Initial Release

cmake/build_variants/CMakeLists.txt

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+# 1 Create an INTERFACE library aggregating all the common parts of the application
+add_library(common_stuff INTERFACE)
+
+# note cmake policy is to use absolute paths for interface libraries.
+target_sources(common_stuff INTERFACE
+        ${CMAKE_CURRENT_LIST_DIR}/main.c
+        ${CMAKE_CURRENT_LIST_DIR}/other.c
+        )
+
+target_compile_definitions(common_stuff INTERFACE
+        A_DEFINE_THAT_IS_SHARED=123
+        )
+
+# can include library dependencies here
+target_link_libraries(common_stuff INTERFACE
+        pico_stdlib
+        )
+
+# 2 Create the first executable including all the common stuff...
+#    we can set compile definitions for this executable here too. Because
+#    we depend on an INTERFACE library (common_stuff) we
+#    will pick up all of its definitions/dependencies too
+add_executable(build_variant1)
+target_link_libraries(build_variant1 common_stuff)
+target_compile_definitions(build_variant1 PRIVATE
+        A_DEFINE_THAT_IS_NOT_SHARED=456)
+pico_add_extra_outputs(build_variant1)
+
+# 3 Create a second executable including all the common stuff
+#    this version also sets the DO_EXTRA define
+add_executable(build_variant2)
+target_link_libraries(build_variant2 common_stuff)
+target_compile_definitions(build_variant2 PRIVATE
+        A_DEFINE_THAT_IS_NOT_SHARED=789
+        DO_EXTRA)
+pico_add_extra_outputs(build_variant2)
+

cmake/build_variants/main.c

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+/*
+ * Copyright (c) 2020 Raspberry Pi (Trading) Ltd.
+ *
+ * SPDX-License-Identifier: BSD-3-Clause
+ */
+
+#include <stdio.h>
+#include "pico/stdlib.h"
+#include "other.h"
+
+int main() {
+    stdio_init_all();
+    do_other();
+#ifdef DO_EXTRA
+    printf("A little extra\n");
+#endif
+    return 0;
+}

cmake/build_variants/other.c

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+/*
+ * Copyright (c) 2020 Raspberry Pi (Trading) Ltd.
+ *
+ * SPDX-License-Identifier: BSD-3-Clause
+ */
+
+#include <stdio.h>
+#include "other.h"
+
+void do_other() {
+    printf("The common thing is %d\n",
+           A_DEFINE_THAT_IS_SHARED);
+    printf("The binary local thing is %d\n",
+           A_DEFINE_THAT_IS_NOT_SHARED);
+}

cmake/build_variants/other.h

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+/*
+ * Copyright (c) 2020 Raspberry Pi (Trading) Ltd.
+ *
+ * SPDX-License-Identifier: BSD-3-Clause
+ */
+
+void do_other();