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diff --git a/Documentation/diffcore.txt b/Documentation/diffcore.txt deleted file mode 100644 index cb4e562004..0000000000 --- a/Documentation/diffcore.txt +++ /dev/null @@ -1,275 +0,0 @@ -Tweaking diff output -==================== -June 2005 - - -Introduction ------------- - -The diff commands git-diff-index, git-diff-files, git-diff-tree, and -git-diff-stages can be told to manipulate differences they find in -unconventional ways before showing diff(1) output. The manipulation -is collectively called "diffcore transformation". This short note -describes what they are and how to use them to produce diff outputs -that are easier to understand than the conventional kind. - - -The chain of operation ----------------------- - -The git-diff-* 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; - - - git-diff-stages compares contents of blobs at two stages in an - unmerged index file. - -In all of these cases, the commands themselves compare -corresponding paths in the two sets of files. 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 6 such transformations: - -- diffcore-pathspec -- diffcore-break -- diffcore-rename -- diffcore-merge-broken -- diffcore-pickaxe -- diffcore-order - -These are applied in sequence. The set of filepairs git-diff-\* -commands find are used as the input to diffcore-pathspec, and -the output from diffcore-pathspec 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-\* commands) or -diff-patch format. - - -diffcore-pathspec: For Ignoring Files Outside Our Consideration ---------------------------------------------------------------- - -The first transformation in the chain is diffcore-pathspec, and -is controlled by giving the pathname parameters to the -git-diff-* commands on the command line. The pathspec is used -to limit the world diff operates in. It removes the filepairs -outside the specified set 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. - -Implementation note. For performance reasons, git-diff-tree -uses the pathname parameters on the command line to cull set of -filepairs it feeds the diffcore mechanism itself, and does not -use diffcore-pathspec, but the end result is the same. - - -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-* 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 SHA1 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 Detection 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-* 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. When the "-C" option is used with `\--find-copies-harder` -option, git-diff-\* 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-\* 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 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 a 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 old version -prefixed with '-', followed by the entire contents of new -version prefixed with '+'. - - -diffcore-pickaxe: For Detecting Addition/Deletion of Specified String ---------------------------------------------------------------------- - -This transformation is used to find filepairs that represent -changes that touch a specified string, and is controlled by the --S option and the `\--pickaxe-all` option to the git-diff-* -commands. - -When diffcore-pickaxe is in use, it checks if there are -filepairs whose "original" side has the specified string and -whose "result" side does not. Such a filepair represents "the -string appeared in this changeset". It also checks for the -opposite case that loses the specified string. - -When `\--pickaxe-all` is not in effect, diffcore-pickaxe leaves -only such filepairs that touch the specified string in its -output. When `\--pickaxe-all` is used, diffcore-pickaxe leaves all -filepairs intact if there is such a filepair, or makes the -output empty otherwise. The latter behaviour is designed to -make reviewing of the 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-* 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 ------------------------------------------------- - |