[clang] Reland: [clang] improve print / dump of anonymous declarations (PR #124858)

[Matheus Izvekov via cfe-commits]

================
@@ -1257,28 +1257,48 @@ void StmtPrinter::VisitConstantExpr(ConstantExpr *Node) {
 }
 
 void StmtPrinter::VisitDeclRefExpr(DeclRefExpr *Node) {
-  if (const auto *OCED = dyn_cast<OMPCapturedExprDecl>(Node->getDecl())) {
+  ValueDecl *VD = Node->getDecl();
+  if (const auto *OCED = dyn_cast<OMPCapturedExprDecl>(VD)) {
     OCED->getInit()->IgnoreImpCasts()->printPretty(OS, nullptr, Policy);
     return;
   }
-  if (const auto *TPOD = dyn_cast<TemplateParamObjectDecl>(Node->getDecl())) {
+  if (const auto *TPOD = dyn_cast<TemplateParamObjectDecl>(VD)) {
     TPOD->printAsExpr(OS, Policy);
     return;
   }
   if (NestedNameSpecifier *Qualifier = Node->getQualifier())
     Qualifier->print(OS, Policy);
   if (Node->hasTemplateKeyword())
     OS << "template ";
-  if (Policy.CleanUglifiedParameters &&
-      isa<ParmVarDecl, NonTypeTemplateParmDecl>(Node->getDecl()) &&
-      Node->getDecl()->getIdentifier())
-    OS << Node->getDecl()->getIdentifier()->deuglifiedName();
-  else
-    Node->getNameInfo().printName(OS, Policy);
+  DeclarationNameInfo NameInfo = Node->getNameInfo();
+  if (IdentifierInfo *ID = NameInfo.getName().getAsIdentifierInfo();
+      ID || NameInfo.getName().getNameKind() != DeclarationName::Identifier) {
+    if (Policy.CleanUglifiedParameters &&
+        isa<ParmVarDecl, NonTypeTemplateParmDecl>(VD) && ID)
+      OS << ID->deuglifiedName();
+    else
+      NameInfo.printName(OS, Policy);
+  } else {
+    switch (VD->getKind()) {
+    case Decl::NonTypeTemplateParm: {
+      auto *TD = cast<NonTypeTemplateParmDecl>(VD);
+      OS << "value-parameter-" << TD->getDepth() << '-' << TD->getIndex() << "";
+      break;
+    }
+    case Decl::ParmVar: {
+      auto *PD = cast<ParmVarDecl>(VD);
+      OS << "function-parameter-" << PD->getFunctionScopeDepth() << '-'
+         << PD->getFunctionScopeIndex();
+      break;
+    }
+    default:
+      llvm_unreachable("Unhandled anonymous declaration kind");
----------------
mizvekov wrote:

This could probably point to some problem in your code.

1) It's strange that you have a DeclRefExpr pointing to a decomposition, instead of one of its bindings.
2) I'd like to understand your use case. We can't refer to a decomposition in source code, so there is no sensible thing the StmtPrinter can do. Before this change, we printed an empty string for any anonymous entity, which was not helpful.

There is likely to be some test case in your downstream where an empty string is being printed and that's not good either.

Is that something which could be reproduced upstream?

We could add some workaround support for printing these, something along the lines of `decomposition-<name-of-first-binding>`.

https://github.com/llvm/llvm-project/pull/124858