Report the system package manager in alr version

src/alire/alire-origins-deployers-system-apt.ads

@@ -12,4 +12,7 @@ package Alire.Origins.Deployers.System.Apt is
    overriding
    function Install (This : Deployer) return Outcome;
 
+   overriding
+   function Executable_Name (This : Deployer) return String is ("apt");
+
 end Alire.Origins.Deployers.System.Apt;

src/alire/alire-origins-deployers-system-homebrew.ads

@@ -12,4 +12,7 @@ package Alire.Origins.Deployers.System.Homebrew is
    overriding
    function Install (This : Deployer) return Outcome;
 
+   overriding
+   function Executable_Name (This : Deployer) return String is ("brew");
+
 end Alire.Origins.Deployers.System.Homebrew;

src/alire/alire-origins-deployers-system-macports.ads

@@ -12,4 +12,7 @@ package Alire.Origins.Deployers.System.Macports is
    overriding
    function Install (This : Deployer) return Outcome;
 
+   overriding
+   function Executable_Name (This : Deployer) return String is ("port");
+
 end Alire.Origins.Deployers.System.Macports;

src/alire/alire-origins-deployers-system-pacman.ads

@@ -12,4 +12,7 @@ package Alire.Origins.Deployers.System.Pacman is
    overriding
    function Install (This : Deployer) return Outcome;
 
+   overriding
+   function Executable_Name (This : Deployer) return String is ("pacman");
+
 end Alire.Origins.Deployers.System.Pacman;

src/alire/alire-origins-deployers-system-rpm_wrappers.adb

@@ -18,6 +18,14 @@ package body Alire.Origins.Deployers.System.RPM_Wrappers is
          when Dnf => "dnf",
          when Yum => "yum");
 
+   ---------------------
+   -- Executable_Name --
+   ---------------------
+
+   overriding
+   function Executable_Name (This : Deployer) return String
+   is (This.Wrapper_Command);
+
    ------------------------------
    -- Package_Name_With_Archit --
    ------------------------------

src/alire/alire-origins-deployers-system-rpm_wrappers.ads

@@ -16,4 +16,7 @@ package Alire.Origins.Deployers.System.RPM_Wrappers is
    overriding
    function Install (This : Deployer) return Outcome;
 
+   overriding
+   function Executable_Name (This : Deployer) return String;
+
 end Alire.Origins.Deployers.System.RPM_Wrappers;

src/alire/alire-origins-deployers-system-zypper.ads

@@ -12,4 +12,7 @@ package Alire.Origins.Deployers.System.Zypper is
    overriding
    function Install (This : Deployer) return Outcome;
 
+   overriding
+   function Executable_Name (This : Deployer) return String is ("zypper");
+
 end Alire.Origins.Deployers.System.Zypper;

src/alire/alire-origins-deployers-system.adb

@@ -4,6 +4,7 @@ with Alire.Origins.Deployers.System.Macports;
 with Alire.Origins.Deployers.System.Pacman;
 with Alire.Origins.Deployers.System.RPM_Wrappers;
 with Alire.Origins.Deployers.System.Zypper;
+with Alire.OS_Lib;
 with Alire.Platforms.Current;
 
 with CLIC.User_Input;
@@ -125,4 +126,17 @@ package body Alire.Origins.Deployers.System is
       This.Ask_Permission := False;
    end Dont_Ask_Permission;
 
+   ---------------------
+   -- Executable_Path --
+   ---------------------
+
+   function Executable_Path return Optional_Absolute_Path is
+      Make : constant Origin := New_System ("make");
+      --  We use a mock system package to be able to obtain a deployer. It
+      --  doesn't matter if this system package doesn't exist.
+   begin
+      return OS_Lib.Locate_Exec_On_Path
+        (Platform_Deployer (Make).Executable_Name);
+   end Executable_Path;
+
 end Alire.Origins.Deployers.System;

src/alire/alire-origins-deployers-system.ads

@@ -46,6 +46,12 @@ package Alire.Origins.Deployers.System is
    --  This procedure tells the deployer not to ask user permission before
    --  deployment.
 
+   not overriding
+   function Executable_Name (This : Deployer) return String is abstract;
+   --  Must return the name of the executable used for installations (apt,
+   --  pacman, etc). For platforms that use several, the top-most wrapper
+   --  should be returned (i.e., apt instead of dpkg, yum instead of rpm...).
+
    -------------
    -- Factory --
    -------------
@@ -56,6 +62,10 @@ package Alire.Origins.Deployers.System is
    function Platform_Deployer (Package_Name : String) return Deployer'Class is
      (Platform_Deployer (Origins.New_System (Package_Name)));
 
+   function Executable_Path return Optional_Absolute_Path;
+   --  Identifies the package manager executable being called in the current
+   --  platform, or "" if none found.
+
 private
 
    type Deployer is abstract new Deployers.Deployer with record

src/alire/alire.ads

@@ -149,6 +149,11 @@ package Alire with Preelaborate is
    function Absolute_Path_Image (Path : Absolute_Path) return String;
    --  Needed for later instantiations
 
+   subtype Optional_Absolute_Path is Any_Path
+     with Dynamic_Predicate =>
+       Optional_Absolute_Path = "" or else
+       Check_Absolute_Path (Optional_Absolute_Path);
+
    subtype Unbounded_Absolute_Path is UString
      with Dynamic_Predicate =>
        +Unbounded_Absolute_Path = "" or else

src/alr/alr-commands-version.adb

@@ -4,6 +4,7 @@ with Alire.Directories;
 with Alire.Index;
 with Alire.Index_On_Disk.Loading;
 with Alire.Milestones;
+with Alire.Origins.Deployers.System;
 with Alire.Paths.Vault;
 with Alire.Platforms.Folders;
 with Alire.Properties;
@@ -116,6 +117,11 @@ package body Alr.Commands.Version is
          end loop;
       end;
 
+      Table
+        .Append ("system package manager:")
+        .Append (Alire.Origins.Deployers.System.Executable_Path)
+        .New_Row;
+
       Table.Append ("").New_Row;
       Table.Append ("WORKSPACE").New_Row;