Proper way to call a found executable in a custom command?

Question

I have a program on my computer, let's say C:/Tools/generate_v23_debug.exe

I have a FindGenerate.cmake file which allows CMake to find that exact path to the executable.

So in my CMake code, I do:

find_program(Generate)
if (NOT Generate_FOUND)
    message(FATAL_ERROR "Generator not found!")

So CMake has found the executable. Now I want to call this program in a custom command statement. Should I use COMMAND Generator or COMMAND ${GENERATOR_EXECUTABLE}? Will both of these do the same thing? Is one preferred over the other? Is name_EXECUTABLE a variable that CMake will define (it's not in the FindGenerate.cmake file), or is it something specific to someone else's example code I'm looking at? Will COMMAND Generator be expanded to the correct path?

add_custom_command(
    OUTPUT blahblah.txt
    COMMAND Generator inputfile1.log
    DEPENDS Generator
)

Answer 1

find_program stores its result into the variable given as a first argument. You can verify this by inserting some debug output:

find_program(GENERATOR Generate)
message(${GENERATOR})

Note that find_program does not set any additional variables beyond that. In particular, you mentioned Generate_FOUND and GENERATOR_EXECUTABLE in your question and neither of those gets introduced implicitly by the find_program call.

The second mistake in your program is the use of the DEPENDS option on the add_custom_command. DEPENDS is used to model inter-target dependencies at build time and not to manipulate control flow in the CMakeLists. For example, additional custom command can DEPEND on the output of your command (blahblah.txt), but a custom command cannot DEPEND on the result of a previous find operation.

A working example might look something like this:

find_program(GENERATOR Generate)
if(NOT GENERATOR)
    message(FATAL_ERROR "Generator not found!")
endif()

add_custom_command(
    OUTPUT blahblah.txt
    COMMAND ${GENERATOR} inputfile1.log
)

P.S.: You asked why the code examples were not properly formatted in your question. You indented everything correctly, but you need an additional newline between normal text and code paragraphs. I edited your question accordingly.