gccrs: Fix compilation of trait-items which map to impl items

When we have paths such as Try::from_error the Try references the Trait
and then from_error references the from_error trait item. So this resolves
directly to a trait implementation which has the type:

  fn <Self> (v: placeholder) -> Self

Remember that a path such as: Try::from_error gets handled by doing a
clever substitution: <T? as Try>::from_error

The main piece here is that we resolve this function type and for
monomoprhization we know this is a trait call but we know that all trait's
have an implicit Self type param which in this case is Result<i32, i32>
so when it comes to knowing which impl block this is we got rid of the old
bad insert/lookup receiver hack and use the specified type to know which
impl block we are talking about to generate the function.

The hard part here is inside rust-compil-item.cc, where we have the
'concete' type which is the trait item fntype of:

  fn <Result<i32, i32>> (v : i32) -> Result<i32,i32>

This does not really match the signiture of the impl item for Result
which is:

  fn <T, E> (v: i32) -> Result<T, E>

So what we need to do is actually infer this by inputing inference
variables on the impl fntype then unify'ing the trait object to this to
compute the types of this to monomorphize this.

Fixes Rust-GCC#3381

gcc/rust/ChangeLog:

	* backend/rust-compile-expr.cc (CompileExpr::visit): remove receiver interface
	* backend/rust-compile-item.cc (CompileItem::visit): monomorphize trait to impl item
	* backend/rust-compile-resolve-path.cc (HIRCompileBase::query_compile): use trait item Self
	* typecheck/rust-hir-type-check-expr.cc (TypeCheckExpr::visit): remove receiver interface
	(TypeCheckExpr::resolve_fn_trait_call): likewise
	* typecheck/rust-hir-type-check-path.cc (TypeCheckExpr::visit): likewise
	(TypeCheckExpr::resolve_segments): likewise
	* typecheck/rust-hir-type-check-type.cc (TypeCheckType::visit): likewise
	* typecheck/rust-hir-type-check.h: likewise
	* typecheck/rust-typecheck-context.cc (TypeCheckContext::insert_receiver): remove
	(TypeCheckContext::lookup_receiver): remove

gcc/testsuite/ChangeLog:

	* rust/execute/torture/issue-3381.rs: New test.

Signed-off-by: Philip Herron <herron.philip@googlemail.com>

9 files changed, 129 insertions, 46 deletions

diff --git a/gcc/rust/backend/rust-compile-expr.cc b/gcc/rust/backend/rust-compile-expr.cc
index a72156b..021495a 100644
--- a/gcc/rust/backend/rust-compile-expr.cc
+++ b/gcc/rust/backend/rust-compile-expr.cc
@@ -1394,8 +1394,8 @@ CompileExpr::visit (HIR::MethodCallExpr &expr)
   TyTy::FnType *fntype = static_cast<TyTy::FnType *> (lookup_fntype);
 
   TyTy::BaseType *receiver = nullptr;
-  ok = ctx->get_tyctx ()->lookup_receiver (expr.get_mappings ().get_hirid (),
-					   &receiver);
+  ok = ctx->get_tyctx ()->lookup_type (
+    expr.get_receiver ().get_mappings ().get_hirid (), &receiver);
   rust_assert (ok);
 
   bool is_dyn_dispatch
@@ -1532,8 +1532,8 @@ CompileExpr::resolve_operator_overload (
 
   TyTy::BaseType *receiver = nullptr;
   bool ok
-    = ctx->get_tyctx ()->lookup_receiver (expr.get_mappings ().get_hirid (),
-					  &receiver);
+    = ctx->get_tyctx ()->lookup_type (lhs_expr.get_mappings ().get_hirid (),
+				      &receiver);
   rust_assert (ok);
 
   bool is_generic_receiver = receiver->get_kind () == TyTy::TypeKind::PARAM;
diff --git a/gcc/rust/backend/rust-compile-item.cc b/gcc/rust/backend/rust-compile-item.cc
index 2b6836a..3e028c3 100644
--- a/gcc/rust/backend/rust-compile-item.cc
+++ b/gcc/rust/backend/rust-compile-item.cc
@@ -19,6 +19,8 @@
 #include "rust-compile-item.h"
 #include "rust-compile-implitem.h"
 #include "rust-compile-extern.h"
+#include "rust-substitution-mapper.h"
+#include "rust-type-util.h"
 #include "rust-immutable-name-resolution-context.h"
 
