Merge branch 'ma/commit-graph-docs' into maint

[thirdparty/git.git] / blame.c

#include "cache.h"
#include "refs.h"
#include "object-store.h"
#include "cache-tree.h"
#include "mergesort.h"
#include "diff.h"
#include "diffcore.h"
#include "tag.h"
#include "blame.h"
#include "alloc.h"
#include "commit-slab.h"

define_commit_slab(blame_suspects, struct blame_origin *);
static struct blame_suspects blame_suspects;

struct blame_origin *get_blame_suspects(struct commit *commit)
{
        struct blame_origin **result;

        result = blame_suspects_peek(&blame_suspects, commit);

        return result ? *result : NULL;
}

static void set_blame_suspects(struct commit *commit, struct blame_origin *origin)
{
        *blame_suspects_at(&blame_suspects, commit) = origin;
}

void blame_origin_decref(struct blame_origin *o)
{
        if (o && --o->refcnt <= 0) {
                struct blame_origin *p, *l = NULL;
                if (o->previous)
                        blame_origin_decref(o->previous);
                free(o->file.ptr);
                /* Should be present exactly once in commit chain */
                for (p = get_blame_suspects(o->commit); p; l = p, p = p->next) {
                        if (p == o) {
                                if (l)
                                        l->next = p->next;
                                else
                                        set_blame_suspects(o->commit, p->next);
                                free(o);
                                return;
                        }
                }
                die("internal error in blame_origin_decref");
        }
}

/*
 * Given a commit and a path in it, create a new origin structure.
 * The callers that add blame to the scoreboard should use
 * get_origin() to obtain shared, refcounted copy instead of calling
 * this function directly.
 */
static struct blame_origin *make_origin(struct commit *commit, const char *path)
{
        struct blame_origin *o;
        FLEX_ALLOC_STR(o, path, path);
        o->commit = commit;
        o->refcnt = 1;
        o->next = get_blame_suspects(commit);
        set_blame_suspects(commit, o);
        return o;
}

/*
 * Locate an existing origin or create a new one.
 * This moves the origin to front position in the commit util list.
 */
static struct blame_origin *get_origin(struct commit *commit, const char *path)
{
        struct blame_origin *o, *l;

        for (o = get_blame_suspects(commit), l = NULL; o; l = o, o = o->next) {
                if (!strcmp(o->path, path)) {
                        /* bump to front */
                        if (l) {
                                l->next = o->next;
                                o->next = get_blame_suspects(commit);
                                set_blame_suspects(commit, o);
                        }
                        return blame_origin_incref(o);
                }
        }
        return make_origin(commit, path);
}



static void verify_working_tree_path(struct repository *repo,
                                     struct commit *work_tree, const char *path)
{
        struct commit_list *parents;
        int pos;

        for (parents = work_tree->parents; parents; parents = parents->next) {
                const struct object_id *commit_oid = &parents->item->object.oid;
                struct object_id blob_oid;
                unsigned mode;

                if (!get_tree_entry(commit_oid, path, &blob_oid, &mode) &&
                    oid_object_info(repo, &blob_oid, NULL) == OBJ_BLOB)
                        return;
        }

        pos = index_name_pos(repo->index, path, strlen(path));
        if (pos >= 0)
                ; /* path is in the index */
        else if (-1 - pos < repo->index->cache_nr &&
                 !strcmp(repo->index->cache[-1 - pos]->name, path))
                ; /* path is in the index, unmerged */
        else
                die("no such path '%s' in HEAD", path);
}

static struct commit_list **append_parent(struct commit_list **tail, const struct object_id *oid)
{
        struct commit *parent;

        parent = lookup_commit_reference(the_repository, oid);
        if (!parent)
                die("no such commit %s", oid_to_hex(oid));
        return &commit_list_insert(parent, tail)->next;
}

static void append_merge_parents(struct commit_list **tail)
{
        int merge_head;
        struct strbuf line = STRBUF_INIT;

        merge_head = open(git_path_merge_head(the_repository), O_RDONLY);
        if (merge_head < 0) {
                if (errno == ENOENT)
                        return;
                die("cannot open '%s' for reading",
                    git_path_merge_head(the_repository));
        }

        while (!strbuf_getwholeline_fd(&line, merge_head, '\n')) {
                struct object_id oid;
                if (line.len < GIT_SHA1_HEXSZ || get_oid_hex(line.buf, &oid))
                        die("unknown line in '%s': %s",
                            git_path_merge_head(the_repository), line.buf);
                tail = append_parent(tail, &oid);
        }
        close(merge_head);
        strbuf_release(&line);
}

/*
 * This isn't as simple as passing sb->buf and sb->len, because we
 * want to transfer ownership of the buffer to the commit (so we
 * must use detach).
 */
static void set_commit_buffer_from_strbuf(struct commit *c, struct strbuf *sb)
{
        size_t len;
        void *buf = strbuf_detach(sb, &len);
        set_commit_buffer(the_repository, c, buf, len);
}

/*
 * Prepare a dummy commit that represents the work tree (or staged) item.
 * Note that annotating work tree item never works in the reverse.
 */
static struct commit *fake_working_tree_commit(struct repository *repo,
                                               struct diff_options *opt,
                                               const char *path,
                                               const char *contents_from)
{
        struct commit *commit;
        struct blame_origin *origin;
        struct commit_list **parent_tail, *parent;
        struct object_id head_oid;
        struct strbuf buf = STRBUF_INIT;
        const char *ident;
        time_t now;
        int len;
        struct cache_entry *ce;
        unsigned mode;
        struct strbuf msg = STRBUF_INIT;

        read_index(repo->index);
        time(&now);
        commit = alloc_commit_node(the_repository);
        commit->object.parsed = 1;
        commit->date = now;
        parent_tail = &commit->parents;

        if (!resolve_ref_unsafe("HEAD", RESOLVE_REF_READING, &head_oid, NULL))
                die("no such ref: HEAD");

        parent_tail = append_parent(parent_tail, &head_oid);
        append_merge_parents(parent_tail);
        verify_working_tree_path(repo, commit, path);

        origin = make_origin(commit, path);

        ident = fmt_ident("Not Committed Yet", "not.committed.yet", NULL, 0);
        strbuf_addstr(&msg, "tree 0000000000000000000000000000000000000000\n");
        for (parent = commit->parents; parent; parent = parent->next)
                strbuf_addf(&msg, "parent %s\n",
                            oid_to_hex(&parent->item->object.oid));
        strbuf_addf(&msg,
                    "author %s\n"
                    "committer %s\n\n"
                    "Version of %s from %s\n",
                    ident, ident, path,
                    (!contents_from ? path :
                     (!strcmp(contents_from, "-") ? "standard input" : contents_from)));
        set_commit_buffer_from_strbuf(commit, &msg);

        if (!contents_from || strcmp("-", contents_from)) {
                struct stat st;
                const char *read_from;
                char *buf_ptr;
                unsigned long buf_len;

                if (contents_from) {
                        if (stat(contents_from, &st) < 0)
                                die_errno("Cannot stat '%s'", contents_from);
                        read_from = contents_from;
                }
                else {
                        if (lstat(path, &st) < 0)
                                die_errno("Cannot lstat '%s'", path);
                        read_from = path;
                }
                mode = canon_mode(st.st_mode);

                switch (st.st_mode & S_IFMT) {
                case S_IFREG:
                        if (opt->flags.allow_textconv &&
                            textconv_object(read_from, mode, &null_oid, 0, &buf_ptr, &buf_len))
                                strbuf_attach(&buf, buf_ptr, buf_len, buf_len + 1);
                        else if (strbuf_read_file(&buf, read_from, st.st_size) != st.st_size)
                                die_errno("cannot open or read '%s'", read_from);
                        break;
                case S_IFLNK:
                        if (strbuf_readlink(&buf, read_from, st.st_size) < 0)
                                die_errno("cannot readlink '%s'", read_from);
                        break;
                default:
                        die("unsupported file type %s", read_from);
                }
        }
        else {
                /* Reading from stdin */
                mode = 0;
                if (strbuf_read(&buf, 0, 0) < 0)
                        die_errno("failed to read from stdin");
        }
        convert_to_git(repo->index, path, buf.buf, buf.len, &buf, 0);
        origin->file.ptr = buf.buf;
        origin->file.size = buf.len;
        pretend_object_file(buf.buf, buf.len, OBJ_BLOB, &origin->blob_oid);

