git-range-diff

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

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

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

DESCRIPTION
       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
       --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.

       --[no-]notes[=<ref>]
           This flag is passed to the git log program (see git-log(1)) that
           generates the patches.

       <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 most of the diff options passed to
       git log when generating those patches.

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

EXAMPLES
       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
       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 assignment 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
       git-log(1)

GIT
       Part of the git(1) suite

Git 2.25.1                        04/26/2023                 GIT-RANGE-DIFF(1)