line-log: extract pathspec parsing from line ranges into a helper function

[alt-git.git] / line-log.c

#include "git-compat-util.h"
#include "line-range.h"
#include "cache.h"
#include "tag.h"
#include "blob.h"
#include "tree.h"
#include "diff.h"
#include "commit.h"
#include "decorate.h"
#include "revision.h"
#include "xdiff-interface.h"
#include "strbuf.h"
#include "log-tree.h"
#include "graph.h"
#include "userdiff.h"
#include "line-log.h"
#include "argv-array.h"

static void range_set_grow(struct range_set *rs, size_t extra)
{
        ALLOC_GROW(rs->ranges, rs->nr + extra, rs->alloc);
}

/* Either initialization would be fine */
#define RANGE_SET_INIT {0}

void range_set_init(struct range_set *rs, size_t prealloc)
{
        rs->alloc = rs->nr = 0;
        rs->ranges = NULL;
        if (prealloc)
                range_set_grow(rs, prealloc);
}

void range_set_release(struct range_set *rs)
{
        FREE_AND_NULL(rs->ranges);
        rs->alloc = rs->nr = 0;
}

/* dst must be uninitialized! */
static void range_set_copy(struct range_set *dst, struct range_set *src)
{
        range_set_init(dst, src->nr);
        COPY_ARRAY(dst->ranges, src->ranges, src->nr);
        dst->nr = src->nr;
}

static void range_set_move(struct range_set *dst, struct range_set *src)
{
        range_set_release(dst);
        dst->ranges = src->ranges;
        dst->nr = src->nr;
        dst->alloc = src->alloc;
        src->ranges = NULL;
        src->alloc = src->nr = 0;
}

/* tack on a _new_ range _at the end_ */
void range_set_append_unsafe(struct range_set *rs, long a, long b)
{
        assert(a <= b);
        range_set_grow(rs, 1);
        rs->ranges[rs->nr].start = a;
        rs->ranges[rs->nr].end = b;
        rs->nr++;
}

void range_set_append(struct range_set *rs, long a, long b)
{
        assert(rs->nr == 0 || rs->ranges[rs->nr-1].end <= a);
        range_set_append_unsafe(rs, a, b);
}

static int range_cmp(const void *_r, const void *_s)
{
        const struct range *r = _r;
        const struct range *s = _s;

        /* this could be simply 'return r.start-s.start', but for the types */
        if (r->start == s->start)
                return 0;
        if (r->start < s->start)
                return -1;
        return 1;
}

/*
 * Check that the ranges are non-empty, sorted and non-overlapping
 */
static void range_set_check_invariants(struct range_set *rs)
{
        unsigned int i;

        if (!rs)
                return;

        if (rs->nr)
                assert(rs->ranges[0].start < rs->ranges[0].end);

        for (i = 1; i < rs->nr; i++) {
                assert(rs->ranges[i-1].end < rs->ranges[i].start);
                assert(rs->ranges[i].start < rs->ranges[i].end);
        }
}

/*
 * In-place pass of sorting and merging the ranges in the range set,
 * to establish the invariants when we get the ranges from the user
 */
void sort_and_merge_range_set(struct range_set *rs)
{
        unsigned int i;
        unsigned int o = 0; /* output cursor */

        QSORT(rs->ranges, rs->nr, range_cmp);

        for (i = 0; i < rs->nr; i++) {
                if (rs->ranges[i].start == rs->ranges[i].end)
                        continue;
                if (o > 0 && rs->ranges[i].start <= rs->ranges[o-1].end) {
                        if (rs->ranges[o-1].end < rs->ranges[i].end)
                                rs->ranges[o-1].end = rs->ranges[i].end;
                } else {
                        rs->ranges[o].start = rs->ranges[i].start;
                        rs->ranges[o].end = rs->ranges[i].end;
                        o++;
                }
        }
        assert(o <= rs->nr);
        rs->nr = o;

        range_set_check_invariants(rs);
}

/*
 * Union of range sets (i.e., sets of line numbers).  Used to merge
 * them when searches meet at a common ancestor.
 *
 * This is also where the ranges are consolidated into canonical form:
 * overlapping and adjacent ranges are merged, and empty ranges are
 * removed.
 */
static void range_set_union(struct range_set *out,
                             struct range_set *a, struct range_set *b)
{
        unsigned int i = 0, j = 0;
        struct range *ra = a->ranges;
        struct range *rb = b->ranges;
        /* cannot make an alias of out->ranges: it may change during grow */

