[LLDB] Add formatters for MSVC STL std::variant (#148554)

Adds a summary and synthetic children for MSVC STL's `std::variant`.

This one is a bit complicated because of DWARF vs PDB differences. I put
the representations in comments. Being able to `GetChildMemberWithName`
a member in an anonymous union would make this a lot simpler
(`std::optional` will have something similar iirc).

Towards #24834.

1 files changed, 25 insertions, 8 deletions

diff --git a/lldb/source/Plugins/Language/CPlusPlus/CPlusPlusLanguage.cpp b/lldb/source/Plugins/Language/CPlusPlus/CPlusPlusLanguage.cpp
index a0d5e1d..481fe61 100644
--- a/lldb/source/Plugins/Language/CPlusPlus/CPlusPlusLanguage.cpp
+++ b/lldb/source/Plugins/Language/CPlusPlus/CPlusPlusLanguage.cpp
@@ -1449,11 +1449,6 @@ static void LoadLibStdcppFormatters(lldb::TypeCategoryImplSP cpp_category_sp) {
       SyntheticChildrenSP(new ScriptedSyntheticChildren(
           stl_synth_flags,
           "lldb.formatters.cpp.gnu_libstdcpp.StdForwardListSynthProvider")));
-  cpp_category_sp->AddTypeSynthetic(
-      "^std::variant<.+>$", eFormatterMatchRegex,
-      SyntheticChildrenSP(new ScriptedSyntheticChildren(
-          stl_synth_flags,
-          "lldb.formatters.cpp.gnu_libstdcpp.VariantSynthProvider")));
 
   stl_summary_flags.SetDontShowChildren(false);
   stl_summary_flags.SetSkipPointers(false);
@@ -1509,9 +1504,6 @@ static void LoadLibStdcppFormatters(lldb::TypeCategoryImplSP cpp_category_sp) {
       TypeSummaryImplSP(new ScriptSummaryFormat(
           stl_summary_flags,
           "lldb.formatters.cpp.gnu_libstdcpp.ForwardListSummaryProvider")));
-  AddCXXSummary(cpp_category_sp, LibStdcppVariantSummaryProvider,
-                "libstdc++ std::variant summary provider", "^std::variant<.+>$",
-                stl_summary_flags, true);
 
   AddCXXSynthetic(
       cpp_category_sp,
@@ -1649,6 +1641,25 @@ GenericOptionalSyntheticFrontEndCreator(CXXSyntheticChildren *children,
   return LibStdcppOptionalSyntheticFrontEndCreator(children, valobj_sp);
 }
 
+static SyntheticChildrenFrontEnd *
+GenericVariantSyntheticFrontEndCreator(CXXSyntheticChildren *children,
+                                       lldb::ValueObjectSP valobj_sp) {
+  if (!valobj_sp)
+    return nullptr;
+
+  if (IsMsvcStlVariant(*valobj_sp))
+    return MsvcStlVariantSyntheticFrontEndCreator(children, valobj_sp);
+  return new ScriptedSyntheticChildren::FrontEnd(
+      "lldb.formatters.cpp.gnu_libstdcpp.VariantSynthProvider", *valobj_sp);
+}
+
+static bool GenericVariantSummaryProvider(ValueObject &valobj, Stream &stream,
+                                          const TypeSummaryOptions &options) {
+  if (IsMsvcStlVariant(valobj))
+    return MsvcStlVariantSummaryProvider(valobj, stream, options);
+  return LibStdcppVariantSummaryProvider(valobj, stream, options);
+}
+
 /// Load formatters that are formatting types from more than one STL
 static void LoadCommonStlFormatters(lldb::TypeCategoryImplSP cpp_category_sp) {
   if (!cpp_category_sp)
@@ -1713,6 +1724,9 @@ static void LoadCommonStlFormatters(lldb::TypeCategoryImplSP cpp_category_sp) {
   AddCXXSynthetic(cpp_category_sp, GenericForwardListSyntheticFrontEndCreator,
                   "std::forward_list synthetic children",
                   "^std::forward_list<.+>(( )?&)?$", stl_synth_flags, true);
+  AddCXXSynthetic(cpp_category_sp, GenericVariantSyntheticFrontEndCreator,
+                  "std::variant synthetic children", "^std::variant<.*>$",
+                  stl_synth_flags, true);
 
   SyntheticChildren::Flags stl_deref_flags = stl_synth_flags;
   stl_deref_flags.SetFrontEndWantsDereference();
@@ -1749,6 +1763,9 @@ static void LoadCommonStlFormatters(lldb::TypeCategoryImplSP cpp_category_sp) {
   AddCXXSummary(cpp_category_sp, GenericOptionalSummaryProvider,
                 "MSVC STL/libstd++ std::optional summary provider",
                 "^std::optional<.+>(( )?&)?$", stl_summary_flags, true);
+  AddCXXSummary(cpp_category_sp, GenericVariantSummaryProvider,
+                "MSVC STL/libstdc++ std::variant summary provider",
+                "^std::variant<.*>$", stl_summary_flags, true);
 }
 
 static void LoadMsvcStlFormatters(lldb::TypeCategoryImplSP cpp_category_sp) {