[RFC/PATCH 16/17] diff: buffer output in emit_line_0

[Stefan Beller <sbeller@google.com>]

emit_line_0 factors out the emission part into emit_line_emission,
and depending on the diff_options->use_buffer the emission
will be performed directly when calling emit_line_0 or after the
whole process is done, i.e. by buffering we have add the possibility
for a second pass over the whole output before doing the actual
output.

In 6440d34 (2012-03-14, diff: tweak a _copy_ of diff_options with
word-diff) we introduced a duplicate diff options struct for word
emissions as we may have different regex settings in there.

When buffering the output, we need to operate on just one buffer,
so we have to copy back the emissions of the word buffer into the main
buffer.

Unconditionally enable output via buffer in this patch as it yields
a great opportunity for testing, i.e. all the diff tests from the
test suite pass without having reordering issues (i.e. only parts
of the output got buffered, and we forgot to buffer other parts).
The test suite passes, which gives confidence that we converted all
functions to use emit_line_* for output.

Signed-off-by: Stefan Beller <sbeller@google.com>
---
 diff.c | 151 +++++++++++++++++++++++++++++++++++++++++++++++++++++------------
 diff.h |  18 ++++++++
 2 files changed, 142 insertions(+), 27 deletions(-)

diff --git a/diff.c b/diff.c
index 68da135..e240e89 100644
--- a/diff.c
+++ b/diff.c
@@ -449,42 +449,86 @@ static void check_blank_at_eof(mmfile_t *mf1, mmfile_t *mf2,
 	ecbdata->blank_at_eof_in_postimage = (at - l2) + 1;
 }
 
-static void emit_line_0(struct diff_options *o, const char *set, const char *reset,
-			int first, const char *line, int len)
+static void emit_line_emission(struct diff_options *o, struct line_emission *e)
 {
-	int has_trailing_newline, has_trailing_carriage_return;
-	int nofirst;
 	FILE *file = o->file;
 
 	fputs(diff_line_prefix(o), file);
 
+	if (e->len || e->first) {
+		if (e->set)
+			fputs(e->set, file);
+		if (e->first)
+			fputc(e->first, file);
+		if (e->whitespace_check) {
+			if (e->reset)
+				fputs(e->reset, file);
+			ws_check_emit(e->line, e->len, e->ws_rule,
+				      file, e->set, e->reset, e->ws);
+		} else {
+			fwrite(e->line, e->len, 1, file);
+			if (e->reset)
+				fputs(e->reset, file);
+		}
+	}
+	if (e->has_trailing_carriage_return)
+		fputc('\r', file);
+	if (e->has_trailing_newline)
+		fputc('\n', file);
+}
+
+static void free_line_emission(struct line_emission *e)
+{
+	/*
+	 * No need to free set, reset, ws as they always point to the
+	 * diff_colors[] static array. We don't own that memory.
+	 */
+	free((char*)e->line);
+}
+
+static void append_line_emission_to_buffer(struct diff_options *o,
+			     struct line_emission *e)
+{
+	struct line_emission *f;
+	ALLOC_GROW(o->line_buffer,
+		   o->line_buffer_nr + 1,
+		   o->line_buffer_alloc);
+	f = &o->line_buffer[o->line_buffer_nr++];
+	memcpy(f, e, sizeof(*e));
+
+	/* duplicate the line for now as it is not a stable pointer */
+	f->line = xmemdupz(e->line, e->len);
+}
+
+static void emit_line_0(struct diff_options *o, const char *set,
+			const char *reset, int first, const char *line, int len)
+{
+	int nofirst;
+	struct line_emission e = LINE_EMISSION_INIT;
+
 	if (len == 0) {
-		has_trailing_newline = (first == '\n');
-		has_trailing_carriage_return = (first == '\r');
-		nofirst = has_trailing_newline || has_trailing_carriage_return;
+		e.has_trailing_newline = (first == '\n');
+		e.has_trailing_carriage_return = (first == '\r');
+		nofirst = e.has_trailing_newline || e.has_trailing_carriage_return;
 	} else {
-		has_trailing_newline = (len > 0 && line[len-1] == '\n');
-		if (has_trailing_newline)
+		e.has_trailing_newline = (len > 0 && line[len-1] == '\n');
+		if (e.has_trailing_newline)
 			len--;
-		has_trailing_carriage_return = (len > 0 && line[len-1] == '\r');
-		if (has_trailing_carriage_return)
+		e.has_trailing_carriage_return = (len > 0 && line[len-1] == '\r');
+		if (e.has_trailing_carriage_return)
 			len--;
 		nofirst = 0;
 	}
 
