revision.h: introduce blob/tree walking in order of the commits

[git/debian.git] / combine-diff.c

#include "cache.h"
#include "commit.h"
#include "blob.h"
#include "diff.h"
#include "diffcore.h"
#include "quote.h"
#include "xdiff-interface.h"
#include "xdiff/xmacros.h"
#include "log-tree.h"
#include "refs.h"
#include "userdiff.h"
#include "sha1-array.h"
#include "revision.h"

static int compare_paths(const struct combine_diff_path *one,
                          const struct diff_filespec *two)
{
        if (!S_ISDIR(one->mode) && !S_ISDIR(two->mode))
                return strcmp(one->path, two->path);

        return base_name_compare(one->path, strlen(one->path), one->mode,
                                 two->path, strlen(two->path), two->mode);
}

static struct combine_diff_path *intersect_paths(struct combine_diff_path *curr, int n, int num_parent)
{
        struct diff_queue_struct *q = &diff_queued_diff;
        struct combine_diff_path *p, **tail = &curr;
        int i, cmp;

        if (!n) {
                for (i = 0; i < q->nr; i++) {
                        int len;
                        const char *path;
                        if (diff_unmodified_pair(q->queue[i]))
                                continue;
                        path = q->queue[i]->two->path;
                        len = strlen(path);
                        p = xmalloc(combine_diff_path_size(num_parent, len));
                        p->path = (char *) &(p->parent[num_parent]);
                        memcpy(p->path, path, len);
                        p->path[len] = 0;
                        p->next = NULL;
                        memset(p->parent, 0,
                               sizeof(p->parent[0]) * num_parent);

                        oidcpy(&p->oid, &q->queue[i]->two->oid);
                        p->mode = q->queue[i]->two->mode;
                        oidcpy(&p->parent[n].oid, &q->queue[i]->one->oid);
                        p->parent[n].mode = q->queue[i]->one->mode;
                        p->parent[n].status = q->queue[i]->status;
                        *tail = p;
                        tail = &p->next;
                }
                return curr;
        }

        /*
         * paths in curr (linked list) and q->queue[] (array) are
         * both sorted in the tree order.
         */
        i = 0;
        while ((p = *tail) != NULL) {
                cmp = ((i >= q->nr)
                       ? -1 : compare_paths(p, q->queue[i]->two));

                if (cmp < 0) {
                        /* p->path not in q->queue[]; drop it */
                        *tail = p->next;
                        free(p);
                        continue;
                }

                if (cmp > 0) {
                        /* q->queue[i] not in p->path; skip it */
                        i++;
                        continue;
                }

                oidcpy(&p->parent[n].oid, &q->queue[i]->one->oid);
                p->parent[n].mode = q->queue[i]->one->mode;
                p->parent[n].status = q->queue[i]->status;

                tail = &p->next;
                i++;
        }
        return curr;
}

/* Lines lost from parent */
struct lline {
        struct lline *next, *prev;
        int len;
        unsigned long parent_map;
        char line[FLEX_ARRAY];
};

/* Lines lost from current parent (before coalescing) */
struct plost {
        struct lline *lost_head, *lost_tail;
        int len;
};

/* Lines surviving in the merge result */
struct sline {
        /* Accumulated and coalesced lost lines */
        struct lline *lost;
        int lenlost;
        struct plost plost;
        char *bol;
        int len;
        /* bit 0 up to (N-1) are on if the parent has this line (i.e.
         * we did not change it).
         * bit N is used for "interesting" lines, including context.
         * bit (N+1) is used for "do not show deletion before this".
         */
        unsigned long flag;
        unsigned long *p_lno;
};

static int match_string_spaces(const char *line1, int len1,
                               const char *line2, int len2,
                               long flags)
{
        if (flags & XDF_WHITESPACE_FLAGS) {
                for (; len1 > 0 && XDL_ISSPACE(line1[len1 - 1]); len1--);
                for (; len2 > 0 && XDL_ISSPACE(line2[len2 - 1]); len2--);
        }

        if (!(flags & (XDF_IGNORE_WHITESPACE | XDF_IGNORE_WHITESPACE_CHANGE)))
                return (len1 == len2 && !memcmp(line1, line2, len1));

        while (len1 > 0 && len2 > 0) {
                len1--;
                len2--;
                if (XDL_ISSPACE(line1[len1]) || XDL_ISSPACE(line2[len2])) {
                        if ((flags & XDF_IGNORE_WHITESPACE_CHANGE) &&
                            (!XDL_ISSPACE(line1[len1]) || !XDL_ISSPACE(line2[len2])))
                                return 0;

                        for (; len1 > 0 && XDL_ISSPACE(line1[len1]); len1--);
                        for (; len2 > 0 && XDL_ISSPACE(line2[len2]); len2--);
                }
                if (line1[len1] != line2[len2])
                        return 0;
        }

        if (flags & XDF_IGNORE_WHITESPACE) {
                /* Consume remaining spaces */
                for (; len1 > 0 && XDL_ISSPACE(line1[len1 - 1]); len1--);
                for (; len2 > 0 && XDL_ISSPACE(line2[len2 - 1]); len2--);
        }

        /* We matched full line1 and line2 */
        if (!len1 && !len2)
                return 1;

        return 0;
}

enum coalesce_direction { MATCH, BASE, NEW };

/* Coalesce new lines into base by finding LCS */
static struct lline *coalesce_lines(struct lline *base, int *lenbase,
                                    struct lline *new, int lennew,
                                    unsigned long parent, long flags)
{
        int **lcs;
        enum coalesce_direction **directions;
        struct lline *baseend, *newend = NULL;
        int i, j, origbaselen = *lenbase;

        if (new == NULL)
                return base;

        if (base == NULL) {
                *lenbase = lennew;
                return new;
        }

