Bugfix for nested empty tables in manifest

src/alire/alire-conditional_trees-case_nodes.adb

@@ -16,7 +16,7 @@ package body Alire.Conditional_Trees.Case_Nodes is
                       return Tree'Class;
 
    overriding
-   function Flatten (This : Case_Node) return Node'Class;
+   function Flatten (This : Case_Node) return Tree'Class;
 
    overriding
    function Image (This : Case_Node) return String;
@@ -183,23 +183,23 @@ package body Alire.Conditional_Trees.Case_Nodes is
    -------------
 
    overriding
-   function Flatten (This : Case_Node) return Node'Class is
+   function Flatten (This : Case_Node) return Tree'Class is
       Flat : Tree;
    begin
       for Key of This.Cases.Keys (Exclude_Others => True, Ada_Like => False)
       loop
          if not This.Cases.Element (+Key).Is_Empty then
-            Flat := Flat and To_Tree (This.Cases.Element (+Key).Root.Flatten);
+            Flat := Flat and Tree (This.Cases.Element (+Key).Root.Flatten);
          end if;
       end loop;
 
       if This.Cases.Has_Others then
          if not This.Cases.Other.Is_Empty then
-            Flat := Flat and To_Tree (This.Cases.Other.Root.Flatten);
+            Flat := Flat and Tree (This.Cases.Other.Root.Flatten);
          end if;
       end if;
 
-      return Flat.Root;
+      return Flat;
    end Flatten;
 
    -------------------------

src/alire/alire-conditional_trees.adb

@@ -151,17 +151,17 @@ package body Alire.Conditional_Trees is
    -------------
 
    overriding
-   function Flatten (This : Vector_Node) return Node'Class is
+   function Flatten (This : Vector_Node) return Tree'Class is
       Result : Tree;
    begin
       for Child of This.Values loop
          case This.Conjunction is
-            when Anded => Result := Result and Child.Flatten.To_Tree;
-            when Ored =>  Result := Result or  Child.Flatten.To_Tree;
+            when Anded => Result := Result and Tree (Child.Flatten);
+            when Ored =>  Result := Result or  Tree (Child.Flatten);
          end case;
       end loop;
 
-      return Result.Root;
+      return Result;
    end Flatten;
 
    ----------
@@ -276,27 +276,27 @@ package body Alire.Conditional_Trees is
 
    function Enumerate (This : Tree) return Collection is
       Col : Collection with Warnings => Off;
-
-      procedure Visit (Inner : Node'Class) is
-         Flat : constant Node'Class := Inner.Flatten;
-         --  This call recursively should result in a flat vector at worst
-      begin
-         if Flat in Leaf_Node then
-            Append (Col, Leaf_Node (Flat).Value.Constant_Reference);
-         elsif Flat in Vector_Node then
-            for Child of Vector_Node (Flat).Values loop
+      Flat : constant Tree :=
+               (if This.Is_Empty
+                then This
+                else Tree (This.Constant_Reference.Flatten));
+   begin
+      if not Flat.Is_Empty then
+         if Flat.Constant_Reference in Leaf_Node then
+            Append (Col, Leaf_Node (Flat.Constant_Reference.Element.all)
+                         .Value.Constant_Reference);
+         elsif Flat.Constant_Reference in Vector_Node then
+            for Child of Vector_Node (Flat.Constant_Reference.Element.all)
+                         .Values
+            loop
                Append (Col, Leaf_Node (Child).Value.Constant_Reference);
             end loop;
          else
             raise Program_Error with
               "Flattened nodes must be leaves or vectors";
          end if;
-      end Visit;
-
-   begin
-      if not This.Is_Empty then
-         Visit (This.Constant_Reference);
       end if;
+
       return Col;
    end Enumerate;
 

src/alire/alire-conditional_trees.ads

@@ -61,13 +61,6 @@ package Alire.Conditional_Trees with Preelaborate is
    function Leaf_Count (This : Node) return Positive is abstract;
    --  Return leaves under this node; for non-leaf nodes, obtain recursively.
 
-   function Flatten (This : Node) return Node'Class is abstract;
-   --  with Post'Class => Flatten'Result in Leaf_Node or else
-   --                     Flatten'Result in Vector_Node;
-   --  Above Post kept for reference but gnat bugs out during instantiation.
-   --  Recursively merge all subtree elements in a single value or vector.
-   --  Since it cannot result in an empty tree, it returns a proper node.
-
    procedure Recursive_Traversal
      (This  : in out Node;
       Apply : access procedure (Value : in out Values)) is abstract;
@@ -93,6 +86,14 @@ package Alire.Conditional_Trees with Preelaborate is
    --  used to store conditional/dynamic properties and dependencies.
    --  Iteration is only over direct children, when the tree is AND/OR vector.
 
+   function Flatten (This : Node) return Tree'Class is abstract
+   with Post'Class => Flatten'Result.Is_Empty or else
+                      Flatten'Result.Is_Value or else
+                      Flatten'Result.Is_Vector;
+   --  Above Post kept for reference but gnat bugs out during instantiation.
+   --  Recursively merge all subtree elements in a single value or vector. It
+   --  can result in an empty tree if a vector is empty, so it returns a tree.
+
    function Root (This : Tree) return Node'Class
      with Pre => not This.Is_Empty;
 
@@ -321,7 +322,7 @@ private
                       Unused  : Properties.Vector) return Tree'Class;
 
    overriding
-   function Flatten (This : Leaf_Node) return Node'Class;
+   function Flatten (This : Leaf_Node) return Tree'Class;
 
    overriding
    function Is_Conditional (N : Leaf_Node) return Boolean;
@@ -364,7 +365,7 @@ private
                       return Tree'Class is (New_Leaf (This.Value.Element));
 
    overriding
-   function Flatten (This : Leaf_Node) return Node'Class is (This);
+   function Flatten (This : Leaf_Node) return Tree'Class is (To_Tree (This));
 
    overriding
    function Is_Conditional (N : Leaf_Node) return Boolean is (False);
@@ -399,7 +400,7 @@ private
                       return Tree'Class;
 
    overriding
-   function Flatten (This : Vector_Node) return Node'Class;
+   function Flatten (This : Vector_Node) return Tree'Class;
 
    function Conjunction (This : Vector_Node) return Conjunctions;
 

testsuite/tests/index/empty-dependency-case/test.py

@@ -0,0 +1,21 @@
+"""
+Test that an empty nested table in dependencies does not cause an error.
+Bugfix #906: https://github.com/alire-project/alire/pull/906
+"""
+
+from drivers.alr import run_alr, init_local_crate, alr_manifest
+from drivers.asserts import assert_match
+
+init_local_crate()
+
+# Create the problematic table
+with open(alr_manifest(), "at") as manifest:
+    manifest.write("[[depends-on]]\n")
+    manifest.write("[depends-on.'case(os)'.linux."
+                   "'case(distribution)'.ubuntu]\n")
+
+# The following command failed pre-bugfix, all is OK if it does not complain
+p = run_alr("update")
+
+
+print('SUCCESS')

testsuite/tests/index/empty-dependency-case/test.yaml

@@ -0,0 +1,3 @@
+driver: python-script
+indexes:
+    basic_index: {}