Migrate error state to optionals

gcc/rust/ChangeLog:

	* ast/rust-ast-builder.cc (Builder::self_ref_param): Remove error state
	and use optional.
	* ast/rust-ast-visitor.cc (DefaultASTVisitor::visit): Check label
	before visiting.
	* ast/rust-ast.cc (ContinueExpr::as_string): Retrieve label value.
	(Lifetime::as_string): Retrieve lifetime value.
	(ReferenceType::as_string): Likewise.
	(SelfParam::as_string): Likewise.
	* ast/rust-ast.h: Remove lifetime and LifetimeParam error state.
	* ast/rust-desugar-for-loops.cc (DesugarForLoops::DesugarCtx::make_break_arm):
	Use optional instead of error state.
	* ast/rust-expr.h (class ContinueExpr): Make label optional.
	* ast/rust-item.h (class SelfParam): Make lifetime optional.
	* ast/rust-type.h (class ReferenceType): Likewise.
	* backend/rust-compile-base.cc: Use optional for self param instead
	of error state.
	* backend/rust-compile-base.h: Update function prototype.
	* expand/rust-derive-clone.cc (DeriveClone::clone_fn): Use optional.
	* hir/rust-ast-lower-base.cc (ASTLoweringBase::lower_self): Lower
	lifetime only if it exists.
	* hir/rust-ast-lower-block.h: Lower loop label only if it exists.
	* hir/rust-ast-lower-expr.cc (ASTLoweringExpr::visit): Likewise.
	* hir/rust-ast-lower-implitem.cc (ASTLowerImplItem::visit): Remove
	references to error state.
	(ASTLowerTraitItem::visit): Lower self param only if it exists.
	* hir/rust-ast-lower-item.cc (ASTLoweringItem::visit): Use nullopt
	for default value instead of SelfParam error state.
	* hir/rust-ast-lower.cc (ASTLoweringExprWithBlock::visit): Lower label
	only if it exists.
	* hir/rust-hir-dump.cc (Dump::do_traitfunctiondecl): Print self only if
	it exists.
	(Dump::visit): Liewise.
	* hir/tree/rust-hir-bound.h: Remove error state.
	* hir/tree/rust-hir-expr.cc (ContinueExpr::ContinueExpr): Use optional
	in constructor for loop label.
	(BreakExpr::BreakExpr): Likewise.
	* hir/tree/rust-hir-expr.h (class ContinueExpr): Remove error state
	implementation.
	(class BreakExpr): Likewise.
	* hir/tree/rust-hir-generic-param.h: Likewise.
	* hir/tree/rust-hir-item.cc (SelfParam::SelfParam): Make lifetime
	optional.
	(Function::Function): Make self param optional.
	* hir/tree/rust-hir-item.h (class Function): Likewise.
	* hir/tree/rust-hir-type.cc (ReferenceType::ReferenceType): Make
	lifetime optional.
	* hir/tree/rust-hir-type.h (class ReferenceType): Likewise.
	* hir/tree/rust-hir.cc (ContinueExpr::as_string): Use new getter.
	(BreakExpr::as_string): Likewise.
	(Lifetime::as_string): Likewise.
	(ReferenceType::as_string): Likewise.
	(TraitFunctionDecl::as_string): Likewise.
	(SelfParam::as_string): Remove error state checking.
	* parse/rust-parse-impl.h (Parser::parse_generic_param): Adapt to
	optional.
	(Parser::parse_lifetime_params): Likewise.
	(Parser::parse_lifetime_params_objs): Likewise.
	(Parser::parse_lifetime_param): Likewise.
	(Parser::parse_lifetime_where_clause_item): Likewise.
	(Parser::parse_type_param_bound): Likewise.
	(Parser::parse_lifetime_bounds): Likewise.
	(Parser::parse_path_generic_args): Likewise.
	(Parser::parse_self_param): Likewise.
	(Parser::parse_break_expr): Likewise.
	(Parser::parse_continue_expr): Likewise.
	(Parser::parse_reference_type_inner): Likewise.
	* parse/rust-parse.h (class ParseLifetimeParamError): Add new class for
	lifetime param parsing errors.
	(class ParseLifetimeError): Add new class for lifetime parsing errors.
	(enum ParseSelfError): Add new class for self param parsing errors.
	* typecheck/rust-hir-type-check-implitem.cc (TypeCheckImplItem::visit):
	Use unchecked getter in checked context. And make anonymous region.
	* typecheck/rust-hir-type-check.cc (TraitItemReference::get_type_from_fn):
	Likewise.

