CMAKE: Creating and building a list within a function -- with directory, or global scope

Question

I am not entirely familiar with the scoping rules of cmake. I need to buildup a list of various files whilst doing RPC code-generation for an IDL.

function(generate_rpc file_name)
  set(PROTO_FILES ${PROTO_FILES} ${file_name})
endfunction(generate_rpc)

generate_rpc(BasicProtocol.proto)
generate_rpc(dummy.proto)

message(STATUS "PROTO FILES: ${PROTO_FILES}")

The list is empty each time. I need append-able list that can be built from within a function.

Answer 1

Although Macros are defined and called in the same manner as functions, there are some differences between them, for example in SCOPE and when its execution.

SCOPE:

• Macro: has global scope.
• Function: has a local scope whether you don't specify.

EXECUTION: it works like C++ or C

• Macro: the variable names are replaced to strings before configuring.

• Function: the variable names are replaced during execution.

In conclusion, add the PARENT_SCOPE flag in set command

set(PROTO_FILES ${PROTO_FILES} ${file_name} PARENT_SCOPE)

Answer 2

Using a macro instead of a function seems to do it:

macro(generate_rpc file_name)
  set(PROTO_FILES ${PROTO_FILES} ${file_name})
endmacro(generate_rpc)

EDIT: According to http://www.cmake.org/cmake/help/syntax.html (should be in the man page, IMO):

CMake functions create a local scope for variables, and macros use the global scope.