[clang] [clang-repl] Refactor locking of runtime PTU stack (NFC) (PR #84176)

[Stefan Gränitz via cfe-commits]

https://github.com/weliveindetail updated https://github.com/llvm/llvm-project/pull/84176

>From ebf00ec8396eabf96c413e861b72ff1c88424685 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Stefan=20Gr=C3=A4nitz?= <stefan.graenitz at gmail.com>
Date: Wed, 6 Mar 2024 12:37:50 +0100
Subject: [PATCH] [clang-repl] Refactor locking of runtime PTU stack (NFC)

The previous implementation seemed hacky, because it required the reader to be familiar with the internal workings of the PTU stack. The concept itself is a pragmatic solution and not very surprising. Keeping it behind a finalization call seems reasonable.
---
 clang/include/clang/Interpreter/Interpreter.h |  1 +
 clang/lib/Interpreter/Interpreter.cpp         | 12 ++++++++----
 2 files changed, 9 insertions(+), 4 deletions(-)

diff --git a/clang/include/clang/Interpreter/Interpreter.h b/clang/include/clang/Interpreter/Interpreter.h
index c8f932e95c4798..988ab86ccf3c8b 100644
--- a/clang/include/clang/Interpreter/Interpreter.h
+++ b/clang/include/clang/Interpreter/Interpreter.h
@@ -142,6 +142,7 @@ class Interpreter {
 
 private:
   size_t getEffectivePTUSize() const;
+  void markUserCodeStart();
 
   bool FindRuntimeInterface();
 
diff --git a/clang/lib/Interpreter/Interpreter.cpp b/clang/lib/Interpreter/Interpreter.cpp
index 37696b28976428..6410aadd1f5abe 100644
--- a/clang/lib/Interpreter/Interpreter.cpp
+++ b/clang/lib/Interpreter/Interpreter.cpp
@@ -280,15 +280,14 @@ Interpreter::create(std::unique_ptr<CompilerInstance> CI) {
   if (Err)
     return std::move(Err);
 
+  // Add runtime code and set a marker to hide it from user code. Undo will not
+  // go through that.
   auto PTU = Interp->Parse(Runtimes);
   if (!PTU)
     return PTU.takeError();
+  Interp->markUserCodeStart();
 
   Interp->ValuePrintingInfo.resize(4);
-  // FIXME: This is a ugly hack. Undo command checks its availability by looking
-  // at the size of the PTU list. However we have parsed something in the
-  // beginning of the REPL so we have to mark them as 'Irrevocable'.
-  Interp->InitPTUSize = Interp->IncrParser->getPTUs().size();
   return std::move(Interp);
 }
 
@@ -345,6 +344,11 @@ const ASTContext &Interpreter::getASTContext() const {
   return getCompilerInstance()->getASTContext();
 }
 
+void Interpreter::markUserCodeStart() {
+  assert(!InitPTUSize && "We only do this once");
+  InitPTUSize = IncrParser->getPTUs().size();
+}
+
 size_t Interpreter::getEffectivePTUSize() const {
   std::list<PartialTranslationUnit> &PTUs = IncrParser->getPTUs();
   assert(PTUs.size() >= InitPTUSize && "empty PTU list?");