Signed-off-by: Pierre-Emmanuel Patry <pierre-emmanuel.patry@embecosm.com>

16 files changed, 137 insertions, 144 deletions

diff --git a/gcc/rust/hir/rust-ast-lower-base.cc b/gcc/rust/hir/rust-ast-lower-base.cc
index 749fe09..a933f1b 100644
--- a/gcc/rust/hir/rust-ast-lower-base.cc
+++ b/gcc/rust/hir/rust-ast-lower-base.cc
@@ -690,8 +690,12 @@ ASTLoweringBase::lower_self (AST::Param &param)
 			     self.get_is_mut (), self.get_locus ());
     }
 
-  AST::Lifetime l = self.get_lifetime ();
-  return HIR::SelfParam (mapping, lower_lifetime (l), self.get_is_mut (),
+  tl::optional<HIR::Lifetime> lifetime = tl::nullopt;
+
+  if (self.has_lifetime ())
+    lifetime = lower_lifetime (self.get_lifetime ());
+
+  return HIR::SelfParam (mapping, lifetime, self.get_is_mut (),
 			 self.get_locus ());
 }
 
diff --git a/gcc/rust/hir/rust-ast-lower-block.h b/gcc/rust/hir/rust-ast-lower-block.h
index 55541a5..d60088b 100644
--- a/gcc/rust/hir/rust-ast-lower-block.h
+++ b/gcc/rust/hir/rust-ast-lower-block.h
@@ -195,7 +195,9 @@ public:
     HIR::BlockExpr *loop_block
       = ASTLoweringBlock::translate (expr.get_loop_block (), &terminated);
 
-    HIR::LoopLabel loop_label = lower_loop_label (expr.get_loop_label ());
+    tl::optional<HIR::LoopLabel> loop_label = tl::nullopt;
+    if (expr.has_loop_label ())
+      loop_label = lower_loop_label (expr.get_loop_label ());
 
     auto crate_num = mappings.get_current_crate ();
     Analysis::NodeMapping mapping (crate_num, expr.get_node_id (),
diff --git a/gcc/rust/hir/rust-ast-lower-expr.cc b/gcc/rust/hir/rust-ast-lower-expr.cc
index 575eea6..7bb7320 100644
--- a/gcc/rust/hir/rust-ast-lower-expr.cc
+++ b/gcc/rust/hir/rust-ast-lower-expr.cc
@@ -597,8 +597,10 @@ ASTLoweringExpr::visit (AST::ForLoopExpr &expr)
 void
 ASTLoweringExpr::visit (AST::BreakExpr &expr)
 {
-  HIR::Lifetime break_label
-    = lower_lifetime (expr.get_label ().get_lifetime ());
+  tl::optional<HIR::Lifetime> break_label = tl::nullopt;
+  if (expr.has_label ())
+    break_label = lower_lifetime (expr.get_label ().get_lifetime ());
+
   HIR::Expr *break_expr
     = expr.has_break_expr ()
 	? ASTLoweringExpr::translate (expr.get_break_expr ())
@@ -618,7 +620,9 @@ ASTLoweringExpr::visit (AST::BreakExpr &expr)
 void
 ASTLoweringExpr::visit (AST::ContinueExpr &expr)
 {
-  HIR::Lifetime break_label = lower_lifetime (expr.get_label ());
+  tl::optional<HIR::Lifetime> break_label;
+  if (expr.has_label ())
+    break_label = lower_lifetime (expr.get_label ());
 
   auto crate_num = mappings.get_current_crate ();
   Analysis::NodeMapping mapping (crate_num, expr.get_node_id (),
diff --git a/gcc/rust/hir/rust-ast-lower-implitem.cc b/gcc/rust/hir/rust-ast-lower-implitem.cc
index 3229f57..66488ac 100644
--- a/gcc/rust/hir/rust-ast-lower-implitem.cc
+++ b/gcc/rust/hir/rust-ast-lower-implitem.cc
@@ -132,7 +132,7 @@ ASTLowerImplItem::visit (AST::Function &function)
   Identifier function_name = function.get_function_name ();
   location_t locus = function.get_locus ();
 
-  HIR::SelfParam self_param = HIR::SelfParam::error ();
+  tl::optional<HIR::SelfParam> self_param = tl::nullopt;
   if (function.has_self_param ())
     self_param = lower_self (function.get_self_param ());
 
