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diff.c

 
/*
 * libgit2 "diff" example - shows how to use the diff API
 *
 * Written by the libgit2 contributors
 *
 * To the extent possible under law, the author(s) have dedicated all copyright
 * and related and neighboring rights to this software to the public domain
 * worldwide. This software is distributed without any warranty.
 *
 * You should have received a copy of the CC0 Public Domain Dedication along
 * with this software. If not, see
 * <http://creativecommons.org/publicdomain/zero/1.0/>.
 */

#include "common.h"

This example demonstrates the use of the libgit2 diff APIs to create git_diff objects and display them, emulating a number of core Git diff command line options.

This covers on a portion of the core Git diff options and doesn't have particularly good error handling, but it should show most of the core libgit2 diff APIs, including various types of diffs and how to do renaming detection and patch formatting.

 
static const char *colors[] = {
  "\033[m", /* reset */
  "\033[1m", /* bold */
  "\033[31m", /* red */
  "\033[32m", /* green */
  "\033[36m" /* cyan */
};

enum {
  OUTPUT_DIFF = (1 << 0),
  OUTPUT_STAT = (1 << 1),
  OUTPUT_SHORTSTAT = (1 << 2),
  OUTPUT_NUMSTAT = (1 << 3),
  OUTPUT_SUMMARY = (1 << 4)
};

enum {
  CACHE_NORMAL = 0,
  CACHE_ONLY = 1,
  CACHE_NONE = 2
};

The 'diff_options' struct captures all the various parsed command line options.

 
struct diff_options {
  git_diff_options diffopts;
  git_diff_find_options findopts;
  int color;
  int no_index;
  int cache;
  int output;
  git_diff_format_t format;
  const char *treeish1;
  const char *treeish2;
  const char *dir;
};

These functions are implemented at the end

 
static void usage(const char *message, const char *arg);
static void parse_opts(struct diff_options *o, int argc, char *argv[]);
static int color_printer(
  const git_diff_delta*, const git_diff_hunk*, const git_diff_line*, void*);
static void diff_print_stats(git_diff *diff, struct diff_options *o);
static void compute_diff_no_index(git_diff **diff, struct diff_options *o);

int lg2_diff(git_repository *repo, int argc, char *argv[])
{
  git_tree *t1 = NULL, *t2 = NULL;
  git_diff *diff;
  struct diff_options o = {
    GIT_DIFF_OPTIONS_INIT, GIT_DIFF_FIND_OPTIONS_INIT,
    -1, -1, 0, 0, GIT_DIFF_FORMAT_PATCH, NULL, NULL, "."
  };

  parse_opts(&o, argc, argv);

Possible argument patterns:

  • <sha1> <sha2>
  • <sha1> --cached
  • <sha1>
  • --cached
  • --nocache (don't use index data in diff at all)
  • --no-index <file1> <file2>
  • nothing

Currently ranged arguments like <sha1>..<sha2> and <sha1>...<sha2> are not supported in this example

 
  if (o.no_index >= 0) {
    compute_diff_no_index(&diff, &o);
  } else {
    if (o.treeish1)
      treeish_to_tree(&t1, repo, o.treeish1);
    if (o.treeish2)
      treeish_to_tree(&t2, repo, o.treeish2);

    if (t1 && t2)
      check_lg2(
        git_diff_tree_to_tree(&diff, repo, t1, t2, &o.diffopts),
        "diff trees", NULL);
    else if (o.cache != CACHE_NORMAL) {
      if (!t1)
        treeish_to_tree(&t1, repo, "HEAD");

      if (o.cache == CACHE_NONE)
        check_lg2(
          git_diff_tree_to_workdir(&diff, repo, t1, &o.diffopts),
          "diff tree to working directory", NULL);
      else
        check_lg2(
          git_diff_tree_to_index(&diff, repo, t1, NULL, &o.diffopts),
          "diff tree to index", NULL);
    }
    else if (t1)
      check_lg2(
        git_diff_tree_to_workdir_with_index(&diff, repo, t1, &o.diffopts),
        "diff tree to working directory", NULL);
    else
      check_lg2(
        git_diff_index_to_workdir(&diff, repo, NULL, &o.diffopts),
        "diff index to working directory", NULL);

Apply rename and copy detection if requested.

 
    if ((o.findopts.flags & GIT_DIFF_FIND_ALL) != 0)
      check_lg2(
        git_diff_find_similar(diff, &o.findopts),
        "finding renames and copies", NULL);
  }

Generate simple output using libgit2 display helper.

 
  if (!o.output)
    o.output = OUTPUT_DIFF;

  if (o.output != OUTPUT_DIFF)
    diff_print_stats(diff, &o);

  if ((o.output & OUTPUT_DIFF) != 0) {
    if (o.color >= 0)
      fputs(colors[0], stdout);

    check_lg2(
      git_diff_print(diff, o.format, color_printer, &o.color),
      "displaying diff", NULL);

    if (o.color >= 0)
      fputs(colors[0], stdout);
  }

Cleanup before exiting.

