Conditional strings for Whiskers.

docs/contributing.rst

@@ -356,6 +356,11 @@ by as many concatenations of its contents as there were sets of variables suppli
 each time replacing any ``<inner>`` items by their respective value. Top-level variables can also be used
 inside such areas.
 
+There are also conditionals of the form ``<?name>...<!name>...</name>``, where template replacements
+continue recursively either in the first or the second segment depending on the value of the boolean
+parameter ``name``. If ``<?+name>...<!+name>...</+name>`` is used, then the check is whether
+the string parameter ``name`` is non-empty.
+
 .. _documentation-style:
 
 Documentation Style Guide

libsolutil/Whiskers.cpp

@@ -132,7 +132,11 @@ string Whiskers::replace(
 	map<string, vector<StringMap>> const& _listParameters
 )
 {
-	static regex listOrTag("<(" + paramRegex() + ")>|<#(" + paramRegex() + ")>((?:.|\\r|\\n)*?)</\\2>|<\\?(" + paramRegex() + ")>((?:.|\\r|\\n)*?)(<!\\4>((?:.|\\r|\\n)*?))?</\\4>");
+	static regex listOrTag(
+		"<(" + paramRegex() + ")>|"
+		"<#(" + paramRegex() + ")>((?:.|\\r|\\n)*?)</\\2>|"
+		"<\\?(\\+?" + paramRegex() + ")>((?:.|\\r|\\n)*?)(<!\\4>((?:.|\\r|\\n)*?))?</\\4>"
+	);
 	return regex_replace(_template, listOrTag, [&](match_results<string::const_iterator> _match) -> string
 	{
 		string tagName(_match[1]);
@@ -164,12 +168,26 @@ string Whiskers::replace(
 		else
 		{
 			assertThrow(!conditionName.empty(), WhiskersError, "");
-			assertThrow(
+			bool conditionValue = false;
-				_conditions.count(conditionName),
+			if (conditionName[0] == '+')
-				WhiskersError, "Condition parameter " + conditionName + " not set."
+			{
-			);
+				string tag = conditionName.substr(1);
+				assertThrow(
+					_parameters.count(tag),
+					WhiskersError, "Tag " + tag + " used as condition but was not set."
+				);
+				conditionValue = !_parameters.at(tag).empty();
+			}
+			else
+			{
+				assertThrow(
+					_conditions.count(conditionName),
+					WhiskersError, "Condition parameter " + conditionName + " not set."
+				);
+				conditionValue = _conditions.at(conditionName);
+			}
 			return replace(
-				_conditions.at(conditionName) ? _match[5] : _match[7],
+				conditionValue ? _match[5] : _match[7],
 				_parameters,
 				_conditions,
 				_listParameters

libsolutil/Whiskers.h

@@ -59,6 +59,9 @@ DEV_SIMPLE_EXCEPTION(WhiskersError);
  *  - Condition parameter: <?name>...<!name>...</name>, where "<!name>" is optional
  *    replaced (and recursively expanded) by the first part if the condition is true
  *    and by the second (or empty string if missing) if the condition is false
+ *  - Conditional string parameter: <?+name>...<!+name>...</+name>
+ *    Works similar to a conditional parameter where the checked condition is
+ *    that the regular (string) parameter called "name" is non-empty.
  *  - List parameter: <#list>...</list>
  *    The part between the tags is repeated as often as values are provided
  *    in the mapping. Each list element can have its own parameter -> value mapping.

test/libsolutil/Whiskers.cpp

@@ -114,6 +114,19 @@ BOOST_AUTO_TEST_CASE(conditional_plus_list)
 	BOOST_CHECK_EQUAL(m.render(), " - ab - ");
 }
 
+BOOST_AUTO_TEST_CASE(string_as_conditional)
+{
+	string templ = "<?+b>+<b><!+b>-</+b>";
+	BOOST_CHECK_EQUAL(Whiskers(templ)("b", "abc").render(), "+abc");
+	BOOST_CHECK_EQUAL(Whiskers(templ)("b", "").render(), "-");
+}
+
+BOOST_AUTO_TEST_CASE(string_as_conditional_wrong)
+{
+	string templ = "<?+b>+<b></b>";
+	BOOST_CHECK_EQUAL(Whiskers(templ)("b", "abc").render(), "<?+b>+abc</b>");
+}
+
 BOOST_AUTO_TEST_CASE(complicated_replacement)
 {
 	string templ = "a <b> x <complicated> \n <nested>>.";