 namespace Rust {
@@ -165,12 +167,33 @@ CompileItem::visit (HIR::Function &function)
       // is given
       if (concrete == nullptr)
 	return;
-      else
+
+      rust_assert (concrete->get_kind () == TyTy::TypeKind::FNDEF);
+      TyTy::FnType *concrete_fnty = static_cast<TyTy::FnType *> (concrete);
+      bool is_trait_item_concrete
+	= ctx->get_mappings ()
+	    .lookup_trait_item_defid (concrete_fnty->get_id ())
+	    .has_value ();
+      if (!is_trait_item_concrete)
 	{
 	  rust_assert (concrete->get_kind () == TyTy::TypeKind::FNDEF);
 	  fntype = static_cast<TyTy::FnType *> (concrete);
-	  fntype->monomorphize ();
 	}
+      else
+	{
+	  TyTy::BaseType *infer
+	    = Resolver::SubstMapper::InferSubst (fntype, function.get_locus ());
+	  TyTy::BaseType *resolved
+	    = Resolver::unify_site (function.get_mappings ().get_hirid (),
+				    TyTy::TyWithLocation (infer),
+				    TyTy::TyWithLocation (concrete),
+				    function.get_locus ());
+
+	  rust_assert (resolved->is<TyTy::FnType> ());
+	  fntype = resolved->as<TyTy::FnType> ();
+	}
+
+      fntype->monomorphize ();
     }
   else
     {
diff --git a/gcc/rust/backend/rust-compile-resolve-path.cc b/gcc/rust/backend/rust-compile-resolve-path.cc
index c862a81..1b9dee6 100644
--- a/gcc/rust/backend/rust-compile-resolve-path.cc
+++ b/gcc/rust/backend/rust-compile-resolve-path.cc
@@ -297,16 +297,20 @@ HIRCompileBase::query_compile (HirId ref, TyTy::BaseType *lookup,
 	    trait->get_mappings ().get_defid (), &trait_ref);
 	  rust_assert (ok);
 
-	  TyTy::BaseType *receiver = nullptr;
-	  ok = ctx->get_tyctx ()->lookup_receiver (mappings.get_hirid (),
-						   &receiver);
-	  rust_assert (ok);
-	  receiver = receiver->destructure ();
-
 	  // the type resolver can only resolve type bounds to their trait
 	  // item so its up to us to figure out if this path should resolve
 	  // to an trait-impl-block-item or if it can be defaulted to the
 	  // trait-impl-item's definition
+	  //
+	  // because we know this is resolved to a trait item we can actually
+	  // just grab the Self type parameter here for the receiver to match
+	  // the appropriate impl block
+
+	  rust_assert (lookup->is<TyTy::FnType> ());
+	  auto fn = lookup->as<TyTy::FnType> ();
+	  rust_assert (fn->get_num_type_params () > 0);
+	  auto &self = fn->get_substs ().at (0);
+	  auto receiver = self.get_param_ty ();
 	  auto candidates
 	    = Resolver::PathProbeImplTrait::Probe (receiver, final_segment,
 						   trait_ref);
diff --git a/gcc/rust/typecheck/rust-hir-type-check-expr.cc b/gcc/rust/typecheck/rust-hir-type-check-expr.cc
index 356a960..2fb4d3c 100644
--- a/gcc/rust/typecheck/rust-hir-type-check-expr.cc
+++ b/gcc/rust/typecheck/rust-hir-type-check-expr.cc
@@ -1105,8 +1105,6 @@ TypeCheckExpr::visit (HIR::MethodCallExpr &expr)
       return;
     }
 
-  context->insert_receiver (expr.get_mappings ().get_hirid (), receiver_tyty);
-
   rust_debug_loc (expr.get_locus (), "attempting to resolve method for %s",
 		  receiver_tyty->debug_str ().c_str ());
   auto candidates
@@ -1750,9 +1748,6 @@ TypeCheckExpr::resolve_operator_overload (
   context->insert_autoderef_mappings (expr.get_lvalue_mappings ().get_hirid (),
 				      std::move (candidate.adjustments));
 
