Implement the new desugaring from try_trait_v2

compiler/rustc_ast_lowering/src/expr.rs

@@ -562,8 +562,8 @@ impl<'hir> LoweringContext<'_, 'hir> {
         )
     }
 
-    /// Desugar `try { <stmts>; <expr> }` into `{ <stmts>; ::std::ops::Try::from_ok(<expr>) }`,
-    /// `try { <stmts>; }` into `{ <stmts>; ::std::ops::Try::from_ok(()) }`
+    /// Desugar `try { <stmts>; <expr> }` into `{ <stmts>; ::std::ops::Try::from_output(<expr>) }`,
+    /// `try { <stmts>; }` into `{ <stmts>; ::std::ops::Try::from_output(()) }`
     /// and save the block id to use it as a break target for desugaring of the `?` operator.
     fn lower_expr_try_block(&mut self, body: &Block) -> hir::ExprKind<'hir> {
         self.with_catch_scope(body.id, |this| {
@@ -592,9 +592,9 @@ impl<'hir> LoweringContext<'_, 'hir> {
             let ok_wrapped_span =
                 this.mark_span_with_reason(DesugaringKind::TryBlock, tail_expr.span, None);
 
-            // `::std::ops::Try::from_ok($tail_expr)`
+            // `::std::ops::Try::from_output($tail_expr)`
             block.expr = Some(this.wrap_in_try_constructor(
-                hir::LangItem::TryFromOk,
+                hir::LangItem::TryTraitFromOutput,
                 try_span,
                 tail_expr,
                 ok_wrapped_span,
@@ -1896,14 +1896,14 @@ impl<'hir> LoweringContext<'_, 'hir> {
             self.allow_try_trait.clone(),
         );
 
-        // `Try::into_result(<expr>)`
+        // `Try::branch(<expr>)`
         let scrutinee = {
             // expand <expr>
             let sub_expr = self.lower_expr_mut(sub_expr);
 
             self.expr_call_lang_item_fn(
                 unstable_span,
-                hir::LangItem::TryIntoResult,
+                hir::LangItem::TryTraitBranch,
                 arena_vec![self; sub_expr],
             )
         };
@@ -1921,8 +1921,8 @@ impl<'hir> LoweringContext<'_, 'hir> {
         };
         let attrs = vec![attr];
 
-        // `Ok(val) => #[allow(unreachable_code)] val,`
-        let ok_arm = {
+        // `ControlFlow::Continue(val) => #[allow(unreachable_code)] val,`
+        let continue_arm = {
             let val_ident = Ident::with_dummy_span(sym::val);
             let (val_pat, val_pat_nid) = self.pat_ident(span, val_ident);
             let val_expr = self.arena.alloc(self.expr_ident_with_attrs(
@@ -1931,27 +1931,21 @@ impl<'hir> LoweringContext<'_, 'hir> {
                 val_pat_nid,
                 ThinVec::from(attrs.clone()),
             ));
-            let ok_pat = self.pat_ok(span, val_pat);
-            self.arm(ok_pat, val_expr)
+            let continue_pat = self.pat_cf_continue(unstable_span, val_pat);
+            self.arm(continue_pat, val_expr)
         };
 
-        // `Err(err) => #[allow(unreachable_code)]
-        //              return Try::from_error(From::from(err)),`
-        let err_arm = {
-            let err_ident = Ident::with_dummy_span(sym::err);
-            let (err_local, err_local_nid) = self.pat_ident(try_span, err_ident);
-            let from_expr = {
-                let err_expr = self.expr_ident_mut(try_span, err_ident, err_local_nid);
-                self.expr_call_lang_item_fn(
-                    try_span,
-                    hir::LangItem::FromFrom,
-                    arena_vec![self; err_expr],
-                )
-            };
-            let from_err_expr = self.wrap_in_try_constructor(
-                hir::LangItem::TryFromError,
-                unstable_span,
-                from_expr,
+        // `ControlFlow::Break(residual) =>
+        //     #[allow(unreachable_code)]
+        //     return Try::from_residual(residual),`
+        let break_arm = {
+            let residual_ident = Ident::with_dummy_span(sym::residual);
+            let (residual_local, residual_local_nid) = self.pat_ident(try_span, residual_ident);
+            let residual_expr = self.expr_ident_mut(try_span, residual_ident, residual_local_nid);
+            let from_residual_expr = self.wrap_in_try_constructor(
+                hir::LangItem::TryTraitFromResidual,
+                try_span,
+                self.arena.alloc(residual_expr),
                 unstable_span,
             );
             let thin_attrs = ThinVec::from(attrs);
@@ -1962,25 +1956,25 @@ impl<'hir> LoweringContext<'_, 'hir> {
                     try_span,
                     hir::ExprKind::Break(
                         hir::Destination { label: None, target_id },
-                        Some(from_err_expr),
+                        Some(from_residual_expr),
                     ),
                     thin_attrs,
                 ))
             } else {
                 self.arena.alloc(self.expr(
                     try_span,
-                    hir::ExprKind::Ret(Some(from_err_expr)),
+                    hir::ExprKind::Ret(Some(from_residual_expr)),
                     thin_attrs,
                 ))
             };
 
