Several optimization ideas about external git pod cache

[xuzhongping]

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Background

In fact, there are some problems with the current downloading and caching methods of external git pods or places that can be optimized. I would like to express my thoughts.

Idea

• It is necessary to fix the problem that shallow cloning cannot be performed when setting the branch parameters. I submitted my specific repair process PR in the cocoapods-downloader gem, and brought a more reasonable judgment logic, which can lead to more efficient downloads(this also works for release pods);
• If there is only one: git options, you can try to get the commit hash of the remote HEAD, which is similar to the processing of the branch parameter, this way is similar to Use git ls-remote to avoid git clones of :branch dependencies #5376, I created a commit in my branch;
• Try shallow git clones as much as possible (this also works for release pods);
• For the cache directory name of the external git pod, some unimportant parameters should be filtered. In fact, only using ‘commit’ to participate in the calculation of the directory name can make the cache reuse rate higher.

These solutions may involve both cocoapods and cocoapods-downloader gems. In order to make the discussion more efficient, I propose them here, thanks!