[lldb][Format] Make function name frame-format variables work without debug-info (#137408)

This patch makes the frame-format variables introduced in
https://github.com/llvm/llvm-project/pull/131836 also work when no
debug-info is available. Previously, we assumed `sc.function` was
available, but without debug-info we might only have `sc.symbol`. We
don't really need the `sc.function` apart from when formatting
arguments.

For the function arguments case I added a fallback that will just print
the arguments we get from the demangler (which is what LLDB does for
stacktraces with no debug-info anyway). Ideally we'd have a separate
`FormatEntity::Entry::Type::FunctionArguments` that will just print the
arguments from the demangler and have something like the following in
the `plugin.cplusplus.display.function-name-format`:
```
{ ${function.formatted-arguments} || ${function.arguments} }
```
I.e., when we can't format the arguments, print the ones from the
demangler. But we currently don't have the `||` operator in the
frame-format language yet.

1 files changed, 36 insertions, 2 deletions

diff --git a/lldb/source/Plugins/Language/CPlusPlus/CPlusPlusLanguage.cpp b/lldb/source/Plugins/Language/CPlusPlus/CPlusPlusLanguage.cpp
index 283e867..ab8e9883 100644
--- a/lldb/source/Plugins/Language/CPlusPlus/CPlusPlusLanguage.cpp
+++ b/lldb/source/Plugins/Language/CPlusPlus/CPlusPlusLanguage.cpp
@@ -381,6 +381,34 @@ GetDemangledScope(const SymbolContext &sc) {
   return demangled_name.slice(info->ScopeRange.first, info->ScopeRange.second);
 }
 
+static bool PrintDemangledArgumentList(Stream &s, const SymbolContext &sc) {
+  assert(sc.symbol);
+
+  Mangled mangled = sc.GetPossiblyInlinedFunctionName();
+  if (!mangled)
+    return false;
+
+  auto demangled_name = mangled.GetDemangledName().GetStringRef();
+  if (demangled_name.empty())
+    return false;
+
+  const std::optional<DemangledNameInfo> &info = mangled.GetDemangledInfo();
+  if (!info)
+    return false;
+
+  // Function without a basename is nonsense.
+  if (!info->hasBasename())
+    return false;
+
+  if (info->ArgumentsRange.second < info->ArgumentsRange.first)
+    return false;
+
+  s << demangled_name.slice(info->ArgumentsRange.first,
+                            info->ArgumentsRange.second);
+
+  return true;
+}
+
 bool CPlusPlusLanguage::CxxMethodName::TrySimplifiedParse() {
   // This method tries to parse simple method definitions which are presumably
   // most comman in user programs. Definitions that can be parsed by this
@@ -1890,8 +1918,6 @@ bool CPlusPlusLanguage::GetFunctionDisplayName(
 bool CPlusPlusLanguage::HandleFrameFormatVariable(
     const SymbolContext &sc, const ExecutionContext *exe_ctx,
     FormatEntity::Entry::Type type, Stream &s) {
-  assert(sc.function);
-
   switch (type) {
   case FormatEntity::Entry::Type::FunctionScope: {
     std::optional<llvm::StringRef> scope = GetDemangledScope(sc);
@@ -1925,6 +1951,14 @@ bool CPlusPlusLanguage::HandleFrameFormatVariable(
   }
 
   case FormatEntity::Entry::Type::FunctionFormattedArguments: {
+    // This ensures we print the arguments even when no debug-info is available.
+    //
+    // FIXME: we should have a Entry::Type::FunctionArguments and
+    // use it in the plugin.cplusplus.display.function-name-format
+    // once we have a "fallback operator" in the frame-format language.
+    if (!sc.function && sc.symbol)
+      return PrintDemangledArgumentList(s, sc);
+
     VariableList args;
     if (auto variable_list_sp = GetFunctionVariableList(sc))
       variable_list_sp->AppendVariablesWithScope(eValueTypeVariableArgument,