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1 | gitdiffcore(7) |
2 | ============== | |
4a1332d0 | 3 | |
30eba7bf CC |
4 | NAME |
5 | ---- | |
6 | gitdiffcore - Tweaking diff output (June 2005) | |
4a1332d0 | 7 | |
30eba7bf CC |
8 | SYNOPSIS |
9 | -------- | |
10 | git diff * | |
11 | ||
12 | DESCRIPTION | |
13 | ----------- | |
4a1332d0 | 14 | |
4cc41a16 JH |
15 | The diff commands git-diff-index, git-diff-files, and git-diff-tree |
16 | can be told to manipulate differences they find in | |
59df2a11 CS |
17 | unconventional ways before showing diff(1) output. The manipulation |
18 | is collectively called "diffcore transformation". This short note | |
19 | describes what they are and how to use them to produce diff outputs | |
20 | that are easier to understand than the conventional kind. | |
4a1332d0 JH |
21 | |
22 | ||
23 | The chain of operation | |
24 | ---------------------- | |
25 | ||
26 | The git-diff-* family works by first comparing two sets of | |
27 | files: | |
28 | ||
215a7ad1 | 29 | - git-diff-index compares contents of a "tree" object and the |
e1ccf53a YS |
30 | working directory (when '\--cached' flag is not used) or a |
31 | "tree" object and the index file (when '\--cached' flag is | |
4a1332d0 JH |
32 | used); |
33 | ||
34 | - git-diff-files compares contents of the index file and the | |
35 | working directory; | |
36 | ||
59df2a11 CS |
37 | - git-diff-tree compares contents of two "tree" objects; |
38 | ||
4a1332d0 JH |
39 | In all of these cases, the commands themselves compare |
40 | corresponding paths in the two sets of files. The result of | |
41 | comparison is passed from these commands to what is internally | |
42 | called "diffcore", in a format similar to what is output when | |
43 | the -p option is not used. E.g. | |
44 | ||
8db9307c JH |
45 | ------------------------------------------------ |
46 | in-place edit :100644 100644 bcd1234... 0123456... M file0 | |
47 | create :000000 100644 0000000... 1234567... A file4 | |
48 | delete :100644 000000 1234567... 0000000... D file5 | |
49 | unmerged :000000 000000 0000000... 0000000... U file6 | |
50 | ------------------------------------------------ | |
4a1332d0 JH |
51 | |
52 | The diffcore mechanism is fed a list of such comparison results | |
53 | (each of which is called "filepair", although at this point each | |
54 | of them talks about a single file), and transforms such a list | |
28f8faff | 55 | into another list. There are currently 6 such transformations: |
4a1332d0 | 56 | |
8db9307c JH |
57 | - diffcore-pathspec |
58 | - diffcore-break | |
59 | - diffcore-rename | |
60 | - diffcore-merge-broken | |
61 | - diffcore-pickaxe | |
62 | - diffcore-order | |
4a1332d0 | 63 | |
8db9307c | 64 | These are applied in sequence. The set of filepairs git-diff-\* |
4a1332d0 JH |
65 | commands find are used as the input to diffcore-pathspec, and |
66 | the output from diffcore-pathspec is used as the input to the | |
67 | next transformation. The final result is then passed to the | |
68 | output routine and generates either diff-raw format (see Output | |
8db9307c | 69 | format sections of the manual for git-diff-\* commands) or |
4a1332d0 JH |
70 | diff-patch format. |
71 | ||
72 | ||
59df2a11 | 73 | diffcore-pathspec: For Ignoring Files Outside Our Consideration |
a67c1d08 | 74 | --------------------------------------------------------------- |
4a1332d0 JH |
75 | |
76 | The first transformation in the chain is diffcore-pathspec, and | |
77 | is controlled by giving the pathname parameters to the | |
78 | git-diff-* commands on the command line. The pathspec is used | |
79 | to limit the world diff operates in. It removes the filepairs | |
a6080a0a | 80 | outside the specified set of pathnames. E.g. If the input set |
59df2a11 CS |
81 | of filepairs included: |
82 | ||
83 | ------------------------------------------------ | |
84 | :100644 100644 bcd1234... 0123456... M junkfile | |
85 | ------------------------------------------------ | |
86 | ||
b1889c36 | 87 | but the command invocation was "git diff-files myfile", then the |
59df2a11 CS |
88 | junkfile entry would be removed from the list because only "myfile" |
89 | is under consideration. | |
4a1332d0 JH |
90 | |
91 | Implementation note. For performance reasons, git-diff-tree | |
92 | uses the pathname parameters on the command line to cull set of | |
93 | filepairs it feeds the diffcore mechanism itself, and does not | |
94 | use diffcore-pathspec, but the end result is the same. | |
95 | ||
96 | ||
59df2a11 | 97 | diffcore-break: For Splitting Up "Complete Rewrites" |
a67c1d08 | 98 | ---------------------------------------------------- |
4a1332d0 JH |
99 | |
100 | The second transformation in the chain is diffcore-break, and is | |
101 | controlled by the -B option to the git-diff-* commands. This is | |
102 | used to detect a filepair that represents "complete rewrite" and | |
103 | break such filepair into two filepairs that represent delete and | |
104 | create. E.g. If the input contained this filepair: | |
105 | ||
