Delegation: support coercion for target expression

compiler/rustc_ast_lowering/src/delegation.rs

@@ -38,7 +38,7 @@
 
 use crate::{ImplTraitPosition, ResolverAstLoweringExt};
 
-use super::{ImplTraitContext, LoweringContext, ParamMode};
+use super::{ImplTraitContext, LoweringContext, ParamMode, ParenthesizedGenericArgs};
 
 use ast::visit::Visitor;
 use hir::def::{DefKind, PartialRes, Res};
@@ -245,12 +245,13 @@ impl<'hir> LoweringContext<'_, 'hir> {
         self.lower_body(|this| {
             let mut parameters: Vec<hir::Param<'_>> = Vec::with_capacity(param_count);
             let mut args: Vec<hir::Expr<'_>> = Vec::with_capacity(param_count);
+            let mut target_expr = None;
 
             for idx in 0..param_count {
                 let (param, pat_node_id) = this.generate_param(span);
                 parameters.push(param);
 
-                let arg = if let Some(block) = block
+                if let Some(block) = block
                     && idx == 0
                 {
                     let mut self_resolver = SelfResolver {
@@ -259,44 +260,105 @@ impl<'hir> LoweringContext<'_, 'hir> {
                         self_param_id: pat_node_id,
                     };
                     self_resolver.visit_block(block);
-                    let block = this.lower_block(block, false);
-                    this.mk_expr(hir::ExprKind::Block(block, None), block.span)
+                    let mut block = this.lower_block_noalloc(block, false);
+                    if block.expr.is_none() {
+                        let pat_hir_id = this.lower_node_id(pat_node_id);
+                        let arg = &*this.arena.alloc(this.generate_arg(pat_hir_id, span));
+                        // Use `self` as a first argument if no expression is provided.
+                        block.expr = Some(arg);
+                    }
+                    target_expr = Some(block);
                 } else {
                     let pat_hir_id = this.lower_node_id(pat_node_id);
-                    this.generate_arg(pat_hir_id, span)
+                    let arg = this.generate_arg(pat_hir_id, span);
+                    args.push(arg);
                 };
-                args.push(arg);
             }
 
-            let final_expr = this.finalize_body_lowering(delegation, args, span);
+            let final_expr = this.finalize_body_lowering(delegation, target_expr, args, span);
             (this.arena.alloc_from_iter(parameters), final_expr)
         })
     }
 
-    // Generates fully qualified call for the resulting body.
+    // Generates expression for the resulting body. If possible, `MethodCall` is used
+    // instead of fully qualified call for the self type coercion.
     fn finalize_body_lowering(
         &mut self,
         delegation: &Delegation,
-        args: Vec<hir::Expr<'hir>>,
+        target_expr: Option<hir::Block<'hir>>,
+        mut args: Vec<hir::Expr<'hir>>,
         span: Span,
     ) -> hir::Expr<'hir> {
-        let path = self.lower_qpath(
-            delegation.id,
-            &delegation.qself,
-            &delegation.path,
-            ParamMode::Optional,
-            ImplTraitContext::Disallowed(ImplTraitPosition::Path),
-            None,
-        );
-
-        let args = self.arena.alloc_from_iter(args);
-        let path_expr = self.arena.alloc(self.mk_expr(hir::ExprKind::Path(path), span));
-        let call = self.arena.alloc(self.mk_expr(hir::ExprKind::Call(path_expr, args), span));
+        let has_generic_args =
+            delegation.path.segments.iter().rev().skip(1).any(|segment| segment.args.is_some());
+
+        let (stmts, call, block_id) = if self
+            .get_resolution_id(delegation.id, span)
+            .and_then(|def_id| Ok(self.has_self(def_id, span)))
+            .unwrap_or_default()
+            && delegation.qself.is_none()
+            && !has_generic_args
+        {
+            let ast_segment = delegation.path.segments.last().unwrap();
+            let segment = self.lower_path_segment(
+                delegation.path.span,
+                ast_segment,
+                ParamMode::Optional,
+                ParenthesizedGenericArgs::Err,
+                ImplTraitContext::Disallowed(ImplTraitPosition::Path),
+                None,
+                None,
+            );
+            let segment = self.arena.alloc(segment);
+
+            let args = &*self.arena.alloc_from_iter(args);
+            let (stmts, receiver, args, block_id) = if let Some(target_expr) = target_expr {
+                let receiver = target_expr.expr.unwrap();
+                (Some(target_expr.stmts), receiver, args, target_expr.hir_id)
+            } else {
+                (None, &args[0], &args[1..], self.next_id())
+            };
+
+            let method_call_id = self.next_id();
+            if let Some(traits) = self.resolver.trait_map.remove(&delegation.id) {
+                self.trait_map.insert(method_call_id.local_id, traits.into_boxed_slice());
+            }
 
