patch 9.1.1009: diff feature can be improved

Problem: diff feature can be improved Solution: include the linematch diff alignment algorithm (Jonathon) closes: #9661 Signed-off-by: Jonathon <jonathonwhite@protonmail.com> Signed-off-by: Christian Brabandt <cb@256bit.org>
2025-01-12 09:58:00 +01:00
parent faf250c9e4
commit 7c7a4e6d1a
53 changed files with 2165 additions and 105 deletions
--- a/src/diff.c
+++ b/src/diff.c
@@ -37,6 +37,7 @@ static int diff_need_update = FALSE; // ex_diffupdate needs to be called
 #define DIFF_INTERNAL	0x200	// use internal xdiff algorithm
 #define DIFF_CLOSE_OFF	0x400	// diffoff when closing window
 #define DIFF_FOLLOWWRAP	0x800	// follow the wrap option
+#define DIFF_LINEMATCH  0x1000  // match most similar lines within diff
 #define ALL_WHITE_DIFF (DIFF_IWHITE | DIFF_IWHITEALL | DIFF_IWHITEEOL)
 static int	diff_flags = DIFF_INTERNAL | DIFF_FILLER | DIFF_CLOSE_OFF;

@@ -398,7 +399,8 @@ diff_mark_adjust_tp(
 	{
 	    // 6. change below line2: only adjust for amount_after; also when
 	    // "deleted" became zero when deleted all lines between two diffs
-	    if (dp->df_lnum[idx] - (deleted + inserted != 0) > line2)
+	    if (dp->df_lnum[idx] - (deleted + inserted != 0) > line2 -
+						(dp->is_linematched ? 1 : 0))
 	    {
 		if (amount_after == 0)
 		    break;	// nothing left to change
@@ -501,8 +503,9 @@ diff_mark_adjust_tp(
 	}

 	// check if this block touches the previous one, may merge them.
-	if (dprev != NULL && dprev->df_lnum[idx] + dprev->df_count[idx]
-							  == dp->df_lnum[idx])
+	if (dprev != NULL && !dp->is_linematched
+				&& dprev->df_lnum[idx] + dprev->df_count[idx]
+							== dp->df_lnum[idx])
 	{
 	    for (i = 0; i < DB_COUNT; ++i)
 		if (tp->tp_diffbuf[i] != NULL)
@@ -570,6 +573,7 @@ diff_alloc_new(tabpage_T *tp, diff_T *dprev, diff_T *dp)
    if (dnew == NULL)
 	return NULL;

+    dnew->is_linematched = FALSE;
    dnew->df_next = dp;
    if (dprev == NULL)
 	tp->tp_first_diff = dnew;
@@ -753,13 +757,16 @@ clear_diffout(diffout_T *dout)
 * Return FAIL for failure.
 */
    static int
-diff_write_buffer(buf_T *buf, diffin_T *din)
+diff_write_buffer(buf_T *buf, diffin_T *din, linenr_T start, linenr_T end)
 {
    linenr_T	lnum;
    char_u	*s;
    long	len = 0;
    char_u	*ptr;

+    if (end < 0)
+      end = buf->b_ml.ml_line_count;
+
    if (buf->b_ml.ml_flags & ML_EMPTY)
    {
 	din->din_mmfile.ptr = NULL;
@@ -768,7 +775,7 @@ diff_write_buffer(buf_T *buf, diffin_T *din)
    }

    // xdiff requires one big block of memory with all the text.
-    for (lnum = 1; lnum <= buf->b_ml.ml_line_count; ++lnum)
+    for (lnum = start; lnum <= end; ++lnum)
 	len += ml_get_buf_len(buf, lnum) + 1;
    ptr = alloc(len);
    if (ptr == NULL)
@@ -790,7 +797,7 @@ diff_write_buffer(buf_T *buf, diffin_T *din)
    din->din_mmfile.size = len;

    len = 0;
-    for (lnum = 1; lnum <= buf->b_ml.ml_line_count; ++lnum)
+    for (lnum = start; lnum <= end; ++lnum)
    {
 	for (s = ml_get_buf(buf, lnum, FALSE); *s != NUL; )
 	{
@@ -841,7 +848,7 @@ diff_write(buf_T *buf, diffin_T *din)
    int		save_cmod_flags;

    if (din->din_fname == NULL)
-	return diff_write_buffer(buf, din);
+	return diff_write_buffer(buf, din, 1, -1);

