[lldb] Return an llvm::Expected from DWARFExpression::Evaluate (NFCI) (#94420)

Change the signature of `DWARFExpression::Evaluate` and
`DWARFExpressionList::Evaluate` to return an `llvm::Expected` instead of a
boolean. This eliminates the `Status` output parameter and generally improves
error handling.

Author: JDevlieghere

lldb/include/lldb/Expression/DWARFExpression.h

@@ -132,13 +132,12 @@ class DWARFExpression {
   /// \return
   ///     True on success; false otherwise.  If error_ptr is non-NULL,
   ///     details of the failure are provided through it.
-  static bool Evaluate(ExecutionContext *exe_ctx, RegisterContext *reg_ctx,
-                       lldb::ModuleSP module_sp, const DataExtractor &opcodes,
-                       const plugin::dwarf::DWARFUnit *dwarf_cu,
-                       const lldb::RegisterKind reg_set,
-                       const Value *initial_value_ptr,
-                       const Value *object_address_ptr, Value &result,
-                       Status *error_ptr);
+  static llvm::Expected<Value>
+  Evaluate(ExecutionContext *exe_ctx, RegisterContext *reg_ctx,
+           lldb::ModuleSP module_sp, const DataExtractor &opcodes,
+           const plugin::dwarf::DWARFUnit *dwarf_cu,
+           const lldb::RegisterKind reg_set, const Value *initial_value_ptr,
+           const Value *object_address_ptr);
 
   static bool ParseDWARFLocationList(const plugin::dwarf::DWARFUnit *dwarf_cu,
                                      const DataExtractor &data,

lldb/include/lldb/Expression/DWARFExpressionList.h

@@ -9,6 +9,7 @@
 #ifndef LLDB_EXPRESSION_DWARFEXPRESSIONLIST_H
 #define LLDB_EXPRESSION_DWARFEXPRESSIONLIST_H
 
+#include "lldb/Core/Value.h"
 #include "lldb/Expression/DWARFExpression.h"
 #include "lldb/Utility/RangeMap.h"
 #include "lldb/lldb-private.h"
@@ -113,10 +114,11 @@ class DWARFExpressionList {
 
   void SetModule(const lldb::ModuleSP &module) { m_module_wp = module; }
 
-  bool Evaluate(ExecutionContext *exe_ctx, RegisterContext *reg_ctx,
-                lldb::addr_t func_load_addr, const Value *initial_value_ptr,
-                const Value *object_address_ptr, Value &result,
-                Status *error_ptr) const;
+  llvm::Expected<Value> Evaluate(ExecutionContext *exe_ctx,
+                                 RegisterContext *reg_ctx,
+                                 lldb::addr_t func_load_addr,
+                                 const Value *initial_value_ptr,
+                                 const Value *object_address_ptr) const;
 
 private:
   // RangeDataVector requires a comparator for DWARFExpression, but it doesn't

lldb/source/Core/ValueObjectVariable.cpp

@@ -164,8 +164,11 @@ bool ValueObjectVariable::UpdateValue() {
                 target);
     }
     Value old_value(m_value);
-    if (expr_list.Evaluate(&exe_ctx, nullptr, loclist_base_load_addr, nullptr,
-                           nullptr, m_value, &m_error)) {
+    llvm::Expected<Value> maybe_value = expr_list.Evaluate(
+        &exe_ctx, nullptr, loclist_base_load_addr, nullptr, nullptr);
+
+    if (maybe_value) {
+      m_value = *maybe_value;
       m_resolved_value = m_value;
       m_value.SetContext(Value::ContextType::Variable, variable);
 
@@ -246,6 +249,7 @@ bool ValueObjectVariable::UpdateValue() {
 
       SetValueIsValid(m_error.Success());
     } else {
+      m_error = maybe_value.takeError();
       // could not find location, won't allow editing
       m_resolved_value.SetContext(Value::ContextType::Invalid, nullptr);
     }