pan: support default/fallback value for built-in function value()

panc-docs/source/standard-functions/standard-functions.rst

@@ -1870,15 +1870,28 @@ Synopsis
 --------
 
 element **value** (string *path*)
+element **value** (string *path*, element *default*)
 
 Description
 -----------
 
 This function returns the element identified by the given path, which
-can be an external path. An error occurs if there is no such element.
+can be an external path. An error occurs if there is no such element
+and no (optional) default is provided.
+If a `default` element is defined as second argument,
+and either there is no element for the given path or
+the (current) element of the given path is `undef`,
+the default element is returned.
 
 ::
 
     # /y will be 200
     '/x' = 100;
     '/y' = 2 * value('/x');
+
+    # /z will be (the default) 10
+    '/z' = value('/nopath', 10);
+
+    # /v will be (the default) 5
+    '/u' = undef;
+    '/v' = value('/u', 5);

panc/src/main/java/org/quattor/pan/dml/functions/Value.java

@@ -20,11 +20,12 @@ Centre National de la Recherche Scientifique (CNRS).
 
 package org.quattor.pan.dml.functions;
 
-import static org.quattor.pan.utils.MessageUtils.MSG_ONE_STRING_ARG_REQ;
+import static org.quattor.pan.utils.MessageUtils.MSG_ONE_OR_TWO_ARGS_REQ;
 
 import org.quattor.pan.dml.Operation;
 import org.quattor.pan.dml.data.Element;
 import org.quattor.pan.dml.data.StringProperty;
+import org.quattor.pan.dml.data.Undef;
 import org.quattor.pan.exceptions.EvaluationException;
 import org.quattor.pan.exceptions.SyntaxException;
 import org.quattor.pan.template.Context;
@@ -33,9 +34,9 @@ Centre National de la Recherche Scientifique (CNRS).
 
 /**
  * Extract a value from the configuration tree based on a given path.
- * 
+ *
  * @author loomis
- * 
+ *
  */
 final public class Value extends BuiltInFunction {
 
@@ -47,51 +48,61 @@ private Value(SourceRange sourceRange, Operation... operations)
 	public static Operation getInstance(SourceRange sourceRange,
 			Operation... operations) throws SyntaxException {
 
-		// Ensure that there is exactly one argument. Since the parser does
-		// little argument checking for function calls, this explicit check is
-		// needed.
-		if (operations.length != 1) {
-			throw SyntaxException.create(sourceRange, MSG_ONE_STRING_ARG_REQ,
+		// This must have either one or two arguments.
+		if (operations.length < 1 || operations.length > 2) {
+			throw SyntaxException.create(sourceRange, MSG_ONE_OR_TWO_ARGS_REQ,
 					"value");
 		}
+		assert (operations.length == 1 || operations.length == 2);
 
 		return new Value(sourceRange, operations);
 	}
 
 	@Override
 	public Element execute(Context context) {
 
-		assert (ops.length == 1);
+		// Retrieve the values of the arguments.
+		Element[] args = calculateArgs(context);
+
+		assert (ops.length == 1 || ops.length == 2);
 
 		throwExceptionIfCompileTimeContext(context);
 
 		Element result = null;
 		Path p = null;
 		try {
-			String s = ((StringProperty) ops[0].execute(context)).getValue();
+			String s = ((StringProperty) args[0]).getValue();
 			try {
 				p = new Path(s);
-				result = context.getElement(p);
+                // errorIfNotFound=false; missing path is handled w optional default below
+				result = context.getElement(p, false);
 			} catch (SyntaxException se) {
 				throw new EvaluationException(se.getSimpleMessage(),
 						sourceRange, context);
 			}
 		} catch (ClassCastException cce) {
-			Element element = ops[0].execute(context);
 			throw new EvaluationException(
 					"value() requires one string argument; "
-							+ element.getTypeAsString() + " found",
+							+ args[0].getTypeAsString() + " found",
 					getSourceRange(), context);
 		}
 