    // Always use 'fileformat' set to "unix".
    save_ff = buf->b_p_ff;
@@ -1922,6 +1929,360 @@ diff_clear(tabpage_T *tp)
    tp->tp_first_diff = NULL;
 }

+/*
+ *  return true if the options are set to use diff linematch
+ */
+    static int
+diff_linematch(diff_T *dp)
+{
+    if (!(diff_flags & DIFF_LINEMATCH))
+	return 0;
+
+    // are there more than three diff buffers?
+    int tsize = 0;
+    for (int i = 0; i < DB_COUNT; i++)
+    {
+	if (curtab->tp_diffbuf[i] != NULL)
+	{
+	    // for the rare case (bug?) that the count of a diff block is
+	    // negative, do not run the algorithm because this will try to
+	    // allocate a negative amount of space and crash
+	    if (dp->df_count[i] < 0)
+		return FALSE;
+	    tsize += dp->df_count[i];
+	}
+    }
+
+    // avoid allocating a huge array because it will lag
+    return tsize <= linematch_lines;
+}
+
+    static int
+get_max_diff_length(const diff_T *dp)
+{
+    int maxlength = 0;
+
+    for (int k = 0; k < DB_COUNT; k++)
+    {
+	if (curtab->tp_diffbuf[k] != NULL)
+	{
+	    if (dp->df_count[k] > maxlength)
+		maxlength = dp->df_count[k];
+	}
+    }
+    return maxlength;
+}
+
+    static void
+find_top_diff_block(
+    diff_T	**thistopdiff,
+    diff_T	**nextblockblock,
+    int		fromidx,
+    int		topline)
+{
+    diff_T	*topdiff = NULL;
+    diff_T	*localtopdiff = NULL;
+    int		topdiffchange = 0;
+
+    for (topdiff = curtab->tp_first_diff; topdiff != NULL;
+						topdiff = topdiff->df_next)
+    {
+	// set the top of the current overlapping diff block set as we
+	// iterate through all of the sets of overlapping diff blocks
+	if (!localtopdiff || topdiffchange)
+	{
+	    localtopdiff = topdiff;
+	    topdiffchange = 0;
+	}
+
+	// check if the fromwin topline is matched by the current diff. if so,
+	// set it to the top of the diff block
+	if (topline >= topdiff->df_lnum[fromidx] && topline <=
+		(topdiff->df_lnum[fromidx] + topdiff->df_count[fromidx]))
+	{
+	    // this line is inside the current diff block, so we will save the
+	    // top block of the set of blocks to refer to later
+	    if ((*thistopdiff) == NULL)
+		(*thistopdiff) = localtopdiff;
+	}
+
+	// check if the next set of overlapping diff blocks is next
+	if (!(topdiff->df_next && (topdiff->df_next->df_lnum[fromidx] ==
+			(topdiff->df_lnum[fromidx] +
+						topdiff->df_count[fromidx]))))
+	{
+	    // mark that the next diff block is belongs to a different set of
+	    // overlapping diff blocks
+	    topdiffchange = 1;
+
+	    // if we already have found that the line number is inside a diff
+	    // block, set the marker of the next block and finish the iteration
+	    if (*thistopdiff)
+	    {
+		(*nextblockblock) = topdiff->df_next;
+		break;
+	    }
+	}
+    }
+}
+
+    static void
+count_filler_lines_and_topline(
+    int			*curlinenum_to,
+    int			*linesfiller,
+    const diff_T	*thistopdiff,
+    const int		toidx,
+    int			virtual_lines_passed)
+{
+    const diff_T	*curdif = thistopdiff;
+    int			ch_virtual_lines = 0;
+    int			isfiller = FALSE;
+
+    while (virtual_lines_passed > 0)
+    {
+	if (ch_virtual_lines)
+	{
+	    virtual_lines_passed--;
+	    ch_virtual_lines--;
+	    if (!isfiller)
+		(*curlinenum_to)++;
+	    else
+		(*linesfiller)++;
+	}
+	else
+	{
+	    (*linesfiller) = 0;
+	    ch_virtual_lines = get_max_diff_length(curdif);
+	    isfiller = (curdif->df_count[toidx] ? FALSE : TRUE);
+	    if (isfiller)
+	    {
+		while (curdif && curdif->df_next &&
+		       curdif->df_lnum[toidx] ==
+					curdif->df_next->df_lnum[toidx] &&
+		       curdif->df_next->df_count[toidx] == 0)
