https://github.com/jeaye updated 
https://github.com/llvm/llvm-project/pull/217147

>From 70e981be85bdd64258434ee30054b05acb833de6 Mon Sep 17 00:00:00 2001
From: jeaye <[email protected]>
Date: Tue, 18 Aug 2026 13:10:09 -0700
Subject: [PATCH] [clang-repl] Stop interpreter init on action failure
MIME-Version: 1.0
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`clang::Interpreter` previously ignored the result of its initial
`CompilerInstance::ExecuteAction()` call and always constructed the
`IncrementalParser`. When the initial action failed, the parser could be
created from an invalid compiler state.

In practice, this failure happens if the incremental PCH included
has expired, due to system headers changing. This happens quite
regularly, after system updates, and is affecting jank.

To fix this, the `Interpreter` now returns an error immediately when the
initial action fails or records a diagnostic error.
---
 clang/lib/Interpreter/Interpreter.cpp |  8 +++++++-
 clang/test/Interpreter/stale-pch.cpp  | 23 +++++++++++++++++++++++
 2 files changed, 30 insertions(+), 1 deletion(-)
 create mode 100644 clang/test/Interpreter/stale-pch.cpp

diff --git a/clang/lib/Interpreter/Interpreter.cpp 
b/clang/lib/Interpreter/Interpreter.cpp
index 0536fdcd548a2..d612c8d878f32 100644
--- a/clang/lib/Interpreter/Interpreter.cpp
+++ b/clang/lib/Interpreter/Interpreter.cpp
@@ -349,7 +349,13 @@ Interpreter::Interpreter(std::unique_ptr<CompilerInstance> 
Instance,
   if (ErrOut)
     return;
 
-  CI->ExecuteAction(*Act);
+  if (!CI->ExecuteAction(*Act) || CI->getDiagnostics().hasErrorOccurred()) {
+    ErrOut = joinErrors(
+        std::move(ErrOut),
+        llvm::createStringError(llvm::errc::not_supported,
+                                "Failed to execute incremental action"));
+    return;
+  }
 
   IncrParser =
       std::make_unique<IncrementalParser>(*CI, Act.get(), ErrOut, PTUs);
diff --git a/clang/test/Interpreter/stale-pch.cpp 
b/clang/test/Interpreter/stale-pch.cpp
new file mode 100644
index 0000000000000..410a91fe7d8f0
--- /dev/null
+++ b/clang/test/Interpreter/stale-pch.cpp
@@ -0,0 +1,23 @@
+// REQUIRES: host-supports-jit
+// UNSUPPORTED: system-aix
+//
+// RUN: rm -rf %t
+// RUN: mkdir -p %t
+// RUN: split-file %s %t
+//
+// RUN: %if system-windows %{ \
+// RUN: %clang -fmax-type-align=16 -Xclang -fdeprecated-macro 
-fno-stack-protector -Xclang -fwrapv -Xclang -fblocks -Xclang 
-fskip-odr-check-in-gmf -fexceptions -fcxx-exceptions -fgnuc-version=0 -target 
%host-jit-triple -Xclang -fblocks -Xclang -fmax-type-align=8 -Xclang 
-fincremental-extensions -Xclang -emit-pch -x c++-header -o %t/include.pch 
%t/include.hpp \
+// RUN: %} \
+// RUN: %else %{ \
+// RUN: %clang -fPIC -fmax-type-align=16 -Xclang -fdeprecated-macro 
-fno-stack-protector -Xclang -fwrapv -Xclang -fblocks -Xclang 
-fskip-odr-check-in-gmf -fexceptions -fcxx-exceptions -fgnuc-version=0 -target 
%host-jit-triple -Xclang -fblocks -Xclang -fmax-type-align=8 -Xclang 
-fincremental-extensions -Xclang -emit-pch -x c++-header -o %t/include.pch 
%t/include.hpp \
+// RUN: %}
+// RUN: echo '// changed after PCH creation' >> %t/include.hpp
+//
+// RUN: not clang-repl -Xcc -fgnuc-version=0 -Xcc -fno-stack-protector -Xcc 
-fwrapv -Xcc -fblocks -Xcc -fskip-odr-check-in-gmf -Xcc -fmax-type-align=8 -Xcc 
-include-pch -Xcc %t/include.pch < /dev/null 2>&1 | FileCheck %s
+
+//--- include.hpp
+
+int f_pch() { return 5; }
+
+// CHECK: fatal error: file '{{.*}}include.hpp' has been modified since the 
precompiled header
+// CHECK: clang-repl: Failed to execute incremental action

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