        assert(out->nr == 0);
        while (i < a->nr || j < b->nr) {
                struct range *new_range;
                if (i < a->nr && j < b->nr) {
                        if (ra[i].start < rb[j].start)
                                new_range = &ra[i++];
                        else if (ra[i].start > rb[j].start)
                                new_range = &rb[j++];
                        else if (ra[i].end < rb[j].end)
                                new_range = &ra[i++];
                        else
                                new_range = &rb[j++];
                } else if (i < a->nr)      /* b exhausted */
                        new_range = &ra[i++];
                else                       /* a exhausted */
                        new_range = &rb[j++];
                if (new_range->start == new_range->end)
                        ; /* empty range */
                else if (!out->nr || out->ranges[out->nr-1].end < new_range->start) {
                        range_set_grow(out, 1);
                        out->ranges[out->nr].start = new_range->start;
                        out->ranges[out->nr].end = new_range->end;
                        out->nr++;
                } else if (out->ranges[out->nr-1].end < new_range->end) {
                        out->ranges[out->nr-1].end = new_range->end;
                }
        }
}

/*
 * Difference of range sets (out = a \ b).  Pass the "interesting"
 * ranges as 'a' and the target side of the diff as 'b': it removes
 * the ranges for which the commit is responsible.
 */
static void range_set_difference(struct range_set *out,
                                  struct range_set *a, struct range_set *b)
{
        unsigned int i, j =  0;
        for (i = 0; i < a->nr; i++) {
                long start = a->ranges[i].start;
                long end = a->ranges[i].end;
                while (start < end) {
                        while (j < b->nr && start >= b->ranges[j].end)
                                /*
                                 * a:         |-------
                                 * b: ------|
                                 */
                                j++;
                        if (j >= b->nr || end < b->ranges[j].start) {
                                /*
                                 * b exhausted, or
                                 * a:  ----|
                                 * b:         |----
                                 */
                                range_set_append(out, start, end);
                                break;
                        }
                        if (start >= b->ranges[j].start) {
                                /*
                                 * a:     |--????
                                 * b: |------|
                                 */
                                start = b->ranges[j].end;
                        } else if (end > b->ranges[j].start) {
                                /*
                                 * a: |-----|
                                 * b:    |--?????
                                 */
                                if (start < b->ranges[j].start)
                                        range_set_append(out, start, b->ranges[j].start);
                                start = b->ranges[j].end;
                        }
                }
        }
}

static void diff_ranges_init(struct diff_ranges *diff)
{
        range_set_init(&diff->parent, 0);
        range_set_init(&diff->target, 0);
}

static void diff_ranges_release(struct diff_ranges *diff)
{
        range_set_release(&diff->parent);
        range_set_release(&diff->target);
}

static void line_log_data_init(struct line_log_data *r)
{
        memset(r, 0, sizeof(struct line_log_data));
        range_set_init(&r->ranges, 0);
}

static void line_log_data_clear(struct line_log_data *r)
{
        range_set_release(&r->ranges);
        if (r->pair)
                diff_free_filepair(r->pair);
}

static void free_line_log_data(struct line_log_data *r)
{
        while (r) {
                struct line_log_data *next = r->next;
                line_log_data_clear(r);
                free(r);
                r = next;
        }
}

static struct line_log_data *
search_line_log_data(struct line_log_data *list, const char *path,
                     struct line_log_data **insertion_point)
{
        struct line_log_data *p = list;
        if (insertion_point)
                *insertion_point = NULL;
        while (p) {
                int cmp = strcmp(p->path, path);
                if (!cmp)
                        return p;
                if (insertion_point && cmp < 0)
                        *insertion_point = p;
                p = p->next;
        }
        return NULL;
}

/*
 * Note: takes ownership of 'path', which happens to be what the only
 * caller needs.
 */
static void line_log_data_insert(struct line_log_data **list,
                                 char *path,
                                 long begin, long end)
{
        struct line_log_data *ip;
        struct line_log_data *p = search_line_log_data(*list, path, &ip);

        if (p) {
                range_set_append_unsafe(&p->ranges, begin, end);
                free(path);
                return;
        }

        p = xcalloc(1, sizeof(struct line_log_data));
        p->path = path;
        range_set_append(&p->ranges, begin, end);
        if (ip) {
                p->next = ip->next;
                ip->next = p;
        } else {
                p->next = *list;
                *list = p;
        }
}

struct collect_diff_cbdata {
        struct diff_ranges *diff;
};

static int collect_diff_cb(long start_a, long count_a,
                           long start_b, long count_b,
                           void *data)
{
        struct collect_diff_cbdata *d = data;

        if (count_a >= 0)
                range_set_append(&d->diff->parent, start_a, start_a + count_a);
        if (count_b >= 0)
                range_set_append(&d->diff->target, start_b, start_b + count_b);

        return 0;
}

static int collect_diff(mmfile_t *parent, mmfile_t *target, struct diff_ranges *out)
{
        struct collect_diff_cbdata cbdata = {NULL};
        xpparam_t xpp;
        xdemitconf_t xecfg;
        xdemitcb_t ecb;

        memset(&xpp, 0, sizeof(xpp));
        memset(&xecfg, 0, sizeof(xecfg));
        xecfg.ctxlen = xecfg.interhunkctxlen = 0;

        cbdata.diff = out;
        xecfg.hunk_func = collect_diff_cb;
        memset(&ecb, 0, sizeof(ecb));
        ecb.priv = &cbdata;
        return xdi_diff(parent, target, &xpp, &xecfg, &ecb);
}

