[clang] [clang-tools-extra] [clangd] Disable PCH for libs that use gRPC (PR #185185)

[Alexis Engelke via cfe-commits]

https://github.com/aengelke created https://github.com/llvm/llvm-project/pull/185185

gRPC adds -pthread, which is incompatible with PCH without it. At some point, we probably should generally switch from -lpthread to -pthread, but until then, disable PCH for affected targets.

Fixes https://github.com/llvm/llvm-project/issues/184759.

>From f0882faafe93401bdafccd85f11ba848ae777b23 Mon Sep 17 00:00:00 2001
From: Alexis Engelke <engelke at in.tum.de>
Date: Sat, 7 Mar 2026 12:50:13 +0000
Subject: [PATCH] [clangd] Disable PCH for libs that use gRPC

gRPC adds -pthread, which is incompatible with PCH without it.
At some point, we probably should generally switch from -lpthread to
-pthread, but until then, disable PCH for affected targets.

Fixes https://github.com/llvm/llvm-project/issues/184759.
---
 clang-tools-extra/clangd/index/remote/CMakeLists.txt         | 3 +++
 .../clangd/index/remote/marshalling/CMakeLists.txt           | 3 +++
 clang-tools-extra/clangd/index/remote/monitor/CMakeLists.txt | 3 +++
 clang-tools-extra/clangd/index/remote/server/CMakeLists.txt  | 3 +++
 clang/cmake/modules/AddGRPC.cmake                            | 5 ++++-
 5 files changed, 16 insertions(+), 1 deletion(-)

diff --git a/clang-tools-extra/clangd/index/remote/CMakeLists.txt b/clang-tools-extra/clangd/index/remote/CMakeLists.txt
index 28df71855a142..ef4d04b47dae2 100644
--- a/clang-tools-extra/clangd/index/remote/CMakeLists.txt
+++ b/clang-tools-extra/clangd/index/remote/CMakeLists.txt
@@ -32,6 +32,9 @@ if (CLANGD_ENABLE_REMOTE)
     DEPENDS
     clangdRemoteIndexProto
     clangdRemoteIndexServiceProto
+
+    # Disable PCH, gRPC adds -pthread.
+    DISABLE_PCH_REUSE
     )
 
   clang_target_link_libraries(clangdRemoteIndex
diff --git a/clang-tools-extra/clangd/index/remote/marshalling/CMakeLists.txt b/clang-tools-extra/clangd/index/remote/marshalling/CMakeLists.txt
index d7e37003e5f98..74963e838677c 100644
--- a/clang-tools-extra/clangd/index/remote/marshalling/CMakeLists.txt
+++ b/clang-tools-extra/clangd/index/remote/marshalling/CMakeLists.txt
@@ -8,4 +8,7 @@ add_clang_library(clangdRemoteMarshalling STATIC
 
   DEPENDS
   clangdRemoteIndexProto
+
+  # Disable PCH, gRPC adds -pthread.
+  DISABLE_PCH_REUSE
   )
diff --git a/clang-tools-extra/clangd/index/remote/monitor/CMakeLists.txt b/clang-tools-extra/clangd/index/remote/monitor/CMakeLists.txt
index 194c7d5128a98..53351ae901b3d 100644
--- a/clang-tools-extra/clangd/index/remote/monitor/CMakeLists.txt
+++ b/clang-tools-extra/clangd/index/remote/monitor/CMakeLists.txt
@@ -6,6 +6,9 @@ add_clang_executable(clangd-index-server-monitor
 
   DEPENDS
   clangdRemoteIndexServiceProto
+
+  # Disable PCH, gRPC adds -pthread.
+  DISABLE_PCH_REUSE
   )
 
 target_link_libraries(clangd-index-server-monitor
diff --git a/clang-tools-extra/clangd/index/remote/server/CMakeLists.txt b/clang-tools-extra/clangd/index/remote/server/CMakeLists.txt
index 3bea34826f8a1..12090d83928fd 100644
--- a/clang-tools-extra/clangd/index/remote/server/CMakeLists.txt
+++ b/clang-tools-extra/clangd/index/remote/server/CMakeLists.txt
@@ -7,6 +7,9 @@ add_clang_executable(clangd-index-server
   DEPENDS
   clangdRemoteIndexProto
   clangdRemoteIndexServiceProto
+
+  # Disable PCH, gRPC adds -pthread.
+  DISABLE_PCH_REUSE
   )
 
 target_link_libraries(clangd-index-server
diff --git a/clang/cmake/modules/AddGRPC.cmake b/clang/cmake/modules/AddGRPC.cmake
index 8989bd757d247..5d752bf86459d 100644
--- a/clang/cmake/modules/AddGRPC.cmake
+++ b/clang/cmake/modules/AddGRPC.cmake
@@ -7,5 +7,8 @@ function(generate_clang_protos_library LibraryName ProtoFile)
 
   add_clang_library(${LibraryName} ${ProtoSource}
     PARTIAL_SOURCES_INTENDED
-    LINK_LIBS PUBLIC grpc++ protobuf)
+    LINK_LIBS PUBLIC grpc++ protobuf
+    # Disable PCH, gRPC adds -pthread.
+    DISABLE_PCH_REUSE
+    )
 endfunction()