 
  git_diff_free(diff);
  git_tree_free(t1);
  git_tree_free(t2);

  return 0;
}

static void compute_diff_no_index(git_diff **diff, struct diff_options *o) {
  git_patch *patch = NULL;
  char *file1_str = NULL;
  char *file2_str = NULL;
  git_buf buf = {0};

  if (!o->treeish1 || !o->treeish2) {
    usage("two files should be provided as arguments", NULL);
  }
  file1_str = read_file(o->treeish1);
  if (file1_str == NULL) {
    usage("file cannot be read", o->treeish1);
  }
  file2_str = read_file(o->treeish2);
  if (file2_str == NULL) {
    usage("file cannot be read", o->treeish2);
  }
  check_lg2(
    git_patch_from_buffers(&patch, file1_str, strlen(file1_str), o->treeish1, file2_str, strlen(file2_str), o->treeish2, &o->diffopts),
    "patch buffers", NULL);
  check_lg2(
    git_patch_to_buf(&buf, patch),
    "patch to buf", NULL);

#ifdef GIT_EXPERIMENTAL_SHA256
  check_lg2(
    git_diff_from_buffer(diff, buf.ptr, buf.size, NULL),
    "diff from patch", NULL);
#else
  check_lg2(
    git_diff_from_buffer(diff, buf.ptr, buf.size),
    "diff from patch", NULL);
#endif

  git_patch_free(patch);
  git_buf_dispose(&buf);
  free(file1_str);
  free(file2_str);
}

static void usage(const char *message, const char *arg)
{
  if (message && arg)
    fprintf(stderr, "%s: %s\n", message, arg);
  else if (message)
    fprintf(stderr, "%s\n", message);
  fprintf(stderr, "usage: diff [<tree-oid> [<tree-oid>]]\n");
  exit(1);
}

This implements very rudimentary colorized output.

 
static int color_printer(
  const git_diff_delta *delta,
  const git_diff_hunk *hunk,
  const git_diff_line *line,
  void *data)
{
  int *last_color = data, color = 0;

  (void)delta; (void)hunk;

  if (*last_color >= 0) {
    switch (line->origin) {
    case GIT_DIFF_LINE_ADDITION:  color = 3; break;
    case GIT_DIFF_LINE_DELETION:  color = 2; break;
    case GIT_DIFF_LINE_ADD_EOFNL: color = 3; break;
    case GIT_DIFF_LINE_DEL_EOFNL: color = 2; break;
    case GIT_DIFF_LINE_FILE_HDR:  color = 1; break;
    case GIT_DIFF_LINE_HUNK_HDR:  color = 4; break;
    default: break;
    }

    if (color != *last_color) {
      if (*last_color == 1 || color == 1)
        fputs(colors[0], stdout);
      fputs(colors[color], stdout);
      *last_color = color;
    }
  }

  return diff_output(delta, hunk, line, stdout);
}

Parse arguments as copied from git-diff.

 
static void parse_opts(struct diff_options *o, int argc, char *argv[])
{
  struct args_info args = ARGS_INFO_INIT;

  for (args.pos = 1; args.pos < argc; ++args.pos) {
    const char *a = argv[args.pos];

