remove c++ std version for aten tests

Differential Revision: D94554543

Pull Request resolved: pytorch#17747

Author: JacobSzwejbka

shim_et/xplat/executorch/build/runtime_wrapper.bzl

@@ -125,14 +125,43 @@ def _patch_build_mode_flags(kwargs):
 
     return kwargs
 
+def _has_pytorch_dep(dep_list):
+    """Check if a dependency list contains PyTorch/ATen dependencies."""
+    if not dep_list:
+        return False
+    for dep in dep_list:
+        if type(dep) == "string":
+            if "torch" in dep or "libtorch" in dep or "caffe2" in dep:
+                return True
+    return False
+
 def _patch_test_compiler_flags(kwargs):
     if "compiler_flags" not in kwargs:
         kwargs["compiler_flags"] = []
 
-    # Required globally by all c++ tests.
-    kwargs["compiler_flags"] += [
-        "-std=c++17",
-    ]
+    # Determine C++ standard based on whether this is an aten test.
+    # Aten tests require at least C++20 to compile against PyTorch, while
+    # non-aten tests are pinned to C++17 for embedded.
+    name = kwargs.get("name", "")
+    external_deps = kwargs.get("external_deps", [])
+    deps = kwargs.get("deps", [])
+    xplat_deps = kwargs.get("xplat_deps", [])
+    fbcode_deps = kwargs.get("fbcode_deps", [])
+    is_aten_test = (
+        "_aten" in name or
+        "aten_" in name or
+        "libtorch" in external_deps or
+        "gtest_aten" in external_deps or
+        "gmock_aten" in external_deps or
+        _has_pytorch_dep(deps) or
+        _has_pytorch_dep(xplat_deps) or
+        _has_pytorch_dep(fbcode_deps)
+    )
+
+    if not is_aten_test:
+        kwargs["compiler_flags"] += [
+            "-std=c++17",
+        ]
 
     # Relaxing some constraints for tests
     kwargs["compiler_flags"] += [

third-party/gtest_defs.bzl

@@ -4,8 +4,7 @@ load("@fbsource//xplat/executorch/build:runtime_wrapper.bzl", "get_aten_mode_opt
 COMPILER_FLAGS = [
     "-std=c++17",
 ]
-COMPILER_FLAGS_ATEN = [
-    "-std=c++17",]
+COMPILER_FLAGS_ATEN = []
 
 # define_gtest_targets
 def define_gtest_targets():