Add proper Alire BuildTargets to build/clean projects

Instead of using the gprbuild-based ones. This is done
through a new aliasing system implemented for Build Targets, via
the new GPS.BuildTarget.set_as_alias API.

For eng/ide/gnatstudio#30

Author: AnthonyLeonardoGracio

builder/src/builder_facility_module-scripts.adb

@@ -132,6 +132,35 @@ package body Builder_Facility_Module.Scripts is
                Data.Set_Return_Value (Arg.all);
             end loop;
          end;
+      elsif Command = "set_as_alias" then
+         declare
+            Inst                : constant Class_Instance :=
+              Nth_Arg (Data, 1, Target_Class);
+            Target_Name         : constant String := Get_Target_Name (Inst);
+            Target              : constant Target_Access :=
+              Get_Target_From_Name
+                (Registry      => Registry,
+                 Name          => Target_Name,
+                 Resolve_Alias => False);
+            Aliased_Target_Name : constant String :=  Nth_Arg (Data, 2, "");
+            Aliased_Target      : constant Target_Access :=
+              Get_Target_From_Name (Registry, Aliased_Target_Name);
+         begin
+            --  The given alias target does not exist: return an error message
+            if Aliased_Target = null and then Aliased_Target_Name /= "" then
+               Set_Error_Msg
+                 (Data,
+                  -"Invalid alias: no target has been registered "
+                  & "with this name: '"
+                  & Aliased_Target_Name
+                  & "'");
+               return;
+            end if;
+
+            Set_As_Alias
+              (Target         => Target,
+               Aliased_Target => Aliased_Target);
+         end;
 
       elsif Command = "get_expanded_command_line" then
          declare
@@ -268,6 +297,14 @@ package body Builder_Facility_Module.Scripts is
          Class        => Target_Class,
          Handler      => Shell_Handler'Access);
 
+      Register_Command
+        (Repo         => Kernel.Scripts,
+         Command      => "set_as_alias",
+         Params       =>
+           (1 => Param ("aliased_target_name",  Optional => True)),
+         Class        => Target_Class,
+         Handler      => Shell_Handler'Access);
+
       Register_Command
         (Kernel, "get_command_line",
          Minimum_Args => 0,

common/core/src/build_configurations.adb

@@ -827,16 +827,34 @@ package body Build_Configurations is
    --------------------------
 
    function Get_Target_From_Name
-     (Registry : Build_Config_Registry_Access;
-      Name     : String) return Target_Access
+     (Registry      : Build_Config_Registry_Access;
+      Name          : String;
+      Resolve_Alias : Boolean := True) return Target_Access
    is
       C : Cursor;
+      Target : Target_Access;
    begin
       C := Registry.Targets.First;
 
       while Has_Element (C) loop
-         if To_String (Element (C).Name) = Name then
-            return Element (C);
+         Target := Element (C);
+
+         if To_String (Target.Name) = Name then
+
+            --  Check if we are dealing with an alias.
+            --  If it's the case, return the aliased target when asked.
+            if not Resolve_Alias
+              or else
+                Target.Properties.Aliased_Target_Name = Null_Unbounded_String
+            then
+               return Target;
+            else
+               return Get_Target_From_Name
+                 (Registry      => Registry,
+                  Name          =>
+                    To_String (Target.Properties.Aliased_Target_Name),
+                  Resolve_Alias => False);
+            end if;
          end if;
 
          Next (C);
@@ -1969,6 +1987,22 @@ package body Build_Configurations is
       Target.Properties.Launch_Mode := Launch_Mode;
    end Set_Launch_Mode;
 
+   ------------------
+   -- Set_As_Alias --
+   ------------------
+
+   procedure Set_As_Alias
+     (Target         : not null Target_Access;
+      Aliased_Target : Target_Access := null) is
+   begin
+      if Aliased_Target /= null then
+         Target.Properties.Aliased_Target_Name := Aliased_Target.Name;
+      else
+         Target.Properties.Aliased_Target_Name :=
+           Ada.Strings.Unbounded.Null_Unbounded_String;
+      end if;
+   end Set_As_Alias;
+
    ----------
    -- Free --
    ----------

common/core/src/build_configurations.ads

@@ -143,10 +143,13 @@ package Build_Configurations is
    --  Remove target named Target_Name from registry
 
    function Get_Target_From_Name
-     (Registry : Build_Config_Registry_Access;
-      Name     : String) return Target_Access;
+     (Registry      : Build_Config_Registry_Access;
+      Name          : String;
+      Resolve_Alias : Boolean := True) return Target_Access;
    --  Get the target corresponding to Name in the Registry; return null if
    --  no such target was found.
+   --  If the target refered by Name is an alias on another target, the
+   --  aliased target is returned instead if Resolve_Alias is set to True.
 
    procedure Duplicate_Target
      (Registry     : Build_Config_Registry_Access;
@@ -327,6 +330,9 @@ package Build_Configurations is
 
       Project_Switches  : Unbounded_String;
       --  Project switches relevant for this target, if any.
+
+      Aliased_Target_Name : Unbounded_String;
+      --  The name of the target being aliased, if any.
    end record;
 
    function Get_Properties (Target : Target_Access) return Target_Properties;
@@ -447,6 +453,21 @@ package Build_Configurations is
    (Target : Target_Access; Launch_Mode : Launch_Mode_Type);
    --  Change Launch_Mode value
 
+   procedure Set_As_Alias
+     (Target         : not null Target_Access;
+      Aliased_Target : Target_Access := null);
+   --  Set the given target as an alias for Aliased_Target.
+   --  Aliases are used to temporarily replace a build target
+   --  (e.g: "Build All") by another one (e.g: "My Custom Build All").
+   --
+   --  This can be used by plugins to execute their own custom build targets
+   --  while the user interacts with the default GNAT Studio build targets,
+   --  either via the UI or through the GPS.BuildTarget Python API.
+   --  In the example given above, clicking on the "Build All" toolbar button
+   --  will actually execute "My Custom Build All" instead.
+   --
+   --  Giving a null aliased target will unset any existing alias.
+
    function Apply_Mode_Args
      (Target   : access Target_Type;
       Mode     : String;

docs/users_guide/GPS.rst

@@ -186,6 +186,8 @@ Classes
 
    .. automethod:: GPS.BuildTarget.remove
 
+   .. automethod:: GPS.BuildTarget.set_as_alias
+
    .. automethod:: GPS.BuildTarget.show
 
 :class:`GPS.Button`

docs/users_guide/GPS/__init__.py

@@ -986,6 +986,26 @@ def show(self):
         """
         pass  # implemented in Ada
 
+    def set_as_alias(aliased_target_name=""):
+        """
+        Set the given target as an alias for target designated by `alias_target_name`.
+        Aliases are used to temporarily replace a build target
+        (e.g: "Build All") by another one (e.g: "My Custom Build All").
+
+        This can be used by plugins to execute their own custom build targets
+        while the user interacts with the default GNAT Studio build targets,
+        either via the UI or through the GPS.BuildTarget Python API.
+        In the example given above, clicking on the "Build All" toolbar button
+        will actually execute "My Custom Build All" instead.
+
+        To unset an just give an empty string for the `aliased_target_name`
+        parameter
+
+        :param str aliased_target_name: The name of the aliased target, or an
+           empty string to unset the alias.
+        """
+        pass  # implemented in Ada
+
     @staticmethod
     def expand_macros(cmd_line):
         """