merge.c

/*
 * libgit2 "merge" example - shows how to perform merges
 *
 * 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"

struct merge_options {
  const char **heads;
  size_t heads_count;

  git_annotated_commit **annotated;
  size_t annotated_count;

  unsigned int no_commit : 1;
};

static void print_usage(void)
{
  fprintf(stderr, "usage: merge [--no-commit] <commit...>\n");
  exit(1);
}

static void merge_options_init(struct merge_options *opts)
{
  memset(opts, 0, sizeof(*opts));

  opts->heads = NULL;
  opts->heads_count = 0;
  opts->annotated = NULL;
  opts->annotated_count = 0;
}

static void opts_add_refish(struct merge_options *opts, const char *refish)
{
  size_t sz;

  assert(opts != NULL);

  sz = ++opts->heads_count * sizeof(opts->heads[0]);
  opts->heads = xrealloc((void *) opts->heads, sz);
  opts->heads[opts->heads_count - 1] = refish;
}

static void parse_options(const char **repo_path, struct merge_options *opts, int argc, char **argv)
{
  struct args_info args = ARGS_INFO_INIT;

  if (argc <= 1)
    print_usage();

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

    if (curr[0] != '-') {
      opts_add_refish(opts, curr);
    } else if (!strcmp(curr, "--no-commit")) {
      opts->no_commit = 1;
    } else if (match_str_arg(repo_path, &args, "--git-dir")) {
      continue;
    } else {
      print_usage();
    }
  }
}

static int resolve_heads(git_repository *repo, struct merge_options *opts)
{
  git_annotated_commit **annotated = calloc(opts->heads_count, sizeof(git_annotated_commit *));
  size_t annotated_count = 0, i;
  int err = 0;

  for (i = 0; i < opts->heads_count; i++) {
    err = resolve_refish(&annotated[annotated_count++], repo, opts->heads[i]);
    if (err != 0) {
      fprintf(stderr, "failed to resolve refish %s: %s\n", opts->heads[i], git_error_last()->message);
      annotated_count--;
      continue;
    }
  }

  if (annotated_count != opts->heads_count) {
    fprintf(stderr, "unable to parse some refish\n");
    free(annotated);
    return -1;
  }

  opts->annotated = annotated;
  opts->annotated_count = annotated_count;
  return 0;
}

static int perform_fastforward(git_repository *repo, const git_oid *target_oid, int is_unborn)
{
  git_checkout_options ff_checkout_options = GIT_CHECKOUT_OPTIONS_INIT;
  git_reference *target_ref;
  git_reference *new_target_ref;
  git_object *target = NULL;
  int err = 0;

  if (is_unborn) {
    const char *symbolic_ref;
    git_reference *head_ref;

    /* HEAD reference is unborn, lookup manually so we don't try to resolve it */
    err = git_reference_lookup(&head_ref, repo, "HEAD");
    if (err != 0) {
      fprintf(stderr, "failed to lookup HEAD ref\n");
      return -1;
    }

    /* Grab the reference HEAD should be pointing to */
    symbolic_ref = git_reference_symbolic_target(head_ref);

    /* Create our master reference on the target OID */
    err = git_reference_create(&target_ref, repo, symbolic_ref, target_oid, 0, NULL);
    if (err != 0) {
      fprintf(stderr, "failed to create master reference\n");
      return -1;
    }

    git_reference_free(head_ref);
  } else {
    /* HEAD exists, just lookup and resolve */
    err = git_repository_head(&target_ref, repo);
    if (err != 0) {
      fprintf(stderr, "failed to get HEAD reference\n");
      return -1;
    }
  }

  /* Lookup the target object */
  err = git_object_lookup(&target, repo, target_oid, GIT_OBJECT_COMMIT);
  if (err != 0) {
    fprintf(stderr, "failed to lookup OID %s\n", git_oid_tostr_s(target_oid));
    return -1;
  }

  /* Checkout the result so the workdir is in the expected state */
  ff_checkout_options.checkout_strategy = GIT_CHECKOUT_SAFE;
  err = git_checkout_tree(repo, target, &ff_checkout_options);
  if (err != 0) {
    fprintf(stderr, "failed to checkout HEAD reference\n");
    return -1;
  }

  /* Move the target reference to the target OID */
  err = git_reference_set_target(&new_target_ref, target_ref, target_oid, NULL);
  if (err != 0) {
    fprintf(stderr, "failed to move HEAD reference\n");
    return -1;
  }

  git_reference_free(target_ref);
  git_reference_free(new_target_ref);
  git_object_free(target);

  return 0;
}

static void output_conflicts(git_index *index)
{
  git_index_conflict_iterator *conflicts;
  const git_index_entry *ancestor;
  const git_index_entry *our;
  const git_index_entry *their;
  int err = 0;

  check_lg2(git_index_conflict_iterator_new(&conflicts, index), "failed to create conflict iterator", NULL);

  while ((err = git_index_conflict_next(&ancestor, &our, &their, conflicts)) == 0) {
    fprintf(stderr, "conflict: a:%s o:%s t:%s\n",
            ancestor ? ancestor->path : "NULL",
            our->path ? our->path : "NULL",
            their->path ? their->path : "NULL");
  }

  if (err != GIT_ITEROVER) {
    fprintf(stderr, "error iterating conflicts\n");
  }

  git_index_conflict_iterator_free(conflicts);
}

static int create_merge_commit(git_repository *repo, git_index *index, struct merge_options *opts)
{
  git_oid tree_oid, commit_oid;
  git_tree *tree;
  git_signature *sign;
  git_reference *merge_ref = NULL;
  git_annotated_commit *merge_commit;
  git_reference *head_ref;
  git_commit **parents = calloc(opts->annotated_count + 1, sizeof(git_commit *));
  const char *msg_target = NULL;
  size_t msglen = 0;
  char *msg;
  size_t i;
  int err;

