optionally disable git lfs when cloning

[sbowman-mitre]

When using CPMAddPackage, it would help if there was a separate parameter for GIT_LFS, similar to GIT_SHALLOW.

Problem: some git repos contain large files for testing that should not be pulled by CPM during build processes. It would help if the user of CPM could enable/disable use of git-lfs with each use of CPMAddPackage.

Proposed Solution: Add a new parameter here for GIT_LFS that is boolean. So it could be used like this:

CPMAddPackage(
  NAME pkg_name
  GIT_REPOSITORY url
  GIT_SHALLOW TRUE
  GIT_LFS FALSE # proposed new parameter
)

The default should be backward compatible: TRUE.

[Avus-c]

Background on CPM Internals

1. CPM relies on CMake’s FetchContent module, which in turn uses CMake’s ExternalProject module. Repository cloning is handled entirely by CMake’s built-in functionality, so any feature changing the behaviour of git depends on CMake supporting the required option.

2. Any arguments passed to CPMAddPackage that CPM does not process are forwarded to FetchContent and then to ExternalProject_Add.

---

The only potential way to modify the git clone command is through the GIT_CONFIG argument in ExternalProject_Add (cmake doc). As far as I can determine, a config parameter to disable Git LFS does not appear to exist. So disabling Git LFS is currently not possible. That being sad I have never used git-lfs and the chances are high that I've overlocked some crucial information in making this work.

Hopefully, this additional context about CPM’s internals will be helpful to you or others. :)

[sbowman-mitre]

😢 OK, thanks for the detailed explanation @Avus-c! That helps narrow down where a potential fix might occur.

[sbowman-mitre]

For reference, also this older discussion along same lines: #518