    if (a[0] != '-') {
      if (o->treeish1 == NULL)
        o->treeish1 = a;
      else if (o->treeish2 == NULL)
        o->treeish2 = a;
      else
        usage("Only one or two tree identifiers can be provided", NULL);
    }
    else if (!strcmp(a, "-p") || !strcmp(a, "-u") ||
         !strcmp(a, "--patch")) {
      o->output |= OUTPUT_DIFF;
      o->format = GIT_DIFF_FORMAT_PATCH;
    }
    else if (!strcmp(a, "--cached")) {
      o->cache = CACHE_ONLY;
      if (o->no_index >= 0) usage("--cached and --no-index are incompatible", NULL);
    } else if (!strcmp(a, "--nocache"))
      o->cache = CACHE_NONE;
    else if (!strcmp(a, "--name-only") || !strcmp(a, "--format=name"))
      o->format = GIT_DIFF_FORMAT_NAME_ONLY;
    else if (!strcmp(a, "--name-status") ||
        !strcmp(a, "--format=name-status"))
      o->format = GIT_DIFF_FORMAT_NAME_STATUS;
    else if (!strcmp(a, "--raw") || !strcmp(a, "--format=raw"))
      o->format = GIT_DIFF_FORMAT_RAW;
    else if (!strcmp(a, "--format=diff-index")) {
      o->format = GIT_DIFF_FORMAT_RAW;
      o->diffopts.id_abbrev = 40;
    }
    else if (!strcmp(a, "--no-index")) {
      o->no_index = 0;
      if (o->cache == CACHE_ONLY) usage("--cached and --no-index are incompatible", NULL);
    } else if (!strcmp(a, "--color"))
      o->color = 0;
    else if (!strcmp(a, "--no-color"))
      o->color = -1;
    else if (!strcmp(a, "-R"))
      o->diffopts.flags |= GIT_DIFF_REVERSE;
    else if (!strcmp(a, "-a") || !strcmp(a, "--text"))
      o->diffopts.flags |= GIT_DIFF_FORCE_TEXT;
    else if (!strcmp(a, "--ignore-space-at-eol"))
      o->diffopts.flags |= GIT_DIFF_IGNORE_WHITESPACE_EOL;
    else if (!strcmp(a, "-b") || !strcmp(a, "--ignore-space-change"))
      o->diffopts.flags |= GIT_DIFF_IGNORE_WHITESPACE_CHANGE;
    else if (!strcmp(a, "-w") || !strcmp(a, "--ignore-all-space"))
      o->diffopts.flags |= GIT_DIFF_IGNORE_WHITESPACE;
    else if (!strcmp(a, "--ignored"))
      o->diffopts.flags |= GIT_DIFF_INCLUDE_IGNORED;
    else if (!strcmp(a, "--untracked"))
      o->diffopts.flags |= GIT_DIFF_INCLUDE_UNTRACKED;
    else if (!strcmp(a, "--patience"))
      o->diffopts.flags |= GIT_DIFF_PATIENCE;
    else if (!strcmp(a, "--minimal"))
      o->diffopts.flags |= GIT_DIFF_MINIMAL;
    else if (!strcmp(a, "--stat"))
      o->output |= OUTPUT_STAT;
    else if (!strcmp(a, "--numstat"))
      o->output |= OUTPUT_NUMSTAT;
    else if (!strcmp(a, "--shortstat"))
      o->output |= OUTPUT_SHORTSTAT;
    else if (!strcmp(a, "--summary"))
      o->output |= OUTPUT_SUMMARY;
    else if (match_uint16_arg(
        &o->findopts.rename_threshold, &args, "-M") ||
      match_uint16_arg(
        &o->findopts.rename_threshold, &args, "--find-renames"))
      o->findopts.flags |= GIT_DIFF_FIND_RENAMES;
    else if (match_uint16_arg(
        &o->findopts.copy_threshold, &args, "-C") ||
      match_uint16_arg(
        &o->findopts.copy_threshold, &args, "--find-copies"))
      o->findopts.flags |= GIT_DIFF_FIND_COPIES;
    else if (!strcmp(a, "--find-copies-harder"))
      o->findopts.flags |= GIT_DIFF_FIND_COPIES_FROM_UNMODIFIED;
    else if (is_prefixed(a, "-B") || is_prefixed(a, "--break-rewrites"))
      /* TODO: parse thresholds */
      o->findopts.flags |= GIT_DIFF_FIND_REWRITES;
    else if (!match_uint32_arg(
        &o->diffopts.context_lines, &args, "-U") &&
      !match_uint32_arg(
        &o->diffopts.context_lines, &args, "--unified") &&
      !match_uint32_arg(
        &o->diffopts.interhunk_lines, &args, "--inter-hunk-context") &&
      !match_uint16_arg(
        &o->diffopts.id_abbrev, &args, "--abbrev") &&
      !match_str_arg(&o->diffopts.old_prefix, &args, "--src-prefix") &&
      !match_str_arg(&o->diffopts.new_prefix, &args, "--dst-prefix") &&
      !match_str_arg(&o->dir, &args, "--git-dir"))
      usage("Unknown command line argument", a);
  }
}

Display diff output with "--stat", "--numstat", or "--shortstat"

 
static void diff_print_stats(git_diff *diff, struct diff_options *o)
{
  git_diff_stats *stats;
  git_buf b = GIT_BUF_INIT;
  git_diff_stats_format_t format = 0;

  check_lg2(
    git_diff_get_stats(&stats, diff), "generating stats for diff", NULL);

  if (o->output & OUTPUT_STAT)
    format |= GIT_DIFF_STATS_FULL;
  if (o->output & OUTPUT_SHORTSTAT)
    format |= GIT_DIFF_STATS_SHORT;
  if (o->output & OUTPUT_NUMSTAT)
    format |= GIT_DIFF_STATS_NUMBER;
  if (o->output & OUTPUT_SUMMARY)
    format |= GIT_DIFF_STATS_INCLUDE_SUMMARY;

  check_lg2(
    git_diff_stats_to_buf(&b, stats, format, 80), "formatting stats", NULL);

  fputs(b.ptr, stdout);

  git_buf_dispose(&b);
  git_diff_stats_free(stats);
}