        /*
         * Read the current index, replace the path entry with
         * origin->blob_sha1 without mucking with its mode or type
         * bits; we are not going to write this index out -- we just
         * want to run "diff-index --cached".
         */
        discard_index(repo->index);
        read_index(repo->index);

        len = strlen(path);
        if (!mode) {
                int pos = index_name_pos(repo->index, path, len);
                if (0 <= pos)
                        mode = repo->index->cache[pos]->ce_mode;
                else
                        /* Let's not bother reading from HEAD tree */
                        mode = S_IFREG | 0644;
        }
        ce = make_empty_cache_entry(repo->index, len);
        oidcpy(&ce->oid, &origin->blob_oid);
        memcpy(ce->name, path, len);
        ce->ce_flags = create_ce_flags(0);
        ce->ce_namelen = len;
        ce->ce_mode = create_ce_mode(mode);
        add_index_entry(repo->index, ce,
                        ADD_CACHE_OK_TO_ADD | ADD_CACHE_OK_TO_REPLACE);

        cache_tree_invalidate_path(repo->index, path);

        return commit;
}



static int diff_hunks(mmfile_t *file_a, mmfile_t *file_b,
                      xdl_emit_hunk_consume_func_t hunk_func, void *cb_data, int xdl_opts)
{
        xpparam_t xpp = {0};
        xdemitconf_t xecfg = {0};
        xdemitcb_t ecb = {NULL};

        xpp.flags = xdl_opts;
        xecfg.hunk_func = hunk_func;
        ecb.priv = cb_data;
        return xdi_diff(file_a, file_b, &xpp, &xecfg, &ecb);
}

/*
 * Given an origin, prepare mmfile_t structure to be used by the
 * diff machinery
 */
static void fill_origin_blob(struct diff_options *opt,
                             struct blame_origin *o, mmfile_t *file, int *num_read_blob)
{
        if (!o->file.ptr) {
                enum object_type type;
                unsigned long file_size;

                (*num_read_blob)++;
                if (opt->flags.allow_textconv &&
                    textconv_object(o->path, o->mode, &o->blob_oid, 1, &file->ptr, &file_size))
                        ;
                else
                        file->ptr = read_object_file(&o->blob_oid, &type,
                                                     &file_size);
                file->size = file_size;

                if (!file->ptr)
                        die("Cannot read blob %s for path %s",
                            oid_to_hex(&o->blob_oid),
                            o->path);
                o->file = *file;
        }
        else
                *file = o->file;
}

static void drop_origin_blob(struct blame_origin *o)
{
        FREE_AND_NULL(o->file.ptr);
}

/*
 * Any merge of blames happens on lists of blames that arrived via
 * different parents in a single suspect.  In this case, we want to
 * sort according to the suspect line numbers as opposed to the final
 * image line numbers.  The function body is somewhat longish because
 * it avoids unnecessary writes.
 */

static struct blame_entry *blame_merge(struct blame_entry *list1,
                                       struct blame_entry *list2)
{
        struct blame_entry *p1 = list1, *p2 = list2,
                **tail = &list1;

        if (!p1)
                return p2;
        if (!p2)
                return p1;

        if (p1->s_lno <= p2->s_lno) {
                do {
                        tail = &p1->next;
                        if ((p1 = *tail) == NULL) {
                                *tail = p2;
                                return list1;
                        }
                } while (p1->s_lno <= p2->s_lno);
        }
        for (;;) {
                *tail = p2;
                do {
                        tail = &p2->next;
                        if ((p2 = *tail) == NULL)  {
                                *tail = p1;
                                return list1;
                        }
                } while (p1->s_lno > p2->s_lno);
                *tail = p1;
                do {
                        tail = &p1->next;
                        if ((p1 = *tail) == NULL) {
                                *tail = p2;
                                return list1;
                        }
                } while (p1->s_lno <= p2->s_lno);
        }
}

static void *get_next_blame(const void *p)
{
        return ((struct blame_entry *)p)->next;
}

static void set_next_blame(void *p1, void *p2)
{
        ((struct blame_entry *)p1)->next = p2;
}

/*
 * Final image line numbers are all different, so we don't need a
 * three-way comparison here.
 */

static int compare_blame_final(const void *p1, const void *p2)
{
        return ((struct blame_entry *)p1)->lno > ((struct blame_entry *)p2)->lno
                ? 1 : -1;
}

static int compare_blame_suspect(const void *p1, const void *p2)
{
        const struct blame_entry *s1 = p1, *s2 = p2;
        /*
         * to allow for collating suspects, we sort according to the
         * respective pointer value as the primary sorting criterion.
         * The actual relation is pretty unimportant as long as it
         * establishes a total order.  Comparing as integers gives us
         * that.
         */
        if (s1->suspect != s2->suspect)
                return (intptr_t)s1->suspect > (intptr_t)s2->suspect ? 1 : -1;
        if (s1->s_lno == s2->s_lno)
                return 0;
        return s1->s_lno > s2->s_lno ? 1 : -1;
}

void blame_sort_final(struct blame_scoreboard *sb)
{
        sb->ent = llist_mergesort(sb->ent, get_next_blame, set_next_blame,
                                  compare_blame_final);
}

static int compare_commits_by_reverse_commit_date(const void *a,
                                                  const void *b,
                                                  void *c)
{
        return -compare_commits_by_commit_date(a, b, c);
}

/*
 * For debugging -- origin is refcounted, and this asserts that
 * we do not underflow.
 */
static void sanity_check_refcnt(struct blame_scoreboard *sb)
{
        int baa = 0;
        struct blame_entry *ent;

        for (ent = sb->ent; ent; ent = ent->next) {
                /* Nobody should have zero or negative refcnt */
                if (ent->suspect->refcnt <= 0) {
                        fprintf(stderr, "%s in %s has negative refcnt %d\n",
                                ent->suspect->path,
                                oid_to_hex(&ent->suspect->commit->object.oid),
                                ent->suspect->refcnt);
                        baa = 1;
                }
        }
        if (baa)
                sb->on_sanity_fail(sb, baa);
}

