Auto merge of #66671 - matthewjasper:ast-address-of, r=Centril

Ast address-of

This is the parts of #64588 that don't affect MIR. If an address-of expression makes it to MIR lowering we error and lower to the best currently expressible approximation to limit further errors.

r? @Centril

Author: bors

src/librustc/hir/intravisit.rs

@@ -1024,7 +1024,7 @@ pub fn walk_expr<'v, V: Visitor<'v>>(visitor: &mut V, expression: &'v Expr) {
             visitor.visit_expr(left_expression);
             visitor.visit_expr(right_expression)
         }
-        ExprKind::AddrOf(_, ref subexpression) | ExprKind::Unary(_, ref subexpression) => {
+        ExprKind::AddrOf(_, _, ref subexpression) | ExprKind::Unary(_, ref subexpression) => {
             visitor.visit_expr(subexpression)
         }
         ExprKind::Cast(ref subexpression, ref typ) | ExprKind::Type(ref subexpression, ref typ) => {

src/librustc/hir/lowering/expr.rs

@@ -65,9 +65,9 @@ impl LoweringContext<'_> {
                 let expr = P(self.lower_expr(expr));
                 hir::ExprKind::Type(expr, self.lower_ty(ty, ImplTraitContext::disallowed()))
             }
-            ExprKind::AddrOf(m, ref ohs) => {
+            ExprKind::AddrOf(k, m, ref ohs) => {
                 let ohs = P(self.lower_expr(ohs));
-                hir::ExprKind::AddrOf(m, ohs)
+                hir::ExprKind::AddrOf(k, m, ohs)
             }
             ExprKind::Let(ref pat, ref scrutinee) => self.lower_expr_let(e.span, pat, scrutinee),
             ExprKind::If(ref cond, ref then, ref else_opt) => {
@@ -1339,7 +1339,11 @@ impl LoweringContext<'_> {
     }
 
     fn expr_mut_addr_of(&mut self, span: Span, e: P<hir::Expr>) -> hir::Expr {
-        self.expr(span, hir::ExprKind::AddrOf(hir::Mutability::Mutable, e), ThinVec::new())
+        self.expr(
+            span,
+            hir::ExprKind::AddrOf(hir::BorrowKind::Ref, hir::Mutability::Mutable, e),
+            ThinVec::new(),
+        )
     }
 
     fn expr_unit(&mut self, sp: Span) -> hir::Expr {

src/librustc/hir/mod.rs

@@ -21,7 +21,8 @@ use syntax_pos::{Span, DUMMY_SP, MultiSpan};
 use syntax::source_map::Spanned;
 use syntax::ast::{self, CrateSugar, Ident, Name, NodeId, AsmDialect};
 use syntax::ast::{Attribute, Label, LitKind, StrStyle, FloatTy, IntTy, UintTy};
-pub use syntax::ast::{Mutability, Constness, Unsafety, Movability, CaptureBy, IsAuto, ImplPolarity};
+pub use syntax::ast::{Mutability, Constness, Unsafety, Movability, CaptureBy};
+pub use syntax::ast::{IsAuto, ImplPolarity, BorrowKind};
 use syntax::attr::{InlineAttr, OptimizeAttr};
 use syntax::symbol::{Symbol, kw};
 use syntax::tokenstream::TokenStream;
@@ -1493,8 +1494,20 @@ impl Expr {
         }
     }
 
-    pub fn is_place_expr(&self) -> bool {
-         match self.kind {
+    // Whether this looks like a place expr, without checking for deref
+    // adjustments.
+    // This will return `true` in some potentially surprising cases such as
+    // `CONSTANT.field`.
+    pub fn is_syntactic_place_expr(&self) -> bool {
+        self.is_place_expr(|_| true)
+    }
+
+    // Whether this is a place expression.
+    // `allow_projections_from` should return `true` if indexing a field or
+    // index expression based on the given expression should be considered a
+    // place expression.
+    pub fn is_place_expr(&self, mut allow_projections_from: impl FnMut(&Self) -> bool) -> bool {
+        match self.kind {
             ExprKind::Path(QPath::Resolved(_, ref path)) => {
                 match path.res {
                     Res::Local(..)
@@ -1504,14 +1517,19 @@ impl Expr {
                 }
             }
 
