80151fe git diff: improve range handling

2 files Authored by Chris Torek 3 years ago, Committed by ddevault 3 years ago,
    git diff: improve range handling
    
    When git diff is given a symmetric difference A...B, it chooses
    some merge base from the two specified commits (as documented).
    
    This fails, however, if there is *no* merge base: instead, you
    see the differences between A and B, which is certainly not what
    is expected.
    
    Moreover, if additional revisions are specified on the command
    line ("git diff A...B C"), the results get a bit weird:
    
     * If there is a symmetric difference merge base, this is used
       as the left side of the diff.  The last final ref is used as
       the right side.
     * If there is no merge base, the symmetric status is completely
       lost.  We will produce a combined diff instead.
    
    Similar weirdness occurs if you use, e.g., "git diff C A...B D".
    Likewise, using multiple two-dot ranges, or tossing extra
    revision specifiers into the command line with two-dot ranges,
    or mixing two and three dot ranges, all produce nonsense.
    
    To avoid all this, add a routine to catch the range cases and
    verify that that the arguments make sense.  As a side effect,
    produce a warning showing *which* merge base is being used when
    there are multiple choices; die if there is no merge base.
    
    Signed-off-by: Chris Torek <chris.torek@gmail.com>
    
        
file modified
+111 -13