line-log: route -L output through the standard diff pipeline

Documentation/line-range-options.adoc

@@ -12,4 +12,8 @@
 	(namely `--raw`, `--numstat`, `--shortstat`, `--dirstat`, `--summary`,
 	`--name-only`, `--name-status`, `--check`) are not currently implemented.
 +
+Patch formatting options such as `--word-diff`, `--color-moved`,
+`--no-prefix`, and whitespace options (`-w`, `-b`) are supported,
+as are pickaxe options (`-S`, `-G`).
++
 include::line-range-format.adoc[]

diff.c

@@ -608,6 +608,52 @@ struct emit_callback {
 	struct strbuf *header;
 };
 
+/*
+ * State for the line-range callback wrappers that sit between
+ * xdi_diff_outf() and fn_out_consume().  xdiff produces a normal,
+ * unfiltered diff; the wrappers intercept each hunk header and line,
+ * track post-image position, and forward only lines that fall within
+ * the requested ranges.  Contiguous in-range lines are collected into
+ * range hunks and flushed with a synthetic @@ header so that
+ * fn_out_consume() sees well-formed unified-diff fragments.
+ *
+ * Removal lines ('-') cannot be classified by post-image position, so
+ * they are buffered in pending_rm until the next '+' or ' ' line
+ * reveals whether they precede an in-range line (flush into range hunk) or
+ * an out-of-range line (discard).
+ */
+struct line_range_callback {
+	xdiff_emit_line_fn orig_line_fn;
+	void *orig_cb_data;
+	const struct range_set *ranges;	/* 0-based [start, end) */
+	unsigned int cur_range;		/* index into the range_set */
+
+	/* Post/pre-image line counters (1-based, set from hunk headers) */
+	long lno_post;
+	long lno_pre;
+
+	/*
+	 * Function name from most recent xdiff hunk header;
+	 * size matches struct func_line.buf in xdiff/xemit.c.
+	 */
+	char func[80];
+	long funclen;
+
+	/* Range hunk being accumulated for the current range */
+	struct strbuf rhunk;
+	long rhunk_old_begin, rhunk_old_count;
+	long rhunk_new_begin, rhunk_new_count;
+	int rhunk_active;
+	int rhunk_has_changes;		/* any '+' or '-' lines? */
+
+	/* Removal lines not yet known to be in-range */
+	struct strbuf pending_rm;
+	int pending_rm_count;
+	long pending_rm_pre_begin;	/* pre-image line of first pending */
+
+	int ret;			/* latched error from orig_line_fn */
+};
+
 static int count_lines(const char *data, int size)
 {
 	int count, ch, completely_empty = 1, nl_just_seen = 0;
@@ -2486,6 +2532,188 @@ static int quick_consume(void *priv, char *line UNUSED, unsigned long len UNUSED
 	return 1;
 }
 
