Use a loop label in break expression

Break expression were using a raw lifetime value instead of a loop label
this behavior would have lead to some errors in ast validation.

gcc/rust/ChangeLog:

	* ast/rust-expr.h (class BreakExpr): Change Lifetime to LoopLabel.
	* hir/rust-ast-lower-expr.cc (ASTLoweringExpr::visit): Lower lifetime
	inside the label instead.
	* resolve/rust-ast-resolve-expr.cc (ResolveExpr::visit): Resolve the
	inner lifetime.

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

gcc/rust/ast/rust-expr.h

@@ -2727,7 +2727,7 @@ class ContinueExpr : public ExprWithoutBlock
 class BreakExpr : public ExprWithoutBlock
 {
   std::vector<Attribute> outer_attrs;
-  Lifetime label;
+  LoopLabel label;
   std::unique_ptr<Expr> break_expr;
   location_t locus;
 
@@ -2745,7 +2745,7 @@ class BreakExpr : public ExprWithoutBlock
   bool has_break_expr () const { return break_expr != nullptr; }
 
   // Constructor for a break expression
-  BreakExpr (Lifetime break_label, std::unique_ptr<Expr> expr_in_break,
+  BreakExpr (LoopLabel break_label, std::unique_ptr<Expr> expr_in_break,
 	     std::vector<Attribute> outer_attribs, location_t locus)
     : outer_attrs (std::move (outer_attribs)), label (std::move (break_label)),
       break_expr (std::move (expr_in_break)), locus (locus)
@@ -2807,7 +2807,7 @@ class BreakExpr : public ExprWithoutBlock
     outer_attrs = std::move (new_attrs);
   }
 
-  Lifetime &get_label () { return label; }
+  LoopLabel &get_label () { return label; }
 
 protected:
   /* Use covariance to implement clone function as returning this object rather

gcc/rust/hir/rust-ast-lower-expr.cc

@@ -589,7 +589,8 @@ ASTLoweringExpr::visit (AST::ForLoopExpr &expr)
 void
 ASTLoweringExpr::visit (AST::BreakExpr &expr)
 {
-  HIR::Lifetime break_label = lower_lifetime (expr.get_label ());
+  HIR::Lifetime break_label
+    = lower_lifetime (expr.get_label ().get_lifetime ());
   HIR::Expr *break_expr
     = expr.has_break_expr ()
 	? ASTLoweringExpr::translate (expr.get_break_expr ().get ())

gcc/rust/resolve/rust-ast-resolve-expr.cc

@@ -452,7 +452,7 @@ ResolveExpr::visit (AST::BreakExpr &expr)
 {
   if (expr.has_label ())
     {
-      auto label = expr.get_label ();
+      auto label = expr.get_label ().get_lifetime ();
       if (label.get_lifetime_type () != AST::Lifetime::LifetimeType::NAMED)
 	{
 	  rust_error_at (label.get_locus (),
@@ -466,7 +466,7 @@ ResolveExpr::visit (AST::BreakExpr &expr)
 				    label.get_lifetime_name ()),
 	    &resolved_node))
 	{
-	  rust_error_at (expr.get_label ().get_locus (), ErrorCode::E0426,
+	  rust_error_at (label.get_locus (), ErrorCode::E0426,
 			 "use of undeclared label %qs in %<break%>",
 			 label.get_lifetime_name ().c_str ());
 	  return;