licenses and readme

CMakeLists.txt

@@ -603,9 +603,20 @@ generate_export_header(${BRAVAIS_EXPORT_HEADER_TARGET}
     NO_EXPORT_MACRO_NAME BRAVAIS_LOCAL
     DEPRECATED_MACRO_NAME BRAVAIS_DEPRECATED
     STATIC_DEFINE BRAVAIS_STATIC_DEFINE
-    EXPORT_FILE_NAME ${CMAKE_CURRENT_BINARY_DIR}/include/bravais/export.h
+    EXPORT_FILE_NAME ${CMAKE_CURRENT_BINARY_DIR}/export.h.raw
 )
 
+# generate_export_header() cannot put anything above its include guard
+# (CUSTOM_CONTENT_FROM_VARIABLE lands at the bottom), so it writes to a scratch
+# file and the SPDX line is stamped on here. configure_file() only rewrites the
+# real header when its content changes, so reconfiguring does not force a
+# rebuild of everything that includes it.
+file(READ ${CMAKE_CURRENT_BINARY_DIR}/export.h.raw _export_h)
+file(WRITE ${CMAKE_CURRENT_BINARY_DIR}/export.h.stamped
+    "// SPDX-License-Identifier: LGPL-2.1-only OR LGPL-3.0-only OR MIT\n${_export_h}")
+configure_file(${CMAKE_CURRENT_BINARY_DIR}/export.h.stamped
+    ${CMAKE_CURRENT_BINARY_DIR}/include/bravais/export.h COPYONLY)
+
 foreach(_target IN LISTS BRAVAIS_LIB_TARGETS)
     set_target_properties(${_target} PROPERTIES
         C_VISIBILITY_PRESET hidden