        /*
         * Coalesce new lines into base by finding the LCS
         * - Create the table to run dynamic programming
         * - Compute the LCS
         * - Then reverse read the direction structure:
         *   - If we have MATCH, assign parent to base flag, and consume
         *   both baseend and newend
         *   - Else if we have BASE, consume baseend
         *   - Else if we have NEW, insert newend lline into base and
         *   consume newend
         */
        lcs = xcalloc(st_add(origbaselen, 1), sizeof(int*));
        directions = xcalloc(st_add(origbaselen, 1), sizeof(enum coalesce_direction*));
        for (i = 0; i < origbaselen + 1; i++) {
                lcs[i] = xcalloc(st_add(lennew, 1), sizeof(int));
                directions[i] = xcalloc(st_add(lennew, 1), sizeof(enum coalesce_direction));
                directions[i][0] = BASE;
        }
        for (j = 1; j < lennew + 1; j++)
                directions[0][j] = NEW;

        for (i = 1, baseend = base; i < origbaselen + 1; i++) {
                for (j = 1, newend = new; j < lennew + 1; j++) {
                        if (match_string_spaces(baseend->line, baseend->len,
                                                newend->line, newend->len, flags)) {
                                lcs[i][j] = lcs[i - 1][j - 1] + 1;
                                directions[i][j] = MATCH;
                        } else if (lcs[i][j - 1] >= lcs[i - 1][j]) {
                                lcs[i][j] = lcs[i][j - 1];
                                directions[i][j] = NEW;
                        } else {
                                lcs[i][j] = lcs[i - 1][j];
                                directions[i][j] = BASE;
                        }
                        if (newend->next)
                                newend = newend->next;
                }
                if (baseend->next)
                        baseend = baseend->next;
        }

        for (i = 0; i < origbaselen + 1; i++)
                free(lcs[i]);
        free(lcs);

        /* At this point, baseend and newend point to the end of each lists */
        i--;
        j--;
        while (i != 0 || j != 0) {
                if (directions[i][j] == MATCH) {
                        baseend->parent_map |= 1<<parent;
                        baseend = baseend->prev;
                        newend = newend->prev;
                        i--;
                        j--;
                } else if (directions[i][j] == NEW) {
                        struct lline *lline;

                        lline = newend;
                        /* Remove lline from new list and update newend */
                        if (lline->prev)
                                lline->prev->next = lline->next;
                        else
                                new = lline->next;
                        if (lline->next)
                                lline->next->prev = lline->prev;

                        newend = lline->prev;
                        j--;

                        /* Add lline to base list */
                        if (baseend) {
                                lline->next = baseend->next;
                                lline->prev = baseend;
                                if (lline->prev)
                                        lline->prev->next = lline;
                        }
                        else {
                                lline->next = base;
                                base = lline;
                        }
                        (*lenbase)++;

                        if (lline->next)
                                lline->next->prev = lline;

                } else {
                        baseend = baseend->prev;
                        i--;
                }
        }

        newend = new;
        while (newend) {
                struct lline *lline = newend;
                newend = newend->next;
                free(lline);
        }

        for (i = 0; i < origbaselen + 1; i++)
                free(directions[i]);
        free(directions);

        return base;
}

static char *grab_blob(const struct object_id *oid, unsigned int mode,
                       unsigned long *size, struct userdiff_driver *textconv,
                       const char *path)
{
        char *blob;
        enum object_type type;

        if (S_ISGITLINK(mode)) {
                struct strbuf buf = STRBUF_INIT;
                strbuf_addf(&buf, "Subproject commit %s\n", oid_to_hex(oid));
                *size = buf.len;
                blob = strbuf_detach(&buf, NULL);
        } else if (is_null_oid(oid)) {
                /* deleted blob */
                *size = 0;
                return xcalloc(1, 1);
        } else if (textconv) {
                struct diff_filespec *df = alloc_filespec(path);
                fill_filespec(df, oid, 1, mode);
                *size = fill_textconv(textconv, df, &blob);
                free_filespec(df);
        } else {
                blob = read_sha1_file(oid->hash, &type, size);
                if (type != OBJ_BLOB)
                        die("object '%s' is not a blob!", oid_to_hex(oid));
        }
        return blob;
}

static void append_lost(struct sline *sline, int n, const char *line, int len)
{
        struct lline *lline;
        unsigned long this_mask = (1UL<<n);
        if (line[len-1] == '\n')
                len--;

        FLEX_ALLOC_MEM(lline, line, line, len);
        lline->len = len;
        lline->next = NULL;
        lline->prev = sline->plost.lost_tail;
        if (lline->prev)
                lline->prev->next = lline;
        else
                sline->plost.lost_head = lline;
        sline->plost.lost_tail = lline;
        sline->plost.len++;
        lline->parent_map = this_mask;
}

struct combine_diff_state {
        unsigned int lno;
        int ob, on, nb, nn;
        unsigned long nmask;
        int num_parent;
        int n;
        struct sline *sline;
        struct sline *lost_bucket;
};

static void consume_line(void *state_, char *line, unsigned long len)
{
        struct combine_diff_state *state = state_;
        if (5 < len && !memcmp("@@ -", line, 4)) {
                if (parse_hunk_header(line, len,
                                      &state->ob, &state->on,
                                      &state->nb, &state->nn))
                        return;
                state->lno = state->nb;
                if (state->nn == 0) {
                        /* @@ -X,Y +N,0 @@ removed Y lines
                         * that would have come *after* line N
                         * in the result.  Our lost buckets hang
                         * to the line after the removed lines,
                         *
                         * Note that this is correct even when N == 0,
                         * in which case the hunk removes the first
                         * line in the file.
                         */
                        state->lost_bucket = &state->sline[state->nb];
                        if (!state->nb)
                                state->nb = 1;
                } else {
                        state->lost_bucket = &state->sline[state->nb-1];
                }
                if (!state->sline[state->nb-1].p_lno)
                        state->sline[state->nb-1].p_lno =
                                xcalloc(state->num_parent,
                                        sizeof(unsigned long));
                state->sline[state->nb-1].p_lno[state->n] = state->ob;
                return;
        }
        if (!state->lost_bucket)
                return; /* not in any hunk yet */
        switch (line[0]) {
        case '-':
                append_lost(state->lost_bucket, state->n, line+1, len-1);
                break;
        case '+':
                state->sline[state->lno-1].flag |= state->nmask;
                state->lno++;
                break;
        }
}

static void combine_diff(const struct object_id *parent, unsigned int mode,
                         mmfile_t *result_file,
                         struct sline *sline, unsigned int cnt, int n,
                         int num_parent, int result_deleted,
                         struct userdiff_driver *textconv,
                         const char *path, long flags)
{
        unsigned int p_lno, lno;
        unsigned long nmask = (1UL << n);
        xpparam_t xpp;
        xdemitconf_t xecfg;
        mmfile_t parent_file;
        struct combine_diff_state state;
        unsigned long sz;

        if (result_deleted)
                return; /* result deleted */

        parent_file.ptr = grab_blob(parent, mode, &sz, textconv, path);
        parent_file.size = sz;
        memset(&xpp, 0, sizeof(xpp));
        xpp.flags = flags;
        memset(&xecfg, 0, sizeof(xecfg));
        memset(&state, 0, sizeof(state));
        state.nmask = nmask;
        state.sline = sline;
        state.lno = 1;
        state.num_parent = num_parent;
        state.n = n;

        if (xdi_diff_outf(&parent_file, result_file, consume_line, &state,
                          &xpp, &xecfg))
                die("unable to generate combined diff for %s",
                    oid_to_hex(parent));
        free(parent_file.ptr);

