Warn when adding a ^0.x dependency

src/alire/alire-releases.adb

@@ -42,6 +42,22 @@ package body Alire.Releases is
        (New_Label (Description,
                    Defaults.Description)));
 
+   -----------------------
+   -- Flat_Dependencies --
+   -----------------------
+
+   function Flat_Dependencies
+     (R : Release;
+      P : Alire.Properties.Vector := Alire.Properties.No_Properties)
+      return Alire.Dependencies.Containers.List
+   is
+      function Enumerate is new Conditional.For_Dependencies.Enumerate
+        (Alire.Dependencies.Containers.List,
+         Alire.Dependencies.Containers.Append);
+   begin
+      return Enumerate (R.Dependencies.Evaluate (P));
+   end Flat_Dependencies;
+
    ---------------
    -- Extending --
    ---------------

src/alire/alire-releases.ads

@@ -2,7 +2,7 @@ with Ada.Containers.Indefinite_Ordered_Maps;
 with Ada.Tags;
 
 with Alire.Conditional;
-with Alire.Dependencies;
+with Alire.Dependencies.Containers;
 with Alire.Interfaces;
 with Alire.Manifest;
 with Alire.Milestones;
@@ -158,6 +158,15 @@ package Alire.Releases is
                           return Conditional.Dependencies;
    --  Retrieve only the dependencies that apply on platform P
 
+   function Flat_Dependencies
+     (R : Release;
+      P : Alire.Properties.Vector := Alire.Properties.No_Properties)
+      return Alire.Dependencies.Containers.List;
+   --  Remove any and/or nodes and return dependencies as a simple list. This
+   --  is useful whenever you need to inspect all direct dependencies, no
+   --  matter how they will be solved. If P is not empty, this function
+   --  also works for platform-dependent dependencies only.
+
    function Property (R   : Release;
                       Key : Alire.Properties.Labeled.Labels)
                       return String;

src/alire/alire-roots.adb

@@ -331,6 +331,7 @@ package body Alire.Roots is
             Solution => This.Solution,
             Deps_Dir => This.Dependencies_Dir);
       end if;
+
    end Sync_Solution_And_Deps;
 
    -------------------------------------------

src/alire/alire-warnings.adb

@@ -0,0 +1,24 @@
+with Alire.Utils;
+
+package body Alire.Warnings is
+
+   Already_Emitted : Utils.String_Set;
+
+   ---------------
+   -- Warn_Once --
+   ---------------
+
+   procedure Warn_Once (Text : String;
+                        ID   : String := "";
+                        Level : Trace.Levels := Trace.Warning)
+   is
+   begin
+      if ID = "" then
+         Warn_Once (Text, Text, Level);
+      elsif not Already_Emitted.Contains (ID) then
+         Already_Emitted.Include (ID);
+         Trace.Log (Text, Level);
+      end if;
+   end Warn_Once;
+
+end Alire.Warnings;

src/alire/alire-warnings.ads

@@ -0,0 +1,10 @@
+package Alire.Warnings with Preelaborate is
+
+   procedure Warn_Once (Text : String;
+                        ID   : String := "";
+                        Level : Trace.Levels := Trace.Warning);
+   --  Emit a warning just once. If it has been already seen, do not warn
+   --  again. ID is used to determine if a warning has already been emitted
+   --  or, when not given, the actual warning text.
+
+end Alire.Warnings;

src/alire/alire-workspace.adb

@@ -12,12 +12,37 @@ with Alire.Paths;
 with Alire.Properties.Actions.Executor;
 with Alire.Roots;
 with Alire.Solutions.Diffs;
-with Alire.Workspace;
+with Alire.Utils.TTY;
+with Alire.Warnings;
 
 package body Alire.Workspace is
 
    use type Conditional.Dependencies;
 
+   -------------------------
+   -- Check_Caret_Warning --
+   -------------------------
+   --  Warn of ^0.x dependencies that probably should be ~0.x
+   procedure Check_Caret_Warning (Root : Roots.Root) is
+      use Alire.Utils;
+      Warning_Id : constant String := "caret or tilde";
+   begin
+      for Dep of Root.Release.Flat_Dependencies loop
+         if Utils.Contains (Dep.Versions.Image, "^0") then
+            Warnings.Warn_Once
+              ("Possible tilde instead of caret intended for a 0.x version.",
+               Warning_Id & "1");
+            Warnings.Warn_Once
+              ("Alire interprets caret and tilde the same way "
+               & "for both pre/post-1 versions.",
+               Warning_Id & "2");
+            Warnings.Warn_Once
+              ("The suspicious dependency is: " & TTY.Version (Dep.Image),
+               Warning_Id & "3");
+         end if;
+      end loop;
+   end Check_Caret_Warning;
+
    -------------------------
    -- Deploy_Dependencies --
    -------------------------
@@ -125,6 +150,12 @@ package body Alire.Workspace is
 
       Solution.Print_Hints (Root.Environment);
 
+      --  Check that the solution does not contain suspicious dependencies,
+      --  taking advantage that this procedure is called whenever a change
+      --  to dependencies is happening.
+
+      Check_Caret_Warning (Root);
+
    end Deploy_Dependencies;
 
    --------------------