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 2.27.0 06/01/2020 GIT-RANGE-DIFF(1)