Add shallow option to ecbuild_bundle

[mcakircali]

Description

Adds a SHALLOW flag to ecbuild_git and ecbuild_bundle.

When SHALLOW is specified, initial checkouts use git clone --depth 1. If a specific BRANCH or TAG is combined with SHALLOW, it instructs Git to only clone that specific branch/tag (--branch ).

When combined with the RECURSIVE option, submodules are also initialized and updated using the --depth 1 flag.

NOTE:
Because Git cannot shallow clone a commit ID directly, SHALLOW will cause to throw if the TAG matches the pattern of a Git commit hash (SHA).

TAG <commit_hash> SHALLOW -> this will throw
TAG <tag_name> SHALLOW -> this will work

Contributor Declaration

By opening this pull request, I affirm the following:

• All authors agree to the Contributor License Agreement.
• The code follows the project's coding standards.
• I have performed self-review and added comments where needed.
• I have added or updated tests to verify that my changes are effective and functional.
• I have run all existing tests and confirmed they pass.

[Copilot]

Pull request overview

Adds a SHALLOW option to the bundle/git helper macros to support shallow checkouts (depth 1) and shallow submodule initialisation, reducing clone time and bandwidth for bundled projects.

Changes:

• Extend ecbuild_git() with a SHALLOW option to add --depth 1 to initial clones and optionally submodule updates.
• Update ecbuild_git() behaviour to avoid fetch/pull operations when SHALLOW is enabled.
• Document the new SHALLOW option in ecbuild_git and ecbuild_bundle.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 2 comments.

File	Description
cmake/ecbuild_git.cmake	Implements SHALLOW cloning/submodule depth logic and adjusts fetch/pull behaviour.
cmake/ecbuild_bundle.cmake	Documents the new SHALLOW option for bundle users (forwarded to ecbuild_git).

---

💡 Add Copilot custom instructions for smarter, more guided reviews. Learn how to get started.