/*
 * These are handy for debugging.  Removing them with #if 0 silences
 * the "unused function" warning.
 */
#if 0
static void dump_range_set(struct range_set *rs, const char *desc)
{
        int i;
        printf("range set %s (%d items):\n", desc, rs->nr);
        for (i = 0; i < rs->nr; i++)
                printf("\t[%ld,%ld]\n", rs->ranges[i].start, rs->ranges[i].end);
}

static void dump_line_log_data(struct line_log_data *r)
{
        char buf[4096];
        while (r) {
                snprintf(buf, 4096, "file %s\n", r->path);
                dump_range_set(&r->ranges, buf);
                r = r->next;
        }
}

static void dump_diff_ranges(struct diff_ranges *diff, const char *desc)
{
        int i;
        assert(diff->parent.nr == diff->target.nr);
        printf("diff ranges %s (%d items):\n", desc, diff->parent.nr);
        printf("\tparent\ttarget\n");
        for (i = 0; i < diff->parent.nr; i++) {
                printf("\t[%ld,%ld]\t[%ld,%ld]\n",
                       diff->parent.ranges[i].start,
                       diff->parent.ranges[i].end,
                       diff->target.ranges[i].start,
                       diff->target.ranges[i].end);
        }
}
#endif


static int ranges_overlap(struct range *a, struct range *b)
{
        return !(a->end <= b->start || b->end <= a->start);
}

/*
 * Given a diff and the set of interesting ranges, determine all hunks
 * of the diff which touch (overlap) at least one of the interesting
 * ranges in the target.
 */
static void diff_ranges_filter_touched(struct diff_ranges *out,
                                       struct diff_ranges *diff,
                                       struct range_set *rs)
{
        unsigned int i, j = 0;

        assert(out->target.nr == 0);

        for (i = 0; i < diff->target.nr; i++) {
                while (diff->target.ranges[i].start > rs->ranges[j].end) {
                        j++;
                        if (j == rs->nr)
                                return;
                }
                if (ranges_overlap(&diff->target.ranges[i], &rs->ranges[j])) {
                        range_set_append(&out->parent,
                                         diff->parent.ranges[i].start,
                                         diff->parent.ranges[i].end);
                        range_set_append(&out->target,
                                         diff->target.ranges[i].start,
                                         diff->target.ranges[i].end);
                }
        }
}

/*
 * Adjust the line counts in 'rs' to account for the lines
 * added/removed in the diff.
 */
static void range_set_shift_diff(struct range_set *out,
                                 struct range_set *rs,
                                 struct diff_ranges *diff)
{
        unsigned int i, j = 0;
        long offset = 0;
        struct range *src = rs->ranges;
        struct range *target = diff->target.ranges;
        struct range *parent = diff->parent.ranges;

        for (i = 0; i < rs->nr; i++) {
                while (j < diff->target.nr && src[i].start >= target[j].start) {
                        offset += (parent[j].end-parent[j].start)
                                - (target[j].end-target[j].start);
                        j++;
                }
                range_set_append(out, src[i].start+offset, src[i].end+offset);
        }
}

/*
 * Given a diff and the set of interesting ranges, map the ranges
 * across the diff.  That is: observe that the target commit takes
 * blame for all the + (target-side) ranges.  So for every pair of
 * ranges in the diff that was touched, we remove the latter and add
 * its parent side.
 */
static void range_set_map_across_diff(struct range_set *out,
                                      struct range_set *rs,
                                      struct diff_ranges *diff,
                                      struct diff_ranges **touched_out)
{
        struct diff_ranges *touched = xmalloc(sizeof(*touched));
        struct range_set tmp1 = RANGE_SET_INIT;
        struct range_set tmp2 = RANGE_SET_INIT;

        diff_ranges_init(touched);
        diff_ranges_filter_touched(touched, diff, rs);
        range_set_difference(&tmp1, rs, &touched->target);
        range_set_shift_diff(&tmp2, &tmp1, diff);
        range_set_union(out, &tmp2, &touched->parent);
        range_set_release(&tmp1);
        range_set_release(&tmp2);

        *touched_out = touched;
}

static struct commit *check_single_commit(struct rev_info *revs)
{
        struct object *commit = NULL;
        int found = -1;
        int i;