+static void discard_pending_rm(struct line_range_callback *s)
+{
+	strbuf_reset(&s->pending_rm);
+	s->pending_rm_count = 0;
+}
+
+static void flush_rhunk(struct line_range_callback *s)
+{
+	struct strbuf hdr = STRBUF_INIT;
+	const char *p, *end;
+
+	if (!s->rhunk_active || s->ret)
+		return;
+
+	/* Drain any pending removal lines into the range hunk */
+	if (s->pending_rm_count) {
+		strbuf_addbuf(&s->rhunk, &s->pending_rm);
+		s->rhunk_old_count += s->pending_rm_count;
+		s->rhunk_has_changes = 1;
+		discard_pending_rm(s);
+	}
+
+	/*
+	 * Suppress context-only hunks: they contain no actual changes
+	 * and would just be noise.  This can happen when the inflated
+	 * ctxlen causes xdiff to emit context covering a range that
+	 * has no changes in this commit.
+	 */
+	if (!s->rhunk_has_changes) {
+		s->rhunk_active = 0;
+		strbuf_reset(&s->rhunk);
+		return;
+	}
+
+	strbuf_addf(&hdr, "@@ -%ld,%ld +%ld,%ld @@",
+		    s->rhunk_old_begin, s->rhunk_old_count,
+		    s->rhunk_new_begin, s->rhunk_new_count);
+	if (s->funclen > 0) {
+		strbuf_addch(&hdr, ' ');
+		strbuf_add(&hdr, s->func, s->funclen);
+	}
+	strbuf_addch(&hdr, '\n');
+
+	s->ret = s->orig_line_fn(s->orig_cb_data, hdr.buf, hdr.len);
+	strbuf_release(&hdr);
+
+	/*
+	 * Replay buffered lines one at a time through fn_out_consume.
+	 * The cast discards const because xdiff_emit_line_fn takes
+	 * char *, though fn_out_consume does not modify the buffer.
+	 */
+	p = s->rhunk.buf;
+	end = p + s->rhunk.len;
+	while (!s->ret && p < end) {
+		const char *eol = memchr(p, '\n', end - p);
+		unsigned long line_len = eol ? (unsigned long)(eol - p + 1)
+					     : (unsigned long)(end - p);
+		s->ret = s->orig_line_fn(s->orig_cb_data, (char *)p, line_len);
+		p += line_len;
+	}
+
+	s->rhunk_active = 0;
+	strbuf_reset(&s->rhunk);
+}
+
+static void line_range_hunk_fn(void *data,
+			       long old_begin, long old_nr UNUSED,
+			       long new_begin, long new_nr UNUSED,
+			       const char *func, long funclen)
+{
+	struct line_range_callback *s = data;
+
+	/*
+	 * When count > 0, begin is 1-based.  When count == 0, begin is
+	 * adjusted down by 1 by xdl_emit_hunk_hdr(), but no lines of
+	 * that type will arrive, so the value is unused.
+	 *
+	 * Any pending removal lines from the previous xdiff hunk are
+	 * intentionally left in pending_rm: the line callback will
+	 * flush or discard them when the next content line reveals
+	 * whether the removals precede in-range content.
+	 */
+	s->lno_post = new_begin;
+	s->lno_pre = old_begin;
+
+	if (funclen > 0) {
+		if (funclen > (long)sizeof(s->func))
+			funclen = sizeof(s->func);
+		memcpy(s->func, func, funclen);
+	}
+	s->funclen = funclen;
+}
+
+static int line_range_line_fn(void *priv, char *line, unsigned long len)
+{
+	struct line_range_callback *s = priv;
+	const struct range *cur;
+	long lno_0, cur_pre;
+
+	if (s->ret)
+		return s->ret;
+
+	if (line[0] == '-') {
+		if (!s->pending_rm_count)
+			s->pending_rm_pre_begin = s->lno_pre;
+		s->lno_pre++;
+		strbuf_add(&s->pending_rm, line, len);
+		s->pending_rm_count++;
+		return s->ret;
+	}
+
+	if (line[0] == '\\') {
+		if (s->pending_rm_count)
+			strbuf_add(&s->pending_rm, line, len);
+		else if (s->rhunk_active)
+			strbuf_add(&s->rhunk, line, len);
+		/* otherwise outside tracked range; drop silently */
+		return s->ret;
+	}
+
+	if (line[0] != '+' && line[0] != ' ')
+		BUG("unexpected diff line type '%c'", line[0]);
+
+	lno_0 = s->lno_post - 1;
+	cur_pre = s->lno_pre;	/* save before advancing for context lines */
+	s->lno_post++;
+	if (line[0] == ' ')
+		s->lno_pre++;
+
+	/* Advance past ranges we've passed */
+	while (s->cur_range < s->ranges->nr &&
+	       lno_0 >= s->ranges->ranges[s->cur_range].end) {
+		if (s->rhunk_active)
+			flush_rhunk(s);
+		discard_pending_rm(s);
+		s->cur_range++;
+	}
+
+	/* Past all ranges */
+	if (s->cur_range >= s->ranges->nr) {
+		discard_pending_rm(s);
+		return s->ret;
+	}
+
+	cur = &s->ranges->ranges[s->cur_range];
+
+	/* Before current range */
+	if (lno_0 < cur->start) {
+		discard_pending_rm(s);
+		return s->ret;
+	}
+
+	/* In range so start a new range hunk if needed */
+	if (!s->rhunk_active) {
+		s->rhunk_active = 1;
+		s->rhunk_has_changes = 0;
+		s->rhunk_new_begin = lno_0 + 1;
+		s->rhunk_old_begin = s->pending_rm_count
+			? s->pending_rm_pre_begin : cur_pre;
+		s->rhunk_old_count = 0;
+		s->rhunk_new_count = 0;
+		strbuf_reset(&s->rhunk);
+	}
+
+	/* Flush pending removals into range hunk */
+	if (s->pending_rm_count) {
+		strbuf_addbuf(&s->rhunk, &s->pending_rm);
+		s->rhunk_old_count += s->pending_rm_count;
+		s->rhunk_has_changes = 1;
+		discard_pending_rm(s);
+	}
+
+	strbuf_add(&s->rhunk, line, len);
+	s->rhunk_new_count++;
+	if (line[0] == '+')
+		s->rhunk_has_changes = 1;
+	else
+		s->rhunk_old_count++;
+
+	return s->ret;
+}
+
 static void pprint_rename(struct strbuf *name, const char *a, const char *b)
 {
 	const char *old_name = a;
@@ -3589,7 +3817,8 @@ static void builtin_diff(const char *name_a,
 			 const char *xfrm_msg,
 			 int must_show_header,
 			 struct diff_options *o,
-			 int complete_rewrite)
+			 int complete_rewrite,
+			 const struct range_set *line_ranges)
 {
 	mmfile_t mf1, mf2;
 	const char *lbl[2];
@@ -3823,6 +4052,52 @@ static void builtin_diff(const char *name_a,
 			 */
 			xdi_diff_outf(&mf1, &mf2, NULL, quick_consume,
 				      &ecbdata, &xpp, &xecfg);
+		} else if (line_ranges) {
+			struct line_range_callback lr_state;
+			unsigned int i;
+			long max_span = 0;
+
+			memset(&lr_state, 0, sizeof(lr_state));
+			lr_state.orig_line_fn = fn_out_consume;
+			lr_state.orig_cb_data = &ecbdata;
+			lr_state.ranges = line_ranges;
+			strbuf_init(&lr_state.rhunk, 0);
+			strbuf_init(&lr_state.pending_rm, 0);
+
+			/*
+			 * Inflate ctxlen so that all changes within
+			 * any single range are merged into one xdiff
+			 * hunk and the inter-change context is emitted.
+			 * The callback clips back to range boundaries.
+			 *
+			 * The optimal ctxlen depends on where changes
+			 * fall within the range, which is only known
+			 * after xdiff runs; the max range span is the
+			 * upper bound that guarantees correctness in a
+			 * single pass.
+			 */
+			for (i = 0; i < line_ranges->nr; i++) {
+				long span = line_ranges->ranges[i].end -
+					    line_ranges->ranges[i].start;
+				if (span > max_span)
+					max_span = span;
+			}
+			if (max_span > xecfg.ctxlen)
+				xecfg.ctxlen = max_span;
+
+			if (xdi_diff_outf(&mf1, &mf2,
+					  line_range_hunk_fn,
+					  line_range_line_fn,
+					  &lr_state, &xpp, &xecfg))
+				die("unable to generate diff for %s",
+				    one->path);
+
+			flush_rhunk(&lr_state);
+			if (lr_state.ret)
+				die("unable to generate diff for %s",
+				    one->path);
+			strbuf_release(&lr_state.rhunk);
+			strbuf_release(&lr_state.pending_rm);
 		} else if (xdi_diff_outf(&mf1, &mf2, NULL, fn_out_consume,
 					 &ecbdata, &xpp, &xecfg))
 			die("unable to generate diff for %s", one->path);
@@ -4660,7 +4935,7 @@ static void run_diff_cmd(const struct external_diff *pgm,
 
