Merge branch 'topic/vadim/delete' into 'main'

Fix delete of slice from an empty string

Closes #5

See merge request eng/shared/vss-text!7

Author: godunko

source/text/implementation/vss-implementation-utf8_strings.adb

@@ -108,7 +108,17 @@ package body VSS.Implementation.UTF8_Strings is
       Success       : Boolean with Unreferenced;
 
    begin
-      if From.Index > To.Index then
+      if Text.Size = 0 then
+         --  An empty string, all components of `Size` are zeros.
+
+         pragma Assert (From.UTF8_Offset = -1);
+         pragma Assert (To.UTF8_Offset = -1);
+         --  The only possible position of the cursors is before the first
+         --  charater.
+
+         Size := (0, 0, 0);
+
+      elsif From.Index > To.Index then
          Size := (0, 0, 0);
 
       else

testsuite/text/test_string-test_delete.adb

@@ -74,4 +74,25 @@ begin
       Test_Support.Assert (SB = "      Ada_With_Private_Absent,");
       Test_Support.Assert (S = "      ,");
    end;
+
+   --  vss-text#5
+   --
+   --  Check that `Delete` of the slice from last character to last character
+   --  in the null and an empty string doesn't raise exception.
+
+   declare
+      SN : VSS.Strings.Virtual_String;
+      SE : VSS.Strings.Virtual_String := "";
+
+   begin
+      SN.Delete (SN.At_Last_Character, SN.At_Last_Character);
+      Test_Support.Assert (SN.Is_Null);
+      Test_Support.Assert (SN.Is_Empty);
+      Test_Support.Assert (SN = SN);
+
+      SE.Delete (SE.At_Last_Character, SE.At_Last_Character);
+      Test_Support.Assert (not SE.Is_Null);
+      Test_Support.Assert (SE.Is_Empty);
+      Test_Support.Assert (SE = SE);
+   end;
 end Test_Delete;