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 `diff_setup()` to initialize this structure.  This sets up
  22   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
  33 * As you find different pairs of files, call `diff_change()` to feed
  34   modified files, `diff_addremove()` to feed created or deleted files,
  35   or `diff_unmerged()` to feed a file whose state is 'unmerged' to the
  36   API.  These are thin wrappers to a lower-level `diff_queue()` function
  37   that is flexible enough to record any of these kinds of changes.
  38
  39 * Once you finish feeding the pairs of files, call `diffcore_std()`.
  40   This will tell the diffcore library to go ahead and do its work.
  41
  42 * Calling `diff_flush()` will produce the output.
  43
  44
  45 Data structures
  46 ---------------
  47
  48 * `struct diff_filespec`
  49
  50 This is the internal representation for a single file (blob).  It
  51 records the blob object name (if known -- for a work tree file it
  52 typically is a NUL SHA-1), filemode and pathname.  This is what the
  53 `diff_addremove()`, `diff_change()` and `diff_unmerged()` synthesize and
  54 feed `diff_queue()` function with.
  55
  56 * `struct diff_filepair`
  57
  58 This records a pair of `struct diff_filespec`; the filespec for a file
  59 in the "old" set (i.e. preimage) is called `one`, and the filespec for a
  60 file in the "new" set (i.e. postimage) is called `two`.  A change that
  61 represents file creation has NULL in `one`, and file deletion has NULL
  62 in `two`.
  63
  64 A `filepair` starts pointing at `one` and `two` that are from the same
  65 filename, but `diffcore_std()` can break pairs and match component
  66 filespecs with other filespecs from a different filepair to form new
  67 filepair.  This is called 'rename detection'.
  68
  69 * `struct diff_queue`
  70
  71 This is a collection of filepairs.  Notable members are:
  72
  73 `queue`::
  74
  75         An array of pointers to `struct diff_filepair`.  This
  76         dynamically grows as you add filepairs;
  77
  78 `alloc`::
  79
  80         The allocated size of the `queue` array;
  81
  82 `nr`::
  83
  84         The number of elements in the `queue` array.
  85
  86
  87 * `struct diff_options`
  88
  89 This describes the set of options the calling program wants to affect
  90 the operation of diffcore library with.
  91
  92 Notable members are:
  93
  94 `output_format`::
  95         The output format used when `diff_flush()` is run.
  96
  97 `context`::
  98         Number of context lines to generate in patch output.
  99
 100 `break_opt`, `detect_rename`, `rename-score`, `rename_limit`::
 101         Affects the way detection logic for complete rewrites, renames
 102         and copies.
 103
 104 `abbrev`::
 105         Number of hexdigits to abbreviate raw format output to.
 106
 107 `pickaxe`::
 108         A constant string (can and typically does contain newlines to
 109         look for a block of text, not just a single line) to filter out
 110         the filepairs that do not change the number of strings contained
 111         in its preimage and postimage of the diff_queue.
 112
 113 `flags`::
 114         This is mostly a collection of boolean options that affects the
 115         operation, but some do not have anything to do with the diffcore
 116         library.
 117
 118 BINARY, TEXT;;
 119         Affects the way how a file that is seemingly binary is treated.
 120
 121 FULL_INDEX;;
 122         Tells the patch output format not to use abbreviated object
 123         names on the "index" lines.
 124
 125 FIND_COPIES_HARDER;;
 126         Tells the diffcore library that the caller is feeding unchanged
 127         filepairs to allow copies from unmodified files be detected.
 128
 129 COLOR_DIFF;;
 130         Output should be colored.
 131
 132 COLOR_DIFF_WORDS;;
 133         Output is a colored word-diff.
 134
 135 NO_INDEX;;
 136         Tells diff-files that the input is not tracked files but files
 137         in random locations on the filesystem.
 138
 139 ALLOW_EXTERNAL;;
 140         Tells output routine that it is Ok to call user specified patch
 141         output routine.  Plumbing disables this to ensure stable output.
 142
 143 QUIET;;
 144         Do not show any output.
 145
 146 REVERSE_DIFF;;
 147         Tells the library that the calling program is feeding the
 148         filepairs reversed; `one` is two, and `two` is one.
 149
 150 EXIT_WITH_STATUS;;
 151         For communication between the calling program and the options
 152         parser; tell the calling program to signal the presence of
 153         difference using program exit code.
 154
 155 HAS_CHANGES;;
 156         Internal; used for optimization to see if there is any change.
 157
 158 SILENT_ON_REMOVE;;
 159         Affects if diff-files shows removed files.
 160
 161 RECURSIVE, TREE_IN_RECURSIVE;;
 162         Tells if tree traversal done by tree-diff should recursively
 163         descend into a tree object pair that are different in preimage
 164         and postimage set.
 165
 166 (JC)