+		{
+		    curdif = curdif->df_next;
+		    ch_virtual_lines += get_max_diff_length(curdif);
+		}
+	    }
+	    if (curdif)
+		curdif = curdif->df_next;
+	}
+    }
+}
+
+    static void
+calculate_topfill_and_topline(
+    const int	fromidx,
+    const int	toidx,
+    const int	from_topline,
+    const int	from_topfill,
+    int		*topfill,
+    linenr_T	*topline)
+{
+    // 1. find the position from the top of the diff block, and the start
+    // of the next diff block
+    diff_T	*thistopdiff = NULL;
+    diff_T	*nextblockblock = NULL;
+    int		virtual_lines_passed = 0;
+
+    find_top_diff_block(&thistopdiff, &nextblockblock, fromidx, from_topline);
+
+    // count the virtual lines that have been passed
+    diff_T *curdif = thistopdiff;
+    while (curdif && (curdif->df_lnum[fromidx] + curdif->df_count[fromidx])
+							<= from_topline)
+    {
+	virtual_lines_passed += get_max_diff_length(curdif);
+
+	curdif = curdif->df_next;
+    }
+
+    if (curdif != nextblockblock)
+	virtual_lines_passed += from_topline - curdif->df_lnum[fromidx];
+    virtual_lines_passed -= from_topfill;
+
+    // count the same amount of virtual lines in the toidx buffer
+    int curlinenum_to = thistopdiff->df_lnum[toidx];
+    int linesfiller = 0;
+
+    count_filler_lines_and_topline(&curlinenum_to, &linesfiller, thistopdiff,
+				   toidx, virtual_lines_passed);
+
+    // count the number of filler lines that would normally be above this line
+    int maxfiller = 0;
+    for (diff_T *dpfillertest = thistopdiff; dpfillertest != NULL;
+					dpfillertest = dpfillertest->df_next)
+    {
+	if (dpfillertest->df_lnum[toidx] == curlinenum_to)
+	{
+	    while (dpfillertest && dpfillertest->df_lnum[toidx] ==
+							curlinenum_to)
+	    {
+		maxfiller += dpfillertest->df_count[toidx] ? 0 :
+					get_max_diff_length(dpfillertest);
+		dpfillertest = dpfillertest->df_next;
+	    }
+	    break;
+	}
+    }
+    (*topfill) = maxfiller - linesfiller;
+    (*topline) = curlinenum_to;
+}
+
+    static int
+linematched_filler_lines(diff_T *dp, int idx, linenr_T lnum, int *linestatus)
+{
+    int filler_lines_d1 = 0;
+
+    while (dp && dp->df_next &&
+	   lnum == (dp->df_lnum[idx] + dp->df_count[idx]) &&
+	   dp->df_next->df_lnum[idx] == lnum)
+    {
+	if (dp->df_count[idx] == 0)
+	    filler_lines_d1 += get_max_diff_length(dp);
+	dp = dp->df_next;
+    }
+
+    if (dp->df_count[idx] == 0)
+	filler_lines_d1 += get_max_diff_length(dp);
+
+    if (lnum < dp->df_lnum[idx] + dp->df_count[idx])
+    {
+	int j = 0;
+
+	for (int i = 0; i < DB_COUNT; i++)
+	{
+	    if (curtab->tp_diffbuf[i] != NULL)
+	    {
+		if (dp->df_count[i])
+		    j++;
+	    }
+	    // is this an added line or a changed line?
+	    if (linestatus)
+		(*linestatus) = (j == 1) ? -2 : -1;
+	}
+    }
+
+    return filler_lines_d1;
+}
+
+// Apply results from the linematch algorithm and apply to 'dp' by splitting it
+// into multiple adjacent diff blocks.
+    static void
+apply_linematch_results(
+    diff_T	*dp,
+    size_t	decisions_length,
+    const int	*decisions)
+{
+    // get the start line number here in each diff buffer, and then increment
+    int		line_numbers[DB_COUNT];
+    int		outputmap[DB_COUNT];
+    size_t	ndiffs = 0;
+
+    for (int i = 0; i < DB_COUNT; i++)
+    {
+	if (curtab->tp_diffbuf[i] != NULL)
+	{
+	    line_numbers[i] = dp->df_lnum[i];
+	    dp->df_count[i] = 0;
+
+	    // Keep track of the index of the diff buffer we are using here.
+	    // We will use this to write the output of the algorithm to
+	    // diff_T structs at the correct indexes
+	    outputmap[ndiffs] = i;