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

        if (!commit)
                die("No commit specified?");

        return (struct commit *) commit;
}

static void fill_blob_sha1(struct commit *commit, struct diff_filespec *spec)
{
        unsigned short mode;
        struct object_id oid;

        if (get_tree_entry(&commit->object.oid, spec->path, &oid, &mode))
                die("There is no path %s in the commit", spec->path);
        fill_filespec(spec, &oid, 1, mode);

        return;
}

static void fill_line_ends(struct repository *r,
                           struct diff_filespec *spec,
                           long *lines,
                           unsigned long **line_ends)
{
        int num = 0, size = 50;
        long cur = 0;
        unsigned long *ends = NULL;
        char *data = NULL;

        if (diff_populate_filespec(r, spec, 0))
                die("Cannot read blob %s", oid_to_hex(&spec->oid));

        ALLOC_ARRAY(ends, size);
        ends[cur++] = 0;
        data = spec->data;
        while (num < spec->size) {
                if (data[num] == '\n' || num == spec->size - 1) {
                        ALLOC_GROW(ends, (cur + 1), size);
                        ends[cur++] = num;
                }
                num++;
        }

        /* shrink the array to fit the elements */
        REALLOC_ARRAY(ends, cur);
        *lines = cur-1;
        *line_ends = ends;
}

struct nth_line_cb {
        struct diff_filespec *spec;
        long lines;
        unsigned long *line_ends;
};

static const char *nth_line(void *data, long line)
{
        struct nth_line_cb *d = data;
        assert(d && line <= d->lines);
        assert(d->spec && d->spec->data);

        if (line == 0)
                return (char *)d->spec->data;
        else
                return (char *)d->spec->data + d->line_ends[line] + 1;
}

static struct line_log_data *
parse_lines(struct repository *r, struct commit *commit,
            const char *prefix, struct string_list *args)
{
        long lines = 0;
        unsigned long *ends = NULL;
        struct nth_line_cb cb_data;
        struct string_list_item *item;
        struct line_log_data *ranges = NULL;
        struct line_log_data *p;

        for_each_string_list_item(item, args) {
                const char *name_part, *range_part;
                char *full_name;
                struct diff_filespec *spec;
                long begin = 0, end = 0;
                long anchor;

                name_part = skip_range_arg(item->string, r->index);
                if (!name_part || *name_part != ':' || !name_part[1])
                        die("-L argument not 'start,end:file' or ':funcname:file': %s",
                            item->string);
                range_part = xstrndup(item->string, name_part - item->string);
                name_part++;

                full_name = prefix_path(prefix, prefix ? strlen(prefix) : 0,
                                        name_part);

                spec = alloc_filespec(full_name);
                fill_blob_sha1(commit, spec);
                fill_line_ends(r, spec, &lines, &ends);
                cb_data.spec = spec;
                cb_data.lines = lines;
                cb_data.line_ends = ends;

                p = search_line_log_data(ranges, full_name, NULL);
                if (p && p->ranges.nr)
                        anchor = p->ranges.ranges[p->ranges.nr - 1].end + 1;
                else
                        anchor = 1;

                if (parse_range_arg(range_part, nth_line, &cb_data,
                                    lines, anchor, &begin, &end,
                                    full_name, r->index))
                        die("malformed -L argument '%s'", range_part);
                if ((!lines && (begin || end)) || lines < begin)
                        die("file %s has only %lu lines", name_part, lines);
                if (begin < 1)
                        begin = 1;
                if (end < 1 || lines < end)
                        end = lines;
                begin--;
                line_log_data_insert(&ranges, full_name, begin, end);

                free_filespec(spec);
                FREE_AND_NULL(ends);
        }

        for (p = ranges; p; p = p->next)
                sort_and_merge_range_set(&p->ranges);

        return ranges;
}

static struct line_log_data *line_log_data_copy_one(struct line_log_data *r)
{
        struct line_log_data *ret = xmalloc(sizeof(*ret));

        assert(r);
        line_log_data_init(ret);
        range_set_copy(&ret->ranges, &r->ranges);

        ret->path = xstrdup(r->path);

        return ret;
}

static struct line_log_data *
line_log_data_copy(struct line_log_data *r)
{
        struct line_log_data *ret = NULL;
        struct line_log_data *tmp = NULL, *prev = NULL;

        assert(r);
        ret = tmp = prev = line_log_data_copy_one(r);
        r = r->next;
        while (r) {
                tmp = line_log_data_copy_one(r);
                prev->next = tmp;
                prev = tmp;
                r = r->next;
        }

        return ret;
}

/* merge two range sets across files */
static struct line_log_data *line_log_data_merge(struct line_log_data *a,
                                                 struct line_log_data *b)
{
        struct line_log_data *head = NULL, **pp = &head;

