PoC: A new hybrid design for Try

compiler/rustc_ast_lowering/src/expr.rs

@@ -462,8 +462,8 @@ 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::continue_with(<expr>) }`,
+    /// `try { <stmts>; }` into `{ <stmts>; ::std::ops::Try::continue_with(()) }`
     /// 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| {
@@ -492,9 +492,9 @@ impl<'hir> LoweringContext<'_, 'hir> {
             let ok_wrapped_span =
                 this.mark_span_with_reason(DesugaringKind::TryBlock, tail_expr.span, None);
 
-            // `::std::ops::Try::from_ok($tail_expr)`
+            // `::std::ops::Try::continue_with($tail_expr)`
             block.expr = Some(this.wrap_in_try_constructor(
-                hir::LangItem::TryFromOk,
+                hir::LangItem::TryContinueWith,
                 try_span,
                 tail_expr,
                 ok_wrapped_span,
@@ -1793,14 +1793,14 @@ 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::TryBranch,
                 arena_vec![self; sub_expr],
             )
         };
@@ -1818,8 +1818,8 @@ 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(
@@ -1828,27 +1828,21 @@ 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)]
+        // `ControlFlow::Break(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,
+        let break_arm = {
+            let holder_ident = Ident::with_dummy_span(sym::holder);
+            let (holder_local, holder_local_nid) = self.pat_ident(try_span, holder_ident);
+            let holder_expr =
+                self.arena.alloc(self.expr_ident_mut(try_span, holder_ident, holder_local_nid));
+            let from_holder_expr = self.wrap_in_try_constructor(
+                hir::LangItem::FromHolder,
                 unstable_span,
-                from_expr,
+                holder_expr,
                 unstable_span,
             );
             let thin_attrs = ThinVec::from(attrs);
@@ -1859,25 +1853,25 @@ impl<'hir> LoweringContext<'_, 'hir> {
                     try_span,
                     hir::ExprKind::Break(
                         hir::Destination { label: None, target_id },
-                        Some(from_err_expr),
+                        Some(from_holder_expr),
                     ),
                     thin_attrs,
                 ))
             } else {
                 self.arena.alloc(self.expr(
                     try_span,
-                    hir::ExprKind::Ret(Some(from_err_expr)),
+                    hir::ExprKind::Ret(Some(from_holder_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(unstable_span, holder_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

@@ -324,7 +324,7 @@ 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::try_trait, sym::try_trait_v2, sym::control_flow_enum][..].into()),
         allow_gen_future: Some([sym::gen_future][..].into()),
     }
     .lower_crate(krate)
@@ -2546,15 +2546,15 @@ 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> {
-        let field = self.single_pat_field(span, pat);
-        self.pat_lang_item_variant(span, hir::LangItem::ResultOk, field)
-    }
+    // fn pat_ok(&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)
+    // }
 
-    fn pat_err(&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)
-    }
+    // fn pat_err(&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)
+    // }
 
     fn pat_some(&mut self, span: Span, pat: &'hir hir::Pat<'hir>) -> &'hir hir::Pat<'hir> {
         let field = self.single_pat_field(span, pat);
@@ -2565,6 +2565,16 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
         self.pat_lang_item_variant(span, hir::LangItem::OptionNone, &[])
     }
 
+    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::ControlFlowContinue, field)
+    }
+
+    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::ControlFlowBreak, field)
+    }
+
     fn single_pat_field(
         &mut self,
         span: Span,

compiler/rustc_hir/src/lang_items.rs

@@ -306,6 +306,9 @@ language_item_table! {
     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 });
+    TryContinueWith,         sym::continue_with,       continue_with_fn,           Target::Method(MethodKind::Trait { body: false });
+    TryBranch,               sym::branch,              branch_fn,                  Target::Method(MethodKind::Trait { body: false });
+    FromHolder,              sym::from_holder,         from_holder_fn,             Target::Method(MethodKind::Trait { body: false });
 
