Refactor ClangUserExpression::Parse [NFC]

[teemperor]

Summary

This patch splits out functionality from the Parse method into different methods.
This benefits the code completion work (which should reuse those methods) and makes the
code a bit more readable.

Note that this patch is as minimal as possible. Some of the code in the new methods definitely
needs more refactoring.

source/Plugins/ExpressionParser/Clang/ClangUserExpression.h

private:
 
   void ScanContext(ExecutionContext &exe_ctx,
                    lldb_private::Status &err) override;
 
   bool AddArguments(ExecutionContext &exe_ctx, std::vector<lldb::addr_t> &args,
                     lldb::addr_t struct_address,
                     DiagnosticManager &diagnostic_manager) override;
 
+  llvm::Optional<lldb::LanguageType> GetLanguageForExpr(
+      DiagnosticManager &diagnostic_manager, ExecutionContext &exe_ctx);
+  bool SetupPersistentState(DiagnosticManager &diagnostic_manager,
+                                   ExecutionContext &exe_ctx);
+  bool PrepareForParsing(DiagnosticManager &diagnostic_manager,
+                         ExecutionContext &exe_ctx);
+
   ClangUserExpressionHelper m_type_system_helper;
 
   class ResultDelegate : public Materializer::PersistentVariableDelegate {
   public:
     ResultDelegate(lldb::TargetSP target) : m_target_sp(target) {}
     ConstString GetName() override;
     void DidDematerialize(lldb::ExpressionVariableSP &variable) override;
 

source/Plugins/ExpressionParser/Clang/ClangUserExpression.cpp

public:
 
   ~OnExit() { m_callback(); }
 
 private:
   Callback m_callback;
 };
 } // namespace
 
-bool ClangUserExpression::Parse(DiagnosticManager &diagnostic_manager,
-                                ExecutionContext &exe_ctx,
-                                lldb_private::ExecutionPolicy execution_policy,
-                                bool keep_result_in_memory,
-                                bool generate_debug_info) {
-  Log *log(lldb_private::GetLogIfAllCategoriesSet(LIBLLDB_LOG_EXPRESSIONS));
-
-  Status err;
-
-  InstallContext(exe_ctx);
-
+bool ClangUserExpression::SetupPersistentState(DiagnosticManager &diagnostic_manager,
+                                 ExecutionContext &exe_ctx) {
   if (Target *target = exe_ctx.GetTargetPtr()) {
     if (PersistentExpressionState *persistent_state =
             target->GetPersistentExpressionStateForLanguage(
                 lldb::eLanguageTypeC)) {
       m_result_delegate.RegisterPersistentState(persistent_state);
     } else {
       diagnostic_manager.PutString(
           eDiagnosticSeverityError,
           "couldn't start parsing (no persistent data)");
       return false;
     }
   } else {
     diagnostic_manager.PutString(eDiagnosticSeverityError,
                                  "error: couldn't start parsing (no target)");
     return false;
   }
-
-  ScanContext(exe_ctx, err);
-
-  if (!err.Success()) {
-    diagnostic_manager.PutString(eDiagnosticSeverityWarning, err.AsCString());
-  }
+  return true;
 
-  ////////////////////////////////////
-  // Generate the expression
-  //
-
-  ApplyObjcCastHack(m_expr_text);
-
-  std::string prefix = m_expr_prefix;
-
+static void SetupDeclVendor(ExecutionContext &exe_ctx, Target *target) {
   if (ClangModulesDeclVendor *decl_vendor =
-          m_target->GetClangModulesDeclVendor()) {
+          target->GetClangModulesDeclVendor()) {
     const ClangModulesDeclVendor::ModuleVector &hand_imported_modules =
         llvm::cast<ClangPersistentVariables>(
-            m_target->GetPersistentExpressionStateForLanguage(
+            target->GetPersistentExpressionStateForLanguage(
                 lldb::eLanguageTypeC))
             ->GetHandLoadedClangModules();
     ClangModulesDeclVendor::ModuleVector modules_for_macros;
 
     for (ClangModulesDeclVendor::ModuleID module : hand_imported_modules) {
       modules_for_macros.push_back(module);
     }
 