8db9307c JH |
106 | ------------------------------------------------ |
107 | :100644 100644 bcd1234... 0123456... M file0 | |
108 | ------------------------------------------------ | |
4a1332d0 JH |
109 | |
110 | and if it detects that the file "file0" is completely rewritten, | |
111 | it changes it to: | |
112 | ||
8db9307c JH |
113 | ------------------------------------------------ |
114 | :100644 000000 bcd1234... 0000000... D file0 | |
115 | :000000 100644 0000000... 0123456... A file0 | |
116 | ------------------------------------------------ | |
4a1332d0 JH |
117 | |
118 | For the purpose of breaking a filepair, diffcore-break examines | |
119 | the extent of changes between the contents of the files before | |
120 | and after modification (i.e. the contents that have "bcd1234..." | |
121 | and "0123456..." as their SHA1 content ID, in the above | |
122 | example). The amount of deletion of original contents and | |
123 | insertion of new material are added together, and if it exceeds | |
124 | the "break score", the filepair is broken into two. The break | |
125 | score defaults to 50% of the size of the smaller of the original | |
126 | and the result (i.e. if the edit shrinks the file, the size of | |
127 | the result is used; if the edit lengthens the file, the size of | |
128 | the original is used), and can be customized by giving a number | |
129 | after "-B" option (e.g. "-B75" to tell it to use 75%). | |
130 | ||
131 | ||
59df2a11 | 132 | diffcore-rename: For Detection Renames and Copies |
a67c1d08 | 133 | ------------------------------------------------- |
4a1332d0 JH |
134 | |
135 | This transformation is used to detect renames and copies, and is | |
136 | controlled by the -M option (to detect renames) and the -C option | |
137 | (to detect copies as well) to the git-diff-* commands. If the | |
138 | input contained these filepairs: | |
139 | ||
8db9307c JH |
140 | ------------------------------------------------ |
141 | :100644 000000 0123456... 0000000... D fileX | |
142 | :000000 100644 0000000... 0123456... A file0 | |
143 | ------------------------------------------------ | |
4a1332d0 JH |
144 | |
145 | and the contents of the deleted file fileX is similar enough to | |
146 | the contents of the created file file0, then rename detection | |
147 | merges these filepairs and creates: | |
148 | ||
8db9307c JH |
149 | ------------------------------------------------ |
150 | :100644 100644 0123456... 0123456... R100 fileX file0 | |
151 | ------------------------------------------------ | |
4a1332d0 | 152 | |
59df2a11 CS |
153 | When the "-C" option is used, the original contents of modified files, |
154 | and deleted files (and also unmodified files, if the | |
155 | "\--find-copies-harder" option is used) are considered as candidates | |
156 | of the source files in rename/copy operation. If the input were like | |
157 | these filepairs, that talk about a modified file fileY and a newly | |
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158 | created file file0: |
159 | ||
8db9307c JH |
160 | ------------------------------------------------ |
161 | :100644 100644 0123456... 1234567... M fileY | |
59df2a11 | 162 | :000000 100644 0000000... bcd3456... A file0 |
8db9307c | 163 | ------------------------------------------------ |
4a1332d0 JH |
164 | |
165 | the original contents of fileY and the resulting contents of | |
166 | file0 are compared, and if they are similar enough, they are | |
167 | changed to: | |
168 | ||
8db9307c JH |
169 | ------------------------------------------------ |
170 | :100644 100644 0123456... 1234567... M fileY | |
59df2a11 | 171 | :100644 100644 0123456... bcd3456... C100 fileY file0 |
8db9307c | 172 | ------------------------------------------------ |
4a1332d0 JH |
173 | |
174 | In both rename and copy detection, the same "extent of changes" | |
175 | algorithm used in diffcore-break is used to determine if two | |
176 | files are "similar enough", and can be customized to use | |
59df2a11 CS |
177 | a similarity score different from the default of 50% by giving a |
178 | number after the "-M" or "-C" option (e.g. "-M8" to tell it to use | |
4a1332d0 JH |
179 | 8/10 = 80%). |
180 | ||
e1ccf53a | 181 | Note. When the "-C" option is used with `\--find-copies-harder` |
8db9307c | 182 | option, git-diff-\* commands feed unmodified filepairs to |
232b75ab JH |
183 | diffcore mechanism as well as modified ones. This lets the copy |
184 | detector consider unmodified files as copy source candidates at | |
e1ccf53a | 185 | the expense of making it slower. Without `\--find-copies-harder`, |
8db9307c | 186 | git-diff-\* commands can detect copies only if the file that was |
232b75ab | 187 | copied happened to have been modified in the same changeset. |
4a1332d0 JH |
188 | |
189 | ||
59df2a11 | 190 | diffcore-merge-broken: For Putting "Complete Rewrites" Back Together |
a67c1d08 | 191 | -------------------------------------------------------------------- |
4a1332d0 JH |
192 | |
193 | This transformation is used to merge filepairs broken by | |
