[clang compat] Fix alias template handling

llvm/llvm-project@7f78f99 removed
SubstTemplateTypeParmType nodes from an instantiated alias template
type. GetProvidedTypes function relied on them to filter out substituted
argument types. Now, it is done "manually" inside the added
GetAliasTemplateProvidedTypes function, as discussed
in llvm/llvm-project#101858.

When traversing instantiated type alias internals, bare RecordType nodes
appear now instead of ones wrapped in SubstTemplateTypeParmType, hence
the new visiting method added into InstantiatedTemplateVisitor. (Enum
types are not expected to need handling there, hence VisitRecordType
instead of VisitTagType.)

A test case added to cover the change inside GetProvidedTypes function
(i.e. correct handling of intermediate alias templates in a chain).

iwyu.cc

@@ -230,6 +230,7 @@ using clang::Preprocessor;
 using clang::QualType;
 using clang::QualifiedTypeLoc;
 using clang::RecordDecl;
+using clang::RecordType;
 using clang::RecursiveASTVisitor;
 using clang::ReferenceType;
 using clang::Sema;
@@ -2602,10 +2603,9 @@ class IwyuBaseAstVisitor : public BaseAstVisitor<Derived> {
               dyn_cast<TemplateSpecializationType>(component)) {
         const NamedDecl* decl = TypeToDeclAsWritten(tpl_spec_type);
         if (const auto* al_tpl_decl = dyn_cast<TypeAliasTemplateDecl>(decl)) {
-          const TypeAliasDecl* al_decl = al_tpl_decl->getTemplatedDecl();
-          InsertAllInto(GetProvidedTypes(tpl_spec_type->desugar().getTypePtr(),
-                                         GetLocation(al_decl)),
-                        &retval);
+          InsertAllInto(
+              GetAliasTemplateProvidedTypes(tpl_spec_type, al_tpl_decl),
+              &retval);
           continue;
         }
       }
@@ -2653,6 +2653,16 @@ class IwyuBaseAstVisitor : public BaseAstVisitor<Derived> {
   bool SourceOrTargetTypeIsProvided(const ASTNode* construct_expr_node) const =
       delete;
 
+  set<const Type*> GetAliasTemplateProvidedTypes(
+      const TemplateSpecializationType* type,
+      const TypeAliasTemplateDecl* al_tpl_decl) const {
+    const TypeAliasDecl* al_decl = al_tpl_decl->getTemplatedDecl();
+    set<const Type*> res = GetProvidedTypes(type->getAliasedType().getTypePtr(),
+                                            GetLocation(al_decl));
+    RemoveAllFrom(GetCanonicalArgComponents(type), &res);
+    return res;
+  }
+
   void ReportTypeUseInternal(SourceLocation used_loc, const Type* type,
                              set<const Type*> blocked_types,
                              DerefKind deref_kind) {
@@ -2729,10 +2739,10 @@ class IwyuBaseAstVisitor : public BaseAstVisitor<Derived> {
       if (template_spec_type->isTypeAlias()) {
         const NamedDecl* decl = TypeToDeclAsWritten(template_spec_type);
         if (const auto* al_tpl_decl = dyn_cast<TypeAliasTemplateDecl>(decl)) {
-          const TypeAliasDecl* al_decl = al_tpl_decl->getTemplatedDecl();
+          InsertAllInto(
+              GetAliasTemplateProvidedTypes(template_spec_type, al_tpl_decl),
+              &blocked_types);
           const Type* type = template_spec_type->getAliasedType().getTypePtr();
-          InsertAllInto(GetProvidedTypes(type, GetLocation(al_decl)),
-                        &blocked_types);
           ReportTypeUseInternal(used_loc, type, blocked_types, deref_kind);
         }
         return;
@@ -3262,6 +3272,22 @@ class InstantiatedTemplateVisitor
     return Base::VisitSubstTemplateTypeParmType(type);
   }
 
+  bool VisitRecordType(RecordType* type) {
+    if (CanIgnoreCurrentASTNode())
+      return true;
+
+    // CanForwardDeclareType function relies on the specific placement of
+    // the type node in the AST. An intermediate SubstTemplateTypeParmType could
+    // break that logic. However, such cases don't even need to be considered
+    // here, because they are handled in VisitSubstTemplateTypeParmType. But
+    // maybe using AncestorIsA, or replacing VisitSubst...Type with
+    // TraverseSubst...Type and Traverse...TypeLoc would be more reliable.
+    if (!current_ast_node()->ParentIsA<SubstTemplateTypeParmType>())
+      AnalyzeTemplateTypeParmUse(type);
+
+    return Base::VisitRecordType(type);
+  }
+
   bool VisitTemplateSpecializationType(TemplateSpecializationType* type) {
     if (CanIgnoreCurrentASTNode())
       return true;

iwyu_ast_util.cc

@@ -148,6 +148,7 @@ using llvm::errs;
 using llvm::isa;
 using llvm::raw_string_ostream;
 using std::function;
+using std::vector;
 
 namespace include_what_you_use {
 
@@ -1617,6 +1618,17 @@ bool CanBeOpaqueDeclared(const EnumType* type) {
   return type->getDecl()->isFixed();
 }
 
