Documentation/technical/api-diff.txt

   1 diff API
   2 ========
   3
   4 The diff API is for programs that compare two sets of files (e.g. two
   5 trees, one tree and the index) and present the found difference in
   6 various ways.  The calling program is responsible for feeding the API
   7 pairs of files, one from the "old" set and the corresponding one from
   8 "new" set, that are different.  The library called through this API is
   9 called diffcore, and is responsible for two things.
  10
  11 * finding total rewrites (`-B`), renames (`-M`) and copies (`-C`), and
  12   changes that touch a string (`-S`), as specified by the caller.
  13
  14 * outputting the differences in various formats, as specified by the
  15   caller.
  16
  17 Calling sequence
  18 ----------------
  19
  20 * Prepare `struct diff_options` to record the set of diff options, and
  21   then call `repo_diff_setup()` to initialize this structure.  This
  22   sets up the vanilla default.
  23
  24 * Fill in the options structure to specify desired output format, rename
  25   detection, etc.  `diff_opt_parse()` can be used to parse options given
  26   from the command line in a way consistent with existing git-diff
  27   family of programs.
  28
  29 * Call `diff_setup_done()`; this inspects the options set up so far for
  30   internal consistency and make necessary tweaking to it (e.g. if
  31   textual patch output was asked, recursive behaviour is turned on);
  32   the callback set_default in diff_options can be used to tweak this more.
  33
  34 * As you find different pairs of files, call `diff_change()` to feed
  35   modified files, `diff_addremove()` to feed created or deleted files,
  36   or `diff_unmerge()` to feed a file whose state is 'unmerged' to the
  37   API.  These are thin wrappers to a lower-level `diff_queue()` function
  38   that is flexible enough to record any of these kinds of changes.
  39
  40 * Once you finish feeding the pairs of files, call `diffcore_std()`.
  41   This will tell the diffcore library to go ahead and do its work.
  42
  43 * Calling `diff_flush()` will produce the output.
  44
  45
  46 Data structures
  47 ---------------
  48
  49 * `struct diff_filespec`
  50
  51 This is the internal representation for a single file (blob).  It
  52 records the blob object name (if known -- for a work tree file it
  53 typically is a NUL SHA-1), filemode and pathname.  This is what the
  54 `diff_addremove()`, `diff_change()` and `diff_unmerge()` synthesize and
  55 feed `diff_queue()` function with.
  56
  57 * `struct diff_filepair`
  58
  59 This records a pair of `struct diff_filespec`; the filespec for a file
  60 in the "old" set (i.e. preimage) is called `one`, and the filespec for a
  61 file in the "new" set (i.e. postimage) is called `two`.  A change that
  62 represents file creation has NULL in `one`, and file deletion has NULL
  63 in `two`.
  64
  65 A `filepair` starts pointing at `one` and `two` that are from the same
  66 filename, but `diffcore_std()` can break pairs and match component
  67 filespecs with other filespecs from a different filepair to form new
  68 filepair.  This is called 'rename detection'.
  69
  70 * `struct diff_queue`
  71
  72 This is a collection of filepairs.  Notable members are:
  73
  74 `queue`::
  75
  76         An array of pointers to `struct diff_filepair`.  This
  77         dynamically grows as you add filepairs;
  78
  79 `alloc`::
  80
  81         The allocated size of the `queue` array;
  82
  83 `nr`::
  84
  85         The number of elements in the `queue` array.
  86
  87
  88 * `struct diff_options`
  89
  90 This describes the set of options the calling program wants to affect
  91 the operation of diffcore library with.
  92
  93 Notable members are:
  94
  95 `output_format`::
  96         The output format used when `diff_flush()` is run.
  97
  98 `context`::
  99         Number of context lines to generate in patch output.
 100
 101 `break_opt`, `detect_rename`, `rename-score`, `rename_limit`::
 102         Affects the way detection logic for complete rewrites, renames
 103         and copies.
 104
 105 `abbrev`::
 106         Number of hexdigits to abbreviate raw format output to.
 107
 108 `pickaxe`::
 109         A constant string (can and typically does contain newlines to
 110         look for a block of text, not just a single line) to filter out
 111         the filepairs that do not change the number of strings contained
 112         in its preimage and postimage of the diff_queue.
 113
 114 `flags`::
 115         This is mostly a collection of boolean options that affects the
 116         operation, but some do not have anything to do with the diffcore
 117         library.
 118
 119 `touched_flags`::
 120         Records whether a flag has been changed due to user request
 121         (rather than just set/unset by default).
 122
 123 `set_default`::
 124         Callback which allows tweaking the options in diff_setup_done().
 125
 126 BINARY, TEXT;;
 127         Affects the way how a file that is seemingly binary is treated.
 128
 129 FULL_INDEX;;
 130         Tells the patch output format not to use abbreviated object
 131         names on the "index" lines.
 132
 133 FIND_COPIES_HARDER;;
 134         Tells the diffcore library that the caller is feeding unchanged
 135         filepairs to allow copies from unmodified files be detected.
 136
 137 COLOR_DIFF;;
 138         Output should be colored.
 139
 140 COLOR_DIFF_WORDS;;
 141         Output is a colored word-diff.
 142
 143 NO_INDEX;;
 144         Tells diff-files that the input is not tracked files but files
 145         in random locations on the filesystem.
 146
 147 ALLOW_EXTERNAL;;
 148         Tells output routine that it is Ok to call user specified patch
 149         output routine.  Plumbing disables this to ensure stable output.
 150
 151 QUIET;;
 152         Do not show any output.
 153
 154 REVERSE_DIFF;;
 155         Tells the library that the calling program is feeding the
 156         filepairs reversed; `one` is two, and `two` is one.
 157
 158 EXIT_WITH_STATUS;;
 159         For communication between the calling program and the options
 160         parser; tell the calling program to signal the presence of
 161         difference using program exit code.
 162
 163 HAS_CHANGES;;
 164         Internal; used for optimization to see if there is any change.
 165
 166 SILENT_ON_REMOVE;;
 167         Affects if diff-files shows removed files.
 168
 169 RECURSIVE, TREE_IN_RECURSIVE;;
 170         Tells if tree traversal done by tree-diff should recursively
 171         descend into a tree object pair that are different in preimage
 172         and postimage set.
 173
 174 (JC)