CMake FetchContent support

[ivan-ushakov]

Is it possible to make FetchContent support? If I use this declaration:

FetchContent_Declare(
  hiredis
  GIT_REPOSITORY https://github.com/redis/hiredis
  GIT_TAG origin/master
  GIT_SHALLOW TRUE
)

set(DISABLE_TESTS OFF)

FetchContent_MakeAvailable(hiredis)

I get header files inside _deps/hiredis-src, not include/hiredis/ and this leads to build error for Redis++ library.

[michael-grunder]

Hi,

I'm honestly not sure what the right way to get this to work is. It looks like using _deps/<project>-src is just what CMake does by default.

Here's a blog post saying as much.

I suppose you would need to somehow forward the custom include directory to redisplusplus, but I'm not familiar enough with CMake to tell you how 😅

Edit: Looks like you can tell redisplusplus where to look for hiredis with
-DCMAKE_PREFIX_PATH=/path/to/hiredis, so perhaps you can set that after fetching and before trying to build redisplusplus.

[bjosv]

@ivan-ushakov I tried this out and got hiredis and redis++ to build using following gist.

I found two issues during this:

• I needed to disable building tests in redis++ as well due to its use of find_library(hiredis)
• redis++ seems to export a different include path than expected.

The tests in redis++ uses find_library(hiredis) instead of find_package(hiredis) and I believe FetchContent only works well with find_package(). By disabling the building of tests the cmake generation works.
To fix the exported include path I had to include <redis++.h> instead of <sw/redis++/redis++.h> in main.cc.
I believe both are possible issues in redis++.

Would the setup from the gist work for you?

[bjosv]

Sorry! The gist above might not work after all..
I found out that I had hiredis installed in an additional non-default/weird place and CMake actually found that when building.. back to the drawing board..

[bjosv]

Updated the gist to make it work, but requires CMake 3.24.
I had to to jump through hoops, so there might be a nicer solution..

[ivan-ushakov]

Updated the gist to make it work, but requires CMake 3.24.
I had to to jump through hoops, so there might be a nicer solution..

With this two hacks:

SOURCE_DIR _deps/hiredis

# Set include directory to enable redis++ to find it
include_directories(${CMAKE_BINARY_DIR}/_deps)

It works, but maybe in future this could be solved without hacks.

[cwaldren]

Thank you for the gist.

A note for people searching: redis-plus-plus's 1.3.8 release breaks this workaround by introducing a feature test using CheckSymbolExists ("Support keepalive with customized interval" changelog entry.)

It seems that the hiredis::hiredis alias isn't available for the macro to use. Haven't found a solution yet.

[vrince]

Worked for me out of the box (the same way I FetchContent other projects):

# hiredis
include(FetchContent)
FetchContent_Declare(hiredis 
  GIT_REPOSITORY https://github.com/redis/hiredis.git 
  GIT_TAG v1.2.0 
  GIT_SHALLOW TRUE 
  GIT_PROGRESS TRUE)

if(NOT hiredis)
    FetchContent_Populate(hiredis)
    add_subdirectory(${hiredis_SOURCE_DIR} ${hiredis_BINARY_DIR} EXCLUDE_FROM_ALL)
endif()

Then later you can use hiredis with:

target_link_libraries(your-target PRIVATE hiredis)
...

Cmake v 3.22.1