TopoSorter: Only allow certain params to be incomplete

For the containers which are allowed to be declared with incomplete
types, it is only the contained types which are allowed to be
incomplete. Other template parameters (e.g. allocators) must always be
defined before use.

oi/type_graph/TopoSorter.cpp

@@ -85,33 +85,31 @@ namespace {
  * Other containers are not required to do this, but might still have this
  * behaviour.
  */
-bool containerAllowsIncompleteParams(const Container& c) {
+bool containerAllowsIncompleteParam(const Container& c, size_t i) {
   switch (c.containerInfo_.ctype) {
     case SEQ_TYPE:
     case LIST_TYPE:
     case UNIQ_PTR_TYPE:
     case SHRD_PTR_TYPE:
       // Also std::forward_list, if we ever support that
       // Would be good to have this as an option in the TOML files
-      return true;
+      return i == 0;
     default:
       return false;
   }
 }
 }  // namespace
 
 void TopoSorter::visit(Container& c) {
-  if (!containerAllowsIncompleteParams(c)) {
-    for (const auto& param : c.templateParams) {
+  for (size_t i = 0; i < c.templateParams.size(); i++) {
+    const auto& param = c.templateParams[i];
+    if (containerAllowsIncompleteParam(c, i)) {
+      acceptAfter(param.type());
+    } else {
       accept(param.type());
     }
   }
   sortedTypes_.push_back(c);
-  if (containerAllowsIncompleteParams(c)) {
-    for (const auto& param : c.templateParams) {
-      acceptAfter(param.type());
-    }
-  }
 }
 
 void TopoSorter::visit(Enum& e) {

test/test_topo_sorter.cpp

@@ -178,24 +178,30 @@ std::map
 }
 
 TEST(TopoSorterTest, ContainersVector) {
-  // std::vector allows forward declared template parameters
+  // std::vector allows a forward declared type
   auto myparam = Class{1, Class::Kind::Struct, "MyParam", 13};
+  auto myalloc = Class{1, Class::Kind::Struct, "MyAlloc", 0};
   auto mycontainer = getVector();
   mycontainer.templateParams.push_back((myparam));
+  mycontainer.templateParams.push_back((myalloc));
 
   test({mycontainer}, R"(
+MyAlloc
 std::vector
 MyParam
 )");
 }
 
 TEST(TopoSorterTest, ContainersList) {
-  // std::list allows forward declared template parameters
+  // std::list allows a forward declared type
   auto myparam = Class{1, Class::Kind::Struct, "MyParam", 13};
+  auto myalloc = Class{1, Class::Kind::Struct, "MyAlloc", 0};
   auto mycontainer = getList();
   mycontainer.templateParams.push_back((myparam));
+  mycontainer.templateParams.push_back((myalloc));
 
   test({mycontainer}, R"(
+MyAlloc
 std::list
 MyParam
 )");