        /* Assign line numbers for this parent.
         *
         * sline[lno].p_lno[n] records the first line number
         * (counting from 1) for parent N if the final hunk display
         * started by showing sline[lno] (possibly showing the lost
         * lines attached to it first).
         */
        for (lno = 0,  p_lno = 1; lno <= cnt; lno++) {
                struct lline *ll;
                sline[lno].p_lno[n] = p_lno;

                /* Coalesce new lines */
                if (sline[lno].plost.lost_head) {
                        struct sline *sl = &sline[lno];
                        sl->lost = coalesce_lines(sl->lost, &sl->lenlost,
                                                  sl->plost.lost_head,
                                                  sl->plost.len, n, flags);
                        sl->plost.lost_head = sl->plost.lost_tail = NULL;
                        sl->plost.len = 0;
                }

                /* How many lines would this sline advance the p_lno? */
                ll = sline[lno].lost;
                while (ll) {
                        if (ll->parent_map & nmask)
                                p_lno++; /* '-' means parent had it */
                        ll = ll->next;
                }
                if (lno < cnt && !(sline[lno].flag & nmask))
                        p_lno++; /* no '+' means parent had it */
        }
        sline[lno].p_lno[n] = p_lno; /* trailer */
}

static unsigned long context = 3;
static char combine_marker = '@';

static int interesting(struct sline *sline, unsigned long all_mask)
{
        /* If some parents lost lines here, or if we have added to
         * some parent, it is interesting.
         */
        return ((sline->flag & all_mask) || sline->lost);
}

static unsigned long adjust_hunk_tail(struct sline *sline,
                                      unsigned long all_mask,
                                      unsigned long hunk_begin,
                                      unsigned long i)
{
        /* i points at the first uninteresting line.  If the last line
         * of the hunk was interesting only because it has some
         * deletion, then it is not all that interesting for the
         * purpose of giving trailing context lines.  This is because
         * we output '-' line and then unmodified sline[i-1] itself in
         * that case which gives us one extra context line.
         */
        if ((hunk_begin + 1 <= i) && !(sline[i-1].flag & all_mask))
                i--;
        return i;
}

static unsigned long find_next(struct sline *sline,
                               unsigned long mark,
                               unsigned long i,
                               unsigned long cnt,
                               int look_for_uninteresting)
{
        /* We have examined up to i-1 and are about to look at i.
         * Find next interesting or uninteresting line.  Here,
         * "interesting" does not mean interesting(), but marked by
         * the give_context() function below (i.e. it includes context
         * lines that are not interesting to interesting() function
         * that are surrounded by interesting() ones.
         */
        while (i <= cnt)
                if (look_for_uninteresting
                    ? !(sline[i].flag & mark)
                    : (sline[i].flag & mark))
                        return i;
                else
                        i++;
        return i;
}

static int give_context(struct sline *sline, unsigned long cnt, int num_parent)
{
        unsigned long all_mask = (1UL<<num_parent) - 1;
        unsigned long mark = (1UL<<num_parent);
        unsigned long no_pre_delete = (2UL<<num_parent);
        unsigned long i;

        /* Two groups of interesting lines may have a short gap of
         * uninteresting lines.  Connect such groups to give them a
         * bit of context.
         *
         * We first start from what the interesting() function says,
         * and mark them with "mark", and paint context lines with the
         * mark.  So interesting() would still say false for such context
         * lines but they are treated as "interesting" in the end.
         */
        i = find_next(sline, mark, 0, cnt, 0);
        if (cnt < i)
                return 0;

        while (i <= cnt) {
                unsigned long j = (context < i) ? (i - context) : 0;
                unsigned long k;

                /* Paint a few lines before the first interesting line. */
                while (j < i) {
                        if (!(sline[j].flag & mark))
                                sline[j].flag |= no_pre_delete;
                        sline[j++].flag |= mark;
                }

        again:
                /* we know up to i is to be included.  where does the
                 * next uninteresting one start?
                 */
                j = find_next(sline, mark, i, cnt, 1);
                if (cnt < j)
                        break; /* the rest are all interesting */

                /* lookahead context lines */
                k = find_next(sline, mark, j, cnt, 0);
                j = adjust_hunk_tail(sline, all_mask, i, j);

                if (k < j + context) {
                        /* k is interesting and [j,k) are not, but
                         * paint them interesting because the gap is small.
                         */
                        while (j < k)
                                sline[j++].flag |= mark;
                        i = k;
                        goto again;
                }

                /* j is the first uninteresting line and there is
                 * no overlap beyond it within context lines.  Paint
                 * the trailing edge a bit.
                 */
                i = k;
                k = (j + context < cnt+1) ? j + context : cnt+1;
                while (j < k)
                        sline[j++].flag |= mark;
        }
        return 1;
}

static int make_hunks(struct sline *sline, unsigned long cnt,
                       int num_parent, int dense)
{
        unsigned long all_mask = (1UL<<num_parent) - 1;
        unsigned long mark = (1UL<<num_parent);
        unsigned long i;
        int has_interesting = 0;

        for (i = 0; i <= cnt; i++) {
                if (interesting(&sline[i], all_mask))
                        sline[i].flag |= mark;
                else
                        sline[i].flag &= ~mark;
        }
        if (!dense)
                return give_context(sline, cnt, num_parent);

