Proposal: Add CPM_MIRROR_PATH to automatically redirect all package fetches to a local mirror with fallback

[TobiasWallner]

I'd like to propose adding a new environment variable/CMake option ¹:

set(CPM_MIRROR_PATH "[email protected]:mirrors/")

This variable would automatically redirect all GITHUB_REPOSITORY or GIT_REPOSITORY downloads to a custom mirror location. For example:

CPMAddPackage("gh:fmtlib/[email protected]")

would internally try:

[email protected]:mirrors/fmt.git

If the mirror clone fails, CPM can then still gracefully fall back to the original upstream GitHub URL. Or not if CMAKE_MIRROR_NO_FALLBACK is set or something like that.

This would:

• Eliminate the need to maintain error-prone CPM_OVERRIDE_* scripts.
• Support transitive dependencies without additional effort.
• Greatly simplify CI setups, air-gapped builds, and enterprise environments.
• Encourage best practices like mirroring for reproducibility without sacrificing convenience.

Let me know if this aligns with the project's direction—I'd be happy to help implement this.

Footnotes

1. I searched for mirror, redirect, override, in discussions/code/readme but could only find the name secific CPM_OVERRIDE_* and not a global one. ↩