gccrs: Make loop label truly optional

A loop label error state was in use to represent missing loop label but
this may be easily forgotten and the optional nature of the label was
misrepresented.

gcc/rust/ChangeLog:

	* ast/rust-ast-builder.cc (Builder::block): Call with a nullopt instead
	of an error loop label.
	(WhileLetLoopExpr::as_string): Use getter function and adapt to
	newtype.
	* ast/rust-ast.cc (WhileLoopExpr::as_string): Likewise.
	(LoopExpr::as_string): Likewise.
	(BreakExpr::as_string): Likewise.
	(ForLoopExpr::as_string): Likewise.
	* ast/rust-expr.h (class BlockExpr): Make loop label optional.
	(class BreakExpr): Likewise.
	* expand/rust-derive-clone.cc (DeriveClone::clone_fn): Use nullopt.
	* expand/rust-derive-debug.cc (DeriveDebug::stub_debug_fn): Likewise.
	* expand/rust-derive-default.cc (DeriveDefault::default_fn): Likewise.
	* expand/rust-derive-eq.cc: Likewise.
	* parse/rust-parse-impl.h (Parser::parse_block_expr): Use optional
	for arguments.
	(Parser::parse_loop_expr): Likewise.
	(Parser::parse_while_loop_expr): Likewise.
	(Parser::parse_while_let_loop_expr): Likewise.
	(Parser::parse_for_loop_expr): Likewise.
	(Parser::parse_labelled_loop_expr): Likewise.
	(Parser::parse_loop_label): Return an optional.
	* parse/rust-parse.h: Update function prototype and use nullopt for
	default values.

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

3 files changed, 27 insertions, 24 deletions

diff --git a/gcc/rust/ast/rust-ast-builder.cc b/gcc/rust/ast/rust-ast-builder.cc
index cdc6eec..5eea469 100644
--- a/gcc/rust/ast/rust-ast-builder.cc
+++ b/gcc/rust/ast/rust-ast-builder.cc
@@ -335,9 +335,9 @@ std::unique_ptr<BlockExpr>
 Builder::block (std::vector<std::unique_ptr<Stmt>> &&stmts,
 		std::unique_ptr<Expr> &&tail_expr) const
 {
-  return std::unique_ptr<BlockExpr> (
-    new BlockExpr (std::move (stmts), std::move (tail_expr), {}, {},
-		   LoopLabel::error (), loc, loc));
+  return std::unique_ptr<BlockExpr> (new BlockExpr (std::move (stmts),
+						    std::move (tail_expr), {},
+						    {}, tl::nullopt, loc, loc));
 }
 
 std::unique_ptr<Expr>
diff --git a/gcc/rust/ast/rust-ast.cc b/gcc/rust/ast/rust-ast.cc
index e4a1b36..c7e0397 100644
--- a/gcc/rust/ast/rust-ast.cc
+++ b/gcc/rust/ast/rust-ast.cc
@@ -2095,7 +2095,7 @@ WhileLoopExpr::as_string () const
   if (!has_loop_label ())
     str += "none";
   else
-    str += loop_label.as_string ();
+    str += get_loop_label ().as_string ();
 
   str += "\n Conditional expr: " + condition->as_string ();
 
@@ -2115,7 +2115,7 @@ WhileLetLoopExpr::as_string () const
   if (!has_loop_label ())
     str += "none";
   else
-    str += loop_label.as_string ();
+    str += get_loop_label ().as_string ();
 
   str += "\n Match arm patterns: ";
   if (match_arm_patterns.empty ())
@@ -2146,7 +2146,7 @@ LoopExpr::as_string () const
   if (!has_loop_label ())
     str += "none";
   else
-    str += loop_label.as_string ();
+    str += get_loop_label ().as_string ();
 
   str += "\n Loop block: " + loop_block->as_string ();
 
@@ -2183,7 +2183,7 @@ BreakExpr::as_string () const
   std::string str ("break ");
 
   if (has_label ())
-    str += label.as_string () + " ";
+    str += get_label ().as_string () + " ";
 
   if (has_break_expr ())
     str += break_expr->as_string ();
@@ -2545,7 +2545,7 @@ ForLoopExpr::as_string () const
   if (!has_loop_label ())
     str += "none";
   else
-    str += loop_label.as_string ();
+    str += get_loop_label ().as_string ();
 
   str += "\n Pattern: " + pattern->as_string ();
 
diff --git a/gcc/rust/ast/rust-expr.h b/gcc/rust/ast/rust-expr.h
index cff09fe..3ce78c6 100644
--- a/gcc/rust/ast/rust-expr.h
+++ b/gcc/rust/ast/rust-expr.h
@@ -2590,7 +2590,7 @@ class BlockExpr : public ExprWithBlock
   std::vector<Attribute> inner_attrs;
   std::vector<std::unique_ptr<Stmt> > statements;
   std::unique_ptr<Expr> expr;
-  LoopLabel label;
+  tl::optional<LoopLabel> label;
   location_t start_locus;
   location_t end_locus;
   bool marked_for_strip = false;
@@ -2607,8 +2607,9 @@ public:
   BlockExpr (std::vector<std::unique_ptr<Stmt> > block_statements,
 	     std::unique_ptr<Expr> block_expr,
 	     std::vector<Attribute> inner_attribs,
-	     std::vector<Attribute> outer_attribs, LoopLabel label,
-	     location_t start_locus, location_t end_locus)
+	     std::vector<Attribute> outer_attribs,
+	     tl::optional<LoopLabel> label, location_t start_locus,
+	     location_t end_locus)
     : outer_attrs (std::move (outer_attribs)),
       inner_attrs (std::move (inner_attribs)),
       statements (std::move (block_statements)), expr (std::move (block_expr)),
@@ -2727,8 +2728,8 @@ public:
     outer_attrs = std::move (new_attrs);
   }
 
