[lldb] Implement SwiftLanguage::AreEqualForFrameComparison

This checks whether the two provided symbol contexts refer to funclets of the
same async function.

In particular, this fixes an issue in the ThreadPlanStepOverRange algorithm for
async functions.
When the plan stops, it compares the current symbol context to the symbol
context of where it started. An initial comparison is done through StackIDs. If
that comparison says the two are equal, the plan then attempts to confirm the
two SymbolContexts are the same by checking whether the underlying functions are
the same. Because different funclets correspond to different low level
functions, this comparison was failing.

Author: felipepiovezan

lldb/source/Plugins/Language/Swift/SwiftLanguage.cpp

@@ -1834,6 +1834,23 @@ bool SwiftLanguage::IgnoreForLineBreakpoints(const SymbolContext &sc) const {
       name);
 }
 
+std::optional<bool>
+SwiftLanguage::AreEqualForFrameComparison(const SymbolContext &sc1,
+                                          const SymbolContext &sc2) const {
+  auto result = SwiftLanguageRuntime::AreFuncletsOfSameAsyncFunction(
+      sc1.GetFunctionName(Mangled::ePreferMangled),
+      sc2.GetFunctionName(Mangled::ePreferMangled));
+  switch (result) {
+  case SwiftLanguageRuntime::FuncletComparisonResult::NotBothFunclets:
+    return {};
+  case SwiftLanguageRuntime::FuncletComparisonResult::SameAsyncFunction:
+    return true;
+  case SwiftLanguageRuntime::FuncletComparisonResult::DifferentAsyncFunctions:
+    return false;
+  }
+  llvm_unreachable("unhandled enumeration in AreEquivalentFunctions");
+}
+
 //------------------------------------------------------------------
 // Static Functions
 //------------------------------------------------------------------

lldb/source/Plugins/Language/Swift/SwiftLanguage.h

@@ -75,6 +75,12 @@ class SwiftLanguage : public Language {
   ConstString
   GetDemangledFunctionNameWithoutArguments(Mangled mangled) const override;
 
+  /// Returns whether two SymbolContexts correspond to funclets of the same
+  /// async function.
+  /// If either SymbolContext is not a funclet, nullopt is returned.
+  std::optional<bool>
+  AreEqualForFrameComparison(const SymbolContext &sc1,
+                             const SymbolContext &sc2) const override;
   //------------------------------------------------------------------
   // Static Functions
   //------------------------------------------------------------------