From 390cc8a262468cd6381ef2193d1bc257a36d0917 Mon Sep 17 00:00:00 2001
From: Chris Eibl <138194463+chris-eibl@users.noreply.github.com>
Date: Mon, 23 Mar 2026 20:06:56 +0100
Subject: [PATCH 1/3] fix building the jit stencils on Windows when the

interpreter is built with a different clang version.
---
 ...-03-23-20-06-35.gh-issue-146210.C01Rmq.rst |  2 ++
 Tools/jit/_llvm.py                            | 19 ++++++++++++++++++-
 2 files changed, 20 insertions(+), 1 deletion(-)
 create mode 100644 Misc/NEWS.d/next/Build/2026-03-23-20-06-35.gh-issue-146210.C01Rmq.rst

diff --git a/Misc/NEWS.d/next/Build/2026-03-23-20-06-35.gh-issue-146210.C01Rmq.rst b/Misc/NEWS.d/next/Build/2026-03-23-20-06-35.gh-issue-146210.C01Rmq.rst
new file mode 100644
index 00000000000000..ce59a9a3a571b4
--- /dev/null
+++ b/Misc/NEWS.d/next/Build/2026-03-23-20-06-35.gh-issue-146210.C01Rmq.rst
@@ -0,0 +1,2 @@
+Fix building the jit stencils on Windows when the interpreter is built with
+a different clang version. Patch by Chris Eibl.
diff --git a/Tools/jit/_llvm.py b/Tools/jit/_llvm.py
index 8b68c1e8636af7..215013aa213305 100644
--- a/Tools/jit/_llvm.py
+++ b/Tools/jit/_llvm.py
@@ -42,9 +42,26 @@ async def _run(tool: str, args: typing.Iterable[str], echo: bool = False) -> str
     async with _CORES:
         if echo:
             print(shlex.join(command))
+
+        if os.name == "nt":
+            env = os.environ.copy()
+            try:
+                # https://github.com/python/cpython/issues/146210
+                # When the Python iterpreter is built with
+                # "/p:PlatformToolset=ClangCL" "/p:LLVMInstallDir=...""
+                # msbuild populates the INCLUDE variable based on this
+                # clang version, which might be different to the one used
+                # for building the jit stencils. Mixing those include paths
+                # can cause mysterious build errors, so we remove the
+                # variable from the environment when invoking LLVM tools.
+                del env["INCLUDE"]
+            except KeyError:
+                pass
+        else:
+            env = None
         try:
             process = await asyncio.create_subprocess_exec(
-                *command, stdout=subprocess.PIPE
+                *command, stdout=subprocess.PIPE, env=env
             )
         except FileNotFoundError:
             return None

From 1a08565b76a82707e61ff4ecbe6c80823262e611 Mon Sep 17 00:00:00 2001
From: Chris Eibl <138194463+chris-eibl@users.noreply.github.com>
Date: Fri, 3 Apr 2026 18:02:27 +0200
Subject: [PATCH 2/3] Use Savannah's much better and shorter description

Co-authored-by: Savannah Ostrowski <savannah@python.org>
---
 Tools/jit/_llvm.py | 12 ++++--------
 1 file changed, 4 insertions(+), 8 deletions(-)

diff --git a/Tools/jit/_llvm.py b/Tools/jit/_llvm.py
index 215013aa213305..0f7d7af640c26f 100644
--- a/Tools/jit/_llvm.py
+++ b/Tools/jit/_llvm.py
@@ -46,14 +46,10 @@ async def _run(tool: str, args: typing.Iterable[str], echo: bool = False) -> str
         if os.name == "nt":
             env = os.environ.copy()
             try:
-                # https://github.com/python/cpython/issues/146210
-                # When the Python iterpreter is built with
-                # "/p:PlatformToolset=ClangCL" "/p:LLVMInstallDir=...""
-                # msbuild populates the INCLUDE variable based on this
-                # clang version, which might be different to the one used
-                # for building the jit stencils. Mixing those include paths
-                # can cause mysterious build errors, so we remove the
-                # variable from the environment when invoking LLVM tools.
+                # When building with /p:PlatformToolset=ClangCL, the VS build
+                # system puts that clang's include path into INCLUDE. The JIT's
+                # clang may be a different version, and mismatched headers cause
+                # build errors. See https://github.com/python/cpython/issues/146210
                 del env["INCLUDE"]
             except KeyError:
                 pass

From 3c001368b0c1d853fc47c2b4f17f887c121a93c7 Mon Sep 17 00:00:00 2001
From: Chris Eibl <138194463+chris-eibl@users.noreply.github.com>
Date: Fri, 3 Apr 2026 18:07:29 +0200
Subject: [PATCH 3/3] env.pop("INCLUDE", None)

---
 Tools/jit/_llvm.py | 13 +++++--------
 1 file changed, 5 insertions(+), 8 deletions(-)

diff --git a/Tools/jit/_llvm.py b/Tools/jit/_llvm.py
index 0f7d7af640c26f..a4aaacdf41249d 100644
--- a/Tools/jit/_llvm.py
+++ b/Tools/jit/_llvm.py
@@ -44,15 +44,12 @@ async def _run(tool: str, args: typing.Iterable[str], echo: bool = False) -> str
             print(shlex.join(command))
 
         if os.name == "nt":
+            # When building with /p:PlatformToolset=ClangCL, the VS build
+            # system puts that clang's include path into INCLUDE. The JIT's
+            # clang may be a different version, and mismatched headers cause
+            # build errors. See https://github.com/python/cpython/issues/146210.
             env = os.environ.copy()
-            try:
-                # When building with /p:PlatformToolset=ClangCL, the VS build
-                # system puts that clang's include path into INCLUDE. The JIT's
-                # clang may be a different version, and mismatched headers cause
-                # build errors. See https://github.com/python/cpython/issues/146210
-                del env["INCLUDE"]
-            except KeyError:
-                pass
+            env.pop("INCLUDE", None)
         else:
             env = None
         try: