From 10b12020a84a5dcd211b6625674eb2a4f46a0ccc Mon Sep 17 00:00:00 2001
From: Yuxuan Shui <yshuiv7@gmail.com>
Date: Wed, 28 Jan 2026 11:35:12 +0000
Subject: [PATCH 1/2] clang-tools: don't include C++ include paths in $CPATH

---
 .../compilers/llvm/common/clang-tools/wrapper | 24 ++++++++++++++++---
 1 file changed, 21 insertions(+), 3 deletions(-)

diff --git a/pkgs/development/compilers/llvm/common/clang-tools/wrapper b/pkgs/development/compilers/llvm/common/clang-tools/wrapper
index fa74a18b3c9f..c4ec3ed764ca 100755
--- a/pkgs/development/compilers/llvm/common/clang-tools/wrapper
+++ b/pkgs/development/compilers/llvm/common/clang-tools/wrapper
@@ -1,6 +1,24 @@
 #!/bin/sh
 
 buildcpath() {
+  local path after
+  while (( $# )); do
+    case $1 in
+        -isystem)
+            shift
+            path=$path${path:+':'}$1
+            ;;
+        -idirafter)
+            shift
+            after=$after${after:+':'}$1
+            ;;
+    esac
+    shift
+  done
+  echo $path${after:+':'}$after
+}
+
+buildcpluspath() {
   local path after
   while (( $# )); do
     case $1 in
@@ -32,9 +50,9 @@ if [ "$extendcpath" = true ]; then
   export CPATH=${CPATH}${CPATH:+':'}$(buildcpath ${NIX_CFLAGS_COMPILE} \
                                                  $(<@clang@/nix-support/libc-cflags))
 
-  export CPLUS_INCLUDE_PATH=${CPLUS_INCLUDE_PATH}${CPLUS_INCLUDE_PATH:+':'}$(buildcpath ${NIX_CFLAGS_COMPILE} \
-                                                                                        $(<@clang@/nix-support/libcxx-cxxflags) \
-                                                                                        $(<@clang@/nix-support/libc-cflags))
+  export CPLUS_INCLUDE_PATH=${CPLUS_INCLUDE_PATH}${CPLUS_INCLUDE_PATH:+':'}$(buildcpluspath ${NIX_CFLAGS_COMPILE} \
+                                                                                            $(<@clang@/nix-support/libcxx-cxxflags) \
+                                                                                            $(<@clang@/nix-support/libc-cflags))
 fi
 
 @out@/bin/$(basename $0)-unwrapped "$@"

From 0273d9cedf93e6a98142d97f6a8d0cabcf2287a1 Mon Sep 17 00:00:00 2001
From: Yuxuan Shui <yshuiv7@gmail.com>
Date: Wed, 28 Jan 2026 11:36:01 +0000
Subject: [PATCH 2/2] clang-tools: use $C_INCLUDE_PATH for C includes

$CPATH is taken to mean the same thing as -I by clang, whereas
$C_INCLUDE_PATH is -isystem. Using $CPATH means tools like clangd will
generate warnings for problems in system headers, which is undesirable.

See llvm/llvm-project#154015
---
 pkgs/development/compilers/llvm/common/clang-tools/wrapper | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/pkgs/development/compilers/llvm/common/clang-tools/wrapper b/pkgs/development/compilers/llvm/common/clang-tools/wrapper
index c4ec3ed764ca..bfd1da73cf61 100755
--- a/pkgs/development/compilers/llvm/common/clang-tools/wrapper
+++ b/pkgs/development/compilers/llvm/common/clang-tools/wrapper
@@ -47,8 +47,8 @@ for arg in "$@"; do
 done
 
 if [ "$extendcpath" = true ]; then
-  export CPATH=${CPATH}${CPATH:+':'}$(buildcpath ${NIX_CFLAGS_COMPILE} \
-                                                 $(<@clang@/nix-support/libc-cflags))
+  export C_INCLUDE_PATH=${CPATH}${CPATH:+':'}$(buildcpath ${NIX_CFLAGS_COMPILE} \
+                                                          $(<@clang@/nix-support/libc-cflags))
 
   export CPLUS_INCLUDE_PATH=${CPLUS_INCLUDE_PATH}${CPLUS_INCLUDE_PATH:+':'}$(buildcpluspath ${NIX_CFLAGS_COMPILE} \
                                                                                             $(<@clang@/nix-support/libcxx-cxxflags) \