[CMake] cmp0026, file(GENERATE...), and configure_file

[Nils Gladitz]

On 04/23/2015 12:13 PM, Alan W. Irwin wrote:
> I think your idea of configure_file(GENERATE...) (where configure_file
> occurs at configure-time without GENERATE to be backwards compatible,
> but it occurs at generate-time if the new GENERATE signature is used)
> is an excellent way to allow users to replace the current clumsiness
> that is required to configure a file with both @ symbols and
> generator expressions.

I suppose for that to work configure_file() would have to either:

1. Store the values of all variables as they were set during the 
configure_file() call so that they can be expanded during generation.

2. Or perform variable substitution in-memory during the call and store 
the intermediate content for generator expressions substitution at 
generation time.

3. Or perform variable substitution during the call and store the 
intermediate content in a temporary file which then gets generator 
expression substitution at generation time.

None of those sound really optimal.

With 1. and 2. memory requirements might get out of hand.

With 3. you are basically back to something that acts like a 
configure_file() + file(GENERATE) wrapper except that cmake now has to 
come up with temporary filenames.

Nils