-  // now its just like a method-call-expr
-  context->insert_receiver (expr.get_mappings ().get_hirid (), lhs);
-
   PathProbeCandidate &resolved_candidate = candidate.candidate;
   TyTy::BaseType *lookup_tyty = candidate.candidate.ty;
   NodeId resolved_node_id
@@ -1997,7 +1992,6 @@ TypeCheckExpr::resolve_fn_trait_call (HIR::CallExpr &expr,
   HirId autoderef_mappings_id = fnexpr.get_mappings ().get_hirid ();
   context->insert_autoderef_mappings (autoderef_mappings_id,
 				      std::move (candidate.adjustments));
-  context->insert_receiver (expr.get_mappings ().get_hirid (), receiver_tyty);
 
   PathProbeCandidate &resolved_candidate = candidate.candidate;
   TyTy::BaseType *lookup_tyty = candidate.candidate.ty;
diff --git a/gcc/rust/typecheck/rust-hir-type-check-path.cc b/gcc/rust/typecheck/rust-hir-type-check-path.cc
index a4f294b..73d9738 100644
--- a/gcc/rust/typecheck/rust-hir-type-check-path.cc
+++ b/gcc/rust/typecheck/rust-hir-type-check-path.cc
@@ -171,7 +171,6 @@ TypeCheckExpr::visit (HIR::QualifiedPathInExpression &expr)
 	  resolver->insert_resolved_name (expr.get_mappings ().get_nodeid (),
 					  root_resolved_node_id);
 	}
-      context->insert_receiver (expr.get_mappings ().get_hirid (), root);
       return;
     }
 
@@ -559,8 +558,6 @@ TypeCheckExpr::resolve_segments (NodeId root_resolved_node_id,
     }
 
   rust_assert (resolved_node_id != UNKNOWN_NODEID);
-  context->insert_receiver (expr_mappings.get_hirid (), prev_segment);
-
   if (flag_name_resolution_2_0)
     {
       auto &nr_ctx = const_cast<Resolver2_0::NameResolutionContext &> (
diff --git a/gcc/rust/typecheck/rust-hir-type-check-type.cc b/gcc/rust/typecheck/rust-hir-type-check-type.cc
index 6dc62d6..ff6813a 100644
--- a/gcc/rust/typecheck/rust-hir-type-check-type.cc
+++ b/gcc/rust/typecheck/rust-hir-type-check-type.cc
@@ -360,8 +360,6 @@ TypeCheckType::visit (HIR::QualifiedPathInType &path)
 	  resolver->insert_resolved_type (path.get_mappings ().get_nodeid (),
 					  root_resolved_node_id);
 	}
-
-      context->insert_receiver (path.get_mappings ().get_hirid (), root);
       return;
     }
 
@@ -704,9 +702,7 @@ TypeCheckType::resolve_segments (
 	}
     }
 
-  context->insert_receiver (expr_mappings.get_hirid (), prev_segment);
   rust_assert (resolved_node_id != UNKNOWN_NODEID);
-
   if (flag_name_resolution_2_0)
     {
       auto &nr_ctx = const_cast<Resolver2_0::NameResolutionContext &> (
diff --git a/gcc/rust/typecheck/rust-hir-type-check.h b/gcc/rust/typecheck/rust-hir-type-check.h
index 42ef2d1..21ecf2c 100644
--- a/gcc/rust/typecheck/rust-hir-type-check.h
+++ b/gcc/rust/typecheck/rust-hir-type-check.h
@@ -202,9 +202,6 @@ public:
   void insert_trait_reference (DefId id, TraitReference &&ref);
   bool lookup_trait_reference (DefId id, TraitReference **ref);
 