f73ae1fc | 194 | diffcore-break, and not transformed into rename/copy by |
4a1332d0 JH |
195 | diffcore-rename, back into a single modification. This always |
196 | runs when diffcore-break is used. | |
197 | ||
198 | For the purpose of merging broken filepairs back, it uses a | |
199 | different "extent of changes" computation from the ones used by | |
200 | diffcore-break and diffcore-rename. It counts only the deletion | |
201 | from the original, and does not count insertion. If you removed | |
202 | only 10 lines from a 100-line document, even if you added 910 | |
203 | new lines to make a new 1000-line document, you did not do a | |
204 | complete rewrite. diffcore-break breaks such a case in order to | |
205 | help diffcore-rename to consider such filepairs as candidate of | |
206 | rename/copy detection, but if filepairs broken that way were not | |
207 | matched with other filepairs to create rename/copy, then this | |
208 | transformation merges them back into the original | |
209 | "modification". | |
210 | ||
211 | The "extent of changes" parameter can be tweaked from the | |
212 | default 80% (that is, unless more than 80% of the original | |
213 | material is deleted, the broken pairs are merged back into a | |
214 | single modification) by giving a second number to -B option, | |
215 | like these: | |
216 | ||
8db9307c JH |
217 | * -B50/60 (give 50% "break score" to diffcore-break, use 60% |
218 | for diffcore-merge-broken). | |
219 | ||
220 | * -B/60 (the same as above, since diffcore-break defaults to 50%). | |
4a1332d0 | 221 | |
366175ef | 222 | Note that earlier implementation left a broken pair as a separate |
f73ae1fc | 223 | creation and deletion patches. This was an unnecessary hack and |
366175ef JH |
224 | the latest implementation always merges all the broken pairs |
225 | back into modifications, but the resulting patch output is | |
f73ae1fc | 226 | formatted differently for easier review in case of such |
366175ef JH |
227 | a complete rewrite by showing the entire contents of old version |
228 | prefixed with '-', followed by the entire contents of new | |
229 | version prefixed with '+'. | |
230 | ||
4a1332d0 | 231 | |
59df2a11 | 232 | diffcore-pickaxe: For Detecting Addition/Deletion of Specified String |
a67c1d08 | 233 | --------------------------------------------------------------------- |
4a1332d0 JH |
234 | |
235 | This transformation is used to find filepairs that represent | |
236 | changes that touch a specified string, and is controlled by the | |
e1ccf53a | 237 | -S option and the `\--pickaxe-all` option to the git-diff-* |
4a1332d0 JH |
238 | commands. |
239 | ||
240 | When diffcore-pickaxe is in use, it checks if there are | |
241 | filepairs whose "original" side has the specified string and | |
242 | whose "result" side does not. Such a filepair represents "the | |
243 | string appeared in this changeset". It also checks for the | |
244 | opposite case that loses the specified string. | |
245 | ||
e1ccf53a | 246 | When `\--pickaxe-all` is not in effect, diffcore-pickaxe leaves |
59df2a11 | 247 | only such filepairs that touch the specified string in its |
e1ccf53a | 248 | output. When `\--pickaxe-all` is used, diffcore-pickaxe leaves all |
4a1332d0 JH |
249 | filepairs intact if there is such a filepair, or makes the |
250 | output empty otherwise. The latter behaviour is designed to | |
251 | make reviewing of the changes in the context of the whole | |
252 | changeset easier. | |
253 | ||
254 | ||
59df2a11 | 255 | diffcore-order: For Sorting the Output Based on Filenames |
a67c1d08 | 256 | --------------------------------------------------------- |
4a1332d0 JH |
257 | |
258 | This is used to reorder the filepairs according to the user's | |
259 | (or project's) taste, and is controlled by the -O option to the | |
260 | git-diff-* commands. | |
261 | ||
59df2a11 | 262 | This takes a text file each of whose lines is a shell glob |
4a1332d0 JH |
263 | pattern. Filepairs that match a glob pattern on an earlier line |
264 | in the file are output before ones that match a later line, and | |
265 | filepairs that do not match any glob pattern are output last. | |
266 | ||
59df2a11 | 267 | As an example, a typical orderfile for the core git probably |
8db9307c | 268 | would look like this: |
4a1332d0 | 269 | |
8db9307c | 270 | ------------------------------------------------ |
df8baa42 JF |
271 | README |
272 | Makefile | |
273 | Documentation | |
274 | *.h | |
275 | *.c | |
276 | t | |
8db9307c | 277 | ------------------------------------------------ |
30eba7bf CC |
278 | |
279 | SEE ALSO | |
280 | -------- | |
281 | linkgit:git-diff[1], | |
282 | linkgit:git-diff-files[1], | |
283 | linkgit:git-diff-index[1], | |
284 | linkgit:git-diff-tree[1], | |
285 | linkgit:git-format-patch[1], | |
286 | linkgit:git-log[1], | |
287 | linkgit:gitglossary[7], | |
288 | link:user-manual.html[The Git User's Manual] | |
289 | ||
290 | GIT | |
291 | --- | |
9e1f0a85 | 292 | Part of the linkgit:git[1] suite. |