feat(cxx_indexer): support decayed types (#5852)

Use the new type when we encounter a decayed/adjusted type
(unless it's null, then try the old one).

NB: according to clang's documentation, an adjusted type
is "a type which was implicitly adjusted by the semantic engine
for arbitrary reasons"

kythe/cxx/indexer/cxx/IndexerASTHooks.cc

@@ -4666,6 +4666,16 @@ NodeSet IndexerASTVisitor::BuildNodeSetForDependentAddressSpace(
   return BuildNodeSetForType(T.getPointeeType());
 }
 
+NodeSet IndexerASTVisitor::BuildNodeSetForAdjusted(
+    const clang::AdjustedType& T) {
+  if (auto S = T.getAdjustedType(); !S.isNull()) {
+    return BuildNodeSetForType(S);
+  } else if (auto U = T.getOriginalType(); !U.isNull()) {
+    return BuildNodeSetForType(U);
+  }
+  return NodeSet::Empty();
+}
+
 GraphObserver::NodeId IndexerASTVisitor::BuildNominalNodeIdForDecl(
     const clang::NamedDecl* Decl) {
   // TODO(shahms): Separate building the node id from emitting it.
@@ -4802,6 +4812,11 @@ NodeSet IndexerASTVisitor::BuildNodeSetForTypeInternal(const clang::Type& T) {
 #define DELEGATE_TYPE(t) \
   case clang::Type::t:   \
     return BuildNodeSetFor##t(clang::cast<clang::t##Type>(T));
+
+#define DELEGATE_TYPE_TO_BASE(t, b) \
+  case clang::Type::t:              \
+    return BuildNodeSetFor##b(clang::cast<clang::b##Type>(T));
+
   // We only care about leaves in the type hierarchy (eg, we shouldn't match
   // on Reference, but instead on LValueReference or RValueReference).
   switch (T.getTypeClass()) {
@@ -4843,15 +4858,15 @@ NodeSet IndexerASTVisitor::BuildNodeSetForTypeInternal(const clang::Type& T) {
     DELEGATE_TYPE(DependentAddressSpace);
     DELEGATE_TYPE(BitInt);
     DELEGATE_TYPE(DependentBitInt);
+    DELEGATE_TYPE(Adjusted);
+    DELEGATE_TYPE_TO_BASE(Decayed, Adjusted);
     UNSUPPORTED_CLANG_TYPE(BTFTagAttributed);
     UNSUPPORTED_CLANG_TYPE(DependentTemplateSpecialization);
     UNSUPPORTED_CLANG_TYPE(Complex);
     UNSUPPORTED_CLANG_TYPE(VariableArray);
     UNSUPPORTED_CLANG_TYPE(DependentSizedExtVector);
     UNSUPPORTED_CLANG_TYPE(Vector);
     UNSUPPORTED_CLANG_TYPE(ExtVector);
-    UNSUPPORTED_CLANG_TYPE(Adjusted);
-    UNSUPPORTED_CLANG_TYPE(Decayed);
     UNSUPPORTED_CLANG_TYPE(TypeOfExpr);
     UNSUPPORTED_CLANG_TYPE(TypeOf);
     UNSUPPORTED_CLANG_TYPE(UnresolvedUsing);
@@ -4876,6 +4891,7 @@ NodeSet IndexerASTVisitor::BuildNodeSetForTypeInternal(const clang::Type& T) {
   }
 #undef UNSUPPORTED_CLANG_TYPE
 #undef DELEGATE_TYPE
+#undef DELEGATE_TYPE_TO_BASE
 }
 
 std::optional<GraphObserver::NodeId>

kythe/cxx/indexer/cxx/IndexerASTHooks.h

@@ -372,6 +372,7 @@ class IndexerASTVisitor : public RecursiveTypeVisitor<IndexerASTVisitor> {
   NodeSet BuildNodeSetForAttributed(const clang::AttributedType& T);
   NodeSet BuildNodeSetForDependentAddressSpace(
       const clang::DependentAddressSpaceType& T);
+  NodeSet BuildNodeSetForAdjusted(const clang::AdjustedType& T);
 
   // Helper function which constructs marked source and records
   // a tnominal node for the given `Decl`.

kythe/cxx/indexer/cxx/testdata/BUILD

@@ -301,6 +301,13 @@ cc_indexer_test(
     tags = ["basic"],
 )
 
+cc_indexer_test(
+    name = "decayed_type",
+    srcs = ["basic/decayed_type.cc"],
+    check_for_singletons = True,
+    tags = ["basic"],
+)
+
 cc_indexer_test(
     name = "decltype_auto",
     srcs = ["basic/decltype_auto.cc"],

kythe/cxx/indexer/cxx/testdata/basic/decayed_type.cc

@@ -0,0 +1,26 @@
+// We support decayed types.
+void i() {
+  //- @i ref FnI
+  //- FnI typed TyI
+  //- @j defines/binding VarJ
+  //- VarJ typed TyJ
+  auto j = i;
+  //- @k defines/binding VarK
+  //- VarK typed TyK
+  int k[1] = {1};
+  //- @l defines/binding VarL
+  //- VarL typed TyL
+  auto* l = k;
+}
+//- @TFnVoidVoid defines/binding AliasFVV
+//- AliasFVV aliases TyI
+using TFnVoidVoid = decltype(i);
+//- @TPtrFnVoidVoid defines/binding AliasPFVV
+//- AliasPFVV aliases TyJ
+using TPtrFnVoidVoid = decltype(i)*;
+//- @TCArrInt defines/binding AliasCAI
+//- AliasCAI aliases TyK
+using TCArrInt = int[1];
+//- @TPtrInt defines/binding AliasPI
+//- AliasPI aliases TyL
+using TPtrInt = int*;