Fix default behavior for API level clamping.

When not specified this was evaluating to an empty string, so CMake
was receiving only one argument...

Test: added a test
Bug: android/ndk#1560
Change-Id: I1340a7b0afd271568c5f8aadbc4ca345479e95fa

build/cmake/android.toolchain.cmake

@@ -167,8 +167,7 @@ elseif(ANDROID_TOOLCHAIN STREQUAL gcc)
 endif()
 
 include(${CMAKE_ANDROID_NDK}/build/cmake/adjust_api_level.cmake)
-adjust_api_level(${ANDROID_PLATFORM} CMAKE_SYSTEM_VERSION)
-message(STATUS "CMAKE_SYSTEM_VERSION=${CMAKE_SYSTEM_VERSION}")
+adjust_api_level("${ANDROID_PLATFORM}" CMAKE_SYSTEM_VERSION)
 
 if(NOT DEFINED CMAKE_ANDROID_STL_TYPE AND DEFINED ANDROID_STL)
   set(CMAKE_ANDROID_STL_TYPE ${ANDROID_STL})

tests/build/cmake_toolchain_defaults/project/CMakeLists.txt

@@ -0,0 +1,4 @@
+cmake_minimum_required(VERSION 3.6)
+project(ToolchainDefaultsTest CXX)
+
+add_library(foo SHARED foo.cpp)

tests/build/cmake_toolchain_defaults/project/foo.cpp

@@ -0,0 +1,8 @@
+#if !defined(__ARM_ARCH_7A__)
+#error ABI did not default to armeabi-v7a
+#endif
+
+// Update this whenever we raise the minimum API level in the NDK.
+#if __ANDROID_API__ != 19
+#error API level did not default to 19
+#endif

tests/build/cmake_toolchain_defaults/test.py

@@ -0,0 +1,51 @@
+#
+# Copyright (C) 2021 The Android Open Source Project
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#      http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+#
+"""Check that the default CMake toolchain behavior works."""
+from pathlib import Path
+import subprocess
+
+from ndk.cmake import find_cmake, find_ninja
+from ndk.test.spec import BuildConfiguration, CMakeToolchainFile
+
+
+def run_test(ndk_path: str, config: BuildConfiguration) -> tuple[bool, str]:
+    """Check that the default CMake toolchain behavior works.
+
+    All our regular CMake tests pass the API level and ABI explicitly. This
+    test checks that the defaults (armeabi-v7a, minimum supported API level)
+    work.
+    """
+    cmake = find_cmake()
+    ninja = find_ninja()
+    toolchain_path = Path(ndk_path) / 'build/cmake/android.toolchain.cmake'
+    project_path = 'project'
+    if config.toolchain_file is CMakeToolchainFile.Legacy:
+        toolchain_mode = 'ON'
+    else:
+        toolchain_mode = 'OFF'
+    cmake_cmd = [
+        str(cmake),
+        f'-DCMAKE_TOOLCHAIN_FILE={toolchain_path}',
+        f'-DCMAKE_MAKE_PROGRAM={ninja}',
+        f'-DANDROID_USE_LEGACY_TOOLCHAIN_FILE={toolchain_mode}',
+        '-GNinja',
+    ]
+    result = subprocess.run(cmake_cmd,
+                            check=False,
+                            cwd=project_path,
+                            capture_output=True,
+                            text=True)
+    return result.returncode == 0, result.stdout

tests/build/cmake_toolchain_defaults/test_config.py

@@ -0,0 +1,10 @@
+from typing import Optional
+
+from ndk.abis import LP32_ABIS
+from ndk.test.types import Test
+
+
+def build_unsupported(test: Test) -> Optional[str]:
+    if test.config.abi in LP32_ABIS:
+        return test.config.abi
+    return None