[clang] Fix error recovery while PTU cleanup (PR #127467)

[Anutosh Bhat via cfe-commits]

https://github.com/anutosh491 created https://github.com/llvm/llvm-project/pull/127467

Fixes #123300

What is seen 
```
clang-repl> int x = 42;
clang-repl> auto capture = [&]() { return x * 2; };
In file included from <<< inputs >>>:1:
input_line_4:1:17: error: non-local lambda expression cannot have a capture-default
    1 | auto capture = [&]() { return x * 2; };
      |                 ^
zsh: segmentation fault  clang-repl --Xcc="-v"
```

Though the error is justified, we shouldn't be interested in exiting through a segfault in such cases.

The issue is that empty named decls weren't being taken care of resulting into this assert 

https://github.com/llvm/llvm-project/blob/c1a229252617ed58f943bf3f4698bd8204ee0f04/clang/include/clang/AST/DeclarationName.h#L503

Can also be seen when the example is attempted through xeus-cpp-lite.

![image](https://github.com/user-attachments/assets/9b0e6ead-138e-4b06-9ad9-fcb9f8d5bf6e)




>From 6ff448ed506e0ef75db2c9974a628a965e85df2f Mon Sep 17 00:00:00 2001
From: anutosh491 <andersonbhat491 at gmail.com>
Date: Mon, 17 Feb 2025 15:33:20 +0530
Subject: [PATCH] Fix error recovery while PTU cleanup

---
 clang/lib/Interpreter/IncrementalParser.cpp     | 4 ++--
 clang/unittests/Interpreter/InterpreterTest.cpp | 7 +++++++
 2 files changed, 9 insertions(+), 2 deletions(-)

diff --git a/clang/lib/Interpreter/IncrementalParser.cpp b/clang/lib/Interpreter/IncrementalParser.cpp
index e43cea1baf43a..1ebef0e434b3d 100644
--- a/clang/lib/Interpreter/IncrementalParser.cpp
+++ b/clang/lib/Interpreter/IncrementalParser.cpp
@@ -178,8 +178,8 @@ void IncrementalParser::CleanUpPTU(TranslationUnitDecl *MostRecentTU) {
     if (!ND)
       continue;
     // Check if we need to clean up the IdResolver chain.
-    if (ND->getDeclName().getFETokenInfo() && !D->getLangOpts().ObjC &&
-        !D->getLangOpts().CPlusPlus)
+    if (!ND->getDeclName().isEmpty() && ND->getDeclName().getFETokenInfo() &&
+        !D->getLangOpts().ObjC && !D->getLangOpts().CPlusPlus)
       S.IdResolver.RemoveDecl(ND);
   }
 }
diff --git a/clang/unittests/Interpreter/InterpreterTest.cpp b/clang/unittests/Interpreter/InterpreterTest.cpp
index 578f1d4c0eac6..56ab155ebf5a4 100644
--- a/clang/unittests/Interpreter/InterpreterTest.cpp
+++ b/clang/unittests/Interpreter/InterpreterTest.cpp
@@ -114,6 +114,13 @@ TEST_F(InterpreterTest, Errors) {
 
   RecoverErr = Interp->Parse("var1 = 424;");
   EXPECT_TRUE(!!RecoverErr);
+
+  Err = Interp->Parse("int x = 5; auto capture = [&]() { return x * 2; };").takeError();
+  EXPECT_THAT(DiagnosticOutput, HasSubstr("error: non-local lambda expression cannot have a capture-default"));
+  EXPECT_EQ("Parsing failed.", llvm::toString(std::move(Err)));
+
+  RecoverErr = Interp->Parse("int validVar = 10;");
+  EXPECT_TRUE(!!RecoverErr);
 }
 
 // Here we test whether the user can mix declarations and statements. The