        while (a || b) {
                struct line_log_data *src;
                struct line_log_data *src2 = NULL;
                struct line_log_data *d;
                int cmp;
                if (!a)
                        cmp = 1;
                else if (!b)
                        cmp = -1;
                else
                        cmp = strcmp(a->path, b->path);
                if (cmp < 0) {
                        src = a;
                        a = a->next;
                } else if (cmp == 0) {
                        src = a;
                        a = a->next;
                        src2 = b;
                        b = b->next;
                } else {
                        src = b;
                        b = b->next;
                }
                d = xmalloc(sizeof(struct line_log_data));
                line_log_data_init(d);
                d->path = xstrdup(src->path);
                *pp = d;
                pp = &d->next;
                if (src2)
                        range_set_union(&d->ranges, &src->ranges, &src2->ranges);
                else
                        range_set_copy(&d->ranges, &src->ranges);
        }

        return head;
}

static void add_line_range(struct rev_info *revs, struct commit *commit,
                           struct line_log_data *range)
{
        struct line_log_data *old_line = NULL;
        struct line_log_data *new_line = NULL;

        old_line = lookup_decoration(&revs->line_log_data, &commit->object);
        if (old_line && range) {
                new_line = line_log_data_merge(old_line, range);
                free_line_log_data(old_line);
        } else if (range)
                new_line = line_log_data_copy(range);

        if (new_line)
                add_decoration(&revs->line_log_data, &commit->object, new_line);
}

static void clear_commit_line_range(struct rev_info *revs, struct commit *commit)
{
        struct line_log_data *r;
        r = lookup_decoration(&revs->line_log_data, &commit->object);
        if (!r)
                return;
        free_line_log_data(r);
        add_decoration(&revs->line_log_data, &commit->object, NULL);
}

static struct line_log_data *lookup_line_range(struct rev_info *revs,
                                               struct commit *commit)
{
        struct line_log_data *ret = NULL;
        struct line_log_data *d;

        ret = lookup_decoration(&revs->line_log_data, &commit->object);

        for (d = ret; d; d = d->next)
                range_set_check_invariants(&d->ranges);

        return ret;
}

static void parse_pathspec_from_ranges(struct pathspec *pathspec,
                                       struct line_log_data *range)
{
        struct line_log_data *r;
        struct argv_array array = ARGV_ARRAY_INIT;
        const char **paths;

        for (r = range; r; r = r->next)
                argv_array_push(&array, r->path);
        paths = argv_array_detach(&array);

        parse_pathspec(pathspec, 0, PATHSPEC_PREFER_FULL, "", paths);
        /* strings are now owned by pathspec */
        free(paths);
}

void line_log_init(struct rev_info *rev, const char *prefix, struct string_list *args)
{
        struct commit *commit = NULL;
        struct line_log_data *range;

        commit = check_single_commit(rev);
        range = parse_lines(rev->diffopt.repo, commit, prefix, args);
        add_line_range(rev, commit, range);

        if (!rev->diffopt.detect_rename)
                parse_pathspec_from_ranges(&rev->diffopt.pathspec, range);
}

static void move_diff_queue(struct diff_queue_struct *dst,
                            struct diff_queue_struct *src)
{
        assert(src != dst);
        memcpy(dst, src, sizeof(struct diff_queue_struct));
        DIFF_QUEUE_CLEAR(src);
}

static void filter_diffs_for_paths(struct line_log_data *range, int keep_deletions)
{
        int i;
        struct diff_queue_struct outq;
        DIFF_QUEUE_CLEAR(&outq);

        for (i = 0; i < diff_queued_diff.nr; i++) {
                struct diff_filepair *p = diff_queued_diff.queue[i];
                struct line_log_data *rg = NULL;

                if (!DIFF_FILE_VALID(p->two)) {
                        if (keep_deletions)
                                diff_q(&outq, p);
                        else
                                diff_free_filepair(p);
                        continue;
                }
                for (rg = range; rg; rg = rg->next) {
                        if (!strcmp(rg->path, p->two->path))
                                break;
                }
                if (rg)
                        diff_q(&outq, p);
                else
                        diff_free_filepair(p);
        }
        free(diff_queued_diff.queue);
        diff_queued_diff = outq;
}

static inline int diff_might_be_rename(void)
{
        int i;
        for (i = 0; i < diff_queued_diff.nr; i++)
                if (!DIFF_FILE_VALID(diff_queued_diff.queue[i]->one)) {
                        /* fprintf(stderr, "diff_might_be_rename found creation of: %s\n", */
                        /*      diff_queued_diff.queue[i]->two->path); */
                        return 1;
                }
        return 0;
}

static void queue_diffs(struct line_log_data *range,
                        struct diff_options *opt,
                        struct diff_queue_struct *queue,
                        struct commit *commit, struct commit *parent)
{
        assert(commit);

