[lldb] Refactor deduction of the instance variable's name (NFC)

Move responsibility of providing the instance variable name (`this`, `self`) from
`TypeSystem` to `Language`.

`Language` the natural place for this, but also has downstream benefits. Some languages
have multiple `TypeSystem` implementations (ex Swift), and by placing this logic in the
`Language`, redundancy is avoided.

This change relies on the tests from D145348 and D146320.

Differential Revision: https://reviews.llvm.org/D146548

lldb/include/lldb/Symbol/CompilerDeclContext.h

@@ -69,14 +69,6 @@ public:
   /// Determines the original language of the decl context.
   lldb::LanguageType GetLanguage();
 
-  /// Determines the name of the instance variable for the this decl context.
-  ///
-  /// For C++ the name is "this", for Objective-C the name is "self".
-  ///
-  /// \return
-  ///     Returns a string for the name of the instance variable.
-  ConstString GetInstanceVariableName(lldb::LanguageType language);
-
   /// Check if the given other decl context is contained in the lookup
   /// of this decl context (for example because the other context is a nested
   /// inline namespace).

lldb/include/lldb/Symbol/TypeSystem.h

@@ -202,10 +202,6 @@ public:
   // TypeSystems can support more than one language
   virtual bool SupportsLanguage(lldb::LanguageType language) = 0;
 
-  /// The name of the variable used for explicitly accessing data scoped to the
-  /// current instance (or type). C++ uses "this", ObjC uses "self".
-  virtual ConstString GetInstanceVariableName(lldb::LanguageType language) = 0;
-
   // Type Completion
 
   virtual bool GetCompleteType(lldb::opaque_compiler_type_t type) = 0;

lldb/include/lldb/Target/Language.h

@@ -326,6 +326,8 @@ public:
     return ConstString();
   }
 
+  virtual ConstString GetInstanceVariableName() { return {}; }
+
 protected:
   // Classes that inherit from Language can see and modify these
 

lldb/source/Plugins/Language/CPlusPlus/CPlusPlusLanguage.h

@@ -165,6 +165,8 @@ public:
   ConstString FindBestAlternateFunctionMangledName(
       const Mangled mangled, const SymbolContext &sym_ctx) const override;
 
+  ConstString GetInstanceVariableName() override { return ConstString("this"); }
+
   // PluginInterface protocol
   llvm::StringRef GetPluginName() override { return GetPluginNameStatic(); }
 };

lldb/source/Plugins/Language/ObjC/ObjCLanguage.h

@@ -155,6 +155,8 @@ public:
       return false;
   }
 
+  ConstString GetInstanceVariableName() override { return ConstString("self"); }
+
   // PluginInterface protocol
   llvm::StringRef GetPluginName() override { return GetPluginNameStatic(); }
 };

lldb/source/Plugins/Language/ObjCPlusPlus/ObjCPlusPlusLanguage.h

@@ -40,6 +40,8 @@ public:
 
   static lldb_private::Language *CreateInstance(lldb::LanguageType language);
 
+  ConstString GetInstanceVariableName() override { return ConstString("self"); }
+
   static llvm::StringRef GetPluginNameStatic() { return "objcplusplus"; }
 
   // PluginInterface protocol

lldb/source/Plugins/TypeSystem/Clang/TypeSystemClang.cpp

@@ -3727,22 +3727,6 @@ bool TypeSystemClang::SupportsLanguage(lldb::LanguageType language) {
   return TypeSystemClangSupportsLanguage(language);
 }
 
-ConstString
-TypeSystemClang::GetInstanceVariableName(lldb::LanguageType language) {
-  switch (language) {
-  case LanguageType::eLanguageTypeC_plus_plus:
-  case LanguageType::eLanguageTypeC_plus_plus_03:
-  case LanguageType::eLanguageTypeC_plus_plus_11:
-  case LanguageType::eLanguageTypeC_plus_plus_14:
-    return ConstString("this");
-  case LanguageType::eLanguageTypeObjC:
-  case LanguageType::eLanguageTypeObjC_plus_plus:
-    return ConstString("self");
-  default:
-    return {};
-  }
-}
-
 std::optional<std::string>
 TypeSystemClang::GetCXXClassName(const CompilerType &type) {
   if (!type)

lldb/source/Plugins/TypeSystem/Clang/TypeSystemClang.h

@@ -711,8 +711,6 @@ public:
 
   bool SupportsLanguage(lldb::LanguageType language) override;
 
-  ConstString GetInstanceVariableName(lldb::LanguageType language) override;
-
   static std::optional<std::string> GetCXXClassName(const CompilerType &type);
 
   // Type Completion

lldb/source/Symbol/CompilerDeclContext.cpp

@@ -46,13 +46,6 @@ lldb::LanguageType CompilerDeclContext::GetLanguage() {
   return {};
 }
 
-ConstString
-CompilerDeclContext::GetInstanceVariableName(lldb::LanguageType language) {
-  if (IsValid())
-    return m_type_system->GetInstanceVariableName(language);
-  return {};
-}
-
 bool CompilerDeclContext::IsContainedInLookup(CompilerDeclContext other) const {
   if (!IsValid())
     return false;

lldb/source/Symbol/SymbolContext.cpp

@@ -19,10 +19,12 @@
 #include "lldb/Symbol/SymbolFile.h"
 #include "lldb/Symbol/SymbolVendor.h"
 #include "lldb/Symbol/Variable.h"
+#include "lldb/Target/Language.h"
 #include "lldb/Target/Target.h"
 #include "lldb/Utility/LLDBLog.h"
 #include "lldb/Utility/Log.h"
 #include "lldb/Utility/StreamString.h"
+#include "lldb/lldb-enumerations.h"
 
 using namespace lldb;
 using namespace lldb_private;
@@ -540,13 +542,17 @@ Block *SymbolContext::GetFunctionBlock() {
 }
 
 ConstString SymbolContext::GetInstanceVariableName() {
+  LanguageType lang_type = eLanguageTypeUnknown;
+
   if (Block *function_block = GetFunctionBlock())
-    if (CompilerDeclContext decl_ctx = function_block->GetDeclContext()) {
-      auto language = decl_ctx.GetLanguage();
-      if (language == eLanguageTypeUnknown)
-        language = GetLanguage();
-      return decl_ctx.GetInstanceVariableName(language);
-    }
+    if (CompilerDeclContext decl_ctx = function_block->GetDeclContext())
+      lang_type = decl_ctx.GetLanguage();
+
+  if (lang_type == eLanguageTypeUnknown)
+    lang_type = GetLanguage();
+
+  if (auto *lang = Language::FindPlugin(lang_type))
+    return lang->GetInstanceVariableName();
 
   return {};
 }