Add default & alternate filters.

Add corresponding regression test and documentation.

Author: TurboGit

docs/tags.rst

@@ -291,6 +291,12 @@ parser.
   Add a parameter into an URL. This routine adds the '?' and '&'
   character if needed. *VALUE* can be a tag variable name.
 
+**ALTERNATE(VALUE)**
+  .. index:: Filter, ALTERNATE
+
+  Returns VALUE if the current value is not the empty string otherwise the
+  current value is returned (that is, the empty string is returned).
+
 **BR_2_EOL(EOL)**
   .. index:: Filter, BR_2_EOL
 
@@ -326,6 +332,12 @@ parser.
 
   Converts any suite of spaces by a single space character.
 
+**DEFAULT(VALUE)**
+  .. index:: Filter, DEFAULT
+
+  Returns VALUE if the current value is the empty string otherwise the
+  current value is returned.
+
 **DEL_PARAM(NAME)**
   .. index:: Filter, DEL_PARAM
 

regtests/tests/0141_default_alternate/test.out

@@ -0,0 +1,6 @@
+
+DEF
+A
+
+
+ALT

regtests/tests/0141_default_alternate/test.py

@@ -0,0 +1,3 @@
+from test_support import *
+
+run('testme', ["testme141.tmplt"])

regtests/tests/0141_default_alternate/test.yaml

@@ -0,0 +1,6 @@
+
+@_DEFAULT(DEF):VAR4_@
+@_DEFAULT(DEF):VAR6_@
+
+@_ALTERNATE(ALT):VAR4_@
+@_ALTERNATE(ALT):VAR6_@

regtests/tests/0141_default_alternate/testme141.tmplt

@@ -1,7 +1,7 @@
 ------------------------------------------------------------------------------
 --                             Templates Parser                             --
 --                                                                          --
---                     Copyright (C) 2003-2018, AdaCore                     --
+--                     Copyright (C) 2003-2022, AdaCore                     --
 --                                                                          --
 --  This library is free software;  you can redistribute it and/or modify   --
 --  it under terms of the  GNU General Public License  as published by the  --
@@ -103,6 +103,8 @@ package body Filter is
    Web_NBSP_Token      : aliased constant String := "WEB_NBSP";
    Wrap_Token          : aliased constant String := "WRAP";
    Yes_No_Token        : aliased constant String := "YES_NO";
+   Default_Token       : aliased constant String := "DEFAULT";
+   Alternate_Token     : aliased constant String := "ALTERNATE";
 
    --  Filters Table
 
@@ -128,6 +130,9 @@ package body Filter is
          Add_Param      =>
            (Add_Param_Token'Access,      Add_Param'Access),
 
+         Alternate      =>
+           (Alternate_Token'Access,      Alternate'Access),
+
          BR_2_EOL       =>
            (BR_2_EOL_Token'Access,       BR_2_EOL'Access),
 
@@ -146,6 +151,9 @@ package body Filter is
          Contract       =>
            (Contract_Token'Access,       Contract'Access),
 
+         Default        =>
+           (Default_Token'Access,        Default'Access),
+
          Del_Param      =>
            (Del_Param_Token'Access,      Del_Param'Access),
 
@@ -343,6 +351,28 @@ package body Filter is
       end if;
    end Add_Param;
 
+   ---------------
+   -- Alternate --
+   ---------------
+
+   function Alternate
+     (S : String;
+      C : not null access Filter_Context;
+      P : Parameter_Data := No_Parameter) return String
+   is
+      pragma Unreferenced (C);
+   begin
+      if P = No_Parameter then
+         raise Template_Error with "missing parameter for ALTERNATE filter";
+      end if;
+
+      if S = "" then
+         return "";
+      else
+         return To_String (P.S);
+      end if;
+   end Alternate;
+
    --------------
    -- BR_2_EOL --
    --------------
@@ -570,6 +600,28 @@ package body Filter is
       end if;
    end Contract;
 
+   -------------
+   -- Default --
+   -------------
+
+   function Default
+     (S : String;
+      C : not null access Filter_Context;
+      P : Parameter_Data := No_Parameter) return String
+   is
+      pragma Unreferenced (C);
+   begin
+      if P = No_Parameter then
+         raise Template_Error with "missing parameter for DEFAULT filter";
+      end if;
+
+      if S = "" then
+         return To_String (P.S);
+      else
+         return S;
+      end if;
+   end Default;
+
    ---------------
    -- Del_Param --
    ---------------

src/templates_parser-filter.adb

@@ -130,6 +130,9 @@ package body Templates_Parser is
          --  Add an HTTP parameter to the string, add the '&' parameter
          --  separator if needed.
 
+         Alternate,
+         --  Returns parameter if value is not null
+
          BR_2_EOL,
          --  Replaces all <BR> HTML tags by a given end-of-line sequence
 
@@ -148,6 +151,9 @@ package body Templates_Parser is
          Contract,
          --  Replaces a suite of spaces by a single space character
 
+         Default,
+         --  Returns parameter if value is empty
+
          Del_Param,
          --  Delete an HTTP parameter from the string, removes the '&'
          --  Parameter separator if needed.
@@ -394,6 +400,11 @@ package body Templates_Parser is
          C : not null access Filter_Context;
          P : Parameter_Data := No_Parameter) return String;
 
+      function Alternate
+        (S : String;
+         C : not null access Filter_Context;
+         P : Parameter_Data := No_Parameter) return String;
+
       function BR_2_EOL
         (S : String;
          C : not null access Filter_Context;
@@ -424,6 +435,11 @@ package body Templates_Parser is
          C : not null access Filter_Context;
          P : Parameter_Data := No_Parameter) return String;
 
+      function Default
+        (S : String;
+         C : not null access Filter_Context;
+         P : Parameter_Data := No_Parameter) return String;
+
       function Del_Param
         (S : String;
          C : not null access Filter_Context;