build error (and suggested fix). CMake has trouble with variables containing '/' characters

[geoffthorpe]

I am encountering a build failure and, upon a little inspection, the issue seems to be here;

libvdeslirp/CMakeLists.txt

Lines 30 to 35 in 01af3c3

	foreach(HEADER IN LISTS HEADERS_REQUIRED)
	check_include_file(${HEADER} ${HEADER}_OK)
	if(NOT ${HEADER}_OK)
	message(FATAL_ERROR "header file ${HEADER} not found")
	endif()
	endforeach(HEADER)

In particular, the HEADERS_REQUIRED variable contains two files; libvdeplug.h and slirp/libslirp.h. It seems that the latter is the problem, because it has a '/' in the path, and using that as part of a variable name (as the second parameter to check_include_file, on line 31) fails on my version of CMake. The following hack allows the build to complete and the resulting tools seem to do what they're supposed to;

 foreach(HEADER IN LISTS HEADERS_REQUIRED)
-  check_include_file(${HEADER} ${HEADER}_OK)
-  if(NOT ${HEADER}_OK)
+  check_include_file(${HEADER} FOOBAR_OK)
+  if(NOT FOOBAR_OK)
     message(FATAL_ERROR "header file ${HEADER} not found")
   endif()
 endforeach(HEADER)

Here, the same result variable is used for each/every header detection, which seems reasonable because you're not remembering/using these detection results later on - the build fails immediately unless they're TRUE. Otherwise, I assume another strategy would be required for having per-header detection variables. The precise CMake rules on what variable names can and can't be is not very clear, but the guidance is to keep it to alphanumeric + '_' + '-'; https://cmake.org/cmake/help/latest/manual/cmake-language.7.html#variables

BTW, this VDE stuff is awesome. Extremely useful. :-) Thanks!