ use syntax::ast::{self, Name}
  use syntax::symbol::InternedString;
  use syntax_pos::{Span, DUMMY_SP};
  use ty::fold::{TypeFoldable, TypeFolder, TypeVisitor};
 -use ty::subst::{Subst, Substs};
 +use ty::subst::{CanonicalUserSubsts, Subst, Substs};
  use ty::{self, AdtDef, CanonicalTy, ClosureSubsts, GeneratorSubsts, Region, Ty, TyCtxt};
  use util::ppaux;
  
@@@ -710,7 -710,7 +710,7 @@@ pub struct LocalDecl<'tcx> 
      /// e.g. via `let x: T`, then we carry that type here. The MIR
      /// borrow checker needs this information since it can affect
      /// region inference.
 -    pub user_ty: Option<(CanonicalTy<'tcx>, Span)>,
 +    pub user_ty: Option<(UserTypeAnnotation<'tcx>, Span)>,
  
      /// Name of the local, used in debuginfo and pretty-printing.
      ///
@@@ -1737,7 -1737,7 +1737,7 @@@ pub enum StatementKind<'tcx> 
      /// - `Contravariant` -- requires that `T_y :> T`
      /// - `Invariant` -- requires that `T_y == T`
      /// - `Bivariant` -- no effect
 -    AscribeUserType(Place<'tcx>, ty::Variance, CanonicalTy<'tcx>),
 +    AscribeUserType(Place<'tcx>, ty::Variance, UserTypeAnnotation<'tcx>),
  
      /// No-op. Useful for deleting instructions without affecting statement indices.
      Nop,
@@@ -1967,7 -1967,10 +1967,10 @@@ impl<'tcx> Place<'tcx> 
          Place::Projection(Box::new(PlaceProjection { base: self, elem }))
      }
  
-     /// Find the innermost `Local` from this `Place`.
+     /// Find the innermost `Local` from this `Place`, *if* it is either a local itself or
+     /// a single deref of a local.
+     ///
+     /// FIXME: can we safely swap the semantics of `fn base_local` below in here instead?
      pub fn local(&self) -> Option<Local> {
          match self {
              Place::Local(local) |
@@@ -1978,6 -1981,15 +1981,15 @@@
              _ => None,
          }
      }
+ 
+     /// Find the innermost `Local` from this `Place`.
+     pub fn base_local(&self) -> Option<Local> {
+         match self {
+             Place::Local(local) => Some(*local),
+             Place::Projection(box Projection { base, elem: _ }) => base.base_local(),
+             Place::Promoted(..) | Place::Static(..) => None,
+         }
+     }
  }
  
  impl<'tcx> Debug for Place<'tcx> {
@@@ -2188,7 -2200,7 +2200,7 @@@ pub enum AggregateKind<'tcx> 
          &'tcx AdtDef,
          usize,
          &'tcx Substs<'tcx>,
 -        Option<CanonicalTy<'tcx>>,
 +        Option<UserTypeAnnotation<'tcx>>,
          Option<usize>,
      ),
  
@@@ -2392,7 -2404,7 +2404,7 @@@ impl<'tcx> Debug for Rvalue<'tcx> 
  /// this does not necessarily mean that they are "==" in Rust -- in
  /// particular one must be wary of `NaN`!
  
 -#[derive(Clone, PartialEq, Eq, Hash, RustcEncodable, RustcDecodable)]
 +#[derive(Copy, Clone, PartialEq, Eq, Hash, RustcEncodable, RustcDecodable)]
  pub struct Constant<'tcx> {
      pub span: Span,
      pub ty: Ty<'tcx>,
@@@ -2402,29 -2414,11 +2414,29 @@@
      /// indicate that `Vec<_>` was explicitly specified.
      ///
      /// Needed for NLL to impose user-given type constraints.
 -    pub user_ty: Option<CanonicalTy<'tcx>>,
 +    pub user_ty: Option<UserTypeAnnotation<'tcx>>,
  
      pub literal: &'tcx ty::Const<'tcx>,
  }
  
 +/// A user-given type annotation attached to a constant.  These arise
 +/// from constants that are named via paths, like `Foo::<A>::new` and
 +/// so forth.
 +#[derive(Copy, Clone, Debug, PartialEq, Eq, Hash, RustcEncodable, RustcDecodable)]
 +pub enum UserTypeAnnotation<'tcx> {
 +    Ty(CanonicalTy<'tcx>),
 +    FnDef(DefId, CanonicalUserSubsts<'tcx>),
 +    AdtDef(&'tcx AdtDef, CanonicalUserSubsts<'tcx>),
 +}
 +
 +EnumTypeFoldableImpl! {
 +    impl<'tcx> TypeFoldable<'tcx> for UserTypeAnnotation<'tcx> {
 +        (UserTypeAnnotation::Ty)(ty),
 +        (UserTypeAnnotation::FnDef)(def, substs),
 +        (UserTypeAnnotation::AdtDef)(def, substs),
 +    }
 +}
 +
  newtype_index! {
      pub struct Promoted {
          DEBUG_FORMAT = "promoted[{}]"