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combine-diff: coalesce lost lines optimally

This replaces the greedy implementation to coalesce lost lines by using
dynamic programming to find the Longest Common Subsequence.

The O(n²) time complexity is obviously bigger than previous
implementation but it can produce shorter diff results (and most likely
easier to read).

List of lost lines is now doubly-linked because we reverse-read it when
reading the direction matrix.

Signed-off-by: Antoine Pelisse <apelisse@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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1 parent fa04ae0 commit 99d3206010ba1fcc9311cbe8376c0b5e78f4a136 @apelisse apelisse committed with gitster Mar 23, 2013
Showing with 320 additions and 64 deletions.
  1. +191 −64 combine-diff.c
  2. +129 −0 t/t4038-diff-combined.sh
View
255 combine-diff.c
@@ -74,16 +74,24 @@ static struct combine_diff_path *intersect_paths(struct combine_diff_path *curr,
/* Lines lost from parent */
struct lline {
- struct lline *next;
+ 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 {
- struct lline *lost_head, **lost_tail;
- struct lline *next_lost;
+ /* 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.
@@ -95,34 +103,6 @@ struct sline {
unsigned long *p_lno;
};
-static char *grab_blob(const unsigned char *sha1, unsigned int mode,
- unsigned long *size, struct userdiff_driver *textconv,
- const char *path)
-{
- char *blob;
- enum object_type type;
-
- if (S_ISGITLINK(mode)) {
- blob = xmalloc(100);
- *size = snprintf(blob, 100,
- "Subproject commit %s\n", sha1_to_hex(sha1));
- } else if (is_null_sha1(sha1)) {
- /* deleted blob */
- *size = 0;
- return xcalloc(1, 1);
- } else if (textconv) {
- struct diff_filespec *df = alloc_filespec(path);
- fill_filespec(df, sha1, 1, mode);
- *size = fill_textconv(textconv, df, &blob);
- free_filespec(df);
- } else {
- blob = read_sha1_file(sha1, &type, size);
- if (type != OBJ_BLOB)
- die("object '%s' is not a blob!", sha1_to_hex(sha1));
- }
- return blob;
-}
-
static int match_string_spaces(const char *line1, int len1,
const char *line2, int len2,
long flags)
@@ -163,36 +143,180 @@ static int match_string_spaces(const char *line1, int len1,
return 0;
}
-static void append_lost(struct sline *sline, int n, const char *line, int len, long flags)
+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)
{
- struct lline *lline;
- unsigned long this_mask = (1UL<<n);
- if (line[len-1] == '\n')
- len--;
+ int **lcs;
+ enum coalesce_direction **directions;
+ struct lline *baseend, *newend = NULL;
+ int i, j, origbaselen = *lenbase;
- /* Check to see if we can squash things */
- if (sline->lost_head) {
- lline = sline->next_lost;
- while (lline) {
- if (match_string_spaces(lline->line, lline->len,
- line, len, flags)) {
- lline->parent_map |= this_mask;
- sline->next_lost = lline->next;
- return;
+ 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 programing
+ * - 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(origbaselen + 1, sizeof(int*));
+ directions = xcalloc(origbaselen + 1, sizeof(enum coalesce_direction*));
+ for (i = 0; i < origbaselen + 1; i++) {
+ lcs[i] = xcalloc(lennew + 1, sizeof(int));
