CMake: Add a subdirectory build regression test
If we have a regression with the "build Mbed Crypto as a subdirectory
with CMake" feature and fail to build, fail the test.
diff --git a/programs/test/cmake_subproject/.gitignore b/programs/test/cmake_subproject/.gitignore
new file mode 100644
index 0000000..464833b
--- /dev/null
+++ b/programs/test/cmake_subproject/.gitignore
@@ -0,0 +1,3 @@
+build
+Makefile
+cmake_subproject
diff --git a/programs/test/cmake_subproject/CMakeLists.txt b/programs/test/cmake_subproject/CMakeLists.txt
new file mode 100644
index 0000000..3afbdb2
--- /dev/null
+++ b/programs/test/cmake_subproject/CMakeLists.txt
@@ -0,0 +1,17 @@
+cmake_minimum_required(VERSION 2.6)
+
+# We use the parent Mbed TLS directory as the MBEDTLS_DIR for this test. Other
+# projects that use Mbed TLS as a subproject are likely to add by their own
+# relative paths.
+set(MBEDTLS_DIR ../../../)
+
+# Add Mbed TLS as a subdirectory.
+add_subdirectory(${MBEDTLS_DIR} build)
+
+# Link against the Mbed Crypto library.
+set(libs
+ mbedcrypto
+)
+
+add_executable(cmake_subproject cmake_subproject.c)
+target_link_libraries(cmake_subproject ${libs})
diff --git a/programs/test/cmake_subproject/cmake_subproject.c b/programs/test/cmake_subproject/cmake_subproject.c
new file mode 100644
index 0000000..ca899bc
--- /dev/null
+++ b/programs/test/cmake_subproject/cmake_subproject.c
@@ -0,0 +1,56 @@
+/*
+ * Simple program to test that CMake builds with Mbed TLS as a subdirectory
+ * work correctly.
+ *
+ * Copyright (C) 2006-2019, ARM Limited, All Rights Reserved
+ * SPDX-License-Identifier: Apache-2.0
+ *
+ * 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.
+ *
+ * This file is part of mbed TLS (https://tls.mbed.org)
+ */
+
+#if !defined(MBEDTLS_CONFIG_FILE)
+#include "mbedtls/config.h"
+#else
+#include MBEDTLS_CONFIG_FILE
+#endif
+
+#if defined(MBEDTLS_PLATFORM_C)
+#include "mbedtls/platform.h"
+#else
+#include <stdio.h>
+#include <stdlib.h>
+#define mbedtls_fprintf fprintf
+#define mbedtls_printf printf
+#define mbedtls_exit exit
+#define MBEDTLS_EXIT_SUCCESS EXIT_SUCCESS
+#define MBEDTLS_EXIT_FAILURE EXIT_FAILURE
+#endif /* MBEDTLS_PLATFORM_C */
+
+#include "mbedtls/version.h"
+
+/* The main reason to build this is for testing the CMake build, so the program
+ * doesn't need to do very much. It calls a single library function to ensure
+ * linkage works, but that is all. */
+int main()
+{
+ /* This version string is 18 bytes long, as advised by version.h. */
+ char version[18];
+
+ mbedtls_version_get_string_full( version );
+
+ mbedtls_printf( "Built against %s\n", version );
+
+ return( 0 );
+}