-	if (len || !nofirst) {
-		if (set)
-			fputs(set, file);
-		if (!nofirst)
-			fputc(first, file);
-		fwrite(line, len, 1, file);
-		if (reset)
-			fputs(reset, file);
-	}
-	if (has_trailing_carriage_return)
-		fputc('\r', file);
-	if (has_trailing_newline)
-		fputc('\n', file);
+	e.set = set;
+	e.first = !nofirst ? first : 0;
+	e.line = line;
+	e.len = len;
+	e.reset = reset;
+	if (!o->use_buffer)
+		emit_line_emission(o, &e);
+	else
+		append_line_emission_to_buffer(o, &e);
 }
 
 static void emit_line(struct diff_options *o, const char *set, const char *reset,
@@ -540,9 +584,22 @@ static void emit_line_checked(const char *reset,
 		emit_line_0(ecbdata->opt, ws, reset, sign, line, len);
 	else {
 		/* Emit just the prefix, then the rest. */
-		emit_line_0(ecbdata->opt, set, reset, sign, "", 0);
-		ws_check_emit(line, len, ecbdata->ws_rule,
-			      ecbdata->opt->file, set, reset, ws);
+		if (ecbdata->opt->use_buffer) {
+			struct line_emission e;
+			e.line = line;
+			e.len = len;
+			e.ws_rule = ecbdata->ws_rule;
+			e.set = set;
+			e.reset = reset;
+			e.ws = ws;
+			e.whitespace_check = 1;
+			e.first = sign;
+			append_line_emission_to_buffer(ecbdata->opt, &e);
+		} else {
+			emit_line_0(ecbdata->opt, set, reset, sign, "", 0);
+			ws_check_emit(line, len, ecbdata->ws_rule,
+				      ecbdata->opt->file, set, reset, ws);
+		}
 	}
 }
 
@@ -1093,6 +1150,22 @@ static void diff_words_flush(struct emit_callback *ecbdata)
 	if (ecbdata->diff_words->minus.text.size ||
 	    ecbdata->diff_words->plus.text.size)
 		diff_words_show(ecbdata->diff_words);
+
+	if (ecbdata->diff_words->opt->line_buffer_nr) {
+		int i;
+		for (i = 0; i < ecbdata->diff_words->opt->line_buffer_nr; i++) {
+			struct line_emission *e =
+				&ecbdata->diff_words->opt->line_buffer[i];
+			ALLOC_GROW(ecbdata->opt->line_buffer,
+				   ecbdata->opt->line_buffer_nr + 1,
+				   ecbdata->opt->line_buffer_alloc);
+			memcpy(&ecbdata->opt->line_buffer
+					[ecbdata->opt->line_buffer_nr],
+				e, sizeof(*e));
+			ecbdata->opt->line_buffer_nr++;
+		}
+		ecbdata->diff_words->opt->line_buffer_nr = 0;
+	}
 }
 
 static void diff_filespec_load_driver(struct diff_filespec *one)
@@ -1128,6 +1201,12 @@ static void init_diff_words_data(struct emit_callback *ecbdata,
 		xcalloc(1, sizeof(struct diff_words_data));
 	ecbdata->diff_words->type = o->word_diff;
 	ecbdata->diff_words->opt = o;
+
+	/* Create our own buffer if needed. */
+	o->line_buffer = NULL;
+	o->line_buffer_nr = 0;
+	o->line_buffer_alloc = 0;
+
 	if (!o->word_regex)
 		o->word_regex = userdiff_word_regex(one);
 	if (!o->word_regex)
@@ -4649,11 +4728,29 @@ static void diff_flush_patch_all_file_pairs(struct diff_options *o)
 {
 	int i;
 	struct diff_queue_struct *q = &diff_queued_diff;
+	/*
+	 * TODO:
+	 * For testing purposes we want to make sure the diff machinery
+	 * works with the buffer. If there is anything emitted outside the
+	 * emit_line_emission, then the order is screwed up and the tests
+	 * will fail.
+	 *
+	 * We'll unset this flag in a later patch.
+	 */
+	o->use_buffer = 1;
 	for (i = 0; i < q->nr; i++) {
 		struct diff_filepair *p = q->queue[i];
 		if (check_pair_status(p))
 			diff_flush_patch(p, o);
 	}
+
+	if (o->use_buffer) {
+		for (i = 0; i < o->line_buffer_nr; i++) {
+			emit_line_emission(o, &o->line_buffer[i]);
+			free_line_emission(&o->line_buffer[i]);
+		}
+		o->line_buffer_nr = 0;
+	}
 }
 
 void diff_flush(struct diff_options *options)
diff --git a/diff.h b/diff.h
index cc5d038..4df6aa5 100644
--- a/diff.h
+++ b/diff.h
@@ -110,6 +110,20 @@ enum diff_words_type {
 	DIFF_WORDS_COLOR
 };
 
+struct line_emission {
+	const char *set;
+	const char *line;
+	const char *ws;
+	const char *reset;
+	int first;
+	int len;
+	int whitespace_check;
+	unsigned ws_rule;
+	int has_trailing_carriage_return;
+	int has_trailing_newline;
+};
+#define LINE_EMISSION_INIT {NULL, NULL, NULL, NULL, 0, 0, 0, 0, 0, 0 }
+
 struct diff_options {
 	const char *orderfile;
 	const char *pickaxe;
@@ -178,6 +192,10 @@ struct diff_options {
 	void *output_prefix_data;
 
 	int diff_path_counter;
+
+	int use_buffer;
+	struct line_emission *line_buffer;
+	int line_buffer_nr, line_buffer_alloc;
 };
 
 void emit_line_fmt(struct diff_options *o, const char *set, const char *reset,
-- 
2.10.0.21.g1da280f.dirty