/*
 * If two blame entries that are next to each other came from
 * contiguous lines in the same origin (i.e. <commit, path> pair),
 * merge them together.
 */
void blame_coalesce(struct blame_scoreboard *sb)
{
        struct blame_entry *ent, *next;

        for (ent = sb->ent; ent && (next = ent->next); ent = next) {
                if (ent->suspect == next->suspect &&
                    ent->s_lno + ent->num_lines == next->s_lno) {
                        ent->num_lines += next->num_lines;
                        ent->next = next->next;
                        blame_origin_decref(next->suspect);
                        free(next);
                        ent->score = 0;
                        next = ent; /* again */
                }
        }

        if (sb->debug) /* sanity */
                sanity_check_refcnt(sb);
}

/*
 * Merge the given sorted list of blames into a preexisting origin.
 * If there were no previous blames to that commit, it is entered into
 * the commit priority queue of the score board.
 */

static void queue_blames(struct blame_scoreboard *sb, struct blame_origin *porigin,
                         struct blame_entry *sorted)
{
        if (porigin->suspects)
                porigin->suspects = blame_merge(porigin->suspects, sorted);
        else {
                struct blame_origin *o;
                for (o = get_blame_suspects(porigin->commit); o; o = o->next) {
                        if (o->suspects) {
                                porigin->suspects = sorted;
                                return;
                        }
                }
                porigin->suspects = sorted;
                prio_queue_put(&sb->commits, porigin->commit);
        }
}

/*
 * Fill the blob_sha1 field of an origin if it hasn't, so that later
 * call to fill_origin_blob() can use it to locate the data.  blob_sha1
 * for an origin is also used to pass the blame for the entire file to
 * the parent to detect the case where a child's blob is identical to
 * that of its parent's.
 *
 * This also fills origin->mode for corresponding tree path.
 */
static int fill_blob_sha1_and_mode(struct repository *repo,
                                   struct blame_origin *origin)
{
        if (!is_null_oid(&origin->blob_oid))
                return 0;
        if (get_tree_entry(&origin->commit->object.oid, origin->path, &origin->blob_oid, &origin->mode))
                goto error_out;
        if (oid_object_info(repo, &origin->blob_oid, NULL) != OBJ_BLOB)
                goto error_out;
        return 0;
 error_out:
        oidclr(&origin->blob_oid);
        origin->mode = S_IFINVALID;
        return -1;
}

/*
 * We have an origin -- check if the same path exists in the
 * parent and return an origin structure to represent it.
 */
static struct blame_origin *find_origin(struct commit *parent,
                                  struct blame_origin *origin)
{
        struct blame_origin *porigin;
        struct diff_options diff_opts;
        const char *paths[2];

        /* First check any existing origins */
        for (porigin = get_blame_suspects(parent); porigin; porigin = porigin->next)
                if (!strcmp(porigin->path, origin->path)) {
                        /*
                         * The same path between origin and its parent
                         * without renaming -- the most common case.
                         */
                        return blame_origin_incref (porigin);
                }

        /* See if the origin->path is different between parent
         * and origin first.  Most of the time they are the
         * same and diff-tree is fairly efficient about this.
         */
        diff_setup(&diff_opts);
        diff_opts.flags.recursive = 1;
        diff_opts.detect_rename = 0;
        diff_opts.output_format = DIFF_FORMAT_NO_OUTPUT;
        paths[0] = origin->path;
        paths[1] = NULL;

        parse_pathspec(&diff_opts.pathspec,
                       PATHSPEC_ALL_MAGIC & ~PATHSPEC_LITERAL,
                       PATHSPEC_LITERAL_PATH, "", paths);
        diff_setup_done(&diff_opts);

        if (is_null_oid(&origin->commit->object.oid))
                do_diff_cache(get_commit_tree_oid(parent), &diff_opts);
        else
                diff_tree_oid(get_commit_tree_oid(parent),
                              get_commit_tree_oid(origin->commit),
                              "", &diff_opts);
        diffcore_std(&diff_opts);

        if (!diff_queued_diff.nr) {
                /* The path is the same as parent */
                porigin = get_origin(parent, origin->path);
                oidcpy(&porigin->blob_oid, &origin->blob_oid);
                porigin->mode = origin->mode;
        } else {
                /*
                 * Since origin->path is a pathspec, if the parent
                 * commit had it as a directory, we will see a whole
                 * bunch of deletion of files in the directory that we
                 * do not care about.
                 */
                int i;
                struct diff_filepair *p = NULL;
                for (i = 0; i < diff_queued_diff.nr; i++) {
                        const char *name;
                        p = diff_queued_diff.queue[i];
                        name = p->one->path ? p->one->path : p->two->path;
                        if (!strcmp(name, origin->path))
                                break;
                }
                if (!p)
                        die("internal error in blame::find_origin");
                switch (p->status) {
                default:
                        die("internal error in blame::find_origin (%c)",
                            p->status);
                case 'M':
                        porigin = get_origin(parent, origin->path);
                        oidcpy(&porigin->blob_oid, &p->one->oid);
                        porigin->mode = p->one->mode;
                        break;
                case 'A':
                case 'T':
                        /* Did not exist in parent, or type changed */
                        break;
                }
        }
        diff_flush(&diff_opts);
        clear_pathspec(&diff_opts.pathspec);
        return porigin;
}

/*
 * We have an origin -- find the path that corresponds to it in its
 * parent and return an origin structure to represent it.
 */
static struct blame_origin *find_rename(struct commit *parent,
                                  struct blame_origin *origin)
{
        struct blame_origin *porigin = NULL;
        struct diff_options diff_opts;
        int i;

        diff_setup(&diff_opts);
        diff_opts.flags.recursive = 1;
        diff_opts.detect_rename = DIFF_DETECT_RENAME;
        diff_opts.output_format = DIFF_FORMAT_NO_OUTPUT;
        diff_opts.single_follow = origin->path;
        diff_setup_done(&diff_opts);

        if (is_null_oid(&origin->commit->object.oid))
                do_diff_cache(get_commit_tree_oid(parent), &diff_opts);
        else
                diff_tree_oid(get_commit_tree_oid(parent),
                              get_commit_tree_oid(origin->commit),
                              "", &diff_opts);
        diffcore_std(&diff_opts);

        for (i = 0; i < diff_queued_diff.nr; i++) {
                struct diff_filepair *p = diff_queued_diff.queue[i];
                if ((p->status == 'R' || p->status == 'C') &&
                    !strcmp(p->two->path, origin->path)) {
                        porigin = get_origin(parent, p->one->path);
                        oidcpy(&porigin->blob_oid, &p->one->oid);
                        porigin->mode = p->one->mode;
                        break;
                }
        }
        diff_flush(&diff_opts);
        clear_pathspec(&diff_opts.pathspec);
        return porigin;
}

/*
 * Append a new blame entry to a given output queue.
 */
static void add_blame_entry(struct blame_entry ***queue,
                            const struct blame_entry *src)
{
        struct blame_entry *e = xmalloc(sizeof(*e));
        memcpy(e, src, sizeof(*e));
        blame_origin_incref(e->suspect);

        e->next = **queue;
        **queue = e;
        *queue = &e->next;
}

/*
 * src typically is on-stack; we want to copy the information in it to
 * a malloced blame_entry that gets added to the given queue.  The
 * origin of dst loses a refcnt.
 */
static void dup_entry(struct blame_entry ***queue,
                      struct blame_entry *dst, struct blame_entry *src)
{
        blame_origin_incref(src->suspect);
        blame_origin_decref(dst->suspect);
        memcpy(dst, src, sizeof(*src));
        dst->next = **queue;
        **queue = dst;
        *queue = &dst->next;
}

const char *blame_nth_line(struct blame_scoreboard *sb, long lno)
{
        return sb->final_buf + sb->lineno[lno];
}