+            let method_call = self.arena.alloc(hir::Expr {
+                hir_id: method_call_id,
+                kind: hir::ExprKind::MethodCall(segment, receiver, args, span),
+                span,
+            });
+
+            (stmts, method_call, block_id)
+        } else {
+            let path = self.lower_qpath(
+                delegation.id,
+                &delegation.qself,
+                &delegation.path,
+                ParamMode::Optional,
+                ImplTraitContext::Disallowed(ImplTraitPosition::Path),
+                None,
+            );
+
+            if let Some(target_expr) = target_expr {
+                let target_expr = self.arena.alloc(target_expr);
+                let fst_arg =
+                    self.mk_expr(hir::ExprKind::Block(target_expr, None), target_expr.span);
+                args.insert(0, fst_arg);
+            }
+
+            let args = self.arena.alloc_from_iter(args);
+            let callee_path = self.arena.alloc(self.mk_expr(hir::ExprKind::Path(path), span));
+
+            let call = self.arena.alloc(self.mk_expr(hir::ExprKind::Call(callee_path, args), span));
+
+            (None, call, self.next_id())
+        };
         let block = self.arena.alloc(hir::Block {
-            stmts: &[],
+            stmts: stmts.unwrap_or(&[]),
             expr: Some(call),
-            hir_id: self.next_id(),
+            hir_id: block_id,
             rules: hir::BlockCheckMode::DefaultBlock,
             span,
             targeted_by_break: false,

compiler/rustc_hir_typeck/src/fn_ctxt/checks.rs

@@ -570,6 +570,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                     IsSuggestion(true),
                     callee_ty.peel_refs(),
                     callee_expr.unwrap().hir_id,
+                    None,
                     TraitsInScope,
                     |mut ctxt| ctxt.probe_for_similar_candidate(),
                 )

compiler/rustc_hir_typeck/src/fn_ctxt/suggestions.rs

@@ -1588,6 +1588,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                         IsSuggestion(true),
                         self_ty,
                         expr.hir_id,
+                        None,
                         ProbeScope::TraitsInScope,
                     )
                 {

compiler/rustc_hir_typeck/src/method/mod.rs

@@ -104,6 +104,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
             IsSuggestion(true),
             self_ty,
             call_expr_id,
+            None,
             ProbeScope::TraitsInScope,
         ) {
             Ok(pick) => {
@@ -182,8 +183,13 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
         self_expr: &'tcx hir::Expr<'tcx>,
         args: &'tcx [hir::Expr<'tcx>],
     ) -> Result<MethodCallee<'tcx>, MethodError<'tcx>> {
-        let pick =
-            self.lookup_probe(segment.ident, self_ty, call_expr, ProbeScope::TraitsInScope)?;
+        let pick = self.lookup_probe(
+            segment.ident,
+            self_ty,
+            call_expr,
+            segment.res.opt_def_id(),
+            ProbeScope::TraitsInScope,
+        )?;
 
         self.lint_edition_dependent_dot_call(
             self_ty, segment, span, call_expr, self_expr, &pick, args,
@@ -208,6 +214,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                     segment.ident,
                     trait_type,
                     call_expr,
+                    None,
                     ProbeScope::TraitsInScope,
                 ) {
                     Ok(ref new_pick) if pick.differs_from(new_pick) => {
@@ -276,6 +283,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
         method_name: Ident,
         self_ty: Ty<'tcx>,
         call_expr: &hir::Expr<'_>,
+        pre_resolved_method: Option<DefId>,
         scope: ProbeScope,
     ) -> probe::PickResult<'tcx> {
         let pick = self.probe_for_name(
@@ -285,6 +293,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
             IsSuggestion(false),
             self_ty,
             call_expr.hir_id,
+            pre_resolved_method,
             scope,
         )?;
         pick.maybe_emit_unstable_name_collision_hint(self.tcx, method_name.span, call_expr.hir_id);
@@ -306,6 +315,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
             IsSuggestion(true),
             self_ty,
             call_expr.hir_id,
+            None,
             scope,
         )?;
         Ok(pick)
@@ -516,6 +526,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
             IsSuggestion(false),
             self_ty,
             expr_id,
+            None,
             ProbeScope::TraitsInScope,
         );
         let pick = match (pick, struct_variant) {

