Add limited support for synthetic items

Author: asarium

README.md

@@ -42,6 +42,8 @@ This already supports a wide array of features available in the Natvis system:
   - `ArrayItems` is supported for the simple case (`Size` and `ValuePointer`)
   - `IndexListItems` including `$i` parameters
   - `ExpandedItem`
+  - Limited support for `Synthetic`. Only the display string part is supported since synthetic items are not possible
+  with the current GDB API
 
 ## Known issues
 - The expression parser does not support all syntax elements yet

src/natvis.py

@@ -187,6 +187,13 @@ def __init__(self, condition: str, expression: str):
         self.condition = condition
 
 
+class ExpandSynthetic(ExpandElement):
+
+    def __init__(self, type: 'NatvisType') -> None:
+        super().__init__()
+        self.type = type
+
+
 class NatvisType:
     expand_items: List[ExpandElement]
 
@@ -239,6 +246,10 @@ def _parse_expanded_item(self, element):
         expr = element.text.lstrip().rstrip()
         self.expand_items.append(ExpandExpandedItem(element.get("Condition", None), expr))
 
+    def _parse_synthetic_item(self, element):
+        parsed = NatvisType(element)
+        self.expand_items.append(ExpandSynthetic(parsed))
+
     def _process_expand(self, element):
         for child in element:
             if child.tag == "Item":
@@ -249,6 +260,8 @@ def _process_expand(self, element):
                 self._parse_array_items_element(child)
             elif child.tag == "ExpandedItem":
                 self._parse_expanded_item(child)
+            elif child.tag == "Synthetic":
+                self._parse_synthetic_item(child)
 
     def typename_matches(self, typename: templates.TemplateType, template_args: List[str] = None) -> bool:
         if template_args is None:
@@ -288,6 +301,8 @@ def enumerate_expressions(self) -> Iterator[Tuple[str, bool]]:
                 if expand.condition is not None:
                     yield expand.condition, True
                 yield expand.expression, True
+            elif isinstance(expand, ExpandSynthetic):
+                yield from expand.type.enumerate_expressions()
 
 
 def remove_namespace(doc, namespace):

src/printer.py

@@ -82,8 +82,8 @@ def _get_value(self, expression, convert_func=None, **kwargs: str):
     def display_hint(self):
         return 'string'
 
-    def to_string(self):
-        for string in self.type.display_parsers:
+    def _get_natvis_type_display_string(self, t: natvis.NatvisType):
+        for string in t.display_parsers:
             if self.check_condition(string.condition):
                 display_args = []
                 for code in string.parser.code_parts:
@@ -98,6 +98,9 @@ def to_string(self):
 
         return "No visualizer available"
 
+    def to_string(self):
+        return self._get_natvis_type_display_string(self.type)
+
     def children(self):
         yield "[display string]", gdb.Value(self.to_string()).cast(gdb.lookup_type("char").pointer())
 
@@ -113,6 +116,11 @@ def children(self):
                 yield from self._expand_array_items(item)
             elif isinstance(item, natvis.ExpandExpandedItem):
                 yield from self._expand_expanded_item(item)
+            elif isinstance(item, natvis.ExpandSynthetic):
+                yield from self._expand_synthetic_item(item)
+
+    def _expand_synthetic_item(self, item: natvis.ExpandSynthetic):
+        yield str(item.type.template_type), self._get_natvis_type_display_string(item.type)
 
     def _expand_expanded_item(self, item: natvis.ExpandExpandedItem):
         if self.check_condition(item.condition):