/*
 * It is known that lines between tlno to same came from parent, and e
 * has an overlap with that range.  it also is known that parent's
 * line plno corresponds to e's line tlno.
 *
 *                <---- e ----->
 *                   <------>
 *                   <------------>
 *             <------------>
 *             <------------------>
 *
 * Split e into potentially three parts; before this chunk, the chunk
 * to be blamed for the parent, and after that portion.
 */
static void split_overlap(struct blame_entry *split,
                          struct blame_entry *e,
                          int tlno, int plno, int same,
                          struct blame_origin *parent)
{
        int chunk_end_lno;
        memset(split, 0, sizeof(struct blame_entry [3]));

        if (e->s_lno < tlno) {
                /* there is a pre-chunk part not blamed on parent */
                split[0].suspect = blame_origin_incref(e->suspect);
                split[0].lno = e->lno;
                split[0].s_lno = e->s_lno;
                split[0].num_lines = tlno - e->s_lno;
                split[1].lno = e->lno + tlno - e->s_lno;
                split[1].s_lno = plno;
        }
        else {
                split[1].lno = e->lno;
                split[1].s_lno = plno + (e->s_lno - tlno);
        }

        if (same < e->s_lno + e->num_lines) {
                /* there is a post-chunk part not blamed on parent */
                split[2].suspect = blame_origin_incref(e->suspect);
                split[2].lno = e->lno + (same - e->s_lno);
                split[2].s_lno = e->s_lno + (same - e->s_lno);
                split[2].num_lines = e->s_lno + e->num_lines - same;
                chunk_end_lno = split[2].lno;
        }
        else
                chunk_end_lno = e->lno + e->num_lines;
        split[1].num_lines = chunk_end_lno - split[1].lno;

        /*
         * if it turns out there is nothing to blame the parent for,
         * forget about the splitting.  !split[1].suspect signals this.
         */
        if (split[1].num_lines < 1)
                return;
        split[1].suspect = blame_origin_incref(parent);
}

/*
 * split_overlap() divided an existing blame e into up to three parts
 * in split.  Any assigned blame is moved to queue to
 * reflect the split.
 */
static void split_blame(struct blame_entry ***blamed,
                        struct blame_entry ***unblamed,
                        struct blame_entry *split,
                        struct blame_entry *e)
{
        if (split[0].suspect && split[2].suspect) {
                /* The first part (reuse storage for the existing entry e) */
                dup_entry(unblamed, e, &split[0]);

                /* The last part -- me */
                add_blame_entry(unblamed, &split[2]);

                /* ... and the middle part -- parent */
                add_blame_entry(blamed, &split[1]);
        }
        else if (!split[0].suspect && !split[2].suspect)
                /*
                 * The parent covers the entire area; reuse storage for
                 * e and replace it with the parent.
                 */
                dup_entry(blamed, e, &split[1]);
        else if (split[0].suspect) {
                /* me and then parent */
                dup_entry(unblamed, e, &split[0]);
                add_blame_entry(blamed, &split[1]);
        }
        else {
                /* parent and then me */
                dup_entry(blamed, e, &split[1]);
                add_blame_entry(unblamed, &split[2]);
        }
}

/*
 * After splitting the blame, the origins used by the
 * on-stack blame_entry should lose one refcnt each.
 */
static void decref_split(struct blame_entry *split)
{
        int i;

        for (i = 0; i < 3; i++)
                blame_origin_decref(split[i].suspect);
}

/*
 * reverse_blame reverses the list given in head, appending tail.
 * That allows us to build lists in reverse order, then reverse them
 * afterwards.  This can be faster than building the list in proper
 * order right away.  The reason is that building in proper order
 * requires writing a link in the _previous_ element, while building
 * in reverse order just requires placing the list head into the
 * _current_ element.
 */

static struct blame_entry *reverse_blame(struct blame_entry *head,
                                         struct blame_entry *tail)
{
        while (head) {
                struct blame_entry *next = head->next;
                head->next = tail;
                tail = head;
                head = next;
        }
        return tail;
}

/*
 * Process one hunk from the patch between the current suspect for
 * blame_entry e and its parent.  This first blames any unfinished
 * entries before the chunk (which is where target and parent start
 * differing) on the parent, and then splits blame entries at the
 * start and at the end of the difference region.  Since use of -M and
 * -C options may lead to overlapping/duplicate source line number
 * ranges, all we can rely on from sorting/merging is the order of the
 * first suspect line number.
 */
static void blame_chunk(struct blame_entry ***dstq, struct blame_entry ***srcq,
                        int tlno, int offset, int same,
                        struct blame_origin *parent)
{
        struct blame_entry *e = **srcq;
        struct blame_entry *samep = NULL, *diffp = NULL;

        while (e && e->s_lno < tlno) {
                struct blame_entry *next = e->next;
                /*
                 * current record starts before differing portion.  If
                 * it reaches into it, we need to split it up and
                 * examine the second part separately.
                 */
                if (e->s_lno + e->num_lines > tlno) {
                        /* Move second half to a new record */
                        int len = tlno - e->s_lno;
                        struct blame_entry *n = xcalloc(1, sizeof (struct blame_entry));
                        n->suspect = e->suspect;
                        n->lno = e->lno + len;
                        n->s_lno = e->s_lno + len;
                        n->num_lines = e->num_lines - len;
                        e->num_lines = len;
                        e->score = 0;
                        /* Push new record to diffp */
                        n->next = diffp;
                        diffp = n;
                } else
                        blame_origin_decref(e->suspect);
                /* Pass blame for everything before the differing
                 * chunk to the parent */
                e->suspect = blame_origin_incref(parent);
                e->s_lno += offset;
                e->next = samep;
                samep = e;
                e = next;
        }
        /*
         * As we don't know how much of a common stretch after this
         * diff will occur, the currently blamed parts are all that we
         * can assign to the parent for now.
         */

        if (samep) {
                **dstq = reverse_blame(samep, **dstq);
                *dstq = &samep->next;
        }
        /*
         * Prepend the split off portions: everything after e starts
         * after the blameable portion.
         */
        e = reverse_blame(diffp, e);

        /*
         * Now retain records on the target while parts are different
         * from the parent.
         */
        samep = NULL;
        diffp = NULL;
        while (e && e->s_lno < same) {
                struct blame_entry *next = e->next;

                /*
                 * If current record extends into sameness, need to split.
                 */
                if (e->s_lno + e->num_lines > same) {
                        /*
                         * Move second half to a new record to be
                         * processed by later chunks
                         */
                        int len = same - e->s_lno;
                        struct blame_entry *n = xcalloc(1, sizeof (struct blame_entry));
                        n->suspect = blame_origin_incref(e->suspect);
                        n->lno = e->lno + len;
                        n->s_lno = e->s_lno + len;
                        n->num_lines = e->num_lines - len;
                        e->num_lines = len;
                        e->score = 0;
                        /* Push new record to samep */
                        n->next = samep;
                        samep = n;
                }
                e->next = diffp;
                diffp = e;
                e = next;
        }
        **srcq = reverse_blame(diffp, reverse_blame(samep, e));
        /* Move across elements that are in the unblamable portion */
        if (diffp)
                *srcq = &diffp->next;
}

struct blame_chunk_cb_data {
        struct blame_origin *parent;
        long offset;
        struct blame_entry **dstq;
        struct blame_entry **srcq;
};

/* diff chunks are from parent to target */
static int blame_chunk_cb(long start_a, long count_a,
                          long start_b, long count_b, void *data)
{
        struct blame_chunk_cb_data *d = data;
        if (start_a - start_b != d->offset)
                die("internal error in blame::blame_chunk_cb");
        blame_chunk(&d->dstq, &d->srcq, start_b, start_a - start_b,
                    start_b + count_b, d->parent);
        d->offset = start_a + count_a - (start_b + count_b);
        return 0;
}

