Consider _global_defines in XcodeToolchain _check_if_extra_flags (#16429

)

* add test

* fix _check_if_extra_flags

conan/tools/apple/xcodetoolchain.py

@@ -109,7 +109,7 @@ def _agreggated_xconfig_filename(self):
 
     @property
     def _check_if_extra_flags(self):
-        return self._global_cflags or self._global_cxxflags or self._global_ldflags
+        return self._global_cflags or self._global_cxxflags or self._global_ldflags or self._global_defines
 
     @property
     def _flags_xcconfig_content(self):

test/integration/toolchains/apple/test_xcodetoolchain.py

@@ -72,3 +72,14 @@ def test_toolchain_flags():
     assert "OTHER_LDFLAGS = $(inherited) flag3 flag4" in conan_global_flags
     conan_global_file = client.load("conan_config.xcconfig")
     assert '#include "conan_global_flags.xcconfig"' in conan_global_file
+
+
+def test_flags_generated_if_only_defines():
+    # https://github.com/conan-io/conan/issues/16422
+    client = TestClient()
+    client.save({"conanfile.txt": "[generators]\nXcodeToolchain\n"})
+    client.run("install . -c 'tools.build:defines=[\"MYDEFINITION\"]'")
+    conan_global_flags = client.load("conan_global_flags.xcconfig")
+    assert "GCC_PREPROCESSOR_DEFINITIONS = $(inherited) MYDEFINITION" in conan_global_flags
+    conan_global_file = client.load("conan_config.xcconfig")
+    assert '#include "conan_global_flags.xcconfig"' in conan_global_file