compiler/rustc_hir_typeck/src/method/probe.rs

@@ -96,6 +96,27 @@ pub(crate) struct ProbeContext<'a, 'tcx> {
 
     scope_expr_id: HirId,
 
+    /// Delegation item can be expanded into method calls or fully qualified calls
+    /// depending on the callee's signature. Method calls are used to allow
+    /// autoref/autoderef for target expression. For example in:
+    ///
+    /// ```ignore (illustrative)
+    /// trait Trait : Sized {
+    ///     fn by_value(self) -> i32 { 1 }
+    ///     fn by_mut_ref(&mut self) -> i32 { 2 }
+    ///     fn by_ref(&self) -> i32 { 3 }
+    /// }
+    ///
+    /// struct NewType(SomeType);
+    /// impl Trait for NewType {
+    ///     reuse Trait::* { self.0 }
+    /// }
+    /// ```
+    ///
+    /// `self.0` will automatically coerce. The difference with existing method lookup
+    /// is that methods in delegation items are pre-resolved by callee path (`Trait::*`).
+    pre_resolved_method: Option<DefId>,
+
     /// Is this probe being done for a diagnostic? This will skip some error reporting
     /// machinery, since we don't particularly care about, for example, similarly named
     /// candidates if we're *reporting* similarly named candidates.
@@ -248,6 +269,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                 IsSuggestion(true),
                 self_ty,
                 scope_expr_id,
+                None,
                 ProbeScope::AllTraits,
                 |probe_cx| Ok(probe_cx.candidate_method_names(candidate_filter)),
             )
@@ -263,6 +285,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                     IsSuggestion(true),
                     self_ty,
                     scope_expr_id,
+                    None,
                     ProbeScope::AllTraits,
                     |probe_cx| probe_cx.pick(),
                 )
@@ -281,6 +304,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
         is_suggestion: IsSuggestion,
         self_ty: Ty<'tcx>,
         scope_expr_id: HirId,
+        pre_resolved_method: Option<DefId>,
         scope: ProbeScope,
     ) -> PickResult<'tcx> {
         self.probe_op(
@@ -291,6 +315,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
             is_suggestion,
             self_ty,
             scope_expr_id,
+            pre_resolved_method,
             scope,
             |probe_cx| probe_cx.pick(),
         )
@@ -315,6 +340,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
             is_suggestion,
             self_ty,
             scope_expr_id,
+            None,
             scope,
             |probe_cx| {
                 Ok(probe_cx
@@ -335,6 +361,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
         is_suggestion: IsSuggestion,
         self_ty: Ty<'tcx>,
         scope_expr_id: HirId,
+        pre_resolved_method: Option<DefId>,
         scope: ProbeScope,
         op: OP,
     ) -> Result<R, MethodError<'tcx>>
@@ -476,6 +503,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                 &orig_values,
                 steps.steps,
                 scope_expr_id,
+                pre_resolved_method,
                 is_suggestion,
             );
 
@@ -571,6 +599,7 @@ impl<'a, 'tcx> ProbeContext<'a, 'tcx> {
         orig_steps_var_values: &'a OriginalQueryValues<'tcx>,
         steps: &'tcx [CandidateStep<'tcx>],
         scope_expr_id: HirId,
+        pre_resolved_method: Option<DefId>,
         is_suggestion: IsSuggestion,
     ) -> ProbeContext<'a, 'tcx> {
         ProbeContext {
@@ -590,6 +619,7 @@ impl<'a, 'tcx> ProbeContext<'a, 'tcx> {
             static_candidates: RefCell::new(Vec::new()),
             unsatisfied_predicates: RefCell::new(Vec::new()),
             scope_expr_id,
+            pre_resolved_method,
             is_suggestion,
         }
     }
@@ -1220,6 +1250,14 @@ impl<'a, 'tcx> ProbeContext<'a, 'tcx> {
     ) -> Option<PickResult<'tcx>> {
         let mut applicable_candidates: Vec<_> = candidates
             .iter()
+            .filter(|candidate| {
+                if let Some(res_id) = self.pre_resolved_method
+                    && candidate.item.def_id != res_id
+                {
+                    return false;
+                }
+                true
+            })
             .map(|probe| {
                 (probe, self.consider_probe(self_ty, probe, possibly_unsatisfied_predicates))
             })
@@ -1677,6 +1715,7 @@ impl<'a, 'tcx> ProbeContext<'a, 'tcx> {
                 self.orig_steps_var_values,
                 self.steps,
                 self.scope_expr_id,
+                None,
                 IsSuggestion(true),
             );
             pcx.allow_similar_names = true;

compiler/rustc_hir_typeck/src/method/suggest.rs

@@ -2034,6 +2034,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                             IsSuggestion(true),
                             rcvr_ty,
                             expr_id,
+                            None,
                             ProbeScope::TraitsInScope,
                         )
                         .is_ok()
@@ -3095,6 +3096,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                 IsSuggestion(true),
                 deref_ty,
                 ty.hir_id,
+                None,
                 ProbeScope::TraitsInScope,
             ) {
                 if deref_ty.is_suggestable(self.tcx, true)