/*
 * We are looking at the origin 'target' and aiming to pass blame
 * for the lines it is suspected to its parent.  Run diff to find
 * which lines came from parent and pass blame for them.
 */
static void pass_blame_to_parent(struct blame_scoreboard *sb,
                                 struct blame_origin *target,
                                 struct blame_origin *parent)
{
        mmfile_t file_p, file_o;
        struct blame_chunk_cb_data d;
        struct blame_entry *newdest = NULL;

        if (!target->suspects)
                return; /* nothing remains for this target */

        d.parent = parent;
        d.offset = 0;
        d.dstq = &newdest; d.srcq = &target->suspects;

        fill_origin_blob(&sb->revs->diffopt, parent, &file_p, &sb->num_read_blob);
        fill_origin_blob(&sb->revs->diffopt, target, &file_o, &sb->num_read_blob);
        sb->num_get_patch++;

        if (diff_hunks(&file_p, &file_o, blame_chunk_cb, &d, sb->xdl_opts))
                die("unable to generate diff (%s -> %s)",
                    oid_to_hex(&parent->commit->object.oid),
                    oid_to_hex(&target->commit->object.oid));
        /* The rest are the same as the parent */
        blame_chunk(&d.dstq, &d.srcq, INT_MAX, d.offset, INT_MAX, parent);
        *d.dstq = NULL;
        queue_blames(sb, parent, newdest);

        return;
}

/*
 * The lines in blame_entry after splitting blames many times can become
 * very small and trivial, and at some point it becomes pointless to
 * blame the parents.  E.g. "\t\t}\n\t}\n\n" appears everywhere in any
 * ordinary C program, and it is not worth to say it was copied from
 * totally unrelated file in the parent.
 *
 * Compute how trivial the lines in the blame_entry are.
 */
unsigned blame_entry_score(struct blame_scoreboard *sb, struct blame_entry *e)
{
        unsigned score;
        const char *cp, *ep;

        if (e->score)
                return e->score;

        score = 1;
        cp = blame_nth_line(sb, e->lno);
        ep = blame_nth_line(sb, e->lno + e->num_lines);
        while (cp < ep) {
                unsigned ch = *((unsigned char *)cp);
                if (isalnum(ch))
                        score++;
                cp++;
        }
        e->score = score;
        return score;
}

/*
 * best_so_far[] and potential[] are both a split of an existing blame_entry
 * that passes blame to the parent.  Maintain best_so_far the best split so
 * far, by comparing potential and best_so_far and copying potential into
 * bst_so_far as needed.
 */
static void copy_split_if_better(struct blame_scoreboard *sb,
                                 struct blame_entry *best_so_far,
                                 struct blame_entry *potential)
{
        int i;

        if (!potential[1].suspect)
                return;
        if (best_so_far[1].suspect) {
                if (blame_entry_score(sb, &potential[1]) <
                    blame_entry_score(sb, &best_so_far[1]))
                        return;
        }

        for (i = 0; i < 3; i++)
                blame_origin_incref(potential[i].suspect);
        decref_split(best_so_far);
        memcpy(best_so_far, potential, sizeof(struct blame_entry[3]));
}

/*
 * We are looking at a part of the final image represented by
 * ent (tlno and same are offset by ent->s_lno).
 * tlno is where we are looking at in the final image.
 * up to (but not including) same match preimage.
 * plno is where we are looking at in the preimage.
 *
 * <-------------- final image ---------------------->
 *       <------ent------>
 *         ^tlno ^same
 *    <---------preimage----->
 *         ^plno
 *
 * All line numbers are 0-based.
 */
static void handle_split(struct blame_scoreboard *sb,
                         struct blame_entry *ent,
                         int tlno, int plno, int same,
                         struct blame_origin *parent,
                         struct blame_entry *split)
{
        if (ent->num_lines <= tlno)
                return;
        if (tlno < same) {
                struct blame_entry potential[3];
                tlno += ent->s_lno;
                same += ent->s_lno;
                split_overlap(potential, ent, tlno, plno, same, parent);
                copy_split_if_better(sb, split, potential);
                decref_split(potential);
        }
}

struct handle_split_cb_data {
        struct blame_scoreboard *sb;
        struct blame_entry *ent;
        struct blame_origin *parent;
        struct blame_entry *split;
        long plno;
        long tlno;
};

static int handle_split_cb(long start_a, long count_a,
                           long start_b, long count_b, void *data)
{
        struct handle_split_cb_data *d = data;
        handle_split(d->sb, d->ent, d->tlno, d->plno, start_b, d->parent,
                     d->split);
        d->plno = start_a + count_a;
        d->tlno = start_b + count_b;
        return 0;
}

/*
 * Find the lines from parent that are the same as ent so that
 * we can pass blames to it.  file_p has the blob contents for
 * the parent.
 */
static void find_copy_in_blob(struct blame_scoreboard *sb,
                              struct blame_entry *ent,
                              struct blame_origin *parent,
                              struct blame_entry *split,
                              mmfile_t *file_p)
{
        const char *cp;
        mmfile_t file_o;
        struct handle_split_cb_data d;

        memset(&d, 0, sizeof(d));
        d.sb = sb; d.ent = ent; d.parent = parent; d.split = split;
        /*
         * Prepare mmfile that contains only the lines in ent.
         */
        cp = blame_nth_line(sb, ent->lno);
        file_o.ptr = (char *) cp;
        file_o.size = blame_nth_line(sb, ent->lno + ent->num_lines) - cp;

        /*
         * file_o is a part of final image we are annotating.
         * file_p partially may match that image.
         */
        memset(split, 0, sizeof(struct blame_entry [3]));
        if (diff_hunks(file_p, &file_o, handle_split_cb, &d, sb->xdl_opts))
                die("unable to generate diff (%s)",
                    oid_to_hex(&parent->commit->object.oid));
        /* remainder, if any, all match the preimage */
        handle_split(sb, ent, d.tlno, d.plno, ent->num_lines, parent, split);
}

/* Move all blame entries from list *source that have a score smaller
 * than score_min to the front of list *small.
 * Returns a pointer to the link pointing to the old head of the small list.
 */

static struct blame_entry **filter_small(struct blame_scoreboard *sb,
                                         struct blame_entry **small,
                                         struct blame_entry **source,
                                         unsigned score_min)
{
        struct blame_entry *p = *source;
        struct blame_entry *oldsmall = *small;
        while (p) {
                if (blame_entry_score(sb, p) <= score_min) {
                        *small = p;
                        small = &p->next;
                        p = *small;
                } else {
                        *source = p;
                        source = &p->next;
                        p = *source;
                }
        }
        *small = oldsmall;
        *source = NULL;
        return small;
}

/*
 * See if lines currently target is suspected for can be attributed to
 * parent.
 */
static void find_move_in_parent(struct blame_scoreboard *sb,
                                struct blame_entry ***blamed,
                                struct blame_entry **toosmall,
                                struct blame_origin *target,
                                struct blame_origin *parent)
{
        struct blame_entry *e, split[3];
        struct blame_entry *unblamed = target->suspects;
        struct blame_entry *leftover = NULL;
        mmfile_t file_p;

        if (!unblamed)
                return; /* nothing remains for this target */

        fill_origin_blob(&sb->revs->diffopt, parent, &file_p, &sb->num_read_blob);
        if (!file_p.ptr)
                return;

