原始文档比较拗口，摘选如下：

--full-diff
Without this flag, git log -p ... shows commits that touch the specified paths, and diffs about the same specified paths. With this, the full diff is shown for commits that touch the specified paths; this means that "…" limits only commits, and doesn’t limit diff for those commits.

说人话，假设你提交了一个 Commit，这个 Commit Z 修改了 文件 A 和 B。

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