-            let err_pat = self.pat_err(try_span, err_local);
-            self.arm(err_pat, ret_expr)
+            let break_pat = self.pat_cf_break(try_span, residual_local);
+            self.arm(break_pat, ret_expr)
         };
 
         hir::ExprKind::Match(
             scrutinee,
-            arena_vec![self; err_arm, ok_arm],
+            arena_vec![self; break_arm, continue_arm],
             hir::MatchSource::TryDesugar,
         )
     }

compiler/rustc_ast_lowering/src/lib.rs

@@ -331,7 +331,7 @@ pub fn lower_crate<'a, 'hir>(
         lifetimes_to_define: Vec::new(),
         is_collecting_in_band_lifetimes: false,
         in_scope_lifetimes: Vec::new(),
-        allow_try_trait: Some([sym::try_trait][..].into()),
+        allow_try_trait: Some([sym::control_flow_enum, sym::try_trait_v2][..].into()),
         allow_gen_future: Some([sym::gen_future][..].into()),
     }
     .lower_crate(krate)
@@ -2479,14 +2479,14 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
         self.pat(span, hir::PatKind::Lit(expr))
     }
 
-    fn pat_ok(&mut self, span: Span, pat: &'hir hir::Pat<'hir>) -> &'hir hir::Pat<'hir> {
+    fn pat_cf_continue(&mut self, span: Span, pat: &'hir hir::Pat<'hir>) -> &'hir hir::Pat<'hir> {
         let field = self.single_pat_field(span, pat);
-        self.pat_lang_item_variant(span, hir::LangItem::ResultOk, field)
+        self.pat_lang_item_variant(span, hir::LangItem::ControlFlowContinue, field)
     }
 
-    fn pat_err(&mut self, span: Span, pat: &'hir hir::Pat<'hir>) -> &'hir hir::Pat<'hir> {
+    fn pat_cf_break(&mut self, span: Span, pat: &'hir hir::Pat<'hir>) -> &'hir hir::Pat<'hir> {
         let field = self.single_pat_field(span, pat);
-        self.pat_lang_item_variant(span, hir::LangItem::ResultErr, field)
+        self.pat_lang_item_variant(span, hir::LangItem::ControlFlowBreak, field)
     }
 
     fn pat_some(&mut self, span: Span, pat: &'hir hir::Pat<'hir>) -> &'hir hir::Pat<'hir> {

compiler/rustc_hir/src/lang_items.rs

@@ -308,12 +308,12 @@ language_item_table! {
 
     Termination,             sym::termination,         termination,                Target::Trait;
 
-    Try,                     kw::Try,                  try_trait,                  Target::Trait;
+    Try,                     sym::Try,                 try_trait,                  Target::Trait;
 
     // Language items from AST lowering
-    TryFromError,            sym::from_error,          from_error_fn,              Target::Method(MethodKind::Trait { body: false });
-    TryFromOk,               sym::from_ok,             from_ok_fn,                 Target::Method(MethodKind::Trait { body: false });
-    TryIntoResult,           sym::into_result,         into_result_fn,             Target::Method(MethodKind::Trait { body: false });
+    TryTraitFromResidual,    sym::from_residual,       from_residual_fn,           Target::Method(MethodKind::Trait { body: false });
+    TryTraitFromOutput,      sym::from_output,         from_output_fn,             Target::Method(MethodKind::Trait { body: false });
+    TryTraitBranch,          sym::branch,              branch_fn,                  Target::Method(MethodKind::Trait { body: false });
 
