Better reporting on failures resolving dependencies

src/alire-os_lib.adb

@@ -27,7 +27,7 @@ package body Alire.OS_Lib is
    function Spawn (Command   : String;
                    Arguments : String := "") return Integer is
    begin
-      Log ("Spawning: " & Command & " " & Arguments, Verbose);
+      Log ("Spawning: " & Command & " " & Arguments, Debug);
       return
         (Spawn (Locate_In_Path (Command),
                 Argument_String_To_List (Arguments).all));

src/alire-query.adb

@@ -25,7 +25,7 @@ package body Alire.Query is
       use Containers.Project_Release_Maps;
    begin
       for Rel of I loop
-         Log ("  " & Rel.Milestone_Image);
+         Log ("  " & Rel.Milestone_Image, Verbose);
       end loop;
    end Print_Solution;
 
@@ -57,7 +57,7 @@ package body Alire.Query is
       is
       begin
          if Unresolved.Is_Empty then
-            Log ("Dependency solution found.");
+            Log ("Dependencies resolved");
             Print_Solution (Frozen);
             return Frozen;
          else
@@ -115,7 +115,11 @@ package body Alire.Query is
    begin
       Success := False;
 
-      return Resolve (Deps, Containers.Project_Release_Maps.Empty_Map, Success);
+      return I : constant Instance := Resolve (Deps, Containers.Project_Release_Maps.Empty_Map, Success) do
+         if not Success then
+            Log ("Dependency resolution failed");
+         end if;
+      end return;
    end Resolve;
 
 end Alire.Query;

src/alire.adb

@@ -8,8 +8,8 @@ package body Alire is
          GNAT.IO.Put_Line
            ((case Level is
                when Terse => "",
-               when Verbose => "> ",
-               when Debug   => ">> ") & S);
+               when Verbose => "-> ",
+               when Debug   => "-->> ") & S);
       end if;
    end Log;