        /* Look at each hunk, and if we have changes from only one
         * parent, or the changes are the same from all but one
         * parent, mark that uninteresting.
         */
        i = 0;
        while (i <= cnt) {
                unsigned long j, hunk_begin, hunk_end;
                unsigned long same_diff;
                while (i <= cnt && !(sline[i].flag & mark))
                        i++;
                if (cnt < i)
                        break; /* No more interesting hunks */
                hunk_begin = i;
                for (j = i + 1; j <= cnt; j++) {
                        if (!(sline[j].flag & mark)) {
                                /* Look beyond the end to see if there
                                 * is an interesting line after this
                                 * hunk within context span.
                                 */
                                unsigned long la; /* lookahead */
                                int contin = 0;
                                la = adjust_hunk_tail(sline, all_mask,
                                                     hunk_begin, j);
                                la = (la + context < cnt + 1) ?
                                        (la + context) : cnt + 1;
                                while (la && j <= --la) {
                                        if (sline[la].flag & mark) {
                                                contin = 1;
                                                break;
                                        }
                                }
                                if (!contin)
                                        break;
                                j = la;
                        }
                }
                hunk_end = j;

                /* [i..hunk_end) are interesting.  Now is it really
                 * interesting?  We check if there are only two versions
                 * and the result matches one of them.  That is, we look
                 * at:
                 *   (+) line, which records lines added to which parents;
                 *       this line appears in the result.
                 *   (-) line, which records from what parents the line
                 *       was removed; this line does not appear in the result.
                 * then check the set of parents the result has difference
                 * from, from all lines.  If there are lines that has
                 * different set of parents that the result has differences
                 * from, that means we have more than two versions.
                 *
                 * Even when we have only two versions, if the result does
                 * not match any of the parents, the it should be considered
                 * interesting.  In such a case, we would have all '+' line.
                 * After passing the above "two versions" test, that would
                 * appear as "the same set of parents" to be "all parents".
                 */
                same_diff = 0;
                has_interesting = 0;
                for (j = i; j < hunk_end && !has_interesting; j++) {
                        unsigned long this_diff = sline[j].flag & all_mask;
                        struct lline *ll = sline[j].lost;
                        if (this_diff) {
                                /* This has some changes.  Is it the
                                 * same as others?
                                 */
                                if (!same_diff)
                                        same_diff = this_diff;
                                else if (same_diff != this_diff) {
                                        has_interesting = 1;
                                        break;
                                }
                        }
                        while (ll && !has_interesting) {
                                /* Lost this line from these parents;
                                 * who are they?  Are they the same?
                                 */
                                this_diff = ll->parent_map;
                                if (!same_diff)
                                        same_diff = this_diff;
                                else if (same_diff != this_diff) {
                                        has_interesting = 1;
                                }
                                ll = ll->next;
                        }
                }

                if (!has_interesting && same_diff != all_mask) {
                        /* This hunk is not that interesting after all */
                        for (j = hunk_begin; j < hunk_end; j++)
                                sline[j].flag &= ~mark;
                }
                i = hunk_end;
        }

        has_interesting = give_context(sline, cnt, num_parent);
        return has_interesting;
}

static void show_parent_lno(struct sline *sline, unsigned long l0, unsigned long l1, int n, unsigned long null_context)
{
        l0 = sline[l0].p_lno[n];
        l1 = sline[l1].p_lno[n];
        printf(" -%lu,%lu", l0, l1-l0-null_context);
}

static int hunk_comment_line(const char *bol)
{
        int ch;

        if (!bol)
                return 0;
        ch = *bol & 0xff;
        return (isalpha(ch) || ch == '_' || ch == '$');
}

static void show_line_to_eol(const char *line, int len, const char *reset)
{
        int saw_cr_at_eol = 0;
        if (len < 0)
                len = strlen(line);
        saw_cr_at_eol = (len && line[len-1] == '\r');

        printf("%.*s%s%s\n", len - saw_cr_at_eol, line,
               reset,
               saw_cr_at_eol ? "\r" : "");
}

static void dump_sline(struct sline *sline, const char *line_prefix,
                       unsigned long cnt, int num_parent,
                       int use_color, int result_deleted)
{
        unsigned long mark = (1UL<<num_parent);
        unsigned long no_pre_delete = (2UL<<num_parent);
        int i;
        unsigned long lno = 0;
        const char *c_frag = diff_get_color(use_color, DIFF_FRAGINFO);
        const char *c_func = diff_get_color(use_color, DIFF_FUNCINFO);
        const char *c_new = diff_get_color(use_color, DIFF_FILE_NEW);
        const char *c_old = diff_get_color(use_color, DIFF_FILE_OLD);
        const char *c_context = diff_get_color(use_color, DIFF_CONTEXT);
        const char *c_reset = diff_get_color(use_color, DIFF_RESET);

        if (result_deleted)
                return; /* result deleted */

        while (1) {
                unsigned long hunk_end;
                unsigned long rlines;
                const char *hunk_comment = NULL;
                unsigned long null_context = 0;

                while (lno <= cnt && !(sline[lno].flag & mark)) {
                        if (hunk_comment_line(sline[lno].bol))
                                hunk_comment = sline[lno].bol;
                        lno++;
                }
                if (cnt < lno)
                        break;
                else {
                        for (hunk_end = lno + 1; hunk_end <= cnt; hunk_end++)
                                if (!(sline[hunk_end].flag & mark))
                                        break;
                }
                rlines = hunk_end - lno;
                if (cnt < hunk_end)
                        rlines--; /* pointing at the last delete hunk */

                if (!context) {
                        /*
                         * Even when running with --unified=0, all
                         * lines in the hunk needs to be processed in
                         * the loop below in order to show the
                         * deletion recorded in lost_head.  However,
                         * we do not want to show the resulting line
                         * with all blank context markers in such a
                         * case.  Compensate.
                         */
                        unsigned long j;
                        for (j = lno; j < hunk_end; j++)
                                if (!(sline[j].flag & (mark-1)))
                                        null_context++;
                        rlines -= null_context;
                }

                printf("%s%s", line_prefix, c_frag);
                for (i = 0; i <= num_parent; i++) putchar(combine_marker);
                for (i = 0; i < num_parent; i++)
                        show_parent_lno(sline, lno, hunk_end, i, null_context);
                printf(" +%lu,%lu ", lno+1, rlines);
                for (i = 0; i <= num_parent; i++) putchar(combine_marker);