        /* At each iteration, unblamed has a NULL-terminated list of
         * entries that have not yet been tested for blame.  leftover
         * contains the reversed list of entries that have been tested
         * without being assignable to the parent.
         */
        do {
                struct blame_entry **unblamedtail = &unblamed;
                struct blame_entry *next;
                for (e = unblamed; e; e = next) {
                        next = e->next;
                        find_copy_in_blob(sb, e, parent, split, &file_p);
                        if (split[1].suspect &&
                            sb->move_score < blame_entry_score(sb, &split[1])) {
                                split_blame(blamed, &unblamedtail, split, e);
                        } else {
                                e->next = leftover;
                                leftover = e;
                        }
                        decref_split(split);
                }
                *unblamedtail = NULL;
                toosmall = filter_small(sb, toosmall, &unblamed, sb->move_score);
        } while (unblamed);
        target->suspects = reverse_blame(leftover, NULL);
}

struct blame_list {
        struct blame_entry *ent;
        struct blame_entry split[3];
};

/*
 * Count the number of entries the target is suspected for,
 * and prepare a list of entry and the best split.
 */
static struct blame_list *setup_blame_list(struct blame_entry *unblamed,
                                           int *num_ents_p)
{
        struct blame_entry *e;
        int num_ents, i;
        struct blame_list *blame_list = NULL;

        for (e = unblamed, num_ents = 0; e; e = e->next)
                num_ents++;
        if (num_ents) {
                blame_list = xcalloc(num_ents, sizeof(struct blame_list));
                for (e = unblamed, i = 0; e; e = e->next)
                        blame_list[i++].ent = e;
        }
        *num_ents_p = num_ents;
        return blame_list;
}

/*
 * For lines target is suspected for, see if we can find code movement
 * across file boundary from the parent commit.  porigin is the path
 * in the parent we already tried.
 */
static void find_copy_in_parent(struct blame_scoreboard *sb,
                                struct blame_entry ***blamed,
                                struct blame_entry **toosmall,
                                struct blame_origin *target,
                                struct commit *parent,
                                struct blame_origin *porigin,
                                int opt)
{
        struct diff_options diff_opts;
        int i, j;
        struct blame_list *blame_list;
        int num_ents;
        struct blame_entry *unblamed = target->suspects;
        struct blame_entry *leftover = NULL;

        if (!unblamed)
                return; /* nothing remains for this target */

        diff_setup(&diff_opts);
        diff_opts.flags.recursive = 1;
        diff_opts.output_format = DIFF_FORMAT_NO_OUTPUT;

        diff_setup_done(&diff_opts);

        /* Try "find copies harder" on new path if requested;
         * we do not want to use diffcore_rename() actually to
         * match things up; find_copies_harder is set only to
         * force diff_tree_oid() to feed all filepairs to diff_queue,
         * and this code needs to be after diff_setup_done(), which
         * usually makes find-copies-harder imply copy detection.
         */
        if ((opt & PICKAXE_BLAME_COPY_HARDEST)
            || ((opt & PICKAXE_BLAME_COPY_HARDER)
                && (!porigin || strcmp(target->path, porigin->path))))
                diff_opts.flags.find_copies_harder = 1;

        if (is_null_oid(&target->commit->object.oid))
                do_diff_cache(get_commit_tree_oid(parent), &diff_opts);
        else
                diff_tree_oid(get_commit_tree_oid(parent),
                              get_commit_tree_oid(target->commit),
                              "", &diff_opts);

        if (!diff_opts.flags.find_copies_harder)
                diffcore_std(&diff_opts);

        do {
                struct blame_entry **unblamedtail = &unblamed;
                blame_list = setup_blame_list(unblamed, &num_ents);

                for (i = 0; i < diff_queued_diff.nr; i++) {
                        struct diff_filepair *p = diff_queued_diff.queue[i];
                        struct blame_origin *norigin;
                        mmfile_t file_p;
                        struct blame_entry potential[3];

                        if (!DIFF_FILE_VALID(p->one))
                                continue; /* does not exist in parent */
                        if (S_ISGITLINK(p->one->mode))
                                continue; /* ignore git links */
                        if (porigin && !strcmp(p->one->path, porigin->path))
                                /* find_move already dealt with this path */
                                continue;

                        norigin = get_origin(parent, p->one->path);
                        oidcpy(&norigin->blob_oid, &p->one->oid);
                        norigin->mode = p->one->mode;
                        fill_origin_blob(&sb->revs->diffopt, norigin, &file_p, &sb->num_read_blob);
                        if (!file_p.ptr)
                                continue;

                        for (j = 0; j < num_ents; j++) {
                                find_copy_in_blob(sb, blame_list[j].ent,
                                                  norigin, potential, &file_p);
                                copy_split_if_better(sb, blame_list[j].split,
                                                     potential);
                                decref_split(potential);
                        }
                        blame_origin_decref(norigin);
                }

                for (j = 0; j < num_ents; j++) {
                        struct blame_entry *split = blame_list[j].split;
                        if (split[1].suspect &&
                            sb->copy_score < blame_entry_score(sb, &split[1])) {
                                split_blame(blamed, &unblamedtail, split,
                                            blame_list[j].ent);
                        } else {
                                blame_list[j].ent->next = leftover;
                                leftover = blame_list[j].ent;
                        }
                        decref_split(split);
                }
                free(blame_list);
                *unblamedtail = NULL;
                toosmall = filter_small(sb, toosmall, &unblamed, sb->copy_score);
        } while (unblamed);
        target->suspects = reverse_blame(leftover, NULL);
        diff_flush(&diff_opts);
        clear_pathspec(&diff_opts.pathspec);
}

/*
 * The blobs of origin and porigin exactly match, so everything
 * origin is suspected for can be blamed on the parent.
 */
static void pass_whole_blame(struct blame_scoreboard *sb,
                             struct blame_origin *origin, struct blame_origin *porigin)
{
        struct blame_entry *e, *suspects;

        if (!porigin->file.ptr && origin->file.ptr) {
                /* Steal its file */
                porigin->file = origin->file;
                origin->file.ptr = NULL;
        }
        suspects = origin->suspects;
        origin->suspects = NULL;
        for (e = suspects; e; e = e->next) {
                blame_origin_incref(porigin);
                blame_origin_decref(e->suspect);
                e->suspect = porigin;
        }
        queue_blames(sb, porigin, suspects);
}

/*
 * We pass blame from the current commit to its parents.  We keep saying
 * "parent" (and "porigin"), but what we mean is to find scapegoat to
 * exonerate ourselves.
 */
static struct commit_list *first_scapegoat(struct rev_info *revs, struct commit *commit,
                                        int reverse)
{
        if (!reverse) {
                if (revs->first_parent_only &&
                    commit->parents &&
                    commit->parents->next) {
                        free_commit_list(commit->parents->next);
                        commit->parents->next = NULL;
                }
                return commit->parents;
        }
        return lookup_decoration(&revs->children, &commit->object);
}

static int num_scapegoats(struct rev_info *revs, struct commit *commit, int reverse)
{
        struct commit_list *l = first_scapegoat(revs, commit, reverse);
        return commit_list_count(l);
}

/* Distribute collected unsorted blames to the respected sorted lists
 * in the various origins.
 */
static void distribute_blame(struct blame_scoreboard *sb, struct blame_entry *blamed)
{
        blamed = llist_mergesort(blamed, get_next_blame, set_next_blame,
                                 compare_blame_suspect);
        while (blamed)
        {
                struct blame_origin *porigin = blamed->suspect;
                struct blame_entry *suspects = NULL;
                do {
                        struct blame_entry *next = blamed->next;
                        blamed->next = suspects;
                        suspects = blamed;
                        blamed = next;
                } while (blamed && blamed->suspect == porigin);
                suspects = reverse_blame(suspects, NULL);
                queue_blames(sb, porigin, suspects);
        }
}

