diff options
Diffstat (limited to 'Documentation/gitdiffcore.txt')
| -rw-r--r-- | Documentation/gitdiffcore.txt | 333 |
1 files changed, 0 insertions, 333 deletions
diff --git a/Documentation/gitdiffcore.txt b/Documentation/gitdiffcore.txt deleted file mode 100644 index 642c51227b..0000000000 --- a/Documentation/gitdiffcore.txt +++ /dev/null @@ -1,333 +0,0 @@ -gitdiffcore(7) -============== - -NAME ----- -gitdiffcore - Tweaking diff output - -SYNOPSIS --------- -[verse] -'git diff' * - -DESCRIPTION ------------ - -The diff commands 'git diff-index', 'git diff-files', and 'git diff-tree' -can be told to manipulate differences they find in -unconventional ways before showing 'diff' output. The manipulation -is collectively called "diffcore transformation". This short note -describes what they are and how to use them to produce 'diff' output -that is easier to understand than the conventional kind. - - -The chain of operation ----------------------- - -The 'git diff-{asterisk}' family works by first comparing two sets of -files: - - - 'git diff-index' compares contents of a "tree" object and the - working directory (when `--cached` flag is not used) or a - "tree" object and the index file (when `--cached` flag is - used); - - - 'git diff-files' compares contents of the index file and the - working directory; - - - 'git diff-tree' compares contents of two "tree" objects; - -In all of these cases, the commands themselves first optionally limit -the two sets of files by any pathspecs given on their command-lines, -and compare corresponding paths in the two resulting sets of files. - -The pathspecs are used to limit the world diff operates in. They remove -the filepairs outside the specified sets of pathnames. E.g. If the -input set of filepairs included: - ------------------------------------------------- -:100644 100644 bcd1234... 0123456... M junkfile ------------------------------------------------- - -but the command invocation was `git diff-files myfile`, then the -junkfile entry would be removed from the list because only "myfile" -is under consideration. - -The result of comparison is passed from these commands to what is -internally called "diffcore", in a format similar to what is output -when the -p option is not used. E.g. - ------------------------------------------------- -in-place edit :100644 100644 bcd1234... 0123456... M file0 -create :000000 100644 0000000... 1234567... A file4 -delete :100644 000000 1234567... 0000000... D file5 -unmerged :000000 000000 0000000... 0000000... U file6 ------------------------------------------------- - -The diffcore mechanism is fed a list of such comparison results -(each of which is called "filepair", although at this point each -of them talks about a single file), and transforms such a list -into another list. There are currently 5 such transformations: - -- diffcore-break -- diffcore-rename -- diffcore-merge-broken -- diffcore-pickaxe -- diffcore-order -- diffcore-rotate - -These are applied in sequence. The set of filepairs 'git diff-{asterisk}' -commands find are used as the input to diffcore-break, and -the output from diffcore-break is used as the input to the -next transformation. The final result is then passed to the -output routine and generates either diff-raw format (see Output -format sections of the manual for 'git diff-{asterisk}' commands) or -diff-patch format. - - -diffcore-break: For Splitting Up Complete Rewrites --------------------------------------------------- - -The second transformation in the chain is diffcore-break, and is -controlled by the -B option to the 'git diff-{asterisk}' commands. This is -used to detect a filepair that represents "complete rewrite" and -break such filepair into two filepairs that represent delete and -create. E.g. If the input contained this filepair: - ------------------------------------------------- -:100644 100644 bcd1234... 0123456... M file0 ------------------------------------------------- - -and if it detects that the file "file0" is completely rewritten, -it changes it to: - ------------------------------------------------- -:100644 000000 bcd1234... 0000000... D file0 -:000000 100644 0000000... 0123456... A file0 ------------------------------------------------- - -For the purpose of breaking a filepair, diffcore-break examines -the extent of changes between the contents of the files before -and after modification (i.e. the contents that have "bcd1234..." -and "0123456..." as their SHA-1 content ID, in the above -example). The amount of deletion of original contents and -insertion of new material are added together, and if it exceeds -the "break score", the filepair is broken into two. The break -score defaults to 50% of the size of the smaller of the original -and the result (i.e. if the edit shrinks the file, the size of -the result is used; if the edit lengthens the file, the size of -the original is used), and can be customized by giving a number -after "-B" option (e.g. "-B75" to tell it to use 75%). - - -diffcore-rename: For Detecting Renames and Copies -------------------------------------------------- - -This transformation is used to detect renames and copies, and is -controlled by the -M option (to detect renames) and the -C option -(to detect copies as well) to the 'git diff-{asterisk}' commands. If the -input contained these filepairs: - ------------------------------------------------- -:100644 000000 0123456... 