+
+        if (result == null) {
+            if (ops.length == 2) {
+                // 2nd arg is default value
+                result = args[1];
+            } else {
+                throw new EvaluationException("referenced path (" + p
+                                              + ") doesn't exist", getSourceRange(), context);
+            }
+        } else if (result instanceof Undef && ops.length == 2) {
+            result = args[1];
+        }
+
 		// Return the result. ALWAYS duplicate the value to ensure that any
 		// changes to returned resources do not inadvertently change the
 		// referenced part of the configuration.
-		if (result != null) {
-			return result.duplicate();
-		} else {
-			throw new EvaluationException("referenced path (" + p
-					+ ") doesn't exist", getSourceRange(), context);
-		}
+        return result.duplicate();
 	}
 }

panc/src/test/pan/Functionality/value/value2.pan

@@ -0,0 +1,10 @@
+# @expect="/nlist[@name="profile"]/long[@name="a"]=0 and /nlist[@name="profile"]/long[@name="value"]=0 and /nlist[@name="profile"]/long[@name="default"]=1"
+# @format=pan
+#
+object template value2;
+
+variable SOMETHING = dict("key", "abc");
+
+"/a" = 0;
+"/value" = value("/a", 1);
+"/default" = value("/nopath", 1);

panc/src/test/pan/Functionality/value/value3.pan

@@ -0,0 +1,7 @@
+# @expect="/nlist[@name='profile']/boolean[@name='undef']='true' and /nlist[@name='profile']/boolean[@name='null']='true'"
+# @format=pan
+#
+object template value3;
+
+"/undef" = !is_defined(value("/nopath", undef));
+"/null" = is_null(value("/nopath", null));

panc/src/test/pan/Functionality/value/value4.pan

@@ -0,0 +1,16 @@
+# @expect="/nlist[@name='profile']/nlist[@name='var']/string[@name='key']='abc' and /nlist[@name='profile']/nlist[@name='othervar']/string[@name='key']='xyz' and /nlist[@name='profile']/nlist[@name='origvar']/string[@name='key']='abc'"
+# @format=pan
+#
+object template value4;
+
+variable SOMETHING = dict("key", "abc");
+
+"/var" = value("/nopath", SOMETHING);
+# test copy of variable
+"/othervar" = {
+    t = value("/nopath", SOMETHING);
+    # modify the value, should not modify the original variable
+    t['key'] = 'xyz';
+    t;
+};
+"/origvar" = SOMETHING;

panc/src/test/pan/Functionality/value/value5.pan

@@ -0,0 +1,7 @@
+# @expect="/nlist[@name='profile']/string[@name='self']='myself'"
+# @format=pan
+#
+object template value5;
+
+"/self" = "myself";
+"/self" = value("/nopath", SELF);

panc/src/test/pan/Functionality/value/value6.pan

@@ -0,0 +1,5 @@
+# @expect=org.quattor.pan.exceptions.EvaluationException
+object template value6;
+
+# reraise Syntax error as Evaluation error
+"/a" = value(list(1));

panc/src/test/pan/Functionality/value/value7.pan

@@ -0,0 +1,4 @@
+# @expect=org.quattor.pan.exceptions.EvaluationException
+object template value7;
+
+"/a" = value("/nopath");

panc/src/test/pan/Functionality/value/value8.pan

@@ -0,0 +1,4 @@
+# @expect=org.quattor.pan.exceptions.EvaluationException
+object template value8;
+
+"/a" = value("/nopath", garbage);

panc/src/test/pan/Functionality/value/value9.pan

@@ -0,0 +1,9 @@
+# @expect="/nlist[@name="profile"]/long[@name="undef"]=0 and /nlist[@name="profile"]/long[@name="value"]=5"
+# @format=pan
+#
+object template value9;
+
+bind "/undef" = long = 0;
+
+"/undef" = undef;
+"/value" = value("/undef", 5);