+ directions[i] = xcalloc(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;
}
- lline = lline->next;
+ 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 unsigned char *sha1, unsigned int mode,
+ unsigned long *size, struct userdiff_driver *textconv,
+ const char *path)
+{
+ char *blob;
+ enum object_type type;
+
+ if (S_ISGITLINK(mode)) {
+ blob = xmalloc(100);
+ *size = snprintf(blob, 100,
+ "Subproject commit %s\n", sha1_to_hex(sha1));
+ } else if (is_null_sha1(sha1)) {
+ /* deleted blob */
+ *size = 0;
+ return xcalloc(1, 1);
+ } else if (textconv) {
+ struct diff_filespec *df = alloc_filespec(path);
+ fill_filespec(df, sha1, 1, mode);
+ *size = fill_textconv(textconv, df, &blob);
+ free_filespec(df);
+ } else {
+ blob = read_sha1_file(sha1, &type, size);
+ if (type != OBJ_BLOB)
+ die("object '%s' is not a blob!", sha1_to_hex(sha1));
+ }
+ 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--;
+
lline = xmalloc(sizeof(*lline) + len + 1);
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;
memcpy(lline->line, line, len);
lline->line[len] = 0;
- *sline->lost_tail = lline;
- sline->lost_tail = &lline->next;
- sline->next_lost = NULL;
}
struct combine_diff_state {
@@ -203,7 +327,6 @@ struct combine_diff_state {
int n;
struct sline *sline;
struct sline *lost_bucket;
- long flags;
};
static void consume_line(void *state_, char *line, unsigned long len)
@@ -236,14 +359,13 @@ static void consume_line(void *state_, char *line, unsigned long len)
xcalloc(state->num_parent,
sizeof(unsigned long));
state->sline[state->nb-1].p_lno[state->n] = state->ob;
- state->lost_bucket->next_lost = state->lost_bucket->lost_head;
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, state->flags);
+ append_lost(state->lost_bucket, state->n, line+1, len-1);
break;
case '+':
state->sline[state->lno-1].flag |= state->nmask;
@@ -276,7 +398,6 @@ static void combine_diff(const unsigned char *parent, unsigned int mode,
xpp.flags = flags;
memset(&xecfg, 0, sizeof(xecfg));
memset(&state, 0, sizeof(state));
- state.flags = flags;
state.nmask = nmask;
state.sline = sline;
state.lno = 1;
@@ -298,8 +419,18 @@ static void combine_diff(const unsigned char *parent, unsigned int mode,
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_head;
+ ll = sline[lno].lost;
while (ll) {
if (ll->parent_map & nmask)
p_lno++; /* '-' means parent had it */
@@ -319,7 +450,7 @@ 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_head);
+ return ((sline->flag & all_mask) || sline->lost);
}
static unsigned long adjust_hunk_tail(struct sline *sline,
@@ -502,7 +633,7 @@ static int make_hunks(struct sline *sline, unsigned long cnt,
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_head;
+ struct lline *ll = sline[j].lost;
if (this_diff) {
/* This has some changes. Is it the
* same as others?
@@ -656,7 +787,7 @@ static void dump_sline(struct sline *sline, const char *line_prefix,
int j;
unsigned long p_mask;
struct sline *sl = &sline[lno++];
- ll = (sl->flag & no_pre_delete) ? NULL : sl->lost_head;
+ 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++) {
@@ -707,7 +838,7 @@ static void reuse_combine_diff(struct sline *sline, unsigned long cnt,
jmask = (1UL<<j);
for (lno = 0; lno <= cnt; lno++) {
- struct lline *ll = sline->lost_head;
+ struct lline *ll = sline->lost;