+	    ndiffs++;
+	}
+    }
+
+    // write the diffs starting with the current diff block
+    diff_T *dp_s = dp;
+    for (size_t i = 0; i < decisions_length; i++)
+    {
+	// Don't allocate on first iter since we can reuse the initial
+	// diffblock
+	if (i != 0 && (decisions[i - 1] != decisions[i]))
+	{
+	    // create new sub diff blocks to segment the original diff block
+	    // which we further divided by running the linematch algorithm
+	    dp_s = diff_alloc_new(curtab, dp_s, dp_s->df_next);
+	    dp_s->is_linematched = TRUE;
+	    for (int j = 0; j < DB_COUNT; j++)
+	    {
+		if (curtab->tp_diffbuf[j] != NULL)
+		{
+		    dp_s->df_lnum[j] = line_numbers[j];
+		    dp_s->df_count[j] = 0;
+		}
+	    }
+	}
+	for (size_t j = 0; j < ndiffs; j++)
+	{
+	    if (decisions[i] & (1 << j))
+	    {
+		// will need to use the map here
+		dp_s->df_count[outputmap[j]]++;
+		line_numbers[outputmap[j]]++;
+	    }
+	}
+    }
+    dp->is_linematched = TRUE;
+}
+
+    static void
+run_linematch_algorithm(diff_T *dp)
+{
+    // define buffers for diff algorithm
+    diffin_T		diffbufs_mm[DB_COUNT];
+    const mmfile_t	*diffbufs[DB_COUNT];
+    int			diff_length[DB_COUNT];
+    size_t		ndiffs = 0;
+
+    for (int i = 0; i < DB_COUNT; i++)
+    {
+	if (curtab->tp_diffbuf[i] != NULL)
+	{
+	    // write the contents of the entire buffer to
+	    // diffbufs_mm[diffbuffers_count]
+	    if (dp->df_count[i] > 0)
+	    {
+		diff_write_buffer(curtab->tp_diffbuf[i], &diffbufs_mm[ndiffs],
+			dp->df_lnum[i], dp->df_lnum[i] + dp->df_count[i] - 1);
+	    }
+	    else
+	    {
+		diffbufs_mm[ndiffs].din_mmfile.size = 0;
+		diffbufs_mm[ndiffs].din_mmfile.ptr = NULL;
+	    }
+
+	    diffbufs[ndiffs] = &diffbufs_mm[ndiffs].din_mmfile;
+
+	    // keep track of the length of this diff block to pass it to the
+	    // linematch algorithm
+	    diff_length[ndiffs] = dp->df_count[i];
+
+	    // increment the amount of diff buffers we are passing to the
+	    // algorithm
+	    ndiffs++;
+	}
+    }
+
+    // we will get the output of the linematch algorithm in the format of an
+    // array of integers (*decisions) and the length of that array
+    // (decisions_length)
+    int *decisions = NULL;
+    const int iwhite = (diff_flags & (DIFF_IWHITEALL | DIFF_IWHITE)) > 0 ? 1 : 0;
+    size_t decisions_length =
+	linematch_nbuffers(diffbufs, diff_length, ndiffs, &decisions, iwhite);
+
+    for (size_t i = 0; i < ndiffs; i++)
+	free(diffbufs_mm[i].din_mmfile.ptr); // TODO should this be vim_free ?
+
+    apply_linematch_results(dp, decisions_length, decisions);
+
+    free(decisions);
+}
+
 /*
 * Check diff status for line "lnum" in buffer "buf":
 * Returns 0 for nothing special
@@ -1930,9 +2291,15 @@ diff_clear(tabpage_T *tp)
 * Returns > 0 for inserting that many filler lines above it (never happens
 * when 'diffopt' doesn't contain "filler").
 * This should only be used for windows where 'diff' is set.
+ * When diffopt contains linematch, a changed/added/deleted line
+ * may also have filler lines above it. In such a case, the possibilities
+ * are no longer mutually exclusive. The number of filler lines is
+ * returned from diff_check, and the integer 'linestatus' passed by
+ * pointer is set to -1 to indicate a changed line, and -2 to indicate an
+ * added line
 */
    int
-diff_check(win_T *wp, linenr_T lnum)
+diff_check_with_linestatus(win_T *wp, linenr_T lnum, int *linestatus)
 {
    int		idx;		// index in tp_diffbuf[] for this buffer
    diff_T	*dp;
@@ -1968,6 +2335,15 @@ diff_check(win_T *wp, linenr_T lnum)
    if (dp == NULL || lnum < dp->df_lnum[idx])
 	return 0;