        DIFF_QUEUE_CLEAR(&diff_queued_diff);
        diff_tree_oid(parent ? get_commit_tree_oid(parent) : NULL,
                      get_commit_tree_oid(commit), "", opt);
        if (opt->detect_rename) {
                filter_diffs_for_paths(range, 1);
                if (diff_might_be_rename())
                        diffcore_std(opt);
                filter_diffs_for_paths(range, 0);
        }
        move_diff_queue(queue, &diff_queued_diff);
}

static char *get_nth_line(long line, unsigned long *ends, void *data)
{
        if (line == 0)
                return (char *)data;
        else
                return (char *)data + ends[line] + 1;
}

static void print_line(const char *prefix, char first,
                       long line, unsigned long *ends, void *data,
                       const char *color, const char *reset, FILE *file)
{
        char *begin = get_nth_line(line, ends, data);
        char *end = get_nth_line(line+1, ends, data);
        int had_nl = 0;

        if (end > begin && end[-1] == '\n') {
                end--;
                had_nl = 1;
        }

        fputs(prefix, file);
        fputs(color, file);
        putc(first, file);
        fwrite(begin, 1, end-begin, file);
        fputs(reset, file);
        putc('\n', file);
        if (!had_nl)
                fputs("\\ No newline at end of file\n", file);
}

static char *output_prefix(struct diff_options *opt)
{
        char *prefix = "";

        if (opt->output_prefix) {
                struct strbuf *sb = opt->output_prefix(opt, opt->output_prefix_data);
                prefix = sb->buf;
        }

        return prefix;
}

static void dump_diff_hacky_one(struct rev_info *rev, struct line_log_data *range)
{
        unsigned int i, j = 0;
        long p_lines, t_lines;
        unsigned long *p_ends = NULL, *t_ends = NULL;
        struct diff_filepair *pair = range->pair;
        struct diff_ranges *diff = &range->diff;

        struct diff_options *opt = &rev->diffopt;
        char *prefix = output_prefix(opt);
        const char *c_reset = diff_get_color(opt->use_color, DIFF_RESET);
        const char *c_frag = diff_get_color(opt->use_color, DIFF_FRAGINFO);
        const char *c_meta = diff_get_color(opt->use_color, DIFF_METAINFO);
        const char *c_old = diff_get_color(opt->use_color, DIFF_FILE_OLD);
        const char *c_new = diff_get_color(opt->use_color, DIFF_FILE_NEW);
        const char *c_context = diff_get_color(opt->use_color, DIFF_CONTEXT);

        if (!pair || !diff)
                return;

        if (pair->one->oid_valid)
                fill_line_ends(rev->diffopt.repo, pair->one, &p_lines, &p_ends);
        fill_line_ends(rev->diffopt.repo, pair->two, &t_lines, &t_ends);

        fprintf(opt->file, "%s%sdiff --git a/%s b/%s%s\n", prefix, c_meta, pair->one->path, pair->two->path, c_reset);
        fprintf(opt->file, "%s%s--- %s%s%s\n", prefix, c_meta,
               pair->one->oid_valid ? "a/" : "",
               pair->one->oid_valid ? pair->one->path : "/dev/null",
               c_reset);
        fprintf(opt->file, "%s%s+++ b/%s%s\n", prefix, c_meta, pair->two->path, c_reset);
        for (i = 0; i < range->ranges.nr; i++) {
                long p_start, p_end;
                long t_start = range->ranges.ranges[i].start;
                long t_end = range->ranges.ranges[i].end;
                long t_cur = t_start;
                unsigned int j_last;

                while (j < diff->target.nr && diff->target.ranges[j].end < t_start)
                        j++;
                if (j == diff->target.nr || diff->target.ranges[j].start > t_end)
                        continue;

                /* Scan ahead to determine the last diff that falls in this range */
                j_last = j;
                while (j_last < diff->target.nr && diff->target.ranges[j_last].start < t_end)
                        j_last++;
                if (j_last > j)
                        j_last--;

                /*
                 * Compute parent hunk headers: we know that the diff
                 * has the correct line numbers (but not all hunks).
                 * So it suffices to shift the start/end according to
                 * the line numbers of the first/last hunk(s) that
                 * fall in this range.
                 */
                if (t_start < diff->target.ranges[j].start)
                        p_start = diff->parent.ranges[j].start - (diff->target.ranges[j].start-t_start);
                else
                        p_start = diff->parent.ranges[j].start;
                if (t_end > diff->target.ranges[j_last].end)
                        p_end = diff->parent.ranges[j_last].end + (t_end-diff->target.ranges[j_last].end);
                else
                        p_end = diff->parent.ranges[j_last].end;

                if (!p_start && !p_end) {
                        p_start = -1;
                        p_end = -1;
                }