sline->p_lno[i] = sline->p_lno[j];
while (ll) {
if (ll->parent_map & jmask)
@@ -966,10 +1097,6 @@ static void show_patch_diff(struct combine_diff_path *elem, int num_parent,
sline = xcalloc(cnt+2, sizeof(*sline));
sline[0].bol = result;
- for (lno = 0; lno <= cnt + 1; lno++) {
- sline[lno].lost_tail = &sline[lno].lost_head;
- sline[lno].flag = 0;
- }
for (lno = 0, cp = result; cp < result + result_size; cp++) {
if (*cp == '\n') {
sline[lno].len = cp - sline[lno].bol;
@@ -1019,8 +1146,8 @@ static void show_patch_diff(struct combine_diff_path *elem, int num_parent,
free(result);
for (lno = 0; lno < cnt; lno++) {
- if (sline[lno].lost_head) {
- struct lline *ll = sline[lno].lost_head;
+ if (sline[lno].lost) {
+ struct lline *ll = sline[lno].lost;
while (ll) {
struct lline *tmp = ll;
ll = ll->next;
View
129 t/t4038-diff-combined.sh
@@ -224,4 +224,133 @@ test_expect_success 'check combined output (ignore all spaces)' '
compare_diff_patch expected actual
'
+test_expect_success 'combine diff coalesce simple' '
+ >test &&
+ git add test &&
+ git commit -m initial &&
+ test_seq 4 >test &&
+ git commit -a -m empty1 &&
+ git branch side1 &&
+ git checkout HEAD^ &&
+ test_seq 5 >test &&
+ git commit -a -m empty2 &&
+ test_must_fail git merge side1 &&
+ >test &&
+ git commit -a -m merge &&
+ git show >actual.tmp &&
+ sed -e "1,/^@@@/d" < actual.tmp >actual &&
+ tr -d Q <<-\EOF >expected &&
+ --1
+ --2
+ --3
+ --4
+ - 5
+ EOF
+ compare_diff_patch expected actual
+'
+
+test_expect_success 'combine diff coalesce tricky' '
+ >test &&
+ git add test &&
+ git commit -m initial --allow-empty &&
+ cat <<-\EOF >test &&
+ 3
+ 1
+ 2
+ 3
+ 4
+ EOF
+ git commit -a -m empty1 &&
+ git branch -f side1 &&
+ git checkout HEAD^ &&
+ cat <<-\EOF >test &&
+ 1
+ 3
+ 5
+ 4
+ EOF
+ git commit -a -m empty2 &&
+ git branch -f side2 &&
+ test_must_fail git merge side1 &&
+ >test &&
+ git commit -a -m merge &&
+ git show >actual.tmp &&
+ sed -e "1,/^@@@/d" < actual.tmp >actual &&
+ tr -d Q <<-\EOF >expected &&
+ -3
+ --1
+ -2
+ --3
+ - 5
+ --4
+ EOF
+ compare_diff_patch expected actual &&
+ git checkout -f side1 &&
+ test_must_fail git merge side2 &&
+ >test &&
+ git commit -a -m merge &&
+ git show >actual.tmp &&
+ sed -e "1,/^@@@/d" < actual.tmp >actual &&
+ tr -d Q <<-\EOF >expected &&
+ - 3
+ --1
+ - 2
+ --3
+ -5
+ --4
+ EOF
+ compare_diff_patch expected actual
+'
+
+test_expect_failure 'combine diff coalesce three parents' '
+ >test &&
+ git add test &&
+ git commit -m initial --allow-empty &&
+ cat <<-\EOF >test &&
+ 3
+ 1
+ 2
+ 3
+ 4
+ EOF
+ git commit -a -m empty1 &&
+ git checkout -B side1 &&
+ git checkout HEAD^ &&
+ cat <<-\EOF >test &&
+ 1
+ 3
+ 7
+ 5
+ 4
+ EOF
+ git commit -a -m empty2 &&
+ git branch -f side2 &&
+ git checkout HEAD^ &&
+ cat <<-\EOF >test &&
+ 3
+ 1
+ 6
+ 5
+ 4
+ EOF
+ git commit -a -m empty3 &&
+ >test &&
+ git add test &&
+ TREE=$(git write-tree) &&
+ COMMIT=$(git commit-tree -p HEAD -p side1 -p side2 -m merge $TREE) &&
+ git show $COMMIT >actual.tmp &&
+ sed -e "1,/^@@@/d" < actual.tmp >actual &&
+ tr -d Q <<-\EOF >expected &&
+ -- 3
+ ---1
+ - 6
+ - 2
+ --3
+ -7
+ - -5
+ ---4
+ EOF
+ compare_diff_patch expected actual
+'
+
test_done

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