@@ -189,13 +189,13 @@ ASTLowerImplItem::visit (AST::Function &function)
 			 std::move (vis), function.get_outer_attrs (),
 			 std::move (self_param), defaultness, locus);
 
-  if (!fn->get_self_param ().is_error ())
+  if (fn->is_method ())
     {
       // insert mappings for self
-      mappings.insert_hir_self_param (&fn->get_self_param ());
+      mappings.insert_hir_self_param (&fn->get_self_param_unchecked ());
       mappings.insert_location (
-	fn->get_self_param ().get_mappings ().get_hirid (),
-	fn->get_self_param ().get_locus ());
+	fn->get_self_param_unchecked ().get_mappings ().get_hirid (),
+	fn->get_self_param_unchecked ().get_locus ());
     }
 
   // add the mappings for the function params at the end
@@ -249,9 +249,9 @@ ASTLowerTraitItem::visit (AST::Function &func)
 
   // set self parameter to error if this is a method
   // else lower to hir
-  HIR::SelfParam self_param = func.has_self_param ()
-				? lower_self (func.get_self_param ())
-				: HIR::SelfParam::error ();
+  tl::optional<HIR::SelfParam> self_param = tl::nullopt;
+  if (func.has_self_param ())
+    self_param = lower_self (func.get_self_param ());
 
   std::vector<HIR::FunctionParam> function_params;
   for (auto &p : func.get_function_params ())
@@ -303,9 +303,10 @@ ASTLowerTraitItem::visit (AST::Function &func)
   if (func.has_self_param ())
     {
       // insert mappings for self
-      mappings.insert_hir_self_param (&self_param);
-      mappings.insert_location (self_param.get_mappings ().get_hirid (),
-				self_param.get_locus ());
+      // TODO: Is this correct ? Looks fishy
+      mappings.insert_hir_self_param (&*self_param);
+      mappings.insert_location (self_param->get_mappings ().get_hirid (),
+				self_param->get_locus ());
     }
 
   // add the mappings for the function params at the end
diff --git a/gcc/rust/hir/rust-ast-lower-item.cc b/gcc/rust/hir/rust-ast-lower-item.cc
index 73ddedf..47b4b71 100644
--- a/gcc/rust/hir/rust-ast-lower-item.cc
+++ b/gcc/rust/hir/rust-ast-lower-item.cc
@@ -460,7 +460,7 @@ ASTLoweringItem::visit (AST::Function &function)
 			 std::move (function_params), std::move (return_type),
 			 std::move (where_clause), std::move (function_body),
 			 std::move (vis), function.get_outer_attrs (),
-			 HIR::SelfParam::error (), defaultness, locus);
+			 tl::nullopt, defaultness, locus);
 
   // add the mappings for the function params at the end
   for (auto &param : fn->get_function_params ())
diff --git a/gcc/rust/hir/rust-ast-lower.cc b/gcc/rust/hir/rust-ast-lower.cc
index c6446aa..f70c787 100644
--- a/gcc/rust/hir/rust-ast-lower.cc
+++ b/gcc/rust/hir/rust-ast-lower.cc
@@ -402,7 +402,10 @@ ASTLoweringExprWithBlock::visit (AST::WhileLoopExpr &expr)
   HIR::BlockExpr *loop_block
     = ASTLoweringBlock::translate (expr.get_loop_block (), &terminated);
 
-  HIR::LoopLabel loop_label = lower_loop_label (expr.get_loop_label ());
+  tl::optional<HIR::LoopLabel> loop_label;
+  if (expr.has_loop_label ())
+    loop_label = lower_loop_label (expr.get_loop_label ());
+
   HIR::Expr *loop_condition
     = ASTLoweringExpr::translate (expr.get_predicate_expr (), &terminated);
 
diff --git a/gcc/rust/hir/rust-hir-dump.cc b/gcc/rust/hir/rust-hir-dump.cc
index b6dcf18..468d855 100644
--- a/gcc/rust/hir/rust-hir-dump.cc
+++ b/gcc/rust/hir/rust-hir-dump.cc
@@ -546,7 +546,8 @@ Dump::do_traitfunctiondecl (TraitFunctionDecl &e)
   else
     put_field ("where_clause", "none");
 