     PollReady,               sym::Ready,               poll_ready_variant,         Target::Variant;
     PollPending,             sym::Pending,             poll_pending_variant,       Target::Variant;
@@ -323,6 +326,9 @@ language_item_table! {
     ResultOk,                sym::Ok,                  result_ok_variant,          Target::Variant;
     ResultErr,               sym::Err,                 result_err_variant,         Target::Variant;
 
+    ControlFlowBreak,        sym::Break,               cf_break_variant,           Target::Variant;
+    ControlFlowContinue,     sym::Continue,            cf_continue_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_middle/src/ty/query/on_disk_cache.rs

@@ -405,7 +405,7 @@ impl<'sess> OnDiskCache<'sess> {
 
             // Encode the position of the footer as the last 8 bytes of the
             // file so we know where to look for it.
-            IntEncodedWithFixedSize(footer_pos).encode(encoder.encoder)?;
+            IntEncodedWithFixedSize(footer_pos).encode(encoder.encoder).map_err(|x| x)?;
 
             // DO NOT WRITE ANYTHING TO THE ENCODER AFTER THIS POINT! The address
             // of the footer must be the last thing in the data stream.

compiler/rustc_span/src/symbol.rs

@@ -126,10 +126,12 @@ symbols! {
         Argument,
         ArgumentV1,
         Arguments,
+        Break,
         C,
         CString,
         Center,
         Clone,
+        Continue,
         Copy,
         Count,
         Debug,
@@ -313,6 +315,7 @@ symbols! {
         box_patterns,
         box_syntax,
         braced_empty_structs,
+        branch,
         breakpoint,
         bridge,
         bswap,
@@ -392,6 +395,8 @@ symbols! {
         constructor,
         contents,
         context,
+        continue_with,
+        control_flow_enum,
         convert,
         copy,
         copy_closures,
@@ -561,6 +566,7 @@ symbols! {
         from_desugaring,
         from_error,
         from_generator,
+        from_holder,
         from_method,
         from_ok,
         from_size_align_unchecked,
@@ -587,6 +593,7 @@ symbols! {
         hash,
         hexagon_target_feature,
         hidden,
+        holder,
         homogeneous_aggregate,
         html_favicon_url,
         html_logo_url,
@@ -1177,6 +1184,7 @@ symbols! {
         try_from_trait,
         try_into_trait,
         try_trait,
+        try_trait_v2,
         tt,
         tuple,
         tuple_from_req,

compiler/rustc_typeck/src/check/expr.rs

@@ -164,7 +164,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
     ) -> Ty<'tcx> {
         debug!(">> type-checking: expr={:?} expected={:?}", expr, expected);
 
-        // True if `expr` is a `Try::from_ok(())` that is a result of desugaring a try block
+        // True if `expr` is a `Try::continue_with(())` that is a result of desugaring a try block
         // without the final expr (e.g. `try { return; }`). We don't want to generate an
         // unreachable_code lint for it since warnings for autogenerated code are confusing.
         let is_try_block_generated_unit_expr = match expr.kind {

library/alloc/src/lib.rs

@@ -137,6 +137,7 @@
 #![feature(alloc_layout_extra)]
 #![feature(trusted_random_access)]
 #![feature(try_trait)]
+#![feature(try_trait_v2)]
 #![feature(type_alias_impl_trait)]
 #![feature(associated_type_bounds)]
 #![feature(slice_group_by)]

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

@@ -129,6 +129,7 @@ where
         }
     }
 
+    #[cfg(bootstrap)]
     #[inline]
     fn try_rfold<B, F, R>(&mut self, init: B, mut f: F) -> R
     where
@@ -149,6 +150,29 @@ where
         }
     }
 