  /* Grab our needed references */
  check_lg2(git_repository_head(&head_ref, repo), "failed to get repo HEAD", NULL);
  if (resolve_refish(&merge_commit, repo, opts->heads[0])) {
    fprintf(stderr, "failed to resolve refish %s", opts->heads[0]);
    free(parents);
    return -1;
  }

  /* Maybe that's a ref, so DWIM it */
  err = git_reference_dwim(&merge_ref, repo, opts->heads[0]);
  check_lg2(err, "failed to DWIM reference", git_error_last()->message);

  /* Grab a signature */
  check_lg2(git_signature_now(&sign, "Me", "me@example.com"), "failed to create signature", NULL);

#define MERGE_COMMIT_MSG "Merge %s '%s'"
  /* Prepare a standard merge commit message */
  if (merge_ref != NULL) {
    check_lg2(git_branch_name(&msg_target, merge_ref), "failed to get branch name of merged ref", NULL);
  } else {
    msg_target = git_oid_tostr_s(git_annotated_commit_id(merge_commit));
  }

  msglen = snprintf(NULL, 0, MERGE_COMMIT_MSG, (merge_ref ? "branch" : "commit"), msg_target);
  if (msglen > 0) msglen++;
  msg = malloc(msglen);
  err = snprintf(msg, msglen, MERGE_COMMIT_MSG, (merge_ref ? "branch" : "commit"), msg_target);

  /* This is only to silence the compiler */
  if (err < 0) goto cleanup;

  /* Setup our parent commits */
  err = git_reference_peel((git_object **)&parents[0], head_ref, GIT_OBJECT_COMMIT);
  check_lg2(err, "failed to peel head reference", NULL);
  for (i = 0; i < opts->annotated_count; i++) {
    git_commit_lookup(&parents[i + 1], repo, git_annotated_commit_id(opts->annotated[i]));
  }

  /* Prepare our commit tree */
  check_lg2(git_index_write_tree(&tree_oid, index), "failed to write merged tree", NULL);
  check_lg2(git_tree_lookup(&tree, repo, &tree_oid), "failed to lookup tree", NULL);

  /* Commit time ! */
  err = git_commit_create(&commit_oid,
                          repo, git_reference_name(head_ref),
                          sign, sign,
                          NULL, msg,
                          tree,
                          opts->annotated_count + 1, parents);
  check_lg2(err, "failed to create commit", NULL);

  /* We're done merging, cleanup the repository state */
  git_repository_state_cleanup(repo);

cleanup:
  free(parents);
  return err;
}

int lg2_merge(git_repository *repo, int argc, char **argv)
{
  struct merge_options opts;
  git_index *index;
  git_repository_state_t state;
  git_merge_analysis_t analysis;
  git_merge_preference_t preference;
  const char *path = ".";
  int err = 0;

  merge_options_init(&opts);
  parse_options(&path, &opts, argc, argv);

  state = git_repository_state(repo);
  if (state != GIT_REPOSITORY_STATE_NONE) {
    fprintf(stderr, "repository is in unexpected state %d\n", state);
    goto cleanup;
  }

  err = resolve_heads(repo, &opts);
  if (err != 0)
    goto cleanup;

  err = git_merge_analysis(&analysis, &preference,
                           repo,
                           (const git_annotated_commit **)opts.annotated,
                           opts.annotated_count);
  check_lg2(err, "merge analysis failed", NULL);

  if (analysis & GIT_MERGE_ANALYSIS_UP_TO_DATE) {
    printf("Already up-to-date\n");
    return 0;
  } else if (analysis & GIT_MERGE_ANALYSIS_UNBORN ||
            (analysis & GIT_MERGE_ANALYSIS_FASTFORWARD &&
            !(preference & GIT_MERGE_PREFERENCE_NO_FASTFORWARD))) {
    const git_oid *target_oid;
    if (analysis & GIT_MERGE_ANALYSIS_UNBORN) {
      printf("Unborn\n");
    } else {
      printf("Fast-forward\n");
    }

    /* Since this is a fast-forward, there can be only one merge head */
    target_oid = git_annotated_commit_id(opts.annotated[0]);
    assert(opts.annotated_count == 1);

    return perform_fastforward(repo, target_oid, (analysis & GIT_MERGE_ANALYSIS_UNBORN));
  } else if (analysis & GIT_MERGE_ANALYSIS_NORMAL) {
    git_merge_options merge_opts = GIT_MERGE_OPTIONS_INIT;
    git_checkout_options checkout_opts = GIT_CHECKOUT_OPTIONS_INIT;

    merge_opts.flags = 0;
    merge_opts.file_flags = GIT_MERGE_FILE_STYLE_DIFF3;

    checkout_opts.checkout_strategy = GIT_CHECKOUT_FORCE|GIT_CHECKOUT_ALLOW_CONFLICTS;

    if (preference & GIT_MERGE_PREFERENCE_FASTFORWARD_ONLY) {
      printf("Fast-forward is preferred, but only a merge is possible\n");
      return -1;
    }

    err = git_merge(repo,
                    (const git_annotated_commit **)opts.annotated, opts.annotated_count,
                    &merge_opts, &checkout_opts);
    check_lg2(err, "merge failed", NULL);
  }

  /* If we get here, we actually performed the merge above */

  check_lg2(git_repository_index(&index, repo), "failed to get repository index", NULL);

  if (git_index_has_conflicts(index)) {
    /* Handle conflicts */
    output_conflicts(index);
  } else if (!opts.no_commit) {
    create_merge_commit(repo, index, &opts);
    printf("Merge made\n");
  }

cleanup:
  free((char **)opts.heads);
  free(opts.annotated);

  return 0;
}