-  put_field ("self", e.get_self ().as_string ());
+  if (e.is_method ())
+    put_field ("self", e.get_self_unchecked ().as_string ());
 
   end ("TraitFunctionDecl");
 }
@@ -1693,7 +1694,8 @@ Dump::visit (Function &e)
     put_field ("where clause", e.get_where_clause ().as_string ());
 
   visit_field ("function_body", e.get_definition ());
-  put_field ("self", e.get_self_param ().as_string ());
+  if (e.is_method ())
+    put_field ("self", e.get_self_param_unchecked ().as_string ());
 
   end ("Function");
 }
diff --git a/gcc/rust/hir/tree/rust-hir-bound.h b/gcc/rust/hir/tree/rust-hir-bound.h
index 78bb133..8fa6a22 100644
--- a/gcc/rust/hir/tree/rust-hir-bound.h
+++ b/gcc/rust/hir/tree/rust-hir-bound.h
@@ -44,18 +44,6 @@ public:
   {}
 
   // Returns true if the lifetime is in an error state.
-  bool is_error () const
-  {
-    return lifetime_type == AST::Lifetime::LifetimeType::NAMED
-	   && lifetime_name.empty ();
-  }
-
-  static Lifetime error ()
-  {
-    return Lifetime (Analysis::NodeMapping::get_error (),
-		     AST::Lifetime::LifetimeType::NAMED, "", UNDEF_LOCATION);
-  }
-
   std::string as_string () const override;
 
   void accept_vis (HIRFullVisitor &vis) override;
diff --git a/gcc/rust/hir/tree/rust-hir-expr.cc b/gcc/rust/hir/tree/rust-hir-expr.cc
index 82a09e9..266c79c 100644
--- a/gcc/rust/hir/tree/rust-hir-expr.cc
+++ b/gcc/rust/hir/tree/rust-hir-expr.cc
@@ -791,13 +791,15 @@ BlockExpr::operator= (BlockExpr const &other)
 }
 
 ContinueExpr::ContinueExpr (Analysis::NodeMapping mappings, location_t locus,
-			    Lifetime label, AST::AttrVec outer_attribs)
+			    tl::optional<Lifetime> label,
+			    AST::AttrVec outer_attribs)
   : ExprWithoutBlock (std::move (mappings), std::move (outer_attribs)),
     label (std::move (label)), locus (locus)
 {}
 
 BreakExpr::BreakExpr (Analysis::NodeMapping mappings, location_t locus,
-		      Lifetime break_label, std::unique_ptr<Expr> expr_in_break,
+		      tl::optional<Lifetime> break_label,
+		      std::unique_ptr<Expr> expr_in_break,
 		      AST::AttrVec outer_attribs)
   : ExprWithoutBlock (std::move (mappings), std::move (outer_attribs)),
     label (std::move (break_label)), break_expr (std::move (expr_in_break)),
diff --git a/gcc/rust/hir/tree/rust-hir-expr.h b/gcc/rust/hir/tree/rust-hir-expr.h
index b304d27..20287b8 100644
--- a/gcc/rust/hir/tree/rust-hir-expr.h
+++ b/gcc/rust/hir/tree/rust-hir-expr.h
@@ -45,9 +45,6 @@ public:
   LoopLabel (Analysis::NodeMapping mapping, Lifetime loop_label,
 	     location_t locus);
 
-  // Returns whether the LoopLabel is in an error state.
-  bool is_error () const { return label.is_error (); }
-
   location_t get_locus () const { return locus; }
 
   Analysis::NodeMapping &get_mappings () { return mappings; }
@@ -1806,25 +1803,27 @@ protected:
 // HIR node representing continue expression within loops
 class ContinueExpr : public ExprWithoutBlock
 {
-  Lifetime label;
+  tl::optional<Lifetime> label;
   location_t locus;
 
 public:
   std::string as_string () const override;
 
   // Returns true if the continue expr has a label.
-  bool has_label () const { return !label.is_error (); }
+  bool has_label () const { return label.has_value (); }
 
   // Constructor for a ContinueExpr with a label.
   ContinueExpr (Analysis::NodeMapping mappings, location_t locus,
-		Lifetime label, AST::AttrVec outer_attribs = AST::AttrVec ());
+		tl::optional<Lifetime> label,
+		AST::AttrVec outer_attribs = AST::AttrVec ());
 
   location_t get_locus () const override final { return locus; }
 
   void accept_vis (HIRFullVisitor &vis) override;
   void accept_vis (HIRExpressionVisitor &vis) override;
 
