Auto merge of #84767 - scottmcm:try_trait_actual, r=lcnr

Implement the new desugaring from `try_trait_v2`

~~Currently blocked on #84782, which has a PR in #84811 Rebased atop that fix.

`try_trait_v2` tracking issue: #84277

Unfortunately this is already touching a ton of things, so if you have suggestions for good ways to split it up, I'd be happy to hear them.  (The combination between the use in the library, the compiler changes, the corresponding diagnostic differences, even MIR tests mean that I don't really have a great plan for it other than trying to have decently-readable commits.

r? `@ghost`

~~(This probably shouldn't go in during the last week before the fork anyway.)~~ Fork happened.

Author: bors

compiler/rustc_ast_lowering/src/expr.rs

@@ -560,8 +560,8 @@ 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| {
@@ -590,9 +590,9 @@ 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,
@@ -1579,14 +1579,14 @@ 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],
             )
         };
@@ -1604,8 +1604,8 @@ 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(
@@ -1614,27 +1614,21 @@ 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);
@@ -1645,25 +1639,25 @@ 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

@@ -332,7 +332,7 @@ 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)
@@ -2490,14 +2490,14 @@ 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,
@@ -411,6 +414,7 @@ symbols! {
         constructor,
         contents,
         context,
+        control_flow_enum,
         convert,
         copy,
         copy_closures,
@@ -511,7 +515,6 @@ symbols! {
         env,
         eq,
         ermsb_target_feature,
-        err,
         exact_div,
         except,
         exchange_malloc,
@@ -581,10 +584,10 @@ 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,
@@ -653,7 +656,6 @@ symbols! {
         instruction_set,
         intel,
         into_iter,
-        into_result,
         into_trait,
         intra_doc_pointers,
         intrinsics,
@@ -965,6 +967,7 @@ symbols! {
         repr_packed,
         repr_simd,
         repr_transparent,
+        residual,
         result,
         result_type,
         rhs,
@@ -1232,7 +1235,7 @@ 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