Add Lowest job priority

for the indexing job. Change job scheduler to keep indexing jobs
while jobs with Fence priority are executing.

Fixes #1362

source/ada/lsp-ada_indexing.ads

@@ -86,7 +86,7 @@ private
 
    overriding function Priority
      (Self : Indexing_Job) return LSP.Server_Jobs.Job_Priority is
-       (LSP.Server_Jobs.Low);
+       (LSP.Server_Jobs.Lowest);
 
    overriding procedure Execute
      (Self   : in out Indexing_Job;

source/server/lsp-job_schedulers.adb

@@ -132,9 +132,11 @@ package body LSP.Job_Schedulers is
       end if;
 
       if Job.Priority = Fence then
-         --  Process other jobs before any Fence job
-         while (for some List of Self.Jobs => not List.Is_Empty) loop
-            Self.Process_Job (Client, Waste);
+         --  Process other jobs (excluding indexing) before any Fence job
+         while
+           (for some List of Self.Jobs (Low .. High) => not List.Is_Empty)
+         loop
+            Self.Process_Job (Client, Waste, From => Low);
 
             if Waste.Assigned then
                return;
@@ -163,14 +165,17 @@ package body LSP.Job_Schedulers is
      (Self   : in out Job_Scheduler'Class;
       Client :
         in out LSP.Client_Message_Receivers.Client_Message_Receiver'Class;
-      Waste  : out LSP.Server_Messages.Server_Message_Access)
+      Waste  : out LSP.Server_Messages.Server_Message_Access;
+      From   : LSP.Server_Jobs.Job_Priority := LSP.Server_Jobs.Lowest)
    is
       Status : LSP.Server_Jobs.Execution_Status;
    begin
       Self.Complete_Last_Fence_Job (null, Waste);
 
       if not Waste.Assigned then
-         for List of reverse Self.Jobs when not List.Is_Empty loop
+         for List of reverse Self.Jobs (From .. LSP.Server_Jobs.High)
+           when not List.Is_Empty
+         loop
             declare
                Job : LSP.Server_Jobs.Server_Job_Access := List.First_Element;
             begin

source/server/lsp-job_schedulers.ads

@@ -68,8 +68,9 @@ package LSP.Job_Schedulers is
      (Self   : in out Job_Scheduler'Class;
       Client :
         in out LSP.Client_Message_Receivers.Client_Message_Receiver'Class;
-      Waste  : out LSP.Server_Messages.Server_Message_Access);
-   --  Execute (already created) jobs with ordinal priority (Low, High).
+      Waste  : out LSP.Server_Messages.Server_Message_Access;
+      From   : LSP.Server_Jobs.Job_Priority := LSP.Server_Jobs.Lowest);
+   --  Execute (already created) jobs with ordinal priority (From .. High).
    --  When a job is done the routine returns (in Waste) the message to be
    --  deallocated by the server. The Client is used to send messages during
    --  the execution of the job.
@@ -88,8 +89,7 @@ private
    package Job_Lists is new Ada.Containers.Doubly_Linked_Lists
      (LSP.Server_Jobs.Server_Job_Access, LSP.Server_Jobs."=");
 
-   subtype Ordinal_Priority is LSP.Server_Jobs.Job_Priority
-     range LSP.Server_Jobs.Low .. LSP.Server_Jobs.High;
+   subtype Ordinal_Priority is LSP.Server_Jobs.Ordinal_Priority;
 
    type Job_List_Array is array (Ordinal_Priority) of Job_Lists.List;
 

source/server/lsp-server_jobs.ads

@@ -21,9 +21,10 @@ with LSP.Server_Messages;
 package LSP.Server_Jobs is
    pragma Preelaborate;
 
-   type Job_Priority is (Low, High, Immediate, Fence);
+   type Job_Priority is (Lowest, Low, High, Immediate, Fence);
    --  Job priority to schedule jobs.
    --
+   --  @value Lowest - indexing jobs
    --  @value Low - long running jobs like find-all-references
    --  @value High - fast queries like hover
    --  @value Immediate - urgent queries like cancel-request
@@ -33,7 +34,7 @@ package LSP.Server_Jobs is
    --  new messages until the job is done. Server execute each job in its
    --  queue before executing any Fence job.
 
-   subtype Ordinal_Priority is Job_Priority range Low .. High;
+   subtype Ordinal_Priority is Job_Priority range Lowest .. High;
 
    type Server_Job is limited interface;