-  Lifetime &get_label () { return label; }
+  Lifetime &get_label () { return label.value (); }
+  const Lifetime &get_label () const { return label.value (); }
 
   ExprType get_expression_type () const final override
   {
@@ -1851,7 +1850,7 @@ protected:
 class BreakExpr : public ExprWithoutBlock
 {
   // bool has_label;
-  Lifetime label;
+  tl::optional<Lifetime> label;
 
   // bool has_break_expr;
   std::unique_ptr<Expr> break_expr;
@@ -1862,7 +1861,7 @@ public:
   std::string as_string () const override;
 
   // Returns whether the break expression has a label or not.
-  bool has_label () const { return !label.is_error (); }
+  bool has_label () const { return label.has_value (); }
 
   /* Returns whether the break expression has an expression used in the break or
    * not. */
@@ -1870,7 +1869,7 @@ public:
 
   // Constructor for a break expression
   BreakExpr (Analysis::NodeMapping mappings, location_t locus,
-	     Lifetime break_label,
+	     tl::optional<Lifetime> break_label,
 	     std::unique_ptr<Expr> expr_in_break = nullptr,
 	     AST::AttrVec outer_attribs = AST::AttrVec ());
 
@@ -1889,7 +1888,8 @@ public:
   void accept_vis (HIRFullVisitor &vis) override;
   void accept_vis (HIRExpressionVisitor &vis) override;
 
-  Lifetime &get_label () { return label; }
+  Lifetime &get_label () { return label.value (); }
+  const Lifetime &get_label () const { return label.value (); }
 
   Expr &get_expr () { return *break_expr; }
 
diff --git a/gcc/rust/hir/tree/rust-hir-generic-param.h b/gcc/rust/hir/tree/rust-hir-generic-param.h
index a1c59bf..960de56 100644
--- a/gcc/rust/hir/tree/rust-hir-generic-param.h
+++ b/gcc/rust/hir/tree/rust-hir-generic-param.h
@@ -97,9 +97,6 @@ public:
 
   AST::AttrVec &get_outer_attrs () override { return outer_attrs; }
 
-  // Returns whether the lifetime param is in an error state.
-  bool is_error () const { return lifetime.is_error (); }
-
   // Constructor
   LifetimeParam (Analysis::NodeMapping mappings, Lifetime lifetime,
 		 location_t locus = UNDEF_LOCATION,
diff --git a/gcc/rust/hir/tree/rust-hir-item.cc b/gcc/rust/hir/tree/rust-hir-item.cc
index 14f53ce..160f710 100644
--- a/gcc/rust/hir/tree/rust-hir-item.cc
+++ b/gcc/rust/hir/tree/rust-hir-item.cc
@@ -123,7 +123,8 @@ TypeBoundWhereClauseItem::get_type_param_bounds ()
 }
 
 SelfParam::SelfParam (Analysis::NodeMapping mappings,
-		      ImplicitSelfKind self_kind, Lifetime lifetime, Type *type)
+		      ImplicitSelfKind self_kind,
+		      tl::optional<Lifetime> lifetime, Type *type)
   : self_kind (self_kind), lifetime (std::move (lifetime)), type (type),
     mappings (mappings)
 {}
@@ -131,13 +132,13 @@ SelfParam::SelfParam (Analysis::NodeMapping mappings,
 SelfParam::SelfParam (Analysis::NodeMapping mappings,
 		      std::unique_ptr<Type> type, bool is_mut, location_t locus)
   : self_kind (is_mut ? ImplicitSelfKind::MUT : ImplicitSelfKind::IMM),
-    lifetime (
-      Lifetime (mappings, AST::Lifetime::LifetimeType::NAMED, "", locus)),
-    type (std::move (type)), locus (locus), mappings (mappings)
+    lifetime (tl::nullopt), type (std::move (type)), locus (locus),
+    mappings (mappings)
 {}
 