-    if (m_target->GetEnableAutoImportClangModules()) {
+    if (target->GetEnableAutoImportClangModules()) {
       if (StackFrame *frame = exe_ctx.GetFramePtr()) {
         if (Block *block = frame->GetFrameBlock()) {
           SymbolContext sc;
 
           block->CalculateSymbolContext(&sc);
 
           if (sc.comp_unit) {
             StreamString error_stream;
 
             decl_vendor->AddModulesForCompileUnit(
                 *sc.comp_unit, modules_for_macros, error_stream);
           }
         }
       }
     }
   }
+}
 
-  lldb::LanguageType lang_type = lldb::eLanguageTypeUnknown;
+llvm::Optional<lldb::LanguageType> ClangUserExpression::GetLanguageForExpr(
+    DiagnosticManager &diagnostic_manager, ExecutionContext &exe_ctx) {
+  lldb::LanguageType lang_type = lldb::LanguageType::eLanguageTypeUnknown;
+
+  std::string prefix = m_expr_prefix;
 
   if (m_options.GetExecutionPolicy() == eExecutionPolicyTopLevel) {
     m_transformed_text = m_expr_text;
   } else {
     std::unique_ptr<ExpressionSourceCode> source_code(
         ExpressionSourceCode::CreateWrapped(prefix.c_str(),
                                             m_expr_text.c_str()));
 
     if (m_in_cplusplus_method)
       lang_type = lldb::eLanguageTypeC_plus_plus;
     else if (m_in_objectivec_method)
       lang_type = lldb::eLanguageTypeObjC;
     else
       lang_type = lldb::eLanguageTypeC;
 
     if (!source_code->GetText(m_transformed_text, lang_type, m_in_static_method,
                               exe_ctx)) {
       diagnostic_manager.PutString(eDiagnosticSeverityError,
                                    "couldn't construct expression body");
-      return false;
-    }
+      return llvm::Optional<lldb::LanguageType>();
+    }
+  }
+  return lang_type;
+}
+
+bool ClangUserExpression::PrepareForParsing(
+    DiagnosticManager &diagnostic_manager, ExecutionContext &exe_ctx) {
+  InstallContext(exe_ctx);
+
+  if (!SetupPersistentState(diagnostic_manager, exe_ctx))
+
+  Status err;
+  ScanContext(exe_ctx, err);
+
+  if (!err.Success()) {
+    diagnostic_manager.PutString(eDiagnosticSeverityWarning, err.AsCString());
+  }
+
+  ////////////////////////////////////
+  // Generate the expression
+  //
+
+  ApplyObjcCastHack(m_expr_text);
+
+  SetupDeclVendor(exe_ctx, m_target);
+  return true;
+
+bool ClangUserExpression::Parse(DiagnosticManager &diagnostic_manager,
+                                ExecutionContext &exe_ctx,
+                                lldb_private::ExecutionPolicy execution_policy,
+                                bool keep_result_in_memory,
+                                bool generate_debug_info) {
+  Log *log(lldb_private::GetLogIfAllCategoriesSet(LIBLLDB_LOG_EXPRESSIONS));
+
+  if (!PrepareForParsing(diagnostic_manager, exe_ctx))
+    return false;
+
+  lldb::LanguageType lang_type = lldb::LanguageType::eLanguageTypeUnknown;
+  if (auto new_lang = GetLanguageForExpr(diagnostic_manager, exe_ctx)) {
+    lang_type = new_lang.getValue();
   }
 
   if (log)
     log->Printf("Parsing the following code:\n%s", m_transformed_text.c_str());
 
   ////////////////////////////////////
   // Set up the target and compiler
   //