+            // Type ascription inherits its place expression kind from its
+            // operand. See:
+            // https://github.com/rust-lang/rfcs/blob/master/text/0803-type-ascription.md#type-ascription-and-temporaries
             ExprKind::Type(ref e, _) => {
-                e.is_place_expr()
+                e.is_place_expr(allow_projections_from)
             }
 
-            ExprKind::Unary(UnDeref, _) |
-            ExprKind::Field(..) |
-            ExprKind::Index(..) => {
-                true
+            ExprKind::Unary(UnDeref, _) => true,
+
+            ExprKind::Field(ref base, _) |
+            ExprKind::Index(ref base, _) => {
+                allow_projections_from(base)
+                    || base.is_place_expr(allow_projections_from)
             }
 
             // Partially qualified paths in expressions can only legally
@@ -1646,8 +1664,8 @@ pub enum ExprKind {
     /// Path to a definition, possibly containing lifetime or type parameters.
     Path(QPath),
 
-    /// A referencing operation (i.e., `&a` or `&mut a`).
-    AddrOf(Mutability, P<Expr>),
+    /// A referencing operation (i.e., `&a`, `&mut a`, `&raw const a`, or `&raw mut a`).
+    AddrOf(BorrowKind, Mutability, P<Expr>),
     /// A `break`, with an optional label to break.
     Break(Destination, Option<P<Expr>>),
     /// A `continue`, with an optional label.

src/librustc/hir/print.rs

@@ -294,16 +294,12 @@ impl<'a> State<'a> {
             }
             hir::TyKind::Ptr(ref mt) => {
                 self.s.word("*");
-                match mt.mutbl {
-                    hir::Mutability::Mutable => self.word_nbsp("mut"),
-                    hir::Mutability::Immutable => self.word_nbsp("const"),
-                }
-                self.print_type(&mt.ty);
+                self.print_mt(mt, true);
             }
             hir::TyKind::Rptr(ref lifetime, ref mt) => {
                 self.s.word("&");
                 self.print_opt_lifetime(lifetime);
-                self.print_mt(mt);
+                self.print_mt(mt, false);
             }
             hir::TyKind::Never => {
                 self.s.word("!");
@@ -1178,11 +1174,18 @@ impl<'a> State<'a> {
     }
 
     fn print_expr_addr_of(&mut self,
+                          kind: hir::BorrowKind,
                           mutability: hir::Mutability,
                           expr: &hir::Expr)
-                          {
+    {
         self.s.word("&");
-        self.print_mutability(mutability);
+        match kind {
+            hir::BorrowKind::Ref => self.print_mutability(mutability, false),
+            hir::BorrowKind::Raw => {
+                self.word_nbsp("raw");
+                self.print_mutability(mutability, true);
+            }
+        }
         self.print_expr_maybe_paren(expr, parser::PREC_PREFIX)
     }
 
@@ -1225,8 +1228,8 @@ impl<'a> State<'a> {
             hir::ExprKind::Unary(op, ref expr) => {
                 self.print_expr_unary(op, &expr);
             }
-            hir::ExprKind::AddrOf(m, ref expr) => {
-                self.print_expr_addr_of(m, &expr);
+            hir::ExprKind::AddrOf(k, m, ref expr) => {
+                self.print_expr_addr_of(k, m, &expr);
             }
             hir::ExprKind::Lit(ref lit) => {
                 self.print_literal(&lit);
@@ -1629,11 +1632,11 @@ impl<'a> State<'a> {
                 match binding_mode {
                     hir::BindingAnnotation::Ref => {
                         self.word_nbsp("ref");
-                        self.print_mutability(hir::Mutability::Immutable);
+                        self.print_mutability(hir::Mutability::Immutable, false);
                     }
                     hir::BindingAnnotation::RefMut => {
                         self.word_nbsp("ref");
-                        self.print_mutability(hir::Mutability::Mutable);
+                        self.print_mutability(hir::Mutability::Mutable, false);
                     }
                     hir::BindingAnnotation::Unannotated => {}
                     hir::BindingAnnotation::Mutable => {
@@ -2060,15 +2063,15 @@ impl<'a> State<'a> {
         }
     }
 