                /* Now output a diff hunk for this range */
                fprintf(opt->file, "%s%s@@ -%ld,%ld +%ld,%ld @@%s\n",
                       prefix, c_frag,
                       p_start+1, p_end-p_start, t_start+1, t_end-t_start,
                       c_reset);
                while (j < diff->target.nr && diff->target.ranges[j].start < t_end) {
                        int k;
                        for (; t_cur < diff->target.ranges[j].start; t_cur++)
                                print_line(prefix, ' ', t_cur, t_ends, pair->two->data,
                                           c_context, c_reset, opt->file);
                        for (k = diff->parent.ranges[j].start; k < diff->parent.ranges[j].end; k++)
                                print_line(prefix, '-', k, p_ends, pair->one->data,
                                           c_old, c_reset, opt->file);
                        for (; t_cur < diff->target.ranges[j].end && t_cur < t_end; t_cur++)
                                print_line(prefix, '+', t_cur, t_ends, pair->two->data,
                                           c_new, c_reset, opt->file);
                        j++;
                }
                for (; t_cur < t_end; t_cur++)
                        print_line(prefix, ' ', t_cur, t_ends, pair->two->data,
                                   c_context, c_reset, opt->file);
        }

        free(p_ends);
        free(t_ends);
}

/*
 * NEEDSWORK: manually building a diff here is not the Right
 * Thing(tm).  log -L should be built into the diff pipeline.
 */
static void dump_diff_hacky(struct rev_info *rev, struct line_log_data *range)
{
        fprintf(rev->diffopt.file, "%s\n", output_prefix(&rev->diffopt));
        while (range) {
                dump_diff_hacky_one(rev, range);
                range = range->next;
        }
}

/*
 * Unlike most other functions, this destructively operates on
 * 'range'.
 */
static int process_diff_filepair(struct rev_info *rev,
                                 struct diff_filepair *pair,
                                 struct line_log_data *range,
                                 struct diff_ranges **diff_out)
{
        struct line_log_data *rg = range;
        struct range_set tmp;
        struct diff_ranges diff;
        mmfile_t file_parent, file_target;

        assert(pair->two->path);
        while (rg) {
                assert(rg->path);
                if (!strcmp(rg->path, pair->two->path))
                        break;
                rg = rg->next;
        }

        if (!rg)
                return 0;
        if (rg->ranges.nr == 0)
                return 0;

        assert(pair->two->oid_valid);
        diff_populate_filespec(rev->diffopt.repo, pair->two, 0);
        file_target.ptr = pair->two->data;
        file_target.size = pair->two->size;

        if (pair->one->oid_valid) {
                diff_populate_filespec(rev->diffopt.repo, pair->one, 0);
                file_parent.ptr = pair->one->data;
                file_parent.size = pair->one->size;
        } else {
                file_parent.ptr = "";
                file_parent.size = 0;
        }

        diff_ranges_init(&diff);
        if (collect_diff(&file_parent, &file_target, &diff))
                die("unable to generate diff for %s", pair->one->path);

        /* NEEDSWORK should apply some heuristics to prevent mismatches */
        free(rg->path);
        rg->path = xstrdup(pair->one->path);

        range_set_init(&tmp, 0);
        range_set_map_across_diff(&tmp, &rg->ranges, &diff, diff_out);
        range_set_release(&rg->ranges);
        range_set_move(&rg->ranges, &tmp);

        diff_ranges_release(&diff);

        return ((*diff_out)->parent.nr > 0);
}

static struct diff_filepair *diff_filepair_dup(struct diff_filepair *pair)
{
        struct diff_filepair *new_filepair = xmalloc(sizeof(struct diff_filepair));
        new_filepair->one = pair->one;
        new_filepair->two = pair->two;
        new_filepair->one->count++;
        new_filepair->two->count++;
        return new_filepair;
}

static void free_diffqueues(int n, struct diff_queue_struct *dq)
{
        int i, j;
        for (i = 0; i < n; i++)
                for (j = 0; j < dq[i].nr; j++)
                        diff_free_filepair(dq[i].queue[j]);
        free(dq);
}

static int process_all_files(struct line_log_data **range_out,
                             struct rev_info *rev,
                             struct diff_queue_struct *queue,
                             struct line_log_data *range)
{
        int i, changed = 0;

