如题：
Given your references to Vim in the question, I'm not sure if this is the answer you want :) but Emacs can do this.
Open the file containing the diff, make sure that you're in diff-mode (if the file is named foo.diff or foo.patch
this happens automatically; otherwise type M-x diff-mode RET), go to the hunk you are interested in and hit C-c C-b
for refine-hunk. Or step through the file one hunk at a time with M-n; that will do the refining automatically.
https://stackoverflow.com/questions/3231759/how-can-i-visualize-per-character-differences-in-a-unified-diff-file
emacs生疏了，不会用。暂时先不弄了。