NAME | SYNOPSIS | DESCRIPTION | OPTIONS | OUTPUT STABILITY | CONFIGURATION | EXAMPLES | ALGORITHM | SEE ALSO | GIT | COLOPHON

GIT-RANGE-DIFF(1)                Git Manual                GIT-RANGE-DIFF(1)

NAME         top

       git-range-diff - Compare two commit ranges (e.g. two versions of a
       branch)

SYNOPSIS         top

       git range-diff [--color=[<when>]] [--no-color] [<diff-options>]
               [--no-dual-color] [--creation-factor=<factor>]
               ( <range1> <range2> | <rev1>...<rev2> | <base> <rev1> <rev2> )

DESCRIPTION         top

       This command shows the differences between two versions of a patch
       series, or more generally, two commit ranges (ignoring merge
       commits).

       To that end, it first finds pairs of commits from both commit ranges
       that correspond with each other. Two commits are said to correspond
       when the diff between their patches (i.e. the author information, the
       commit message and the commit diff) is reasonably small compared to
       the patches' size. See ``Algorithm`` below for details.

       Finally, the list of matching commits is shown in the order of the
       second commit range, with unmatched commits being inserted just after
       all of their ancestors have been shown.

OPTIONS         top

       --no-dual-color
           When the commit diffs differ, ‘git range-diff` recreates the
           original diffs’ coloring, and adds outer -/+ diff markers with
           the background being red/green to make it easier to see e.g. when
           there was a change in what exact lines were added.

           Additionally, the commit diff lines that are only present in the
           first commit range are shown "dimmed" (this can be overridden
           using the color.diff.<slot> config setting where <slot> is one of
           contextDimmed, oldDimmed and newDimmed), and the commit diff
           lines that are only present in the second commit range are shown
           in bold (which can be overridden using the config settings
           color.diff.<slot> with <slot> being one of contextBold, oldBold
           or newBold).

           This is known to range-diff as "dual coloring". Use
           --no-dual-color to revert to color all lines according to the
           outer diff markers (and completely ignore the inner diff when it
           comes to color).

       --creation-factor=<percent>
           Set the creation/deletion cost fudge factor to <percent>.
           Defaults to 60. Try a larger value if git range-diff erroneously
           considers a large change a total rewrite (deletion of one commit
           and addition of another), and a smaller one in the reverse case.
           See the ``Algorithm`` section below for an explanation why this
           is needed.

       <range1> <range2>
           Compare the commits specified by the two ranges, where <range1>
           is considered an older version of <range2>.

       <rev1>...<rev2>
           Equivalent to passing <rev2>..<rev1> and <rev1>..<rev2>.

       <base> <rev1> <rev2>
           Equivalent to passing <base>..<rev1> and <base>..<rev2>. Note
           that <base> does not need to be the exact branch point of the
           branches. Example: after rebasing a branch my-topic, git
           range-diff my-topic@{u} my-topic@{1} my-topic would show the
           differences introduced by the rebase.

       git range-diff also accepts the regular diff options (see
       git-diff(1)), most notably the --color=[<when>] and --no-color
       options. These options are used when generating the "diff between
       patches", i.e. to compare the author, commit message and diff of
       corresponding old/new commits. There is currently no means to tweak
       the diff options passed to git log when generating those patches.

OUTPUT STABILITY         top

       The output of the range-diff command is subject to change. It is
       intended to be human-readable porcelain output, not something that
       can be used across versions of Git to get a textually stable
       range-diff (as opposed to something like the --stable option to
       git-patch-id(1)). There’s also no equivalent of git-apply(1) for
       range-diff, the output is not intended to be machine-readable.

       This is particularly true when passing in diff options. Currently
       some options like --stat can, as an emergent effect, produce output
       that’s quite useless in the context of range-diff. Future versions of
       range-diff may learn to interpret such options in a manner specific
       to range-diff (e.g. for --stat producing human-readable output which
       summarizes how the diffstat changed).

CONFIGURATION         top

       This command uses the diff.color.* and pager.range-diff settings (the
       latter is on by default). See git-config(1).

EXAMPLES         top

       When a rebase required merge conflicts to be resolved, compare the
       changes introduced by the rebase directly afterwards using:

           $ git range-diff @{u} @{1} @

       A typical output of git range-diff would look like this:

           -:  ------- > 1:  0ddba11 Prepare for the inevitable!
           1:  c0debee = 2:  cab005e Add a helpful message at the start
           2:  f00dbal ! 3:  decafe1 Describe a bug
               @@ -1,3 +1,3 @@
                Author: A U Thor <author@example.com>

               -TODO: Describe a bug
               +Describe a bug
               @@ -324,5 +324,6
                 This is expected.

