A Wrapper Around FetchContent

Introduction

fetch_content(...) is a wrapper around the CMake module FetchContent

That standard module is a tool to pull a code base or library from a remote repo into a project that will use it.

For example, the consumer of a remote library might have some lines in their CMakeLists.txt file like these:

include(FetchContent)
FetchContent_Declare(ExternalLib URL https:://github.com/.../ExternalLib.git ...)
FetchContent_MakeAvailable(ExternalLib)

Those trailing …’s in that first FetchContent_Declare call represent the many options that function can have. Some of those options should be the default. Adding those defaults is the primary purpose of fetch_content.

Usage

Assuming the fetch_content.cmake file is located in a top-level cmake directory in the CMakeLists.txt file, you might use the function as follows:

list(APPEND CMAKE_MODULE_PATH "${CMAKE_SOURCE_DIR}/cmake")
include(fetch_content)
fetch_content(ExternalLib URL https:://github.com/.../ExternalLib.git ...)

This will essentially do the FetchContent_Declare, and FetchContent_MakeAvailable calls above but will also add several recommended options to those calls. In particular, it will tell FetchContent to check to see if the package is already available on the system, avoiding cloning any repo. It will also ensure that any repo clones done will be as shallow as possible to speed things up.

This module will probably change in the future as FetchContent develops.

The CMake Package Manager CPM is a much fuller featured wrapper around FetchContent.