[Pather] fix using trees when append=True

masque/builder/pather.py

@@ -16,7 +16,7 @@ from numpy import pi
 from numpy.typing import ArrayLike
 
 from ..pattern import Pattern
-from ..library import ILibrary, TreeView
+from ..library import ILibrary, TreeView, SINGLE_USE_PREFIX
 from ..error import BuildError, PortError
 from ..ports import PortList, Port
 from ..abstract import Abstract
@@ -1067,9 +1067,24 @@ class Pather(PortList):
             tool_port_names = ('A', 'B')
             pat = Pattern()
 
+            def validate_tree(portspec: str, batch: list[RenderStep], tree: ILibrary) -> None:
+                missing = sorted(
+                    name
+                    for name in tree.dangling_refs(tree.top())
+                    if isinstance(name, str) and name.startswith(SINGLE_USE_PREFIX)
+                    )
+                if not missing:
+                    return
+
+                tool_name = type(batch[0].tool).__name__
+                raise BuildError(
+                    f'Tool {tool_name}.render() returned missing single-use refs for {portspec}: {missing}'
+                    )
+
             def render_batch(portspec: str, batch: list[RenderStep], append: bool) -> None:
                 assert batch[0].tool is not None
                 tree = batch[0].tool.render(batch, port_names=tool_port_names)
+                validate_tree(portspec, batch, tree)
                 name = self.library << tree
                 if portspec in pat.ports:
                     del pat.ports[portspec]

masque/builder/tools.py

@@ -451,7 +451,9 @@ class Tool:
             else:
                 continue
 
-            pat.plug(seg_tree.top_pattern(), {port_names[1]: port_names[0]}, append=True)
+            seg_name = lib << seg_tree
+            pat.plug(lib[seg_name], {port_names[1]: port_names[0]}, append=True)
+            del lib[seg_name]
 
         return lib