Ensure template classes are instantiated in correct order

- If it depends on a base class, the base needs to be initialized first
- Not all template classes exist in the header (in particular, CRTP) so
  anything not found in the current header gets initialized first

Author: virtuald

robotpy_build/autowrap/cxxparser.py

@@ -1987,19 +1987,29 @@ def parse_header(
         if doc_add:
             doc_add = f"\n{doc_add}"
 
-        hctx.template_instances.append(
-            TemplateInstanceContext(
-                scope_var=visitor._get_module_var(tmpl_data),
-                var_name=f"tmplCls{i}",
-                py_name=k,
-                full_cpp_name_identifier=qualname,
-                binder_typename=f"bind_{qualname}_{i}",
-                params=tmpl_data.params,
-                header_name=f"{qualname}.hpp",
-                doc_set=visitor._quote_doc(tmpl_data.doc),
-                doc_add=visitor._quote_doc(doc_add),
-            )
+        tctx = TemplateInstanceContext(
+            scope_var=visitor._get_module_var(tmpl_data),
+            var_name=f"tmplCls{i}",
+            py_name=k,
+            full_cpp_name_identifier=qualname,
+            binder_typename=f"bind_{qualname}_{i}",
+            params=tmpl_data.params,
+            header_name=f"{qualname}.hpp",
+            doc_set=visitor._quote_doc(tmpl_data.doc),
+            doc_add=visitor._quote_doc(doc_add),
         )
+        hctx.template_instances.append(tctx)
+
+        # Ensure that template instances are created in class order if the
+        # template class is in this header file
+        # - not matching here is not an error
+        qualname_match = tmpl_data.qualname.lstrip(":")
+        for cctx in hctx.classes:
+            if cctx.dep_cpp_name.lstrip(":") == qualname_match:
+                assert cctx.template
+                tctx.matched = True
+                cctx.template.instances.append(tctx)
+                break
 
         for param in tmpl_data.params:
             visitor._add_user_type_caster(param)

robotpy_build/autowrap/header.cpp.j2

@@ -64,13 +64,19 @@ struct rpybuild_{{ hname }}_initializer {
 {% endfor %}
 
 {# template decls #}
-{% for tmpl_data in template_instances %}
+{% for tmpl_data in template_instances if not tmpl_data.matched %}
   rpygen::{{ tmpl_data.binder_typename }} {{ tmpl_data.var_name }};
 {% endfor %}
 
 {# class decls #}
-{%- for cls in classes if not cls.template %}
-  {{ pybind11.cls_decl(cls) }}
+{%- for cls in classes %}
+  {% if not cls.template -%}
+    {{ pybind11.cls_decl(cls) }}
+  {%- else -%}
+    {%- for tmpl_data in cls.template.instances %}
+      rpygen::{{ tmpl_data.binder_typename }} {{ tmpl_data.var_name }};
+    {% endfor -%}
+  {%- endif -%}
 {% endfor %}
 
   py::module &m;
@@ -86,12 +92,18 @@ struct rpybuild_{{ hname }}_initializer {
     enum{{ loop.index }}{{ pybind11.enum_init(enum.scope_var, enum) }},
   {% endfor %}
 
-  {% for tmpl_data in template_instances %}
+  {% for tmpl_data in template_instances if not tmpl_data.matched %}
     {{ tmpl_data.var_name }}({{ tmpl_data.scope_var }}, "{{ tmpl_data.py_name }}"),
   {% endfor %}
 
-  {% for cls in classes if not cls.template %}
-    {{ pybind11.cls_init(cls, '"' + cls.py_name + '"') }}
+  {% for cls in classes %}
+    {% if not cls.template -%}
+      {{ pybind11.cls_init(cls, '"' + cls.py_name + '"') }}
+    {%- else -%}
+      {%- for tmpl_data in cls.template.instances %}
+        {{ tmpl_data.var_name }}({{ tmpl_data.scope_var }}, "{{ tmpl_data.py_name }}"),
+      {% endfor -%}
+    {%- endif %}
   {% endfor %}
 
     m(m)

robotpy_build/autowrap/j2_context.py

@@ -353,6 +353,9 @@ class ClassTemplateData:
     #: the specified C++ code is inserted into the template definition
     inline_code: str
 
+    #: Instances of this class
+    instances: typing.List["TemplateInstanceContext"] = field(default_factory=list)
+
 
 @dataclass
 class ClassContext:
@@ -493,6 +496,9 @@ class TemplateInstanceContext:
     doc_set: Documentation
     doc_add: Documentation
 
+    #: If true, instantiated in class order
+    matched: bool = False
+
 
 @dataclass
 class HeaderContext:

tests/cpp/gen/ft/tdependent_base.yml

@@ -0,0 +1,11 @@
+classes:
+  TDBase:
+  TDChild:
+    template_params:
+    - T
+
+templates:
+  TDChild:
+    qualname: TDChild
+    params:
+    - int

tests/cpp/pyproject.toml.tmpl

@@ -101,6 +101,7 @@ generate = [
     {tvchild = "templates/tvchild.h"},
 
     {tbasic = "templates/basic.h"},
+    {tdependent_base = "templates/dependent_base.h"},
     {tdependent_param = "templates/dependent_param.h"},
     {tdependent_using = "templates/dependent_using.h"},
     {tdependent_using2 = "templates/dependent_using2.h"},

tests/cpp/rpytest/ft/include/templates/dependent_base.h

@@ -0,0 +1,10 @@
+#pragma once
+
+// Template class that has a non-template base class in the same file
+
+struct TDBase  {
+    virtual ~TDBase() {}
+};
+
+template <typename T>
+struct TDChild : TDBase {};