                if (hunk_comment) {
                        int comment_end = 0;
                        for (i = 0; i < 40; i++) {
                                int ch = hunk_comment[i] & 0xff;
                                if (!ch || ch == '\n')
                                        break;
                                if (!isspace(ch))
                                    comment_end = i;
                        }
                        if (comment_end)
                                printf("%s%s %s%s", c_reset,
                                                    c_context, c_reset,
                                                    c_func);
                        for (i = 0; i < comment_end; i++)
                                putchar(hunk_comment[i]);
                }

                printf("%s\n", c_reset);
                while (lno < hunk_end) {
                        struct lline *ll;
                        int j;
                        unsigned long p_mask;
                        struct sline *sl = &sline[lno++];
                        ll = (sl->flag & no_pre_delete) ? NULL : sl->lost;
                        while (ll) {
                                printf("%s%s", line_prefix, c_old);
                                for (j = 0; j < num_parent; j++) {
                                        if (ll->parent_map & (1UL<<j))
                                                putchar('-');
                                        else
                                                putchar(' ');
                                }
                                show_line_to_eol(ll->line, -1, c_reset);
                                ll = ll->next;
                        }
                        if (cnt < lno)
                                break;
                        p_mask = 1;
                        fputs(line_prefix, stdout);
                        if (!(sl->flag & (mark-1))) {
                                /*
                                 * This sline was here to hang the
                                 * lost lines in front of it.
                                 */
                                if (!context)
                                        continue;
                                fputs(c_context, stdout);
                        }
                        else
                                fputs(c_new, stdout);
                        for (j = 0; j < num_parent; j++) {
                                if (p_mask & sl->flag)
                                        putchar('+');
                                else
                                        putchar(' ');
                                p_mask <<= 1;
                        }
                        show_line_to_eol(sl->bol, sl->len, c_reset);
                }
        }
}

static void reuse_combine_diff(struct sline *sline, unsigned long cnt,
                               int i, int j)
{
        /* We have already examined parent j and we know parent i
         * and parent j are the same, so reuse the combined result
         * of parent j for parent i.
         */
        unsigned long lno, imask, jmask;
        imask = (1UL<<i);
        jmask = (1UL<<j);

        for (lno = 0; lno <= cnt; lno++) {
                struct lline *ll = sline->lost;
                sline->p_lno[i] = sline->p_lno[j];
                while (ll) {
                        if (ll->parent_map & jmask)
                                ll->parent_map |= imask;
                        ll = ll->next;
                }
                if (sline->flag & jmask)
                        sline->flag |= imask;
                sline++;
        }
        /* the overall size of the file (sline[cnt]) */
        sline->p_lno[i] = sline->p_lno[j];
}

static void dump_quoted_path(const char *head,
                             const char *prefix,
                             const char *path,
                             const char *line_prefix,
                             const char *c_meta, const char *c_reset)
{
        static struct strbuf buf = STRBUF_INIT;

        strbuf_reset(&buf);
        strbuf_addstr(&buf, line_prefix);
        strbuf_addstr(&buf, c_meta);
        strbuf_addstr(&buf, head);
        quote_two_c_style(&buf, prefix, path, 0);
        strbuf_addstr(&buf, c_reset);
        puts(buf.buf);
}

static void show_combined_header(struct combine_diff_path *elem,
                                 int num_parent,
                                 int dense,
                                 struct rev_info *rev,
                                 const char *line_prefix,
                                 int mode_differs,
                                 int show_file_header)
{
        struct diff_options *opt = &rev->diffopt;
        int abbrev = DIFF_OPT_TST(opt, FULL_INDEX) ? GIT_SHA1_HEXSZ : DEFAULT_ABBREV;
        const char *a_prefix = opt->a_prefix ? opt->a_prefix : "a/";
        const char *b_prefix = opt->b_prefix ? opt->b_prefix : "b/";
        const char *c_meta = diff_get_color_opt(opt, DIFF_METAINFO);
        const char *c_reset = diff_get_color_opt(opt, DIFF_RESET);
        const char *abb;
        int added = 0;
        int deleted = 0;
        int i;

        if (rev->loginfo && !rev->no_commit_id)
                show_log(rev);

        dump_quoted_path(dense ? "diff --cc " : "diff --combined ",
                         "", elem->path, line_prefix, c_meta, c_reset);
        printf("%s%sindex ", line_prefix, c_meta);
        for (i = 0; i < num_parent; i++) {
                abb = find_unique_abbrev(elem->parent[i].oid.hash,
                                         abbrev);
                printf("%s%s", i ? "," : "", abb);
        }
        abb = find_unique_abbrev(elem->oid.hash, abbrev);
        printf("..%s%s\n", abb, c_reset);

        if (mode_differs) {
                deleted = !elem->mode;

                /* We say it was added if nobody had it */
                added = !deleted;
                for (i = 0; added && i < num_parent; i++)
                        if (elem->parent[i].status !=
                            DIFF_STATUS_ADDED)
                                added = 0;
                if (added)
                        printf("%s%snew file mode %06o",
                               line_prefix, c_meta, elem->mode);
                else {
                        if (deleted)
                                printf("%s%sdeleted file ",
                                       line_prefix, c_meta);
                        printf("mode ");
                        for (i = 0; i < num_parent; i++) {
                                printf("%s%06o", i ? "," : "",
                                       elem->parent[i].mode);
                        }
                        if (elem->mode)
                                printf("..%06o", elem->mode);
                }
                printf("%s\n", c_reset);
        }

        if (!show_file_header)
                return;

        if (added)
                dump_quoted_path("--- ", "", "/dev/null",
                                 line_prefix, c_meta, c_reset);
        else
                dump_quoted_path("--- ", a_prefix, elem->path,
                                 line_prefix, c_meta, c_reset);
        if (deleted)
                dump_quoted_path("+++ ", "", "/dev/null",
                                 line_prefix, c_meta, c_reset);
        else
                dump_quoted_path("+++ ", b_prefix, elem->path,
                                 line_prefix, c_meta, c_reset);
}

static void show_patch_diff(struct combine_diff_path *elem, int num_parent,
                            int dense, int working_tree_file,
                            struct rev_info *rev)
{
        struct diff_options *opt = &rev->diffopt;
        unsigned long result_size, cnt, lno;
        int result_deleted = 0;
        char *result, *cp;
        struct sline *sline; /* survived lines */
        int mode_differs = 0;
        int i, show_hunks;
        mmfile_t result_file;
        struct userdiff_driver *userdiff;
        struct userdiff_driver *textconv = NULL;
        int is_binary;
        const char *line_prefix = diff_line_prefix(opt);

        context = opt->context;
        userdiff = userdiff_find_by_path(elem->path);
        if (!userdiff)
                userdiff = userdiff_find_by_name("default");
        if (DIFF_OPT_TST(opt, ALLOW_TEXTCONV))
                textconv = userdiff_get_textconv(userdiff);

