From 5c2b05d0eb5fe08cb1cbb4b7d133e30308c49835 Mon Sep 17 00:00:00 2001
From: "J. Nick Koston" <nick@koston.org>
Date: Sat, 17 Oct 2026 09:00:51 -1000
Subject: [PATCH] [ci] Run the C++ unit tests on macOS without a sanitizer
 whose runtime aborts (#21000)

---
 script/cpp_unit_test.py | 57 ++++++++++++++++++++++++++++++++++++++---
 1 file changed, 53 insertions(+), 4 deletions(-)

diff --git a/script/cpp_unit_test.py b/script/cpp_unit_test.py
index c5179a1b1e9..c2b34e1b409 100755
--- a/script/cpp_unit_test.py
+++ b/script/cpp_unit_test.py
@@ -3,7 +3,9 @@ import argparse
 from functools import partial
 import os
 from pathlib import Path
+import subprocess
 import sys
+import tempfile
 
 from build_helpers import (
     PLATFORMIO_GOOGLE_TEST_LIB,
@@ -12,6 +14,9 @@ from build_helpers import (
 )
 from helpers import get_all_components, root_path
 
+from esphome.core import EsphomeError
+from esphome.host.toolchain import find_compilers
+
 # Path to /tests/components
 COMPONENTS_TESTS_DIR: Path = Path(root_path) / "tests" / "components"
 
@@ -20,11 +25,55 @@ BUILD_FLAGS = [
     "-g3",  # max debug info
     "-ggdb3",
     "-DESPHOME_DEBUG",  # enable debug assertions
-    # Enable the address and undefined behavior sanitizers
-    "-fsanitize=address",
-    "-fsanitize=undefined",
     "-fno-omit-frame-pointer",
 ]
+SANITIZER_FLAGS = ["-fsanitize=address", "-fsanitize=undefined"]
+
+
+def sanitizer_flags() -> list[str]:
+    """The sanitizer flags to build with: all of them, except on macOS the ones whose runtime
+    does not start. Apple clang 15's AddressSanitizer aborts before main() on macOS 26, which
+    would fail every test for a toolchain problem, so each flag is tried on an empty program
+    first. A compiler that cannot build the empty program is an error, not a dropped flag.
+    CI keeps every flag.
+    """
+    if sys.platform != "darwin":
+        return SANITIZER_FLAGS
+    try:
+        cxx = find_compilers().cxx
+    except EsphomeError as err:
+        sys.exit(str(err))
+    flags: list[str] = []
+    with tempfile.TemporaryDirectory() as tmp:
+        program = Path(tmp) / "probe"
+        for flag in SANITIZER_FLAGS:
+            compiled = subprocess.run(
+                [*cxx, flag, "-x", "c++", "-", "-o", program],
+                check=False,
+                input=b"int main() { return 0; }",
+                capture_output=True,
+            )
+            if compiled.returncode != 0:
+                sys.exit(
+                    f"{cxx[0]} cannot build an empty program with {flag}:\n"
+                    f"{compiled.stderr.decode(errors='replace').strip()}"
+                )
+            ran = subprocess.run([program], check=False, capture_output=True)
+            if ran.returncode == 0:
+                flags.append(flag)
+                continue
+            lines = [
+                line
+                for line in ran.stderr.decode(errors="replace").splitlines()
+                if line.strip()
+            ]
+            print(
+                f"{flag} aborts at start with {cxx[0]}: "
+                f"{lines[0] if lines else f'exit code {ran.returncode}'}\n"
+                "  building the tests without it; set CXX to a compiler whose runtime works to keep it",
+                file=sys.stderr,
+            )
+    return flags
 
 
 def run_tests(selected_components: list[str]) -> int:
@@ -39,7 +88,7 @@ def run_tests(selected_components: list[str]) -> int:
         config_prefix="cpptests",
         friendly_name="CPP Unit Tests",
         libraries=PLATFORMIO_GOOGLE_TEST_LIB,
-        build_flags=BUILD_FLAGS,
+        build_flags=BUILD_FLAGS + sanitizer_flags(),
         main_entry="main.cpp",
         label="unit tests",
     )