Fix tests failures related to subprogram called on a null entity

Closes eng/ide/ada_language_server#1493

Author: Boulanger

liblsp_3_17/source/lsp-server_messages.ads

@@ -12,10 +12,6 @@ package LSP.Server_Messages is
    type Server_Message is abstract tagged limited null record;
    --  Base class of messages send by a client to a server
 
-   function Assigned (Self : access Server_Message'Class) return Boolean
-     is (Self /= null);
-   --  Check if the argument is not null
-
    type Server_Message_Access is access all Server_Message'Class;
 
    procedure Visit_Server_Message_Visitor

source/server/lsp-job_schedulers.adb

@@ -37,9 +37,11 @@ package body LSP.Job_Schedulers is
    procedure Complete_Last_Fence_Job
      (Self  : in out Job_Scheduler'Class;
       Next  : LSP.Server_Messages.Server_Message_Access;
-      Waste : out LSP.Server_Messages.Server_Message_Access) is
+      Waste : out LSP.Server_Messages.Server_Message_Access)
+   is
+      use type LSP.Server_Jobs.Server_Job_Access;
    begin
-      if Self.Done.Assigned then
+      if Self.Done /= null then
          Self.Done.Complete (Next);
          Waste := Self.Done.Message;
          Free (Self.Done);
@@ -55,6 +57,7 @@ package body LSP.Job_Schedulers is
       Message : in out LSP.Server_Messages.Server_Message_Access;
       Waste   : out LSP.Server_Messages.Server_Message_Access)
    is
+      use type LSP.Server_Jobs.Server_Job_Access;
       Cursor : constant Handler_Maps.Cursor :=
         Self.Handlers.Find (Message'Tag);
 
@@ -65,7 +68,7 @@ package body LSP.Job_Schedulers is
          Self.Complete_Last_Fence_Job (Message, Waste);
          Job := Handler_Maps.Element (Cursor).Create_Job (Message);
 
-         if Job.Assigned then
+         if Job /= null then
             Message := null;
             Self.Enqueue (Job);
          end if;
@@ -91,9 +94,11 @@ package body LSP.Job_Schedulers is
    -- Has_Jobs --
    --------------
 
-   function Has_Jobs (Self : Job_Scheduler'Class) return Boolean is
+   function Has_Jobs (Self : Job_Scheduler'Class) return Boolean
+   is
+      use type LSP.Server_Jobs.Server_Job_Access;
    begin
-      return Self.Blocker.Assigned or else
+      return Self.Blocker /= null or else
         (for some List of Self.Jobs => not List.Is_Empty);
    end Has_Jobs;
 
@@ -121,13 +126,15 @@ package body LSP.Job_Schedulers is
    is
       use all type LSP.Server_Jobs.Job_Priority;
       use all type LSP.Server_Jobs.Execution_Status;
+      use type LSP.Server_Jobs.Server_Job_Access;
+      use type LSP.Server_Messages.Server_Message_Access;
 
       Job : LSP.Server_Jobs.Server_Job_Access renames Self.Blocker;
       Status : LSP.Server_Jobs.Execution_Status := Continue;
    begin
       Waste := null;
 
-      if not Job.Assigned then
+      if Job = null then
          return;
       end if;
 
@@ -138,7 +145,7 @@ package body LSP.Job_Schedulers is
          loop
             Self.Process_Job (Client, Waste, From => Low);
 
-            if Waste.Assigned then
+            if Waste /= null then
                return;
             end if;
          end loop;
@@ -168,11 +175,12 @@ package body LSP.Job_Schedulers is
       Waste  : out LSP.Server_Messages.Server_Message_Access;
       From   : LSP.Server_Jobs.Job_Priority := LSP.Server_Jobs.Lowest)
    is
+      use type LSP.Server_Messages.Server_Message_Access;
       Status : LSP.Server_Jobs.Execution_Status;
    begin
       Self.Complete_Last_Fence_Job (null, Waste);
 
-      if not Waste.Assigned then
+      if Waste = null then
          for List of reverse Self.Jobs (From .. LSP.Server_Jobs.High)
            when not List.Is_Empty
          loop

source/server/lsp-server_jobs.ads

@@ -76,9 +76,6 @@ package LSP.Server_Jobs is
      return LSP.Server_Messages.Server_Message_Access is abstract;
    --  Message to be destroyed when the job is done
 
-   function Assigned (Self : access Server_Job'Class) return Boolean is
-      (Self /= null);
-
    type Server_Job_Access is access all Server_Job'Class;
 
 end LSP.Server_Jobs;

source/server/lsp-servers.adb

@@ -817,6 +817,7 @@ package body LSP.Servers is
 
    task body Processing_Task_Type is
 
+      use type LSP.Server_Messages.Server_Message_Access;
       Input_Queue : Input_Message_Queues.Queue renames Server.Input_Queue;
 
       procedure Process_Message (Message : in out Server_Message_Access);
@@ -846,7 +847,7 @@ package body LSP.Servers is
                   --  job if any.
                   Server.Scheduler.Process_Job (Server.all, Waste);
 
-                  if Waste.Assigned then
+                  if Waste /= null then
                      Server.Destroy_Queue.Enqueue (Waste);
                   end if;
 
@@ -869,19 +870,19 @@ package body LSP.Servers is
       begin
          Server.Scheduler.Create_Job (Message, Waste);
 
-         if Waste.Assigned then
+         if Waste /= null then
             Server.Destroy_Queue.Enqueue (Waste);
          end if;
 
-         if Message.Assigned then
+         if Message /= null then
             --  Scheduler wasn't able to process message, destroy it
             Server.Destroy_Queue.Enqueue (Message);
          end if;
 
          loop
             Server.Scheduler.Process_High_Priority_Job (Server.all, Waste);
 
-            exit when not Waste.Assigned;
+            exit when Waste = null;
 
             Server.Destroy_Queue.Enqueue (Waste);
          end loop;
@@ -919,7 +920,7 @@ package body LSP.Servers is
                   Continue := False;
                end select;
 
-               if Request.Assigned then
+               if Request /= null then
                   Process_Message (Request);
                end if;
             end loop;
@@ -930,7 +931,7 @@ package body LSP.Servers is
 
          Execute_Jobs (Server.Look_Ahead);
 
-         if not Server.Look_Ahead.Assigned then
+         if Server.Look_Ahead = null then
             --  there is no jobs any more, just wait for input messages
 
             select
@@ -961,7 +962,7 @@ package body LSP.Servers is
          end;
       end loop;
 
-      if Server.Look_Ahead.Assigned then
+      if Server.Look_Ahead /= null then
          Free (Server.Look_Ahead);
       end if;