-SelfParam::SelfParam (Analysis::NodeMapping mappings, Lifetime lifetime,
-		      bool is_mut, location_t locus)
+SelfParam::SelfParam (Analysis::NodeMapping mappings,
+		      tl::optional<Lifetime> lifetime, bool is_mut,
+		      location_t locus)
   : self_kind (is_mut ? ImplicitSelfKind::MUT_REF : ImplicitSelfKind::IMM_REF),
     lifetime (std::move (lifetime)), locus (locus), mappings (mappings)
 {}
@@ -263,7 +264,7 @@ Function::Function (Analysis::NodeMapping mappings, Identifier function_name,
 		    std::vector<FunctionParam> function_params,
 		    std::unique_ptr<Type> return_type, WhereClause where_clause,
 		    std::unique_ptr<BlockExpr> function_body, Visibility vis,
-		    AST::AttrVec outer_attrs, SelfParam self,
+		    AST::AttrVec outer_attrs, tl::optional<SelfParam> self,
 		    Defaultness defaultness, location_t locus)
   : VisItem (std::move (mappings), std::move (vis), std::move (outer_attrs)),
     qualifiers (std::move (qualifiers)),
@@ -612,9 +613,9 @@ StaticItem::operator= (StaticItem const &other)
 
 TraitFunctionDecl::TraitFunctionDecl (
   Identifier function_name, FunctionQualifiers qualifiers,
-  std::vector<std::unique_ptr<GenericParam>> generic_params, SelfParam self,
-  std::vector<FunctionParam> function_params, std::unique_ptr<Type> return_type,
-  WhereClause where_clause)
+  std::vector<std::unique_ptr<GenericParam>> generic_params,
+  tl::optional<SelfParam> self, std::vector<FunctionParam> function_params,
+  std::unique_ptr<Type> return_type, WhereClause where_clause)
   : qualifiers (std::move (qualifiers)),
     function_name (std::move (function_name)),
     generic_params (std::move (generic_params)),
diff --git a/gcc/rust/hir/tree/rust-hir-item.h b/gcc/rust/hir/tree/rust-hir-item.h
index 0a59a53..f45d743 100644
--- a/gcc/rust/hir/tree/rust-hir-item.h
+++ b/gcc/rust/hir/tree/rust-hir-item.h
@@ -371,13 +371,13 @@ public:
 
 private:
   ImplicitSelfKind self_kind;
-  Lifetime lifetime;
+  tl::optional<Lifetime> lifetime;
   std::unique_ptr<Type> type;
   location_t locus;
   Analysis::NodeMapping mappings;
 
   SelfParam (Analysis::NodeMapping mappings, ImplicitSelfKind self_kind,
-	     Lifetime lifetime, Type *type);
+	     tl::optional<Lifetime> lifetime, Type *type);
 
 public:
   // Type-based self parameter (not ref, no lifetime)
@@ -385,8 +385,8 @@ public:
 	     bool is_mut, location_t locus);
 
   // Lifetime-based self parameter (is ref, no type)
-  SelfParam (Analysis::NodeMapping mappings, Lifetime lifetime, bool is_mut,
-	     location_t locus);
+  SelfParam (Analysis::NodeMapping mappings, tl::optional<Lifetime> lifetime,
+	     bool is_mut, location_t locus);
 
   // Copy constructor requires clone
   SelfParam (SelfParam const &other);
@@ -398,22 +398,13 @@ public:
   SelfParam (SelfParam &&other) = default;
   SelfParam &operator= (SelfParam &&other) = default;
 
-  static SelfParam error ()
-  {
-    return SelfParam (Analysis::NodeMapping::get_error (),
-		      ImplicitSelfKind::NONE, Lifetime::error (), nullptr);
-  }
-
   // Returns whether the self-param has a type field.
   bool has_type () const { return type != nullptr; }
 
   // Returns whether the self-param has a valid lifetime.
-  bool has_lifetime () const { return !lifetime.is_error (); }
-
-  const Lifetime &get_lifetime () const { return lifetime; }
+  bool has_lifetime () const { return lifetime.has_value (); }
 
-  // Returns whether the self-param is in an error state.
-  bool is_error () const { return self_kind == ImplicitSelfKind::NONE; }
+  const Lifetime &get_lifetime () const { return lifetime.value (); }
 
   std::string as_string () const;
 
@@ -961,7 +952,7 @@ class Function : public VisItem, public ImplItem
   std::unique_ptr<Type> return_type;
   WhereClause where_clause;
   std::unique_ptr<BlockExpr> function_body;
-  SelfParam self;
+  tl::optional<SelfParam> self;
   location_t locus;
 