+    // Don't run linematch when lnum is offscreen.  Useful for scrollbind
+    // calculations which need to count all the filler lines above the screen.
+    if (lnum >= wp->w_topline && lnum < wp->w_botline
+				&& !dp->is_linematched && diff_linematch(dp))
+      run_linematch_algorithm(dp);
+
+    if (dp->is_linematched)
+      return linematched_filler_lines(dp, idx, lnum, linestatus);
+
    if (lnum < dp->df_lnum[idx] + dp->df_count[idx])
    {
 	int	zero = FALSE;
@@ -2014,13 +2390,16 @@ diff_check(win_T *wp, linenr_T lnum)

    // Insert filler lines above the line just below the change.  Will return
    // 0 when this buf had the max count.
-    maxcount = 0;
-    for (i = 0; i < DB_COUNT; ++i)
-	if (curtab->tp_diffbuf[i] != NULL && dp->df_count[i] > maxcount)
-	    maxcount = dp->df_count[i];
+    maxcount = get_max_diff_length(dp);
    return maxcount - dp->df_count[idx];
 }

+    int
+diff_check(win_T *wp, linenr_T lnum)
+{
+    return diff_check_with_linestatus(wp, lnum, NULL);
+}
+
 /*
 * Compare two entries in diff "*dp" and return TRUE if they are equal.
 */
@@ -2194,53 +2573,64 @@ diff_set_topline(win_T *fromwin, win_T *towin)
 	towin->w_topline = lnum + (dp->df_lnum[toidx] - dp->df_lnum[fromidx]);
 	if (lnum >= dp->df_lnum[fromidx])
 	{
-	    // Inside a change: compute filler lines. With three or more
-	    // buffers we need to know the largest count.
-	    max_count = 0;
-	    for (i = 0; i < DB_COUNT; ++i)
-		if (curtab->tp_diffbuf[i] != NULL
-					       && max_count < dp->df_count[i])
-		    max_count = dp->df_count[i];
+	    if (dp->is_linematched)
+	    {
+		calculate_topfill_and_topline(fromidx, toidx,
+						fromwin->w_topline,
+						fromwin->w_topfill,
+						&towin->w_topfill,
+						&towin->w_topline);
+	    }
+	    else
+	    {
+		// Inside a change: compute filler lines. With three or more
+		// buffers we need to know the largest count.
+		max_count = 0;
+		for (i = 0; i < DB_COUNT; ++i)
+		    if (curtab->tp_diffbuf[i] != NULL
+						   && max_count < dp->df_count[i])
+			max_count = dp->df_count[i];

-	    if (dp->df_count[toidx] == dp->df_count[fromidx])
-	    {
-		// same number of lines: use same filler count
-		towin->w_topfill = fromwin->w_topfill;
-	    }
-	    else if (dp->df_count[toidx] > dp->df_count[fromidx])
-	    {
-		if (lnum == dp->df_lnum[fromidx] + dp->df_count[fromidx])
+		if (dp->df_count[toidx] == dp->df_count[fromidx])
 		{
-		    // more lines in towin and fromwin doesn't show diff
-		    // lines, only filler lines
-		    if (max_count - fromwin->w_topfill >= dp->df_count[toidx])
-		    {
-			// towin also only shows filler lines
-			towin->w_topline = dp->df_lnum[toidx]
-						       + dp->df_count[toidx];
-			towin->w_topfill = fromwin->w_topfill;
-		    }
-		    else
-			// towin still has some diff lines to show
-			towin->w_topline = dp->df_lnum[toidx]
-					     + max_count - fromwin->w_topfill;
+		    // same number of lines: use same filler count
+		    towin->w_topfill = fromwin->w_topfill;
 		}
-	    }
-	    else if (towin->w_topline >= dp->df_lnum[toidx]
-							+ dp->df_count[toidx])
-	    {
-		// less lines in towin and no diff lines to show: compute
-		// filler lines
-		towin->w_topline = dp->df_lnum[toidx] + dp->df_count[toidx];
-		if (diff_flags & DIFF_FILLER)
+		else if (dp->df_count[toidx] > dp->df_count[fromidx])
 		{
 		    if (lnum == dp->df_lnum[fromidx] + dp->df_count[fromidx])
-			// fromwin is also out of diff lines
-			towin->w_topfill = fromwin->w_topfill;
-		    else
-			// fromwin has some diff lines
-			towin->w_topfill = dp->df_lnum[fromidx]
-							   + max_count - lnum;
+		    {
+			// more lines in towin and fromwin doesn't show diff
+			// lines, only filler lines
+			if (max_count - fromwin->w_topfill >= dp->df_count[toidx])
+			{
+			    // towin also only shows filler lines
+			    towin->w_topline = dp->df_lnum[toidx]
+							   + dp->df_count[toidx];
+			    towin->w_topfill = fromwin->w_topfill;
+			}
+			else
+			    // towin still has some diff lines to show
+			    towin->w_topline = dp->df_lnum[toidx]
+						 + max_count - fromwin->w_topfill;
+		    }
+		}
+		else if (towin->w_topline >= dp->df_lnum[toidx]
+							    + dp->df_count[toidx])
+		{
+		    // less lines in towin and no diff lines to show: compute
+		    // filler lines
+		    towin->w_topline = dp->df_lnum[toidx] + dp->df_count[toidx];
+		    if (diff_flags & DIFF_FILLER)
+		    {
+			if (lnum == dp->df_lnum[fromidx] + dp->df_count[fromidx])
+			    // fromwin is also out of diff lines
+			    towin->w_topfill = fromwin->w_topfill;
+			else
+			    // fromwin has some diff lines
+			    towin->w_topfill = dp->df_lnum[fromidx] +
+							max_count - lnum;
+		    }
 		}
 	    }
 	}
@@ -2278,6 +2668,7 @@ diffopt_changed(void)
 {
    char_u	*p;
    int		diff_context_new = 6;
+    int		linematch_lines_new = 0;
    int		diff_flags_new = 0;
    int		diff_foldcolumn_new = 2;
    long	diff_algorithm_new = 0;
@@ -2390,6 +2781,12 @@ diffopt_changed(void)
 	    else
 		return FAIL;
 	}
+	else if (STRNCMP(p, "linematch:", 10) == 0 && VIM_ISDIGIT(p[11]))
+	{
+	    p += 10;
+	    linematch_lines_new = getdigits(&p);
+	    diff_flags_new |= DIFF_LINEMATCH;
+	}