        /* Read the result of merge first */
        if (!working_tree_file)
                result = grab_blob(&elem->oid, elem->mode, &result_size,
                                   textconv, elem->path);
        else {
                /* Used by diff-tree to read from the working tree */
                struct stat st;
                int fd = -1;

                if (lstat(elem->path, &st) < 0)
                        goto deleted_file;

                if (S_ISLNK(st.st_mode)) {
                        struct strbuf buf = STRBUF_INIT;

                        if (strbuf_readlink(&buf, elem->path, st.st_size) < 0) {
                                error_errno("readlink(%s)", elem->path);
                                return;
                        }
                        result_size = buf.len;
                        result = strbuf_detach(&buf, NULL);
                        elem->mode = canon_mode(st.st_mode);
                } else if (S_ISDIR(st.st_mode)) {
                        struct object_id oid;
                        if (resolve_gitlink_ref(elem->path, "HEAD", oid.hash) < 0)
                                result = grab_blob(&elem->oid, elem->mode,
                                                   &result_size, NULL, NULL);
                        else
                                result = grab_blob(&oid, elem->mode,
                                                   &result_size, NULL, NULL);
                } else if (textconv) {
                        struct diff_filespec *df = alloc_filespec(elem->path);
                        fill_filespec(df, &null_oid, 0, st.st_mode);
                        result_size = fill_textconv(textconv, df, &result);
                        free_filespec(df);
                } else if (0 <= (fd = open(elem->path, O_RDONLY))) {
                        size_t len = xsize_t(st.st_size);
                        ssize_t done;
                        int is_file, i;

                        elem->mode = canon_mode(st.st_mode);
                        /* if symlinks don't work, assume symlink if all parents
                         * are symlinks
                         */
                        is_file = has_symlinks;
                        for (i = 0; !is_file && i < num_parent; i++)
                                is_file = !S_ISLNK(elem->parent[i].mode);
                        if (!is_file)
                                elem->mode = canon_mode(S_IFLNK);

                        result_size = len;
                        result = xmallocz(len);

                        done = read_in_full(fd, result, len);
                        if (done < 0)
                                die_errno("read error '%s'", elem->path);
                        else if (done < len)
                                die("early EOF '%s'", elem->path);

                        /* If not a fake symlink, apply filters, e.g. autocrlf */
                        if (is_file) {
                                struct strbuf buf = STRBUF_INIT;

                                if (convert_to_git(&the_index, elem->path, result, len, &buf, safe_crlf)) {
                                        free(result);
                                        result = strbuf_detach(&buf, &len);
                                        result_size = len;
                                }
                        }
                }
                else {
                deleted_file:
                        result_deleted = 1;
                        result_size = 0;
                        elem->mode = 0;
                        result = xcalloc(1, 1);
                }

                if (0 <= fd)
                        close(fd);
        }

        for (i = 0; i < num_parent; i++) {
                if (elem->parent[i].mode != elem->mode) {
                        mode_differs = 1;
                        break;
                }
        }

        if (textconv)
                is_binary = 0;
        else if (userdiff->binary != -1)
                is_binary = userdiff->binary;
        else {
                is_binary = buffer_is_binary(result, result_size);
                for (i = 0; !is_binary && i < num_parent; i++) {
                        char *buf;
                        unsigned long size;
                        buf = grab_blob(&elem->parent[i].oid,
                                        elem->parent[i].mode,
                                        &size, NULL, NULL);
                        if (buffer_is_binary(buf, size))
                                is_binary = 1;
                        free(buf);
                }
        }
        if (is_binary) {
                show_combined_header(elem, num_parent, dense, rev,
                                     line_prefix, mode_differs, 0);
                printf("Binary files differ\n");
                free(result);
                return;
        }

        for (cnt = 0, cp = result; cp < result + result_size; cp++) {
                if (*cp == '\n')
                        cnt++;
        }
        if (result_size && result[result_size-1] != '\n')
                cnt++; /* incomplete line */

        sline = xcalloc(st_add(cnt, 2), sizeof(*sline));
        sline[0].bol = result;
        for (lno = 0, cp = result; cp < result + result_size; cp++) {
                if (*cp == '\n') {
                        sline[lno].len = cp - sline[lno].bol;
                        lno++;
                        if (lno < cnt)
                                sline[lno].bol = cp + 1;
                }
        }
        if (result_size && result[result_size-1] != '\n')
                sline[cnt-1].len = result_size - (sline[cnt-1].bol - result);

        result_file.ptr = result;
        result_file.size = result_size;

        /* Even p_lno[cnt+1] is valid -- that is for the end line number
         * for deletion hunk at the end.
         */
        sline[0].p_lno = xcalloc(st_mult(st_add(cnt, 2), num_parent), sizeof(unsigned long));
        for (lno = 0; lno <= cnt; lno++)
                sline[lno+1].p_lno = sline[lno].p_lno + num_parent;

        for (i = 0; i < num_parent; i++) {
                int j;
                for (j = 0; j < i; j++) {
                        if (!oidcmp(&elem->parent[i].oid,
                                     &elem->parent[j].oid)) {
                                reuse_combine_diff(sline, cnt, i, j);
                                break;
                        }
                }
                if (i <= j)
                        combine_diff(&elem->parent[i].oid,
                                     elem->parent[i].mode,
                                     &result_file, sline,
                                     cnt, i, num_parent, result_deleted,
                                     textconv, elem->path, opt->xdl_opts);
        }

        show_hunks = make_hunks(sline, cnt, num_parent, dense);

        if (show_hunks || mode_differs || working_tree_file) {
                show_combined_header(elem, num_parent, dense, rev,
                                     line_prefix, mode_differs, 1);
                dump_sline(sline, line_prefix, cnt, num_parent,
                           opt->use_color, result_deleted);
        }
        free(result);

        for (lno = 0; lno < cnt; lno++) {
                if (sline[lno].lost) {
                        struct lline *ll = sline[lno].lost;
                        while (ll) {
                                struct lline *tmp = ll;
                                ll = ll->next;
                                free(tmp);
                        }
                }
        }
        free(sline[0].p_lno);
        free(sline);
}

static void show_raw_diff(struct combine_diff_path *p, int num_parent, struct rev_info *rev)
{
        struct diff_options *opt = &rev->diffopt;
        int line_termination, inter_name_termination, i;
        const char *line_prefix = diff_line_prefix(opt);

        line_termination = opt->line_termination;
        inter_name_termination = '\t';
        if (!line_termination)
                inter_name_termination = 0;

        if (rev->loginfo && !rev->no_commit_id)
                show_log(rev);


        if (opt->output_format & DIFF_FORMAT_RAW) {
                printf("%s", line_prefix);