   // NOTE: This should be moved to the trait item base class once we start
@@ -1001,8 +992,8 @@ public:
 	    std::vector<FunctionParam> function_params,
 	    std::unique_ptr<Type> return_type, WhereClause where_clause,
 	    std::unique_ptr<BlockExpr> function_body, Visibility vis,
-	    AST::AttrVec outer_attrs, SelfParam self, Defaultness defaultness,
-	    location_t locus);
+	    AST::AttrVec outer_attrs, tl::optional<SelfParam> self,
+	    Defaultness defaultness, location_t locus);
 
   // Copy constructor with clone
   Function (Function const &other);
@@ -1056,9 +1047,13 @@ public:
   // TODO: is this better? Or is a "vis_block" better?
   Type &get_return_type () { return *return_type; }
 
-  bool is_method () const { return !self.is_error (); }
+  bool is_method () const { return self.has_value (); }
 
-  SelfParam &get_self_param () { return self; }
+  tl::optional<SelfParam> &get_self_param () { return self; }
+  const tl::optional<SelfParam> &get_self_param () const { return self; }
+
+  SelfParam &get_self_param_unchecked () { return self.value (); }
+  const SelfParam &get_self_param_unchecked () const { return self.value (); }
 
   std::string get_impl_item_name () const override final
   {
@@ -1913,13 +1908,14 @@ private:
   std::vector<FunctionParam> function_params;
   std::unique_ptr<Type> return_type;
   WhereClause where_clause;
-  SelfParam self;
+  tl::optional<SelfParam> self;
 
 public:
   // Mega-constructor
   TraitFunctionDecl (Identifier function_name, FunctionQualifiers qualifiers,
 		     std::vector<std::unique_ptr<GenericParam>> generic_params,
-		     SelfParam self, std::vector<FunctionParam> function_params,
+		     tl::optional<SelfParam> self,
+		     std::vector<FunctionParam> function_params,
 		     std::unique_ptr<Type> return_type,
 		     WhereClause where_clause);
 
@@ -1951,9 +1947,13 @@ public:
 
   WhereClause &get_where_clause () { return where_clause; }
 
-  bool is_method () const { return !self.is_error (); }
+  bool is_method () const { return self.has_value (); }
+
+  SelfParam &get_self_unchecked () { return self.value (); }
+  const SelfParam &get_self_unchecked () const { return self.value (); }
 
-  SelfParam &get_self () { return self; }
+  tl::optional<SelfParam> &get_self () { return self; }
+  const tl::optional<SelfParam> &get_self () const { return self; }
 
   Identifier get_function_name () const { return function_name; }
 
diff --git a/gcc/rust/hir/tree/rust-hir-type.cc b/gcc/rust/hir/tree/rust-hir-type.cc
index 6a6c319..ec48425 100644
--- a/gcc/rust/hir/tree/rust-hir-type.cc
+++ b/gcc/rust/hir/tree/rust-hir-type.cc
@@ -162,7 +162,7 @@ RawPointerType::operator= (RawPointerType const &other)
 
 ReferenceType::ReferenceType (Analysis::NodeMapping mappings, Mutability mut,
 			      std::unique_ptr<Type> type_no_bounds,
-			      location_t locus, Lifetime lifetime)
+			      location_t locus, tl::optional<Lifetime> lifetime)
   : TypeNoBounds (mappings, locus), lifetime (std::move (lifetime)), mut (mut),
     type (std::move (type_no_bounds))
 {}
diff --git a/gcc/rust/hir/tree/rust-hir-type.h b/gcc/rust/hir/tree/rust-hir-type.h
index bf733e7..d6a0e09 100644
--- a/gcc/rust/hir/tree/rust-hir-type.h
+++ b/gcc/rust/hir/tree/rust-hir-type.h
@@ -291,7 +291,7 @@ protected:
 class ReferenceType : public TypeNoBounds
 {
   // bool has_lifetime; // TODO: handle in lifetime or something?
-  Lifetime lifetime;
+  tl::optional<Lifetime> lifetime;
 
   Mutability mut;
   std::unique_ptr<Type> type;
@@ -301,12 +301,12 @@ public:
   bool is_mut () const { return mut == Mutability::Mut; }
 
   // Returns whether the reference has a lifetime.
-  bool has_lifetime () const { return !lifetime.is_error (); }
+  bool has_lifetime () const { return lifetime.has_value (); }
 
   // Constructor
   ReferenceType (Analysis::NodeMapping mappings, Mutability mut,
 		 std::unique_ptr<Type> type_no_bounds, location_t locus,
-		 Lifetime lifetime);
+		 tl::optional<Lifetime> lifetime);
 