 		builtin_diff(name, other ? other : name,
 			     one, two, xfrm_msg, must_show_header,
-			     o, complete_rewrite);
+			     o, complete_rewrite, p->line_ranges);
 		if (p->status == DIFF_STATUS_COPIED ||
 		    p->status == DIFF_STATUS_RENAMED)
 			o->found_changes = 1;

diffcore.h

@@ -19,6 +19,17 @@ struct userdiff_driver;
  * in anything else.
  */
 
+/* A range [start, end).  Lines are numbered starting at 0. */
+struct range {
+	long start, end;
+};
+
+/* A set of ranges.  The ranges must always be disjoint and sorted. */
+struct range_set {
+	unsigned int alloc, nr;
+	struct range *ranges;
+};
+
 /* We internally use unsigned short as the score value,
  * and rely on an int capable to hold 32-bits.  -B can take
  * -Bmerge_score/break_score format and the two scores are
@@ -106,6 +117,11 @@ int diff_filespec_is_binary(struct repository *, struct diff_filespec *);
 struct diff_filepair {
 	struct diff_filespec *one;
 	struct diff_filespec *two;
+	/*
+	 * Tracked line ranges for -L filtering; borrowed from
+	 * line_log_data and must not be freed.
+	 */
+	const struct range_set *line_ranges;
 	unsigned short int score;
 	char status; /* M C R A D U etc. (see Documentation/diff-format.adoc or DIFF_STATUS_* in diff.h) */
 	unsigned broken_pair : 1;