fix: isolate tvm-ffi from TVM's C++20 build standard

CMakeLists.txt

@@ -672,7 +672,11 @@ if(USE_IOS_RPC)
   add_subdirectory("apps/ios_rpc")
 endif()
 
+set(TVM_CXX_STANDARD ${CMAKE_CXX_STANDARD})
+set(CMAKE_CXX_STANDARD 17)
 add_subdirectory(3rdparty/tvm-ffi)
+set(CMAKE_CXX_STANDARD ${TVM_CXX_STANDARD})
+unset(TVM_CXX_STANDARD)
 
 if(TVM_DEBUG_WITH_ABI_CHANGE)
   message(STATUS "Building with debug code that may cause ABI changes...")

tests/scripts/task_build.py

@@ -17,9 +17,11 @@
 # under the License.
 # ruff: noqa: E402
 import argparse
+import json
 import logging
 import multiprocessing
 import os
+import re
 import shutil
 import sys
 from pathlib import Path
@@ -29,6 +31,68 @@
 sys.path.append(str(REPO_ROOT / "ci" / "scripts" / "jenkins"))
 from cmd_utils import REPO_ROOT, Sh, init_log
 
+
+def _check_cxx_standard(build_dir):
+    compile_commands_path = REPO_ROOT / build_dir / "compile_commands.json"
+    with open(compile_commands_path, encoding="utf-8") as compile_commands_file:
+        compile_commands = json.load(compile_commands_file)
+
+    standard_flag_pattern = re.compile(r"^(?:-std=(?:c|gnu)\+\+|/std:c\+\+)(.+)$", re.IGNORECASE)
+    tvm_ffi_commands = []
+    tvm_commands = []
+
+    for compile_command in compile_commands:
+        source = Path(compile_command["file"])
+        if not source.is_absolute():
+            source = Path(compile_command["directory"]) / source
+        try:
+            source = source.resolve().relative_to(REPO_ROOT)
+        except ValueError:
+            continue
+
+        if source.suffix.lower() not in {".cc", ".cpp", ".cxx"}:
+            continue
+
+        arguments = compile_command.get("arguments")
+        if arguments is None:
+            arguments = compile_command["command"].split()
+        standard_flags = []
+        for argument in arguments:
+            argument = argument.strip("\"'")
+            match = standard_flag_pattern.match(argument)
+            if match:
+                standard_flags.append((argument, match.group(1).lower()))
+
+        if source.parts[:2] == ("3rdparty", "tvm-ffi"):
+            tvm_ffi_commands.append((source, standard_flags, compile_command))
+        elif source.parts[0] == "src":
+            tvm_commands.append((source, standard_flags, compile_command))
+
+    if not tvm_ffi_commands:
+        raise RuntimeError("No C++ compile commands found for 3rdparty/tvm-ffi")
+    if not tvm_commands:
+        raise RuntimeError("No C++ compile commands found for TVM src/")
+
+    for source, standard_flags, compile_command in tvm_ffi_commands:
+        if standard_flags and standard_flags[-1][1] not in {"17", "1z"}:
+            raise RuntimeError(
+                f"tvm-ffi source {source} must use C++17, but its compile command contains "
+                f"{', '.join(flag for flag, _ in standard_flags)}: {compile_command}"
+            )
+
+    for source, standard_flags, compile_command in tvm_commands:
+        if not standard_flags or standard_flags[-1][1] not in {"20", "2a"}:
+            raise RuntimeError(
+                f"TVM source {source} must use C++20, but its compile command is: {compile_command}"
+            )
+
+    logging.info(
+        "Verified C++ standards in %s tvm-ffi and %s TVM compile commands",
+        len(tvm_ffi_commands),
+        len(tvm_commands),
+    )
+
+
 if __name__ == "__main__":
     init_log()
 
@@ -90,6 +154,8 @@
     else:
         sh.run("cmake -GNinja -DCMAKE_BUILD_TYPE=RelWithDebInfo ..", cwd=build_dir)
 
+    _check_cxx_standard(build_dir)
+
     target = ""
     if args.cmake_target:
         target = args.cmake_target