                /* As many colons as there are parents */
                for (i = 0; i < num_parent; i++)
                        putchar(':');

                /* Show the modes */
                for (i = 0; i < num_parent; i++)
                        printf("%06o ", p->parent[i].mode);
                printf("%06o", p->mode);

                /* Show sha1's */
                for (i = 0; i < num_parent; i++)
                        printf(" %s", diff_aligned_abbrev(&p->parent[i].oid,
                                                          opt->abbrev));
                printf(" %s ", diff_aligned_abbrev(&p->oid, opt->abbrev));
        }

        if (opt->output_format & (DIFF_FORMAT_RAW | DIFF_FORMAT_NAME_STATUS)) {
                for (i = 0; i < num_parent; i++)
                        putchar(p->parent[i].status);
                putchar(inter_name_termination);
        }

        write_name_quoted(p->path, stdout, line_termination);
}

/*
 * The result (p->elem) is from the working tree and their
 * parents are typically from multiple stages during a merge
 * (i.e. diff-files) or the state in HEAD and in the index
 * (i.e. diff-index).
 */
void show_combined_diff(struct combine_diff_path *p,
                       int num_parent,
                       int dense,
                       struct rev_info *rev)
{
        struct diff_options *opt = &rev->diffopt;

        if (opt->output_format & (DIFF_FORMAT_RAW |
                                  DIFF_FORMAT_NAME |
                                  DIFF_FORMAT_NAME_STATUS))
                show_raw_diff(p, num_parent, rev);
        else if (opt->output_format & DIFF_FORMAT_PATCH)
                show_patch_diff(p, num_parent, dense, 1, rev);
}

static void free_combined_pair(struct diff_filepair *pair)
{
        free(pair->two);
        free(pair);
}

/*
 * A combine_diff_path expresses N parents on the LHS against 1 merge
 * result. Synthesize a diff_filepair that has N entries on the "one"
 * side and 1 entry on the "two" side.
 *
 * In the future, we might want to add more data to combine_diff_path
 * so that we can fill fields we are ignoring (most notably, size) here,
 * but currently nobody uses it, so this should suffice for now.
 */
static struct diff_filepair *combined_pair(struct combine_diff_path *p,
                                           int num_parent)
{
        int i;
        struct diff_filepair *pair;
        struct diff_filespec *pool;

        pair = xmalloc(sizeof(*pair));
        pool = xcalloc(st_add(num_parent, 1), sizeof(struct diff_filespec));
        pair->one = pool + 1;
        pair->two = pool;

        for (i = 0; i < num_parent; i++) {
                pair->one[i].path = p->path;
                pair->one[i].mode = p->parent[i].mode;
                oidcpy(&pair->one[i].oid, &p->parent[i].oid);
                pair->one[i].oid_valid = !is_null_oid(&p->parent[i].oid);
                pair->one[i].has_more_entries = 1;
        }
        pair->one[num_parent - 1].has_more_entries = 0;

        pair->two->path = p->path;
        pair->two->mode = p->mode;
        oidcpy(&pair->two->oid, &p->oid);
        pair->two->oid_valid = !is_null_oid(&p->oid);
        return pair;
}

static void handle_combined_callback(struct diff_options *opt,
                                     struct combine_diff_path *paths,
                                     int num_parent,
                                     int num_paths)
{
        struct combine_diff_path *p;
        struct diff_queue_struct q;
        int i;

        q.queue = xcalloc(num_paths, sizeof(struct diff_filepair *));
        q.alloc = num_paths;
        q.nr = num_paths;
        for (i = 0, p = paths; p; p = p->next)
                q.queue[i++] = combined_pair(p, num_parent);
        opt->format_callback(&q, opt, opt->format_callback_data);
        for (i = 0; i < num_paths; i++)
                free_combined_pair(q.queue[i]);
        free(q.queue);
}

static const char *path_path(void *obj)
{
        struct combine_diff_path *path = (struct combine_diff_path *)obj;

        return path->path;
}


/* find set of paths that every parent touches */
static struct combine_diff_path *find_paths_generic(const struct object_id *oid,
        const struct oid_array *parents, struct diff_options *opt)
{
        struct combine_diff_path *paths = NULL;
        int i, num_parent = parents->nr;

        int output_format = opt->output_format;
        const char *orderfile = opt->orderfile;

        opt->output_format = DIFF_FORMAT_NO_OUTPUT;
        /* tell diff_tree to emit paths in sorted (=tree) order */
        opt->orderfile = NULL;

        /* D(A,P1...Pn) = D(A,P1) ^ ... ^ D(A,Pn)  (wrt paths) */
        for (i = 0; i < num_parent; i++) {
                /*
                 * show stat against the first parent even when doing
                 * combined diff.
                 */
                int stat_opt = (output_format &
                                (DIFF_FORMAT_NUMSTAT|DIFF_FORMAT_DIFFSTAT));
                if (i == 0 && stat_opt)
                        opt->output_format = stat_opt;
                else
                        opt->output_format = DIFF_FORMAT_NO_OUTPUT;
                diff_tree_oid(&parents->oid[i], oid, "", opt);
                diffcore_std(opt);
                paths = intersect_paths(paths, i, num_parent);

                /* if showing diff, show it in requested order */
                if (opt->output_format != DIFF_FORMAT_NO_OUTPUT &&
                    orderfile) {
                        diffcore_order(orderfile);
                }

                diff_flush(opt);
        }

        opt->output_format = output_format;
        opt->orderfile = orderfile;
        return paths;
}