#define MAXSG 16

static void pass_blame(struct blame_scoreboard *sb, struct blame_origin *origin, int opt)
{
        struct rev_info *revs = sb->revs;
        int i, pass, num_sg;
        struct commit *commit = origin->commit;
        struct commit_list *sg;
        struct blame_origin *sg_buf[MAXSG];
        struct blame_origin *porigin, **sg_origin = sg_buf;
        struct blame_entry *toosmall = NULL;
        struct blame_entry *blames, **blametail = &blames;

        num_sg = num_scapegoats(revs, commit, sb->reverse);
        if (!num_sg)
                goto finish;
        else if (num_sg < ARRAY_SIZE(sg_buf))
                memset(sg_buf, 0, sizeof(sg_buf));
        else
                sg_origin = xcalloc(num_sg, sizeof(*sg_origin));

        /*
         * The first pass looks for unrenamed path to optimize for
         * common cases, then we look for renames in the second pass.
         */
        for (pass = 0; pass < 2 - sb->no_whole_file_rename; pass++) {
                struct blame_origin *(*find)(struct commit *, struct blame_origin *);
                find = pass ? find_rename : find_origin;

                for (i = 0, sg = first_scapegoat(revs, commit, sb->reverse);
                     i < num_sg && sg;
                     sg = sg->next, i++) {
                        struct commit *p = sg->item;
                        int j, same;

                        if (sg_origin[i])
                                continue;
                        if (parse_commit(p))
                                continue;
                        porigin = find(p, origin);
                        if (!porigin)
                                continue;
                        if (!oidcmp(&porigin->blob_oid, &origin->blob_oid)) {
                                pass_whole_blame(sb, origin, porigin);
                                blame_origin_decref(porigin);
                                goto finish;
                        }
                        for (j = same = 0; j < i; j++)
                                if (sg_origin[j] &&
                                    !oidcmp(&sg_origin[j]->blob_oid, &porigin->blob_oid)) {
                                        same = 1;
                                        break;
                                }
                        if (!same)
                                sg_origin[i] = porigin;
                        else
                                blame_origin_decref(porigin);
                }
        }

        sb->num_commits++;
        for (i = 0, sg = first_scapegoat(revs, commit, sb->reverse);
             i < num_sg && sg;
             sg = sg->next, i++) {
                struct blame_origin *porigin = sg_origin[i];
                if (!porigin)
                        continue;
                if (!origin->previous) {
                        blame_origin_incref(porigin);
                        origin->previous = porigin;
                }
                pass_blame_to_parent(sb, origin, porigin);
                if (!origin->suspects)
                        goto finish;
        }

        /*
         * Optionally find moves in parents' files.
         */
        if (opt & PICKAXE_BLAME_MOVE) {
                filter_small(sb, &toosmall, &origin->suspects, sb->move_score);
                if (origin->suspects) {
                        for (i = 0, sg = first_scapegoat(revs, commit, sb->reverse);
                             i < num_sg && sg;
                             sg = sg->next, i++) {
                                struct blame_origin *porigin = sg_origin[i];
                                if (!porigin)
                                        continue;
                                find_move_in_parent(sb, &blametail, &toosmall, origin, porigin);
                                if (!origin->suspects)
                                        break;
                        }
                }
        }

        /*
         * Optionally find copies from parents' files.
         */
        if (opt & PICKAXE_BLAME_COPY) {
                if (sb->copy_score > sb->move_score)
                        filter_small(sb, &toosmall, &origin->suspects, sb->copy_score);
                else if (sb->copy_score < sb->move_score) {
                        origin->suspects = blame_merge(origin->suspects, toosmall);
                        toosmall = NULL;
                        filter_small(sb, &toosmall, &origin->suspects, sb->copy_score);
                }
                if (!origin->suspects)
                        goto finish;

                for (i = 0, sg = first_scapegoat(revs, commit, sb->reverse);
                     i < num_sg && sg;
                     sg = sg->next, i++) {
                        struct blame_origin *porigin = sg_origin[i];
                        find_copy_in_parent(sb, &blametail, &toosmall,
                                            origin, sg->item, porigin, opt);
                        if (!origin->suspects)
                                goto finish;
                }
        }

finish:
        *blametail = NULL;
        distribute_blame(sb, blames);
        /*
         * prepend toosmall to origin->suspects
         *
         * There is no point in sorting: this ends up on a big
         * unsorted list in the caller anyway.
         */
        if (toosmall) {
                struct blame_entry **tail = &toosmall;
                while (*tail)
                        tail = &(*tail)->next;
                *tail = origin->suspects;
                origin->suspects = toosmall;
        }
        for (i = 0; i < num_sg; i++) {
                if (sg_origin[i]) {
                        drop_origin_blob(sg_origin[i]);
                        blame_origin_decref(sg_origin[i]);
                }
        }
        drop_origin_blob(origin);
        if (sg_buf != sg_origin)
                free(sg_origin);
}

/*
 * The main loop -- while we have blobs with lines whose true origin
 * is still unknown, pick one blob, and allow its lines to pass blames
 * to its parents. */
void assign_blame(struct blame_scoreboard *sb, int opt)
{
        struct rev_info *revs = sb->revs;
        struct commit *commit = prio_queue_get(&sb->commits);

        while (commit) {
                struct blame_entry *ent;
                struct blame_origin *suspect = get_blame_suspects(commit);

                /* find one suspect to break down */
                while (suspect && !suspect->suspects)
                        suspect = suspect->next;

                if (!suspect) {
                        commit = prio_queue_get(&sb->commits);
                        continue;
                }

                assert(commit == suspect->commit);

                /*
                 * We will use this suspect later in the loop,
                 * so hold onto it in the meantime.
                 */
                blame_origin_incref(suspect);
                parse_commit(commit);
                if (sb->reverse ||
                    (!(commit->object.flags & UNINTERESTING) &&
                     !(revs->max_age != -1 && commit->date < revs->max_age)))
                        pass_blame(sb, suspect, opt);
                else {
                        commit->object.flags |= UNINTERESTING;
                        if (commit->object.parsed)
                                mark_parents_uninteresting(commit);
                }
                /* treat root commit as boundary */
                if (!commit->parents && !sb->show_root)
                        commit->object.flags |= UNINTERESTING;

                /* Take responsibility for the remaining entries */
                ent = suspect->suspects;
                if (ent) {
                        suspect->guilty = 1;
                        for (;;) {
                                struct blame_entry *next = ent->next;
                                if (sb->found_guilty_entry)
                                        sb->found_guilty_entry(ent, sb->found_guilty_entry_data);
                                if (next) {
                                        ent = next;
                                        continue;
                                }
                                ent->next = sb->ent;
                                sb->ent = suspect->suspects;
                                suspect->suspects = NULL;
                                break;
                        }
                }
                blame_origin_decref(suspect);

                if (sb->debug) /* sanity */
                        sanity_check_refcnt(sb);
        }
}

static const char *get_next_line(const char *start, const char *end)
{
        const char *nl = memchr(start, '\n', end - start);
        return nl ? nl + 1 : end;
}

/*
 * To allow quick access to the contents of nth line in the
 * final image, prepare an index in the scoreboard.
 */
static int prepare_lines(struct blame_scoreboard *sb)
{
        const char *buf = sb->final_buf;
        unsigned long len = sb->final_buf_size;
        const char *end = buf + len;
        const char *p;
        int *lineno;
        int num = 0;

        for (p = buf; p < end; p = get_next_line(p, end))
                num++;

