Rollup merge of #134140 - compiler-errors:unsafe-binders-ast, r=oli-obk

Add AST support for unsafe binders

I'm splitting up #130514 into pieces. It's impossible for me to keep up with a huge PR like that. I'll land type system support for this next, probably w/o MIR lowering, which will come later.

r? `@oli-obk`
cc `@BoxyUwU` and `@lcnr` who also may want to look at this, though this PR doesn't do too much yet

compiler/rustc_parse/src/parser/expr.rs

@@ -15,7 +15,7 @@ use rustc_ast::visit::{Visitor, walk_expr};
 use rustc_ast::{
     self as ast, AnonConst, Arm, AttrStyle, AttrVec, BinOp, BinOpKind, BlockCheckMode, CaptureBy,
     ClosureBinder, DUMMY_NODE_ID, Expr, ExprField, ExprKind, FnDecl, FnRetTy, Label, MacCall,
-    MetaItemLit, Movability, Param, RangeLimits, StmtKind, Ty, TyKind, UnOp,
+    MetaItemLit, Movability, Param, RangeLimits, StmtKind, Ty, TyKind, UnOp, UnsafeBinderCastKind,
 };
 use rustc_ast_pretty::pprust;
 use rustc_data_structures::stack::ensure_sufficient_stack;
@@ -1931,6 +1931,12 @@ impl<'a> Parser<'a> {
             Ok(match ident.name {
                 sym::offset_of => Some(this.parse_expr_offset_of(lo)?),
                 sym::type_ascribe => Some(this.parse_expr_type_ascribe(lo)?),
+                sym::wrap_binder => {
+                    Some(this.parse_expr_unsafe_binder_cast(lo, UnsafeBinderCastKind::Wrap)?)
+                }
+                sym::unwrap_binder => {
+                    Some(this.parse_expr_unsafe_binder_cast(lo, UnsafeBinderCastKind::Unwrap)?)
+                }
                 _ => None,
             })
         })
@@ -2006,6 +2012,17 @@ impl<'a> Parser<'a> {
         Ok(self.mk_expr(span, ExprKind::Type(expr, ty)))
     }
 
+    pub(crate) fn parse_expr_unsafe_binder_cast(
+        &mut self,
+        lo: Span,
+        kind: UnsafeBinderCastKind,
+    ) -> PResult<'a, P<Expr>> {
+        let expr = self.parse_expr()?;
+        let ty = if self.eat(&TokenKind::Comma) { Some(self.parse_ty()?) } else { None };
+        let span = lo.to(self.token.span);
+        Ok(self.mk_expr(span, ExprKind::UnsafeBinderCast(kind, expr, ty)))
+    }
+
     /// Returns a string literal if the next token is a string literal.
     /// In case of error returns `Some(lit)` if the next token is a literal with a wrong kind,
     /// and returns `None` if the next token is not literal at all.
@@ -4016,7 +4033,9 @@ impl MutVisitor for CondChecker<'_> {
                 mut_visit::walk_expr(self, e);
                 self.forbid_let_reason = forbid_let_reason;
             }
-            ExprKind::Cast(ref mut op, _) | ExprKind::Type(ref mut op, _) => {
+            ExprKind::Cast(ref mut op, _)
+            | ExprKind::Type(ref mut op, _)
+            | ExprKind::UnsafeBinderCast(_, ref mut op, _) => {
                 let forbid_let_reason = self.forbid_let_reason;
                 self.forbid_let_reason = Some(OtherForbidden);
                 self.visit_expr(op);

compiler/rustc_parse/src/parser/ty.rs

@@ -5,7 +5,7 @@ use rustc_ast::{
     self as ast, BareFnTy, BoundAsyncness, BoundConstness, BoundPolarity, DUMMY_NODE_ID, FnRetTy,
     GenericBound, GenericBounds, GenericParam, Generics, Lifetime, MacCall, MutTy, Mutability,
     Pinnedness, PolyTraitRef, PreciseCapturingArg, TraitBoundModifiers, TraitObjectSyntax, Ty,
-    TyKind,
+    TyKind, UnsafeBinderTy,
 };
 use rustc_errors::{Applicability, PResult};
 use rustc_span::symbol::{Ident, kw, sym};
@@ -348,6 +348,10 @@ impl<'a> Parser<'a> {
                     TyKind::Err(guar)
                 }
             }
+        } else if self.check_keyword(kw::Unsafe)
+            && self.look_ahead(1, |tok| matches!(tok.kind, token::Lt))
+        {
+            self.parse_unsafe_binder_ty()?
         } else {
             let msg = format!("expected type, found {}", super::token_descr(&self.token));
             let mut err = self.dcx().struct_span_err(lo, msg);
@@ -369,6 +373,19 @@ impl<'a> Parser<'a> {
         if allow_qpath_recovery { self.maybe_recover_from_bad_qpath(ty) } else { Ok(ty) }
     }
 
+    fn parse_unsafe_binder_ty(&mut self) -> PResult<'a, TyKind> {
+        let lo = self.token.span;
+        assert!(self.eat_keyword(kw::Unsafe));
+        self.expect_lt()?;
+        let generic_params = self.parse_generic_params()?;
+        self.expect_gt()?;
+        let inner_ty = self.parse_ty()?;
+        let span = lo.to(self.prev_token.span);
+        self.psess.gated_spans.gate(sym::unsafe_binders, span);
+
+        Ok(TyKind::UnsafeBinder(P(UnsafeBinderTy { generic_params, inner_ty })))
+    }
+
     /// Parses either:
     /// - `(TYPE)`, a parenthesized type.
     /// - `(TYPE,)`, a tuple with a single field of type TYPE.