/*
 * find set of paths that everybody touches, assuming diff is run without
 * rename/copy detection, etc, comparing all trees simultaneously (= faster).
 */
static struct combine_diff_path *find_paths_multitree(
        const struct object_id *oid, const struct oid_array *parents,
        struct diff_options *opt)
{
        int i, nparent = parents->nr;
        const struct object_id **parents_oid;
        struct combine_diff_path paths_head;
        struct strbuf base;

        ALLOC_ARRAY(parents_oid, nparent);
        for (i = 0; i < nparent; i++)
                parents_oid[i] = &parents->oid[i];

        /* fake list head, so worker can assume it is non-NULL */
        paths_head.next = NULL;

        strbuf_init(&base, PATH_MAX);
        diff_tree_paths(&paths_head, oid, parents_oid, nparent, &base, opt);

        strbuf_release(&base);
        free(parents_oid);
        return paths_head.next;
}


void diff_tree_combined(const struct object_id *oid,
                        const struct oid_array *parents,
                        int dense,
                        struct rev_info *rev)
{
        struct diff_options *opt = &rev->diffopt;
        struct diff_options diffopts;
        struct combine_diff_path *p, *paths;
        int i, num_paths, needsep, show_log_first, num_parent = parents->nr;
        int need_generic_pathscan;

        /* nothing to do, if no parents */
        if (!num_parent)
                return;

        show_log_first = !!rev->loginfo && !rev->no_commit_id;
        needsep = 0;
        if (show_log_first) {
                show_log(rev);

                if (rev->verbose_header && opt->output_format &&
                    opt->output_format != DIFF_FORMAT_NO_OUTPUT &&
                    !commit_format_is_empty(rev->commit_format))
                        printf("%s%c", diff_line_prefix(opt),
                               opt->line_termination);
        }

        diffopts = *opt;
        copy_pathspec(&diffopts.pathspec, &opt->pathspec);
        DIFF_OPT_SET(&diffopts, RECURSIVE);
        DIFF_OPT_CLR(&diffopts, ALLOW_EXTERNAL);

        /* find set of paths that everybody touches
         *
         * NOTE
         *
         * Diffcore transformations are bound to diff_filespec and logic
         * comparing two entries - i.e. they do not apply directly to combine
         * diff.
         *
         * If some of such transformations is requested - we launch generic
         * path scanning, which works significantly slower compared to
         * simultaneous all-trees-in-one-go scan in find_paths_multitree().
         *
         * TODO some of the filters could be ported to work on
         * combine_diff_paths - i.e. all functionality that skips paths, so in
         * theory, we could end up having only multitree path scanning.
         *
         * NOTE please keep this semantically in sync with diffcore_std()
         */
        need_generic_pathscan = opt->skip_stat_unmatch  ||
                        DIFF_OPT_TST(opt, FOLLOW_RENAMES)       ||
                        opt->break_opt != -1    ||
                        opt->detect_rename      ||
                        opt->pickaxe            ||
                        opt->filter;


        if (need_generic_pathscan) {
                /*
                 * NOTE generic case also handles --stat, as it computes
                 * diff(sha1,parent_i) for all i to do the job, specifically
                 * for parent0.
                 */
                paths = find_paths_generic(oid, parents, &diffopts);
        }
        else {
                int stat_opt;
                paths = find_paths_multitree(oid, parents, &diffopts);

                /*
                 * show stat against the first parent even
                 * when doing combined diff.
                 */
                stat_opt = (opt->output_format &
                                (DIFF_FORMAT_NUMSTAT|DIFF_FORMAT_DIFFSTAT));
                if (stat_opt) {
                        diffopts.output_format = stat_opt;

                        diff_tree_oid(&parents->oid[0], oid, "", &diffopts);
                        diffcore_std(&diffopts);
                        if (opt->orderfile)
                                diffcore_order(opt->orderfile);
                        diff_flush(&diffopts);
                }
        }

        /* find out number of surviving paths */
        for (num_paths = 0, p = paths; p; p = p->next)
                num_paths++;

        /* order paths according to diffcore_order */
        if (opt->orderfile && num_paths) {
                struct obj_order *o;

                ALLOC_ARRAY(o, num_paths);
                for (i = 0, p = paths; p; p = p->next, i++)
                        o[i].obj = p;
                order_objects(opt->orderfile, path_path, o, num_paths);
                for (i = 0; i < num_paths - 1; i++) {
                        p = o[i].obj;
                        p->next = o[i+1].obj;
                }

                p = o[num_paths-1].obj;
                p->next = NULL;
                paths = o[0].obj;
                free(o);
        }


        if (num_paths) {
                if (opt->output_format & (DIFF_FORMAT_RAW |
                                          DIFF_FORMAT_NAME |
                                          DIFF_FORMAT_NAME_STATUS)) {
                        for (p = paths; p; p = p->next)
                                show_raw_diff(p, num_parent, rev);
                        needsep = 1;
                }
                else if (opt->output_format &
                         (DIFF_FORMAT_NUMSTAT|DIFF_FORMAT_DIFFSTAT))
                        needsep = 1;
                else if (opt->output_format & DIFF_FORMAT_CALLBACK)
                        handle_combined_callback(opt, paths, num_parent, num_paths);

                if (opt->output_format & DIFF_FORMAT_PATCH) {
                        if (needsep)
                                printf("%s%c", diff_line_prefix(opt),
                                       opt->line_termination);
                        for (p = paths; p; p = p->next)
                                show_patch_diff(p, num_parent, dense,
                                                0, rev);
                }
        }

        /* Clean things up */
        while (paths) {
                struct combine_diff_path *tmp = paths;
                paths = paths->next;
                free(tmp);
        }

        clear_pathspec(&diffopts.pathspec);
}

void diff_tree_combined_merge(const struct commit *commit, int dense,
                              struct rev_info *rev)
{
        struct commit_list *parent = get_saved_parents(rev, commit);
        struct oid_array parents = OID_ARRAY_INIT;

        while (parent) {
                oid_array_append(&parents, &parent->item->object.oid);
                parent = parent->next;
        }
        diff_tree_combined(&commit->object.oid, &parents, dense, rev);
        oid_array_clear(&parents);
}