        ALLOC_ARRAY(sb->lineno, num + 1);
        lineno = sb->lineno;

        for (p = buf; p < end; p = get_next_line(p, end))
                *lineno++ = p - buf;

        *lineno = len;

        sb->num_lines = num;
        return sb->num_lines;
}

static struct commit *find_single_final(struct rev_info *revs,
                                        const char **name_p)
{
        int i;
        struct commit *found = NULL;
        const char *name = NULL;

        for (i = 0; i < revs->pending.nr; i++) {
                struct object *obj = revs->pending.objects[i].item;
                if (obj->flags & UNINTERESTING)
                        continue;
                obj = deref_tag(the_repository, obj, NULL, 0);
                if (obj->type != OBJ_COMMIT)
                        die("Non commit %s?", revs->pending.objects[i].name);
                if (found)
                        die("More than one commit to dig from %s and %s?",
                            revs->pending.objects[i].name, name);
                found = (struct commit *)obj;
                name = revs->pending.objects[i].name;
        }
        if (name_p)
                *name_p = xstrdup_or_null(name);
        return found;
}

static struct commit *dwim_reverse_initial(struct rev_info *revs,
                                           const char **name_p)
{
        /*
         * DWIM "git blame --reverse ONE -- PATH" as
         * "git blame --reverse ONE..HEAD -- PATH" but only do so
         * when it makes sense.
         */
        struct object *obj;
        struct commit *head_commit;
        struct object_id head_oid;

        if (revs->pending.nr != 1)
                return NULL;

        /* Is that sole rev a committish? */
        obj = revs->pending.objects[0].item;
        obj = deref_tag(the_repository, obj, NULL, 0);
        if (obj->type != OBJ_COMMIT)
                return NULL;

        /* Do we have HEAD? */
        if (!resolve_ref_unsafe("HEAD", RESOLVE_REF_READING, &head_oid, NULL))
                return NULL;
        head_commit = lookup_commit_reference_gently(the_repository,
                                                     &head_oid, 1);
        if (!head_commit)
                return NULL;

        /* Turn "ONE" into "ONE..HEAD" then */
        obj->flags |= UNINTERESTING;
        add_pending_object(revs, &head_commit->object, "HEAD");

        if (name_p)
                *name_p = revs->pending.objects[0].name;
        return (struct commit *)obj;
}

static struct commit *find_single_initial(struct rev_info *revs,
                                          const char **name_p)
{
        int i;
        struct commit *found = NULL;
        const char *name = NULL;

        /*
         * There must be one and only one negative commit, and it must be
         * the boundary.
         */
        for (i = 0; i < revs->pending.nr; i++) {
                struct object *obj = revs->pending.objects[i].item;
                if (!(obj->flags & UNINTERESTING))
                        continue;
                obj = deref_tag(the_repository, obj, NULL, 0);
                if (obj->type != OBJ_COMMIT)
                        die("Non commit %s?", revs->pending.objects[i].name);
                if (found)
                        die("More than one commit to dig up from, %s and %s?",
                            revs->pending.objects[i].name, name);
                found = (struct commit *) obj;
                name = revs->pending.objects[i].name;
        }

        if (!name)
                found = dwim_reverse_initial(revs, &name);
        if (!name)
                die("No commit to dig up from?");

        if (name_p)
                *name_p = xstrdup(name);
        return found;
}

void init_scoreboard(struct blame_scoreboard *sb)
{
        memset(sb, 0, sizeof(struct blame_scoreboard));
        sb->move_score = BLAME_DEFAULT_MOVE_SCORE;
        sb->copy_score = BLAME_DEFAULT_COPY_SCORE;
}

void setup_scoreboard(struct blame_scoreboard *sb,
                      const char *path,
                      struct blame_origin **orig)
{
        const char *final_commit_name = NULL;
        struct blame_origin *o;
        struct commit *final_commit = NULL;
        enum object_type type;

        init_blame_suspects(&blame_suspects);

        if (sb->reverse && sb->contents_from)
                die(_("--contents and --reverse do not blend well."));

        if (!sb->repo)
                BUG("repo is NULL");

        if (!sb->reverse) {
                sb->final = find_single_final(sb->revs, &final_commit_name);
                sb->commits.compare = compare_commits_by_commit_date;
        } else {
                sb->final = find_single_initial(sb->revs, &final_commit_name);
                sb->commits.compare = compare_commits_by_reverse_commit_date;
        }

        if (sb->final && sb->contents_from)
                die(_("cannot use --contents with final commit object name"));

        if (sb->reverse && sb->revs->first_parent_only)
                sb->revs->children.name = NULL;

        if (!sb->final) {
                /*
                 * "--not A B -- path" without anything positive;
                 * do not default to HEAD, but use the working tree
                 * or "--contents".
                 */
                setup_work_tree();
                sb->final = fake_working_tree_commit(sb->repo,
                                                     &sb->revs->diffopt,
                                                     path, sb->contents_from);
                add_pending_object(sb->revs, &(sb->final->object), ":");
        }

        if (sb->reverse && sb->revs->first_parent_only) {
                final_commit = find_single_final(sb->revs, NULL);
                if (!final_commit)
                        die(_("--reverse and --first-parent together require specified latest commit"));
        }

        /*
         * If we have bottom, this will mark the ancestors of the
         * bottom commits we would reach while traversing as
         * uninteresting.
         */
        if (prepare_revision_walk(sb->revs))
                die(_("revision walk setup failed"));

        if (sb->reverse && sb->revs->first_parent_only) {
                struct commit *c = final_commit;

                sb->revs->children.name = "children";
                while (c->parents &&
                       oidcmp(&c->object.oid, &sb->final->object.oid)) {
                        struct commit_list *l = xcalloc(1, sizeof(*l));

                        l->item = c;
                        if (add_decoration(&sb->revs->children,
                                           &c->parents->item->object, l))
                                BUG("not unique item in first-parent chain");
                        c = c->parents->item;
                }

                if (oidcmp(&c->object.oid, &sb->final->object.oid))
                        die(_("--reverse --first-parent together require range along first-parent chain"));
        }

        if (is_null_oid(&sb->final->object.oid)) {
                o = get_blame_suspects(sb->final);
                sb->final_buf = xmemdupz(o->file.ptr, o->file.size);
                sb->final_buf_size = o->file.size;
        }
        else {
                o = get_origin(sb->final, path);
                if (fill_blob_sha1_and_mode(sb->repo, o))
                        die(_("no such path %s in %s"), path, final_commit_name);

                if (sb->revs->diffopt.flags.allow_textconv &&
                    textconv_object(path, o->mode, &o->blob_oid, 1, (char **) &sb->final_buf,
                                    &sb->final_buf_size))
                        ;
                else
                        sb->final_buf = read_object_file(&o->blob_oid, &type,
                                                         &sb->final_buf_size);

                if (!sb->final_buf)
                        die(_("cannot read blob %s for path %s"),
                            oid_to_hex(&o->blob_oid),
                            path);
        }
        sb->num_read_blob++;
        prepare_lines(sb);

        if (orig)
                *orig = o;

        free((char *)final_commit_name);
}



struct blame_entry *blame_entry_prepend(struct blame_entry *head,
                                        long start, long end,
                                        struct blame_origin *o)
{
        struct blame_entry *new_head = xcalloc(1, sizeof(struct blame_entry));
        new_head->lno = start;
        new_head->num_lines = end - start;
        new_head->suspect = o;
        new_head->s_lno = start;
        new_head->next = head;
        blame_origin_incref(o);
        return new_head;
}