cmake: struggling with add_custom_command dependencies

user_176886 0
Viewed 22934

I'm trying to get a file produced by an add_custom_command in one directory to be a dependency of an add_custom_command in another directory.

In the first directory (lib/core) I have a build command that looks like this:

add_custom_command(
    OUTPUT libcore.bc
    COMMAND tartln -filetype=bc -link-as-library -o libcore.bc ${STDLIB_BC_FILES}
    DEPENDS ${STDLIB_BC_FILES} tartln
    COMMENT "Linking libcore.bc")

In the second directory, I have a command that uses the output of that command:

add_custom_command(OUTPUT ${OBJ_FILE}
    COMMAND tartln -disable-fp-elim -filetype=obj -o ${OBJ_FILE} ${BC_FILE}
        "${PROJECT_BINARY_DIR}/lib/core/libcore.bc"
    MAIN_DEPENDENCY "${BC_FILE}" 
    DEPENDS "${PROJECT_BINARY_DIR}/lib/core/libcore.bc"
    COMMENT "Linking Tart bitcode file ${BC_FILE}")

However, when I try to build, I get the following error:

make[3]: *** No rule to make target `lib/core/libcore.bc', needed by `test/stdlib/ReflectionTest.o'.  Stop.

One weird thing that I see is that the path in the error message is a relative, not an absolute path, despite the fact that I know that ${PROJECT_BINARY_DIR} is a full, correct path. I don't know if this is a problem or just a strangeness of make.

I've also tried making a top-level target for the libcore library, in the lib/core directory:

add_custom_target(libcore DEPENDS libcore.bc libcore.deps)

And then using that in the DEPENDS clause. The strange thing about that is it works the first time you do a clean build, but gives an error on any subsequent build. In any case, my understanding is DEPENDS is only supposed to work for file dependencies, so this doesn't seem like the correct solution. (How do you have a custom command that depends on a top-level target then?)

I've also tried putting absolute paths everywhere, no effect.

cmake
4 Answers

This is a non-answer but a clarification to one of your answers above.

According to the cmake documents, a custom target created by add_custom_target is always considered out of date and is always built.

IMO, the cmake documents should say instead:

A custom target created by add_custom_target is always considered out of date and is always built, but only when requested.

That means that if all of your targets are marked as EXCLUDE_FROM_ALL, and you have add_custom_target commands that create new targets, and you type make from the command line with no targets specified, the targets added with add_custom_target are not built. But if you spell them out on the make command line explicitly, then they are built. Also, there is the ALL keyword that you can specify to the add_custom_target to force those to be built as a part of the all rule, which I believe means when make is executed without arguments.

user_2579240
user_104220630
Related