        *range_out = line_log_data_copy(range);

        for (i = 0; i < queue->nr; i++) {
                struct diff_ranges *pairdiff = NULL;
                struct diff_filepair *pair = queue->queue[i];
                if (process_diff_filepair(rev, pair, *range_out, &pairdiff)) {
                        /*
                         * Store away the diff for later output.  We
                         * tuck it in the ranges we got as _input_,
                         * since that's the commit that caused the
                         * diff.
                         *
                         * NEEDSWORK not enough when we get around to
                         * doing something interesting with merges;
                         * currently each invocation on a merge parent
                         * trashes the previous one's diff.
                         *
                         * NEEDSWORK tramples over data structures not owned here
                         */
                        struct line_log_data *rg = range;
                        changed++;
                        while (rg && strcmp(rg->path, pair->two->path))
                                rg = rg->next;
                        assert(rg);
                        rg->pair = diff_filepair_dup(queue->queue[i]);
                        memcpy(&rg->diff, pairdiff, sizeof(struct diff_ranges));
                }
                free(pairdiff);
        }

        return changed;
}

int line_log_print(struct rev_info *rev, struct commit *commit)
{

        show_log(rev);
        if (!(rev->diffopt.output_format & DIFF_FORMAT_NO_OUTPUT)) {
                struct line_log_data *range = lookup_line_range(rev, commit);
                dump_diff_hacky(rev, range);
        }
        return 1;
}

static int process_ranges_ordinary_commit(struct rev_info *rev, struct commit *commit,
                                          struct line_log_data *range)
{
        struct commit *parent = NULL;
        struct diff_queue_struct queue;
        struct line_log_data *parent_range;
        int changed;

        if (commit->parents)
                parent = commit->parents->item;

        queue_diffs(range, &rev->diffopt, &queue, commit, parent);
        changed = process_all_files(&parent_range, rev, &queue, range);
        if (parent)
                add_line_range(rev, parent, parent_range);
        free_line_log_data(parent_range);
        return changed;
}

static int process_ranges_merge_commit(struct rev_info *rev, struct commit *commit,
                                       struct line_log_data *range)
{
        struct diff_queue_struct *diffqueues;
        struct line_log_data **cand;
        struct commit **parents;
        struct commit_list *p;
        int i;
        int nparents = commit_list_count(commit->parents);

        if (nparents > 1 && rev->first_parent_only)
                nparents = 1;

        ALLOC_ARRAY(diffqueues, nparents);
        ALLOC_ARRAY(cand, nparents);
        ALLOC_ARRAY(parents, nparents);

        p = commit->parents;
        for (i = 0; i < nparents; i++) {
                parents[i] = p->item;
                p = p->next;
                queue_diffs(range, &rev->diffopt, &diffqueues[i], commit, parents[i]);
        }

        for (i = 0; i < nparents; i++) {
                int changed;
                cand[i] = NULL;
                changed = process_all_files(&cand[i], rev, &diffqueues[i], range);
                if (!changed) {
                        /*
                         * This parent can take all the blame, so we
                         * don't follow any other path in history
                         */
                        add_line_range(rev, parents[i], cand[i]);
                        clear_commit_line_range(rev, commit);
                        commit_list_append(parents[i], &commit->parents);
                        free(parents);
                        free(cand);
                        free_diffqueues(nparents, diffqueues);
                        /* NEEDSWORK leaking like a sieve */
                        return 0;
                }
        }

        /*
         * No single parent took the blame.  We add the candidates
         * from the above loop to the parents.
         */
        for (i = 0; i < nparents; i++) {
                add_line_range(rev, parents[i], cand[i]);
        }

        clear_commit_line_range(rev, commit);
        free(parents);
        free(cand);
        free_diffqueues(nparents, diffqueues);
        return 1;

        /* NEEDSWORK evil merge detection stuff */
        /* NEEDSWORK leaking like a sieve */
}

static int process_ranges_arbitrary_commit(struct rev_info *rev, struct commit *commit)
{
        struct line_log_data *range = lookup_line_range(rev, commit);
        int changed = 0;

        if (range) {
                if (!commit->parents || !commit->parents->next)
                        changed = process_ranges_ordinary_commit(rev, commit, range);
                else
                        changed = process_ranges_merge_commit(rev, commit, range);
        }

        if (!changed)
                commit->object.flags |= TREESAME;

        return changed;
}

static enum rewrite_result line_log_rewrite_one(struct rev_info *rev, struct commit **pp)
{
        for (;;) {
                struct commit *p = *pp;
                if (p->parents && p->parents->next)
                        return rewrite_one_ok;
                if (p->object.flags & UNINTERESTING)
                        return rewrite_one_ok;
                if (!(p->object.flags & TREESAME))
                        return rewrite_one_ok;
                if (!p->parents)
                        return rewrite_one_noparents;
                *pp = p->parents->item;
        }
}

int line_log_filter(struct rev_info *rev)
{
        struct commit *commit;
        struct commit_list *list = rev->commits;
        struct commit_list *out = NULL, **pp = &out;

        while (list) {
                struct commit_list *to_free = NULL;
                commit = list->item;
                if (process_ranges_arbitrary_commit(rev, commit)) {
                        *pp = list;
                        pp = &list->next;
                } else
                        to_free = list;
                list = list->next;
                free(to_free);
        }
        *pp = NULL;

        for (list = out; list; list = list->next)
                rewrite_parents(rev, list->item, line_log_rewrite_one);

        rev->commits = out;

        return 0;
}