               -+What is unexpected is that it will also crash.
               ++Unexpectedly, it also crashes. This is a bug, and the jury is
               ++still out there how to fix it best. See ticket #314 for details.

                 Contact
           3:  bedead < -:  ------- TO-UNDO

       In this example, there are 3 old and 3 new commits, where the
       developer removed the 3rd, added a new one before the first two, and
       modified the commit message of the 2nd commit as well its diff.

       When the output goes to a terminal, it is color-coded by default,
       just like regular git diff's output. In addition, the first line
       (adding a commit) is green, the last line (deleting a commit) is red,
       the second line (with a perfect match) is yellow like the commit
       header of git show's output, and the third line colors the old commit
       red, the new one green and the rest like git show's commit header.

       A naive color-coded diff of diffs is actually a bit hard to read,
       though, as it colors the entire lines red or green. The line that
       added "What is unexpected" in the old commit, for example, is
       completely red, even if the intent of the old commit was to add
       something.

       To help with that, range uses the --dual-color mode by default. In
       this mode, the diff of diffs will retain the original diff colors,
       and prefix the lines with -/+ markers that have their background red
       or green, to make it more obvious that they describe how the diff
       itself changed.

ALGORITHM         top

       The general idea is this: we generate a cost matrix between the
       commits in both commit ranges, then solve the least-cost assignment.

       The cost matrix is populated thusly: for each pair of commits, both
       diffs are generated and the "diff of diffs" is generated, with 3
       context lines, then the number of lines in that diff is used as cost.

       To avoid false positives (e.g. when a patch has been removed, and an
       unrelated patch has been added between two iterations of the same
       patch series), the cost matrix is extended to allow for that, by
       adding fixed-cost entries for wholesale deletes/adds.

       Example: Let commits 1--2 be the first iteration of a patch series
       and A--C the second iteration. Let’s assume that A is a cherry-pick
       of 2, and C is a cherry-pick of 1 but with a small modification (say,
       a fixed typo). Visualize the commits as a bipartite graph:

               1            A

               2            B

                            C

       We are looking for a "best" explanation of the new series in terms of
       the old one. We can represent an "explanation" as an edge in the
       graph:

               1            A
                          /
               2 --------'  B

                            C

       This explanation comes for "free" because there was no change.
       Similarly C could be explained using 1, but that comes at some cost
       c>0 because of the modification:

               1 ----.      A
                     |    /
               2 ----+---'  B
                     |
                     `----- C
                     c>0

       In mathematical terms, what we are looking for is some sort of a
       minimum cost bipartite matching; ‘1` is matched to C at some cost,
       etc. The underlying graph is in fact a complete bipartite graph; the
       cost we associate with every edge is the size of the diff between the
       two commits’ patches. To explain also new commits, we introduce dummy
       nodes on both sides:

               1 ----.      A
                     |    /
               2 ----+---'  B
                     |
               o     `----- C
                     c>0
               o            o

               o            o

       The cost of an edge o--C is the size of C's diff, modified by a fudge
       factor that should be smaller than 100%. The cost of an edge o--o is
       free. The fudge factor is necessary because even if 1 and C have
       nothing in common, they may still share a few empty lines and such,
       possibly making the assignment 1--C, o--o slightly cheaper than 1--o,
       o--C even if 1 and C have nothing in common. With the fudge factor we
       require a much larger common part to consider patches as
       corresponding.

       The overall time needed to compute this algorithm is the time needed
       to compute n+m commit diffs and then n*m diffs of patches, plus the
       time needed to compute the least-cost assigment between n and m
       diffs. Git uses an implementation of the Jonker-Volgenant algorithm
       to solve the assignment problem, which has cubic runtime complexity.
       The matching found in this case will look like this:

               1 ----.      A
                     |    /
               2 ----+---'  B
                  .--+-----'
               o -'  `----- C
                     c>0
               o ---------- o

               o ---------- o

SEE ALSO         top

       git-log(1)

GIT         top

       Part of the git(1) suite

COLOPHON         top

       This page is part of the git (Git distributed version control system)
       project.  Information about the project can be found at 
       ⟨http://git-scm.com/⟩.  If you have a bug report for this manual page,
       see ⟨http://git-scm.com/community⟩.  This page was obtained from the
       project's upstream Git repository ⟨https://github.com/git/git.git⟩ on
       2019-05-09.  (At that time, the date of the most recent commit that
       was found in the repository was 2019-05-09.)  If you discover any
       rendering problems in this HTML version of the page, or you believe
       there is a better or more up-to-date source for the page, or you have
       corrections or improvements to the information in this COLOPHON
       (which is not part of the original manual page), send a mail to
       man-pages@man7.org

Git 2.21.0.896.g6a6c0f           05/08/2019                GIT-RANGE-DIFF(1)

Pages that refer to this page: git(1)git-config(1)git-format-patch(1)