+    #[cfg(not(bootstrap))]
+    #[inline]
+    fn try_rfold<B, F, R>(&mut self, init: B, mut f: F) -> R
+    where
+        Self: Sized,
+        F: FnMut(B, Self::Item) -> R,
+        R: Try<Ok = B>,
+    {
+        use crate::ops::ControlFlow;
+
+        match self.peeked.take() {
+            Some(None) => try { init },
+            Some(Some(v)) => match self.iter.try_rfold(init, &mut f).branch() {
+                ControlFlow::Continue(acc) => f(acc, v),
+                ControlFlow::Break(h) => {
+                    self.peeked = Some(Some(v));
+                    R::from_holder(h)
+                }
+            },
+            None => self.iter.try_rfold(init, f),
+        }
+    }
+
     #[inline]
     fn rfold<Acc, Fold>(self, init: Acc, mut fold: Fold) -> Acc
     where

library/core/src/iter/traits/iterator.rs

@@ -3,7 +3,7 @@
 // can't split that into multiple files.
 
 use crate::cmp::{self, Ordering};
-use crate::ops::{Add, ControlFlow, Try};
+use crate::ops::{self, Add, ControlFlow, Try};
 
 use super::super::TrustedRandomAccess;
 use super::super::{Chain, Cloned, Copied, Cycle, Enumerate, Filter, FilterMap, Fuse};
@@ -2388,13 +2388,14 @@ pub trait Iterator {
     /// let result = a.iter().try_find(|&&s| is_my_num(s, 5));
     /// assert!(result.is_err());
     /// ```
+    #[cfg(bootstrap)]
     #[inline]
     #[unstable(feature = "try_find", reason = "new API", issue = "63178")]
     fn try_find<F, R>(&mut self, f: F) -> Result<Option<Self::Item>, R::Error>
     where
         Self: Sized,
         F: FnMut(&Self::Item) -> R,
-        R: Try<Ok = bool>,
+        R: ops::Try<Ok = bool>,
     {
         #[inline]
         fn check<F, T, R>(mut f: F) -> impl FnMut((), T) -> ControlFlow<Result<T, R::Error>>
@@ -2412,6 +2413,59 @@ pub trait Iterator {
         self.try_fold((), check(f)).break_value().transpose()
     }
 
+    /// Applies function to the elements of iterator and returns
+    /// the first true result or the first error.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// #![feature(try_find)]
+    ///
+    /// let a = ["1", "2", "lol", "NaN", "5"];
+    ///
+    /// let is_my_num = |s: &str, search: i32| -> Result<bool, std::num::ParseIntError> {
+    ///     Ok(s.parse::<i32>()?  == search)
+    /// };
+    ///
+    /// let result = a.iter().try_find(|&&s| is_my_num(s, 2));
+    /// assert_eq!(result, Ok(Some(&"2")));
+    ///
+    /// let result = a.iter().try_find(|&&s| is_my_num(s, 5));
+    /// assert!(result.is_err());
+    /// ```
+    #[cfg(not(bootstrap))]
+    #[inline]
+    #[unstable(feature = "try_find", reason = "new API", issue = "63178")]
+    fn try_find<F, R>(
+        &mut self,
+        f: F,
+    ) -> <R::Holder as ops::BreakHolder<Option<Self::Item>>>::Output
+    where
+        Self: Sized,
+        F: FnMut(&Self::Item) -> R,
+        R: ops::Try<Ok = bool>,
+        R::Holder: ops::BreakHolder<Option<Self::Item>>,
+    {
+        #[inline]
+        fn check<F, T, R>(mut f: F) -> impl FnMut((), T) -> ControlFlow<Result<T, R::Holder>>
+        where
+            F: FnMut(&T) -> R,
+            R: Try<Ok = bool>,
+        {
+            move |(), x| match f(&x).branch() {
+                ControlFlow::Continue(false) => ControlFlow::CONTINUE,
+                ControlFlow::Continue(true) => ControlFlow::Break(Ok(x)),
+                ControlFlow::Break(h) => ControlFlow::Break(Err(h)),
+            }
+        }
+
+        match self.try_fold((), check(f)) {
+            ControlFlow::Continue(()) => ops::TryCore::continue_with(None),
+            ControlFlow::Break(Ok(x)) => ops::TryCore::continue_with(Some(x)),
+            ControlFlow::Break(Err(h)) => Try::from_holder(h),
+        }
+    }
+
     /// Searches for an element in an iterator, returning its index.
     ///
     /// `position()` takes a closure that returns `true` or `false`. It applies