   // Copy constructor with custom clone method
   ReferenceType (ReferenceType const &other);
@@ -323,7 +323,8 @@ public:
   void accept_vis (HIRFullVisitor &vis) override;
   void accept_vis (HIRTypeVisitor &vis) override;
 
-  Lifetime &get_lifetime () { return lifetime; }
+  Lifetime &get_lifetime () { return lifetime.value (); }
+  const Lifetime &get_lifetime () const { return lifetime.value (); }
 
   Mutability get_mut () const { return mut; }
 
diff --git a/gcc/rust/hir/tree/rust-hir.cc b/gcc/rust/hir/tree/rust-hir.cc
index 14f8646..4fc6b1a 100644
--- a/gcc/rust/hir/tree/rust-hir.cc
+++ b/gcc/rust/hir/tree/rust-hir.cc
@@ -1314,7 +1314,7 @@ ContinueExpr::as_string () const
 
   if (has_label ())
     {
-      str += label.as_string ();
+      str += get_label ().as_string ();
     }
 
   return str;
@@ -1816,7 +1816,7 @@ BreakExpr::as_string () const
 
   if (has_label ())
     {
-      str += label.as_string () + " ";
+      str += get_label ().as_string () + " ";
     }
 
   if (has_break_expr ())
@@ -2101,11 +2101,6 @@ QualifiedPathInType::as_string () const
 std::string
 Lifetime::as_string () const
 {
-  if (is_error ())
-    {
-      return "error lifetime";
-    }
-
   switch (lifetime_type)
     {
     case AST::Lifetime::LifetimeType::NAMED:
@@ -2760,7 +2755,7 @@ ReferenceType::as_string () const
 
   if (has_lifetime ())
     {
-      str += lifetime.as_string () + " ";
+      str += get_lifetime ().as_string () + " ";
     }
 
   if (is_mut ())
@@ -3411,7 +3406,7 @@ TraitFunctionDecl::as_string () const
   str += "\n Function params: ";
   if (is_method ())
     {
-      str += self.as_string () + (has_params () ? ", " : "");
+      str += get_self_unchecked ().as_string () + (has_params () ? ", " : "");
     }
 
   if (has_params ())
@@ -3525,70 +3520,63 @@ TraitItemType::as_string () const
 std::string
 SelfParam::as_string () const
 {
-  if (is_error ())
-    {
-      return "error";
-    }
-  else
+  if (has_type ())
     {
-      if (has_type ())
+      // type (i.e. not ref, no lifetime)
+      std::string str;
+
+      if (is_mut ())
 	{
-	  // type (i.e. not ref, no lifetime)
-	  std::string str;
+	  str += "mut ";
+	}
 
-	  if (is_mut ())
-	    {
-	      str += "mut ";
-	    }
+      str += "self : ";
 
-	  str += "self : ";
+      str += type->as_string ();
 
-	  str += type->as_string ();
+      return str;
+    }
+  else if (has_lifetime ())
+    {
+      // ref and lifetime
+      std::string str = "&" + get_lifetime ().as_string () + " ";
 
-	  return str;
-	}
-      else if (has_lifetime ())
+      if (is_mut ())
 	{
-	  // ref and lifetime
-	  std::string str = "&" + lifetime.as_string () + " ";
+	  str += "mut ";
+	}
 
-	  if (is_mut ())
-	    {
-	      str += "mut ";
-	    }
+      str += "self";
 
-	  str += "self";
+      return str;
+    }
+  else if (is_ref ())
+    {
+      // ref with no lifetime
+      std::string str = "&";
 
-	  return str;
-	}
-      else if (is_ref ())
+      if (is_mut ())
 	{
-	  // ref with no lifetime
-	  std::string str = "&";
+	  str += " mut ";
+	}
 
-	  if (is_mut ())
-	    {
-	      str += " mut ";
-	    }
+      str += "self";
 
-	  str += "self";
+      return str;
+    }
+  else
+    {
+      // no ref, no type
+      std::string str;
 
-	  return str;
-	}
-      else
+      if (is_mut ())
 	{
-	  // no ref, no type
-	  std::string str;
-
-	  if (is_mut ())
-	    {
-	      str += "mut ";
-	    }
+	  str += "mut ";
+	}
 
-	  str += "self";
+      str += "self";
 
-	  return str;
-	}
+      return str;
     }
 }