-  bool has_label () { return !label.is_error (); }
-  LoopLabel &get_label () { return label; }
+  bool has_label () { return label.has_value (); }
+  LoopLabel &get_label () { return label.value (); }
 
   Expr::Kind get_expr_kind () const override { return Expr::Kind::Block; }
 
@@ -2901,7 +2902,7 @@ protected:
 class BreakExpr : public ExprWithoutBlock
 {
   std::vector<Attribute> outer_attrs;
-  LoopLabel label;
+  tl::optional<LoopLabel> label;
   std::unique_ptr<Expr> break_expr;
   location_t locus;
 
@@ -2912,7 +2913,7 @@ 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. */
@@ -2981,7 +2982,8 @@ public:
     outer_attrs = std::move (new_attrs);
   }
 
-  LoopLabel &get_label () { return label; }
+  LoopLabel &get_label () { return label.value (); }
+  const LoopLabel &get_label () const { return label.value (); }
 
   Expr::Kind get_expr_kind () const override { return Expr::Kind::Break; }
 
@@ -3657,7 +3659,7 @@ class BaseLoopExpr : public ExprWithBlock
 protected:
   // protected to allow subclasses better use of them
   std::vector<Attribute> outer_attrs;
-  LoopLabel loop_label;
+  tl::optional<LoopLabel> loop_label;
   std::unique_ptr<BlockExpr> loop_block;
 
 private:
@@ -3666,7 +3668,7 @@ private:
 protected:
   // Constructor for BaseLoopExpr
   BaseLoopExpr (std::unique_ptr<BlockExpr> loop_block, location_t locus,
-		LoopLabel loop_label = LoopLabel::error (),
+		tl::optional<LoopLabel> loop_label = tl::nullopt,
 		std::vector<Attribute> outer_attribs
 		= std::vector<Attribute> ())
     : outer_attrs (std::move (outer_attribs)),
@@ -3706,9 +3708,10 @@ protected:
   BaseLoopExpr &operator= (BaseLoopExpr &&other) = default;
 
 public:
-  bool has_loop_label () const { return !loop_label.is_error (); }
+  bool has_loop_label () const { return loop_label.has_value (); }
 
-  LoopLabel &get_loop_label () { return loop_label; }
+  LoopLabel &get_loop_label () { return loop_label.value (); }
+  const LoopLabel &get_loop_label () const { return loop_label.value (); }
 
   location_t get_locus () const override final { return locus; }
 
@@ -3752,7 +3755,7 @@ public:
 
   // Constructor for LoopExpr
   LoopExpr (std::unique_ptr<BlockExpr> loop_block, location_t locus,
-	    LoopLabel loop_label = LoopLabel::error (),
+	    tl::optional<LoopLabel> loop_label = tl::nullopt,
 	    std::vector<Attribute> outer_attribs = std::vector<Attribute> ())
     : BaseLoopExpr (std::move (loop_block), locus, std::move (loop_label),
 		    std::move (outer_attribs))
@@ -3785,7 +3788,7 @@ public:
   // Constructor for while loop with loop label
   WhileLoopExpr (std::unique_ptr<Expr> loop_condition,
 		 std::unique_ptr<BlockExpr> loop_block, location_t locus,
-		 LoopLabel loop_label = LoopLabel::error (),
+		 tl::optional<LoopLabel> loop_label = tl::nullopt,
 		 std::vector<Attribute> outer_attribs
 		 = std::vector<Attribute> ())
     : BaseLoopExpr (std::move (loop_block), locus, std::move (loop_label),
@@ -3851,7 +3854,7 @@ public:
   WhileLetLoopExpr (std::vector<std::unique_ptr<Pattern> > match_arm_patterns,
 		    std::unique_ptr<Expr> scrutinee,
 		    std::unique_ptr<BlockExpr> loop_block, location_t locus,
-		    LoopLabel loop_label = LoopLabel::error (),
+		    tl::optional<LoopLabel> loop_label = tl::nullopt,
 		    std::vector<Attribute> outer_attribs
 		    = std::vector<Attribute> ())
     : BaseLoopExpr (std::move (loop_block), locus, std::move (loop_label),
@@ -3938,7 +3941,7 @@ public:
   ForLoopExpr (std::unique_ptr<Pattern> loop_pattern,
 	       std::unique_ptr<Expr> iterator_expr,
 	       std::unique_ptr<BlockExpr> loop_body, location_t locus,
-	       LoopLabel loop_label = LoopLabel::error (),
+	       tl::optional<LoopLabel> loop_label = tl::nullopt,
 	       std::vector<Attribute> outer_attribs = std::vector<Attribute> ())
     : BaseLoopExpr (std::move (loop_body), locus, std::move (loop_label),
 		    std::move (outer_attribs)),