+vector<const Type*> GetCanonicalArgComponents(
+    const TemplateSpecializationType* type) {
+  vector<const Type*> res;
+  SugaredTypeEnumerator enumerator;
+  for (const TemplateArgument& arg : type->template_arguments()) {
+    for (const Type* component : enumerator.Enumerate(arg))
+      res.push_back(GetCanonicalType(component));
+  }
+  return res;
+}
+
 // --- Utilities for Stmt.
 
 bool IsAddressOf(const Expr* expr) {

iwyu_ast_util.h

@@ -16,6 +16,7 @@
 #include <map>                          // for map
 #include <set>                          // for set
 #include <string>                       // for string
+#include <vector>                       // for vector
 
 #include "clang/AST/NestedNameSpecifier.h"
 #include "clang/AST/TemplateBase.h"
@@ -46,6 +47,7 @@ class Stmt;
 class TagDecl;
 class TemplateDecl;
 class TemplateName;
+class TemplateSpecializationType;
 class TranslationUnitDecl;
 class TypeDecl;
 class ValueDecl;
@@ -858,6 +860,11 @@ TemplateInstantiationData GetTplInstDataForClassNoComponentTypes(
 // according to the standard.
 bool CanBeOpaqueDeclared(const clang::EnumType* type);
 
+// Collects template argument type components and returns them desugared.
+// The result may contain duplicates.
+std::vector<const clang::Type*> GetCanonicalArgComponents(
+    const clang::TemplateSpecializationType*);
+
 // --- Utilities for Stmt.
 
 // Returns true if the given expr is '&<something>'.

tests/cxx/typedef_chain_in_template-d5.h

@@ -28,3 +28,8 @@ struct Tpl {
 
 using TplWithNonProvidedAliased1 = Tpl<NonProvidingAlias>;
 using TplWithNonProvidedAliased2 = Tpl<NonProvidingAliasTpl<1>>;
+
+class TypedefChainClass;
+
+template <int>
+using NonProvidingAliasByOther = IdentityAlias2<TypedefChainClass>;

tests/cxx/typedef_chain_in_template-i1.h

@@ -18,4 +18,7 @@ struct TypedefWrapper {
   typedef value_type& reference;
 };
 
+template <typename T>
+using IdentityAlias2 = T;
+
 #endif  // INCLUDE_WHAT_YOU_USE_TESTS_CXX_TYPEDEF_CHAIN_IN_TEMPLATE_I1_H_

tests/cxx/typedef_chain_in_template.cc

@@ -74,6 +74,11 @@ void Fn() {
   (void)sizeof(TplWithNonProvidedAliased1);
   // IWYU: TypedefChainClass is...*typedef_chain_class.h
   (void)sizeof(TplWithNonProvidedAliased2);
+
+  // IWYU: TypedefChainClass is...*typedef_chain_class.h
+  NonProvidingAliasByOther<1> npabo;
+  // IWYU: TypedefChainClass is...*typedef_chain_class.h
+  npabo.Method();
 }
 
 /**** IWYU_SUMMARY
@@ -89,6 +94,6 @@ The full include-list for tests/cxx/typedef_chain_in_template.cc:
 #include "tests/cxx/typedef_chain_in_template-d2.h"  // for ContainerAsLibcpp
 #include "tests/cxx/typedef_chain_in_template-d3.h"  // for ContainerShortTypedefChain
 #include "tests/cxx/typedef_chain_in_template-d4.h"  // for ContainerLongTypedefChain
-#include "tests/cxx/typedef_chain_in_template-d5.h"  // for IdentityAliasComplex, IdentityStructComplex, TplWithNonProvidedAliased1, TplWithNonProvidedAliased2
+#include "tests/cxx/typedef_chain_in_template-d5.h"  // for IdentityAliasComplex, IdentityStructComplex, NonProvidingAliasByOther, TplWithNonProvidedAliased1, TplWithNonProvidedAliased2
 
 ***** IWYU_SUMMARY */