     PollReady,               sym::Ready,               poll_ready_variant,         Target::Variant;
     PollPending,             sym::Pending,             poll_pending_variant,       Target::Variant;
@@ -331,6 +331,9 @@ language_item_table! {
     ResultOk,                sym::Ok,                  result_ok_variant,          Target::Variant;
     ResultErr,               sym::Err,                 result_err_variant,         Target::Variant;
 
+    ControlFlowContinue,     sym::Continue,            cf_continue_variant,        Target::Variant;
+    ControlFlowBreak,        sym::Break,               cf_break_variant,           Target::Variant;
+
     IntoIterIntoIter,        sym::into_iter,           into_iter_fn,               Target::Method(MethodKind::Trait { body: false });
     IteratorNext,            sym::next,                next_fn,                    Target::Method(MethodKind::Trait { body: false});
 

compiler/rustc_span/src/symbol.rs

@@ -130,10 +130,12 @@ symbols! {
         BTreeSet,
         BinaryHeap,
         Borrow,
+        Break,
         C,
         CString,
         Center,
         Clone,
+        Continue,
         Copy,
         Count,
         Debug,
@@ -326,6 +328,7 @@ symbols! {
         box_patterns,
         box_syntax,
         braced_empty_structs,
+        branch,
         breakpoint,
         bridge,
         bswap,
@@ -410,6 +413,7 @@ symbols! {
         constructor,
         contents,
         context,
+        control_flow_enum,
         convert,
         copy,
         copy_closures,
@@ -510,7 +514,6 @@ symbols! {
         env,
         eq,
         ermsb_target_feature,
-        err,
         exact_div,
         except,
         exchange_malloc,
@@ -580,10 +583,10 @@ symbols! {
         frem_fast,
         from,
         from_desugaring,
-        from_error,
         from_generator,
         from_method,
-        from_ok,
+        from_output,
+        from_residual,
         from_size_align_unchecked,
         from_trait,
         from_usize,
@@ -652,7 +655,6 @@ symbols! {
         instruction_set,
         intel,
         into_iter,
-        into_result,
         into_trait,
         intra_doc_pointers,
         intrinsics,
@@ -962,6 +964,7 @@ symbols! {
         repr_packed,
         repr_simd,
         repr_transparent,
+        residual,
         result,
         result_type,
         rhs,
@@ -1227,7 +1230,7 @@ symbols! {
         try_blocks,
         try_from_trait,
         try_into_trait,
-        try_trait,
+        try_trait_v2,
         tt,
         tuple,
         tuple_from_req,

library/alloc/src/collections/vec_deque/iter.rs

@@ -66,7 +66,7 @@ impl<'a, T> Iterator for Iter<'a, T> {
     where
         Self: Sized,
         F: FnMut(B, Self::Item) -> R,
-        R: Try<Ok = B>,
+        R: Try<Output = B>,
     {
         let (mut iter, final_res);
         if self.tail <= self.head {
@@ -140,7 +140,7 @@ impl<'a, T> DoubleEndedIterator for Iter<'a, T> {
     where
         Self: Sized,
         F: FnMut(B, Self::Item) -> R,
-        R: Try<Ok = B>,
+        R: Try<Output = B>,
     {
         let (mut iter, final_res);
         if self.tail <= self.head {

library/alloc/src/lib.rs

@@ -140,7 +140,8 @@
 #![feature(maybe_uninit_extra, maybe_uninit_slice, maybe_uninit_uninit_array)]
 #![feature(alloc_layout_extra)]
 #![feature(trusted_random_access)]
-#![feature(try_trait)]
+#![cfg_attr(bootstrap, feature(try_trait))]
+#![cfg_attr(not(bootstrap), feature(try_trait_v2))]
 #![feature(min_type_alias_impl_trait)]
 #![feature(associated_type_bounds)]
 #![feature(slice_group_by)]

