Add xml.Node.__repr__()

The repr of an xml.Node only includes arguments where the value differs
from the default.

Do not print positional arg name in repr(xml.Node)

"tag" is a non-optional positional argument, it makes for cleaner repr()
output if we also omit the name.

Author: mzagozen

base/src/xml.act

@@ -23,6 +23,28 @@ n.text and c.tail for all children of n.
     def encode(self) -> str:
         NotImplemented
 
+    def __repr__(self):
+        # Building the arguments to xml.Node() and skip arguments where the
+        # current value equals the default. We do this with appending to a
+        # string because that does not leak the *mut* effect, unlike appending
+        # to a list.
+        args = repr(self.tag)
+        if len(self.nsdefs) != 0:
+            args += f", nsdefs={repr(self.nsdefs)}"
+        if self.prefix is not None:
+            args += f", prefix={repr(self.prefix)}"
+        if len(self.attributes) != 0:
+            args += f", attributes={repr(self.attributes)}"
+        if len(self.children) != 0:
+            args += f", children={repr(self.children)}"
+        if self.text is not None:
+            args += f", text={repr(self.text)}"
+        if self.tail is not None:
+            args += f", tail={repr(self.tail)}"
+
+        return "xml.Node({args})"
+
+
 class XmlParseError(ValueError):
     """Exception raised for XML parsing errors
 

test/stdlib_tests/src/test_xml.act

@@ -178,3 +178,8 @@ def _test_xml_namespace_attributes_undefined():
     testing.assertEqual(child_attr.1, 'child', "Undefined namespace: child attribute value not preserved")
     e = xml.encode(d)
     testing.assertEqual(e, test_xml, "Undefined namespace: roundtrip failed")
+
+def _test_xml_repr():
+    test_xml = """<data xmlns="http://default"><a xmlns:ns="http://foo" ns:operation="remove"><ns:b ns:type="element">text</ns:b></a></data>"""
+    d = xml.decode(test_xml)
+    testing.assertEqual(repr(d), "xml.Node('data', nsdefs=[(None, 'http://default')], children=[xml.Node('a', nsdefs=[('ns', 'http://foo')], attributes=[('ns:operation', 'remove')], children=[xml.Node('b', prefix='ns', attributes=[('ns:type', 'element')], text='text')])])")