[clang] [clang-repl] Fix assertion failure in CleanUpPTU() (PR #85378)

[Stefan Gränitz via cfe-commits]

https://github.com/weliveindetail created https://github.com/llvm/llvm-project/pull/85378

This assertion failure is one (fortunate) symptom:
```
clang/include/clang/AST/DeclBase.h:1337: reference clang::DeclListNode::iterator::operator*() const: Assertion `Ptr && "dereferencing end() iterator"' failed.
```

Using `remove()` from `DeclContext::lookup_result` list invalidates iterators. It can't be used while iterating.

>From 6fbd6e36133af7af008c84a1a2e44c243aed26be Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Stefan=20Gr=C3=A4nitz?= <stefan.graenitz at gmail.com>
Date: Fri, 15 Mar 2024 11:01:09 +0100
Subject: [PATCH] [clang-repl] Fix assertion failure in CleanUpPTU()

`remove()` from `DeclContext::lookup_result` list invalidates iterators. This assertion failure is one symptom:
```
clang/include/clang/AST/DeclBase.h:1337: reference clang::DeclListNode::iterator::operator*() const: Assertion `Ptr && "dereferencing end() iterator"' failed.
```
---
 clang/lib/Interpreter/IncrementalParser.cpp | 19 +++++++++++++------
 1 file changed, 13 insertions(+), 6 deletions(-)

diff --git a/clang/lib/Interpreter/IncrementalParser.cpp b/clang/lib/Interpreter/IncrementalParser.cpp
index 370bcbfee8b014..fdb7b686ecfdcc 100644
--- a/clang/lib/Interpreter/IncrementalParser.cpp
+++ b/clang/lib/Interpreter/IncrementalParser.cpp
@@ -13,6 +13,7 @@
 #include "IncrementalParser.h"
 
 #include "clang/AST/DeclContextInternals.h"
+#include "clang/AST/DeclarationName.h"
 #include "clang/CodeGen/BackendUtil.h"
 #include "clang/CodeGen/CodeGenAction.h"
 #include "clang/CodeGen/ModuleBuilder.h"
@@ -375,16 +376,22 @@ void IncrementalParser::CleanUpPTU(PartialTranslationUnit &PTU) {
   TranslationUnitDecl *MostRecentTU = PTU.TUPart;
   TranslationUnitDecl *FirstTU = MostRecentTU->getFirstDecl();
   if (StoredDeclsMap *Map = FirstTU->getPrimaryContext()->getLookupPtr()) {
-    for (auto I = Map->begin(); I != Map->end(); ++I) {
-      StoredDeclsList &List = I->second;
+    for (auto &&[Key, List] : *Map) {
       DeclContextLookupResult R = List.getLookupResult();
+      std::vector<NamedDecl *> NamedDeclsToRemove;
+      bool RemoveAll = true;
       for (NamedDecl *D : R) {
-        if (D->getTranslationUnitDecl() == MostRecentTU) {
+        if (D->getTranslationUnitDecl() == MostRecentTU)
+          NamedDeclsToRemove.push_back(D);
+        else
+          RemoveAll = false;
+      }
+      if (LLVM_LIKELY(RemoveAll)) {
+        Map->erase(Key);
+      } else {
+        for (NamedDecl *D : NamedDeclsToRemove)
           List.remove(D);
-        }
       }
-      if (List.isNull())
-        Map->erase(I);
     }
   }
 }