0000000... D fileX -:000000 100644 0000000... 0123456... A file0 ------------------------------------------------- - -and the contents of the deleted file fileX is similar enough to -the contents of the created file file0, then rename detection -merges these filepairs and creates: - ------------------------------------------------- -:100644 100644 0123456... 0123456... R100 fileX file0 ------------------------------------------------- - -When the "-C" option is used, the original contents of modified files, -and deleted files (and also unmodified files, if the -"--find-copies-harder" option is used) are considered as candidates -of the source files in rename/copy operation. If the input were like -these filepairs, that talk about a modified file fileY and a newly -created file file0: - ------------------------------------------------- -:100644 100644 0123456... 1234567... M fileY -:000000 100644 0000000... bcd3456... A file0 ------------------------------------------------- - -the original contents of fileY and the resulting contents of -file0 are compared, and if they are similar enough, they are -changed to: - ------------------------------------------------- -:100644 100644 0123456... 1234567... M fileY -:100644 100644 0123456... bcd3456... C100 fileY file0 ------------------------------------------------- - -In both rename and copy detection, the same "extent of changes" -algorithm used in diffcore-break is used to determine if two -files are "similar enough", and can be customized to use -a similarity score different from the default of 50% by giving a -number after the "-M" or "-C" option (e.g. "-M8" to tell it to use -8/10 = 80%). - -Note that when rename detection is on but both copy and break -detection are off, rename detection adds a preliminary step that first -checks if files are moved across directories while keeping their -filename the same. If there is a file added to a directory whose -contents are sufficiently similar to a file with the same name that got -deleted from a different directory, it will mark them as renames and -exclude them from the later quadratic step (the one that pairwise -compares all unmatched files to find the "best" matches, determined by -the highest content similarity). So, for example, if a deleted -docs/ext.txt and an added docs/config/ext.txt are similar enough, they -will be marked as a rename and prevent an added docs/ext.md that may -be even more similar to the deleted docs/ext.txt from being considered -as the rename destination in the later step. For this reason, the -preliminary "match same filename" step uses a bit higher threshold to -mark a file pair as a rename and stop considering other candidates for -better matches. At most, one comparison is done per file in this -preliminary pass; so if there are several remaining ext.txt files -throughout the directory hierarchy after exact rename detection, this -preliminary step may be skipped for those files. - -Note. When the "-C" option is used with `--find-copies-harder` -option, 'git diff-{asterisk}' commands feed unmodified filepairs to -diffcore mechanism as well as modified ones. This lets the copy -detector consider unmodified files as copy source candidates at -the expense of making it slower. Without `--find-copies-harder`, -'git diff-{asterisk}' commands can detect copies only if the file that was -copied happened to have been modified in the same changeset. - - -diffcore-merge-broken: For Putting Complete Rewrites Back Together ------------------------------------------------------------------- - -This transformation is used to merge filepairs broken by -diffcore-break, and not transformed into rename/copy by -diffcore-rename, back into a single modification. This always -runs when diffcore-break is used. - -For the purpose of merging broken filepairs back, it uses a -different "extent of changes" computation from the ones used by -diffcore-break and diffcore-rename. It counts only the deletion -from the original, and does not count insertion. If you removed -only 10 lines from a 100-line document, even if you added 910 -new lines to make a new 1000-line document, you did not do a -complete rewrite. diffcore-break breaks such a case in order to -help diffcore-rename to consider such filepairs as a candidate of -rename/copy detection, but if filepairs broken that way were not -matched with other filepairs to create rename/copy, then this -transformation merges them back into the original -"modification". - -The "extent of changes" parameter can be tweaked from the -default 80% (that is, unless more than 80% of the original -material is deleted, the broken pairs are merged back into a -single modification) by giving a second number to -B option, -like these: - -* -B50/60 (give 50% "break score" to diffcore-break, use 60% - for diffcore-merge-broken). - -* -B/60 (the same as above, since diffcore-break defaults to 50%). - -Note that earlier implementation left a broken pair as separate -creation and deletion patches. This was an unnecessary hack, and -the latest implementation always merges all the broken pairs -back into modifications, but the resulting patch output is -formatted differently for easier review in case of such -a complete rewrite by showing the entire contents of the old version -prefixed with '-', followed by the entire contents of the new -version prefixed with '+'. - - -diffcore-pickaxe: For Detecting Addition/Deletion of Specified String ---------------------------------------------------------------------- - -This transformation limits the set of filepairs to those that change -specified strings between the preimage and the postimage in a certain -way. -S<block-of-text> and -G<regular-expression> options are used to -specify different ways these strings are sought. - -"-S<block-of-text>" detects filepairs whose preimage and postimage -have different number of occurrences of the specified block of text. -By definition, it will not detect in-file moves. Also, when a -changeset moves a file wholesale without affecting the interesting -string, diffcore-rename kicks in as usual, and `-S` omits the filepair -(since the number of occurrences of that string didn't change in that -rename-detected filepair). When used with `--pickaxe-regex`, treat -the <block-of-text> as an extended POSIX regular expression to match, -instead of a literal string. - -"-G<regular-expression>" (mnemonic: grep) detects filepairs whose -textual diff has an added or a deleted line that matches the given -regular expression. This means that it will detect in-file (or what -rename-detection considers the same file) moves, which is noise. The -implementation runs diff twice and greps, and this can be quite -expensive. To speed things up, binary files without textconv filters -will be ignored. - -When `-S` or `-G` are used without `--pickaxe-all`, only filepairs -that match their respective criterion are kept in the output. When -`--pickaxe-all` is used, if even one filepair matches their respective -criterion in a changeset, the entire changeset is kept. This behavior -is designed to make reviewing changes in the context of the whole -changeset easier. - -diffcore-order: For Sorting the Output Based on Filenames ---------------------------------------------------------- - -This is used to reorder the filepairs according to the user's -(or project's) taste, and is controlled by the -O option to the -'git diff-{asterisk}' commands. - -This takes a text file each of whose lines is a shell glob -pattern. Filepairs that match a glob pattern on an earlier line -in the file are output before ones that match a later line, and -filepairs that do not match any glob pattern are output last. - -As an example, a typical orderfile for the core Git probably -would look like this: - ------------------------------------------------- -README -Makefile -Documentation -*.h -*.c -t ------------------------------------------------- - -diffcore-rotate: For Changing At Which Path Output Starts ---------------------------------------------------------- - -This transformation takes one pathname, and rotates the set of -filepairs so that the filepair for the given pathname comes first, -optionally discarding the paths that come before it. This is used -to implement the `--skip-to` and the `--rotate-to` options. It is -an error when the specified pathname is not in the set of filepairs, -but it is not useful to error out when used with "git log" family of -commands, because it is unreasonable to expect that a given path -would be modified by each and every commit shown by the "git log" -command. For this reason, when used with "git log", the filepair -that sorts the same as, or the first one that sorts after, the given -pathname is where the output starts. - -Use of this transformation combined with diffcore-order will produce -unexpected results, as the input to this transformation is likely -not sorted when diffcore-order is in effect. - - -SEE ALSO --------- -linkgit:git-diff[1], -linkgit:git-diff-files[1], -linkgit:git-diff-index[1], -linkgit:git-diff-tree[1], -linkgit:git-format-patch[1], -linkgit:git-log[1], -linkgit:gitglossary[7], -link:user-manual.html[The Git User's Manual] - -GIT ---- -Part of the linkgit:git[1] suite |