Fix template instantiation reporting

Full template specialization type use requires full information about
its template-argument-dependent fields and nested typedefs. But earlier,
it wasn't reported in many cases when template specialization type isn't
written explicitly in non-fwd-decl context.

iwyu.cc

@@ -1665,6 +1665,10 @@ class IwyuBaseAstVisitor : public BaseAstVisitor<Derived> {
                                                                  comment);
       }
     } else {
+      if (const auto* template_spec_type =
+              dyn_cast<TemplateSpecializationType>(Desugar(type))) {
+        this->getDerived().ReportTplSpecComponentTypes(template_spec_type);
+      }
       if (const NamedDecl* decl = TypeToDeclAsWritten(type)) {
         decl = GetDefinitionAsWritten(decl);
         VERRS(6) << "(For type " << PrintableType(type) << "):\n";
@@ -2670,6 +2674,17 @@ class IwyuBaseAstVisitor : public BaseAstVisitor<Derived> {
     visitor_state_->processed_overload_locs.insert(loc);
   }
 
+  // Report types needed for template instantiation in cases when template
+  // specialization type isn't explicitly written in a source code
+  // in a non-fwd-declarable context (otherwise, they should be reported from
+  // VisitTemplateSpecializationType), e.g.:
+  // template <class T> struct S { T t; };
+  // void fn(const S<Class>& s) { // Forward declarations are sufficient here.
+  //   (void)s.t; // Full 'Class' type is needed due to template instantiation.
+  // }
+  void ReportTplSpecComponentTypes(const TemplateSpecializationType*) {
+  }
+
   // Do not add any variables here!  If you do, they will not be shared
   // between the normal iwyu ast visitor and the
   // template-instantiation visitor, which is almost always a mistake.
@@ -4197,6 +4212,16 @@ class IwyuAstConsumer
     return true;
   }
 
+  // --- Handler declared in IwyuBaseASTVisitor.
+
+  void ReportTplSpecComponentTypes(const TemplateSpecializationType* type) {
+    const map<const Type*, const Type*> resugar_map =
+        GetTplTypeResugarMapForClass(type);
+    ASTNode node(type);
+    node.SetParent(current_ast_node());
+    instantiated_template_visitor_.ScanInstantiatedType(&node, resugar_map);
+  }
+
  private:
   // Class we call to handle instantiated template functions and classes.
   InstantiatedTemplateVisitor instantiated_template_visitor_;

tests/cxx/badinc.cc

@@ -1565,17 +1565,17 @@ int main() {
   // IWYU: i1_ns::I1_NamespaceClass is...*badinc-i1.h
   I1_Class* i1_class_tpl_ctor = new I1_Class(&i1_namespace_class, 1);
 
-  // TODO(csilvers): IWYU: I2_Class needs a declaration
+  // IWYU: I2_Class is...*badinc-i2.h
   // IWYU: I2_Class::~I2_Class is...*badinc-i2-inl.h
   // IWYU: I1_Struct is...*badinc-i1.h
   // IWYU: I1_TemplateClass is...*badinc-i1.h
   delete newed_i1_template_class;
-  // TODO(csilvers): IWYU: I2_Class needs a declaration
+  // IWYU: I2_Class is...*badinc-i2.h
   // IWYU: I2_Class::~I2_Class is...*badinc-i2-inl.h
   // IWYU: I1_Struct is...*badinc-i1.h
   // IWYU: I1_TemplateClass is...*badinc-i1.h
   delete[] newed_i1_template_class_array;
-  // TODO(csilvers): IWYU: I2_Class needs a declaration
+  // IWYU: I2_Class is...*badinc-i2.h
   // IWYU: I2_Class::~I2_Class is...*badinc-i2-inl.h
   // IWYU: I1_Struct is...*badinc-i1.h
   // IWYU: I1_TemplateClass is...*badinc-i1.h

tests/cxx/placement_new.cc

@@ -90,6 +90,7 @@ void PlacementNewOfTemplate() {
 
   // Make sure we handle it right when we explicitly call the dtor, as well.
   // IWYU: ClassTemplate is...*placement_new-i1.h
+  // IWYU: IndirectClass is...*indirect.h
   placement_newed_template->~ClassTemplate();
 }