[Lldb-commits] [PATCH] D137983: [lldb] Disable looking at pointee types to find synthetic value for non-ObjC

[Arthur Eubanks via Phabricator via lldb-commits]

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After D134378 <https://reviews.llvm.org/D134378>, we started seeing crashes with incomplete types (in the
context of shared libraries).

When trying to print a `std::vector<int> &` with only debug info for a
declaration, we now try to use the formatter after D134378 <https://reviews.llvm.org/D134378>. With an
incomplete type, this somehow goes into infinite recursion with the
frames

  lldb_private::ValueObject::Dereference
  lldb_private::ValueObjectSynthetic::CreateSynthFilter
  lldb_private::ValueObjectSynthetic::ValueObjectSynthetic
  lldb_private::ValueObject::CalculateSyntheticValue
  lldb_private::ValueObject::HasSyntheticValue

The reason this only started appearing after D134378 <https://reviews.llvm.org/D134378> was because
previously with incomplete types, for names with `<`, lldb would attempt
to parse template parameter DIEs, which were empty, then create an empty
`ClassTemplateSpecializationDecl` which overrode the name used to lookup
a formatter in `FormattersMatchData()` to not include template
parameters (e.g. `std::vector<> &`). After D134378 <https://reviews.llvm.org/D134378> we don't create a
`ClassTemplateSpecializationDecl` when there are no template parameters
and the name to lookup a formatter is the original name (e.g.
`std::vector<int> &`).

The code to try harder with incomplete child compiler types was added in
D79554 <https://reviews.llvm.org/D79554> for ObjC purposes.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D137983

Files:
  lldb/source/Core/ValueObject.cpp


Index: lldb/source/Core/ValueObject.cpp
===================================================================
--- lldb/source/Core/ValueObject.cpp
+++ lldb/source/Core/ValueObject.cpp
@@ -2673,7 +2673,10 @@
     // In case of incomplete child compiler type, use the pointee type and try
     // to recreate a new ValueObjectChild using it.
     if (!m_deref_valobj) {
-      if (HasSyntheticValue()) {
+      // FIXME: C++ stdlib formatters break with incomplete types (e.g.
+      // `std::vector<int> &`). Remove ObjC restriction once that's resolved.
+      if (Language::LanguageIsObjC(GetPreferredDisplayLanguage()) &&
+          HasSyntheticValue()) {
         child_compiler_type = compiler_type.GetPointeeType();
 
         if (child_compiler_type) {


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