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diff --git a/Documentation/git-range-diff.txt b/Documentation/git-range-diff.txt new file mode 100644 index 0000000000..9701c1e5fd --- /dev/null +++ b/Documentation/git-range-diff.txt @@ -0,0 +1,273 @@ +git-range-diff(1) +================= + +NAME +---- +git-range-diff - Compare two commit ranges (e.g. two versions of a branch) + +SYNOPSIS +-------- +[verse] +'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 linkgit: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 +linkgit: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 +linkgit:git-patch-id[1]). There's also no equivalent of +linkgit: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 linkgit: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 +-------- +linkgit:git-log[1] + +GIT +--- +Part of the linkgit:git[1] suite |