-  void insert_receiver (HirId id, TyTy::BaseType *t);
-  bool lookup_receiver (HirId id, TyTy::BaseType **ref);
-
   void insert_associated_trait_impl (HirId id,
 				     AssociatedImplTrait &&associated);
   bool lookup_associated_trait_impl (HirId id,
@@ -282,7 +279,6 @@ private:
   std::vector<TyTy::BaseType *> loop_type_stack;
   StackedContexts<TypeCheckBlockContextItem> block_stack;
   std::map<DefId, TraitReference> trait_context;
-  std::map<HirId, TyTy::BaseType *> receiver_context;
   std::map<HirId, AssociatedImplTrait> associated_impl_traits;
 
   // trait-id -> list of < self-tyty:impl-id>
diff --git a/gcc/rust/typecheck/rust-typecheck-context.cc b/gcc/rust/typecheck/rust-typecheck-context.cc
index d3ff29a..4cee74a 100644
--- a/gcc/rust/typecheck/rust-typecheck-context.cc
+++ b/gcc/rust/typecheck/rust-typecheck-context.cc
@@ -255,23 +255,6 @@ TypeCheckContext::lookup_trait_reference (DefId id, TraitReference **ref)
 }
 
 void
-TypeCheckContext::insert_receiver (HirId id, TyTy::BaseType *t)
-{
-  receiver_context[id] = t;
-}
-
-bool
-TypeCheckContext::lookup_receiver (HirId id, TyTy::BaseType **ref)
-{
-  auto it = receiver_context.find (id);
-  if (it == receiver_context.end ())
-    return false;
-
-  *ref = it->second;
-  return true;
-}
-
-void
 TypeCheckContext::insert_associated_trait_impl (
   HirId id, AssociatedImplTrait &&associated)
 {
diff --git a/gcc/testsuite/rust/execute/torture/issue-3381.rs b/gcc/testsuite/rust/execute/torture/issue-3381.rs
new file mode 100644
index 0000000..62dbcd0
--- /dev/null
+++ b/gcc/testsuite/rust/execute/torture/issue-3381.rs
@@ -0,0 +1,90 @@
+/* { dg-output "Err: 15\r*\n" } */
+#[lang = "sized"]
+trait Sized {}
+
+enum Result<T, E> {
+    #[lang = "Ok"]
+    Ok(T),
+    #[lang = "Err"]
+    Err(E),
+}
+
+#[lang = "try"]
+pub trait Try {
+    type Ok;
+    type Error;
+
+    #[lang = "into_result"]
+    #[unstable(feature = "try_trait", issue = "42327")]
+    fn into_result(self) -> Result<Self::Ok, Self::Error>;
+
+    #[lang = "from_error"]
+    #[unstable(feature = "try_trait", issue = "42327")]
+    fn from_error(v: Self::Ok) -> Self;
+
+    #[lang = "from_ok"]
+    #[unstable(feature = "try_trait", issue = "42327")]
+    fn from_ok(v: Self::Error) -> Self;
+}
+
+impl<T, E> Try for Result<T, E> {
+    type Ok = T;
+    type Error = E;
+
+    fn into_result(self) -> Result<T, E> {
+        self
+    }
+
+    fn from_ok(v: T) -> Self {
+        Result::Ok(v)
+    }
+
+    fn from_error(v: E) -> Self {
+        Result::Err(v)
+    }
+}
+
+pub trait From<T>: Sized {
+    fn from(_: T) -> Self;
+}
+
+impl<T> From<T> for T {
+    fn from(t: T) -> Self {
+        t
+    }
+}
+
+fn print(s: &str, value: i32) {
+    extern "C" {
+        fn printf(s: *const i8, ...);
+    }
+
+    unsafe {
+        printf(s as *const str as *const i8, value);
+    }
+}
+
+fn baz() -> Result<i32, i32> {
+    Result::Err(15)
+}
+
+fn foo() -> Result<i32, i32> {
+    let b = match baz() {
+        Result::Ok(value) => value,
+        Result::Err(err) => {
+            return Try::from_error(From::from(err));
+        }
+    };
+
+    Result::Ok(15 + b)
+}
+
+fn main() -> i32 {
+    let a = foo();
+    match a {
+        Result::Ok(value) => print("Ok: %i\n", value),
+        Result::Err(err) => print("Err: %i\n", err),
+    };
+
+    0
+}