# HG changeset patch
# User Franz Glasner <f.glasner@feldmann-mg.com>
# Date 1624555613 -7200
# Node ID 2b209bdf6995d570d4d4740ddd5868f347449090
# Parent  efbf7ba40287a7df4456dcb222f40574228d10dc
Implement the "Empty" filter.

This is like the "None" filter but returning an empty string instead of None.

diff -r efbf7ba40287 -r 2b209bdf6995 configmix/config.py
--- a/configmix/config.py	Thu Jun 24 19:23:06 2021 +0200
+++ b/configmix/config.py	Thu Jun 24 19:26:53 2021 +0200
@@ -348,6 +348,9 @@
                 if "None" in filters:
                     varvalue = self._apply_filters(
                         filters, self.getvar_s(varname, default=None))
+                elif "Empty" in filters:
+                    varvalue = self._apply_filters(
+                        filters, self.getvar_s(varname, default=u("")))
                 else:
                     varvalue = self._apply_filters(
                         filters, self.getvar_s(varname))
diff -r efbf7ba40287 -r 2b209bdf6995 configmix/variables.py
--- a/configmix/variables.py	Thu Jun 24 19:23:06 2021 +0200
+++ b/configmix/variables.py	Thu Jun 24 19:26:53 2021 +0200
@@ -255,6 +255,17 @@
     return v
 
 
+@filter("Empty")
+def Empty_filter_impl(config, v):
+    """Identity.
+
+    The `Empty` filter is just a marker to not throw `KeyError` but return
+    the empty string.
+
+    """
+    return v
+
+
 # Register the default namespaces
 add_varns("ENV", _envlookup)
 add_varns("OS", _oslookup)
diff -r efbf7ba40287 -r 2b209bdf6995 tests/test.py
--- a/tests/test.py	Thu Jun 24 19:23:06 2021 +0200
+++ b/tests/test.py	Thu Jun 24 19:26:53 2021 +0200
@@ -417,6 +417,11 @@
         x = cfg.expand_variable("A{{non-existing|None}}Z")
         self.assertEquals("AZ", x)
 
+    def test10_Empty_filtersingle(self):
+        cfg = self._load()
+        x = cfg.expand_variable("{{non-existing|Empty}}")
+        self.assertEquals("", x)
+
 
 class T02LoadAndMerge(_T02MixinLoadAndMerge, unittest.TestCase):