library/core/src/iter/adapters/chain.rs

@@ -98,7 +98,7 @@ where
     where
         Self: Sized,
         F: FnMut(Acc, Self::Item) -> R,
-        R: Try<Ok = Acc>,
+        R: Try<Output = Acc>,
     {
         if let Some(ref mut a) = self.a {
             acc = a.try_fold(acc, &mut f)?;
@@ -281,7 +281,7 @@ where
     where
         Self: Sized,
         F: FnMut(Acc, Self::Item) -> R,
-        R: Try<Ok = Acc>,
+        R: Try<Output = Acc>,
     {
         if let Some(ref mut b) = self.b {
             acc = b.try_rfold(acc, &mut f)?;

library/core/src/iter/adapters/cloned.rs

@@ -46,7 +46,7 @@ where
     where
         Self: Sized,
         F: FnMut(B, Self::Item) -> R,
-        R: Try<Ok = B>,
+        R: Try<Output = B>,
     {
         self.it.try_fold(init, clone_try_fold(f))
     }
@@ -82,7 +82,7 @@ where
     where
         Self: Sized,
         F: FnMut(B, Self::Item) -> R,
-        R: Try<Ok = B>,
+        R: Try<Output = B>,
     {
         self.it.try_rfold(init, clone_try_fold(f))
     }

library/core/src/iter/adapters/copied.rs

@@ -50,7 +50,7 @@ where
     where
         Self: Sized,
         F: FnMut(B, Self::Item) -> R,
-        R: Try<Ok = B>,
+        R: Try<Output = B>,
     {
         self.it.try_fold(init, copy_try_fold(f))
     }
@@ -98,7 +98,7 @@ where
     where
         Self: Sized,
         F: FnMut(B, Self::Item) -> R,
-        R: Try<Ok = B>,
+        R: Try<Output = B>,
     {
         self.it.try_rfold(init, copy_try_fold(f))
     }

library/core/src/iter/adapters/cycle.rs

@@ -53,7 +53,7 @@ where
     fn try_fold<Acc, F, R>(&mut self, mut acc: Acc, mut f: F) -> R
     where
         F: FnMut(Acc, Self::Item) -> R,
-        R: Try<Ok = Acc>,
+        R: Try<Output = Acc>,
     {
         // fully iterate the current iterator. this is necessary because
         // `self.iter` may be empty even when `self.orig` isn't

library/core/src/iter/adapters/enumerate.rs

@@ -71,7 +71,7 @@ where
     where
         Self: Sized,
         Fold: FnMut(Acc, Self::Item) -> R,
-        R: Try<Ok = Acc>,
+        R: Try<Output = Acc>,
     {
         #[inline]
         fn enumerate<'a, T, Acc, R>(
@@ -150,7 +150,7 @@ where
     where
         Self: Sized,
         Fold: FnMut(Acc, Self::Item) -> R,
-        R: Try<Ok = Acc>,
+        R: Try<Output = Acc>,
     {
         // Can safely add and subtract the count, as `ExactSizeIterator` promises
         // that the number of elements fits into a `usize`.

library/core/src/iter/adapters/filter.rs

@@ -37,7 +37,7 @@ fn filter_fold<T, Acc>(
     move |acc, item| if predicate(&item) { fold(acc, item) } else { acc }
 }
 
-fn filter_try_fold<'a, T, Acc, R: Try<Ok = Acc>>(
+fn filter_try_fold<'a, T, Acc, R: Try<Output = Acc>>(
     predicate: &'a mut impl FnMut(&T) -> bool,
     mut fold: impl FnMut(Acc, T) -> R + 'a,
 ) -> impl FnMut(Acc, T) -> R + 'a {
@@ -88,7 +88,7 @@ where
     where
         Self: Sized,
         Fold: FnMut(Acc, Self::Item) -> R,
-        R: Try<Ok = Acc>,
+        R: Try<Output = Acc>,
     {
         self.iter.try_fold(init, filter_try_fold(&mut self.predicate, fold))
     }
@@ -117,7 +117,7 @@ where
     where
         Self: Sized,
         Fold: FnMut(Acc, Self::Item) -> R,
-        R: Try<Ok = Acc>,
+        R: Try<Output = Acc>,
     {
         self.iter.try_rfold(init, filter_try_fold(&mut self.predicate, fold))
     }