Preparation to generalized version restrictions

src/alire-properties-versions.ads

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+package Alire.Properties.Versions with Preelaborate is
+
+   --  Internally we manage versions as a tree of conditions, so arbitrary logical expressions can be used
+
+   package Values is new Properties.values (Semantic_Versioning.Version);
+
+   function New_Version (V : Semantic_Versioning.Version) return Property'Class is
+      (Values.New_Property (V));
+
+end Alire.Properties.Versions;

src/alire-requisites-versions.ads

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+with Alire.Properties.Versions;
+
+package Alire.Requisites.Versions with Preelaborate is
+
+   package Semver renames Semantic_Versioning;
+
+   function Exactly (V : Semver.Version) return Requisite'Class;
+
+private
+
+   package Props renames Alire.Properties.Versions;
+
+   package Version_Requisites is new Typed_Requisites (Props.Values.Property'Class);
+
+   type Version_Requisite is new Version_Requisites.Requisite with record
+      Set : Semver.Version_Set;
+   end record;
+
+   ------------------
+   -- Is_Satisfied --
+   ------------------
+
+   overriding function Is_Satisfied (R : Version_Requisite;
+                                     P : Props.Values.Property'Class) return Boolean is
+     (Semver.Is_In (V => P.Element, VS => R.Set));
+
+   -------------
+   -- Exactly --
+   -------------
+
+   function Exactly (V : Semver.Version) return Requisite'Class is
+      (Version_Requisite'(Set => Semver.Exactly (V)));
+
+end Alire.Requisites.Versions;