-    pub fn print_mutability(&mut self, mutbl: hir::Mutability) {
+    pub fn print_mutability(&mut self, mutbl: hir::Mutability, print_const: bool) {
         match mutbl {
             hir::Mutability::Mutable => self.word_nbsp("mut"),
-            hir::Mutability::Immutable => {},
+            hir::Mutability::Immutable => if print_const { self.word_nbsp("const") },
         }
     }
 
-    pub fn print_mt(&mut self, mt: &hir::MutTy) {
-        self.print_mutability(mt.mutbl);
+    pub fn print_mt(&mut self, mt: &hir::MutTy, print_const: bool) {
+        self.print_mutability(mt.mutbl, print_const);
         self.print_type(&mt.ty)
     }
 

src/librustc/middle/expr_use_visitor.rs

@@ -276,7 +276,7 @@ impl<'a, 'tcx> ExprUseVisitor<'a, 'tcx> {
                 self.consume_exprs(exprs);
             }
 
-            hir::ExprKind::AddrOf(m, ref base) => {   // &base
+            hir::ExprKind::AddrOf(_, m, ref base) => {   // &base
                 // make sure that the thing we are pointing out stays valid
                 // for the lifetime `scope_r` of the resulting ptr:
                 let bk = ty::BorrowKind::from_mutbl(m);

src/librustc/middle/region.rs

@@ -1241,7 +1241,7 @@ fn resolve_local<'tcx>(
         blk_id: Option<Scope>,
     ) {
         match expr.kind {
-            hir::ExprKind::AddrOf(_, ref subexpr) => {
+            hir::ExprKind::AddrOf(_, _, ref subexpr) => {
                 record_rvalue_scope_if_borrow_expr(visitor, &subexpr, blk_id);
                 record_rvalue_scope(visitor, &subexpr, blk_id);
             }
@@ -1301,7 +1301,7 @@ fn resolve_local<'tcx>(
             visitor.scope_tree.record_rvalue_scope(expr.hir_id.local_id, blk_scope);
 
             match expr.kind {
-                hir::ExprKind::AddrOf(_, ref subexpr) |
+                hir::ExprKind::AddrOf(_, _, ref subexpr) |
                 hir::ExprKind::Unary(hir::UnDeref, ref subexpr) |
                 hir::ExprKind::Field(ref subexpr, _) |
                 hir::ExprKind::Index(ref subexpr, _) => {

src/librustc_error_codes/error_codes.rs

@@ -409,6 +409,7 @@ E0741: include_str!("./error_codes/E0741.md"),
 E0742: include_str!("./error_codes/E0742.md"),
 E0743: include_str!("./error_codes/E0743.md"),
 E0744: include_str!("./error_codes/E0744.md"),
+E0745: include_str!("./error_codes/E0745.md"),
 ;
 //  E0006, // merged with E0005
 //  E0008, // cannot bind by-move into a pattern guard

src/librustc_error_codes/error_codes/E0745.md

@@ -0,0 +1,20 @@
+Cannot take address of temporary value.
+
+Erroneous code example:
+
+```compile_fail,E0745
+# #![feature(raw_ref_op)]
+fn temp_address() {
+    let ptr = &raw const 2;   // ERROR
+}
+```
+
+To avoid the error, first bind the temporary to a named local variable.
+
+```ignore
+# #![feature(raw_ref_op)]
+fn temp_address() {
+    let val = 2;
+    let ptr = &raw const val;
+}
+```