 	if (*p != ',' && *p != NUL)
 	    return FAIL;
@@ -2411,6 +2808,7 @@ diffopt_changed(void)

    diff_flags = diff_flags_new;
    diff_context = diff_context_new == 0 ? 1 : diff_context_new;
+    linematch_lines = linematch_lines_new;
    diff_foldcolumn = diff_foldcolumn_new;
    diff_algorithm = diff_algorithm_new;

@@ -2489,6 +2887,13 @@ diff_find_change(
    FOR_ALL_DIFFBLOCKS_IN_TAB(curtab, dp)
 	if (lnum <= dp->df_lnum[idx] + dp->df_count[idx])
 	    break;
+    if (dp->is_linematched)
+    {
+	while (dp && dp->df_next
+			&& lnum == dp->df_count[idx] + dp->df_lnum[idx]
+			&& dp->df_next->df_lnum[idx] == lnum)
+	    dp = dp->df_next;
+    }
    if (dp == NULL || diff_check_sanity(curtab, dp) == FAIL)
    {
 	vim_free(line_org);
@@ -2829,6 +3234,19 @@ ex_diffgetput(exarg_T *eap)
    dprev = NULL;
    for (dp = curtab->tp_first_diff; dp != NULL; )
    {
+	if (!eap->addr_count)
+	{
+	    // handle the case with adjacent diff blocks
+	    while (dp->is_linematched
+		    && dp->df_next
+		    && dp->df_next->df_lnum[idx_cur] == dp->df_lnum[idx_cur] +
+							dp->df_count[idx_cur]
+		    && dp->df_next->df_lnum[idx_cur] == eap->line1 + off + 1)
+	    {
+		dprev = dp;
+		dp = dp->df_next;
+	    }
+	}
 	if (dp->df_lnum[idx_cur] > eap->line2 + off)
 	    break;	// past the range that was specified

@@ -3445,10 +3863,11 @@ f_diff_hlID(typval_T *argvars UNUSED, typval_T *rettv UNUSED)
 	    || fnum != curbuf->b_fnum)
    {
 	// New line, buffer, change: need to get the values.
-	filler_lines = diff_check(curwin, lnum);
-	if (filler_lines < 0)
+	int linestatus = 0;
+	filler_lines = diff_check_with_linestatus(curwin, lnum, &linestatus);
+	if (filler_lines < 0 || linestatus < 0)
 	{
-	    if (filler_lines == -1)
+	    if (filler_lines == -1 || linestatus == -1)
 	    {
 		change_start = MAXCOL;
 		change_end = -1;