find_package only works with -DCMAKE_PREFIX_PATH with default install directory

Usage
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1

Hi!
I have a library, say A, which depends on B. A uses find_dependency in its AConfig.cmake and B is downloaded via FetchContent. A is, before being built manually with cmake, installed in some directory C:/Program files (x86)/A. It contains:

# C:/Program files (x86)/
A/
  include/
  lib/
    B.lib
    Bd.lib
    cmake/
      A/
        AConfig.cmake
        AConfigVersion.cmake
        ATargets.cmake
      B/
        B-config.cmake
        B-config-version.cmake
        B-targets-cmake
        # debug and release cmake files

In another project, say C, I want to use A. I’m doing this in the following manner:

# boilerplate ...
find_package(A CONFIG REQUIRED)
target_link_libraries(my-target A::A)

But I’m getting the error it cant find the dependency of A (B in this case). It says I have to set B_dir (or CMAKE_PREFIX_PATH), but this “feels” weird, because the dependency B is in the same installation directory as A. What can I do to solve this without using B_dir, if this is even possible? Related note: AConfig.cmake looks as follows:

include(CMakeFindDependencyMacro)
find_dependency(B)

include("${CMAKE_CURRENT_LIST_DIR}/ATargets.cmake")
2

Can you expand on how you’ve arranged for B to be downloaded using FetchContent, specifically what details were in its FetchContent_Declare() call? In order for find_dependency(B) to be redirected to the B that you obtained with FetchContent, you need to use the appropriate options in FetchContent_Declare().

3

The FetchContent_Declare isn’t too exciting I think. Also, I think it is handy to know that the code did work on my Linux (Ubuntu) laptop. Anyway, the following code is used:

FetchContent_Declare(B
	URL https://github.com/Blib/B/archive/refs/tags/9.1.0.tar.gz 
	UPDATE_DISCONNECTED YES 
	URL_MD5 21fac48cae8f3b4a5783ae06b443973a
	DOWNLOAD_EXTRACT_TIMESTAMP TRUE
)
FetchContent_MakeAvailable(B)
# ...
target_link_libraries(A INTERFACE B::B)

Using

#...
find_dependency(B HINTS "${CMAKE_CURRENT_LIST_DIR}/../B/"

Also solves the problem, but again, I don’t think this is meant to be.

4

That FetchContent_Declare() call won’t set up the redirection of find_package(B) or find_dependency(B) calls. You would have to add either OVERRIDE_FIND_PACKAGE or FIND_PACKAGE_ARGS to the FetchContent_Declare() call to trigger that behavior. Please take a look at the FetchContent docs for what those options do and how to use them appropriately.

That seems dubious. It suggests your Linux case was picking up a different B from somewhere else.

6

So adding:

FetchContent_Declare(B
    URL https://github.com/Blib/B/archive/refs/tags/9.1.0.tar.gz 
    UPDATE_DISCONNECTED YES 
    URL_MD5 21fac48cae8f3b4a5783ae06b443973a
    DOWNLOAD_EXTRACT_TIMESTAMP TRUE
    OVERRIDE_FIND_PACKAGE # <----
)

Would be sufficient? (if so, this unfortunately does not work) If not, then I am not sure I understand the documentation, or maybe my question was formulated poorly. I’d also like to point out again that A is an installed library in C:/Program Files (x86)/A, and C is somewhere located in C:/Users/my-name/Documents/C.

7

Taking a step back, I wouldn’t recommend using FetchContent calls embedded in A’s AConfig.cmake to provide B unless that’s the only way B can be obtained (i.e. B does not provide its own BConfig.cmake). Even then, I’d only typically consider that for a company environment where things are fairly controlled, not for a general open source project where people may want to use it in all sorts of different ways. I don’t know which situation you are in.

I don’t know that I can help too much without seeing the whole picture with more details. I won’t be around for the next few weeks though, so you may need others to help you out.

8

That is rather unfortunate since the discourse what sort of my “last resort”. However, the problem is not that important and it can wait a few weeks because, and this is a nice bridge to what you asked earlier:

Actually, it is a hobby open-source project so maybe it is better to see the whole picture. The CMakeLists can be found here: cpp-lazy/CMakeLists.txt at master · MarcDirven/cpp-lazy · GitHub.

Basically, I want people to give the freedom to do one of the following:

  1. Use my project in their project using FetchContent, which is already possible.
  2. Use my project in theirs, using find_package(cpp-lazy CONFIG REQUIRED) without -DCMAKE_PREFIX_PATH or -Dfmt_DIR after they’ve (built cpp-lazy from source and) installed it. But this gives the error describe above. It can’t find the fmt dir, which is a dependency of cpp-lazy. Ofcourse, this only should be possible if it is installed in a default installation directory; i.e. C:\Program Files\cpp-lazy or some Linux equivalent.