[PATCH 3/4] pack-objects.c: do stdin parsing via revision.c's API

["Ævar Arnfjörð Bjarmason" <avarab@gmail.com>]

Change the fgets(..., stdin) parsing in pack-objects.c to use a
now-extended version of the rev_info stdin parsing API.

The fgets() loop being refactored away here was first added in Linus's
c323ac7d9c5 (git-pack-objects: create a packed object representation.,
2005-06-25).

Later on rev-list started doing similar parsing in 42cabc341c4 (Teach
rev-list an option to read revs from the standard input., 2006-09-05),
and that code was promoted to a more general API in 1fc561d169a (Move
read_revisions_from_stdin from builtin-rev-list.c to revision.c,
2008-07-05).

Since then the API in revision.c has received improvements that have
been missed here. E.g. the arbitrary limit of 1000 bytes was removed
in 63d564b3002 (read_revision_from_stdin(): use strbuf, 2009-11-20),
and it moved to a more simpler strbuf API in 6e8d46f9d4b (revision:
read --stdin with strbuf_getline(), 2015-10-28).

Let's do the same here, as in 6e8d46f9d4b we can remove the "if (len
&& line[len - 1] == '\n')" check, it's now redundant to using
strbuf_getline(), and we get to skip the whole
"warn_on_object_refname_ambiguity" dance. The
read_revisions_from_stdin() function in revision.c we're now using
does it for us.

For now there isn't all that much point in this whole exercises. We
just end up calling setup_revisions() to loop over stdin for us, but
the callback we define makes no use of REV_INFO_STDIN_LINE_PROCESS, we
still need to call handle_revision_arg() ourselves because we'd like
to call it with different flags.

This very light use of the API will be further refined in a subsequent
commit, for now we're just doing the bare minimum to move this
existing code over to the new callback pattern without any functional
changes, and making it as friendly to "git show -w" and "the
--color-moved-ws=allow-indentation-change" mode as possible.

Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
---
 builtin/pack-objects.c | 66 +++++++++++++++++++++---------------------
 revision.c             | 27 +++++++++++++++++
 revision.h             | 31 ++++++++++++++++++++
 3 files changed, 91 insertions(+), 33 deletions(-)

diff --git a/builtin/pack-objects.c b/builtin/pack-objects.c
index 1fbaa34f91..cbb01f2b2d 100644
--- a/builtin/pack-objects.c
+++ b/builtin/pack-objects.c
@@ -3745,15 +3745,43 @@ static void mark_bitmap_preferred_tips(void)
 	}
 }
 
+static enum rev_info_stdin_line get_object_list_handle_stdin_line(
+	struct rev_info *revs, struct strbuf *line_sb, void *stdin_line_priv)
+{
+	int *flags = stdin_line_priv;
+	char *line = line_sb->buf;
+	size_t len = line_sb->len;
+
+	if (!len)
+		return REV_INFO_STDIN_LINE_BREAK;
+	if (*line == '-') {
+		if (!strcmp(line, "--not")) {
+			*flags ^= UNINTERESTING;
+			write_bitmap_index = 0;
+			return REV_INFO_STDIN_LINE_CONTINUE;
+		}
+		if (starts_with(line, "--shallow ")) {
+			struct object_id oid;
+			if (get_oid_hex(line + 10, &oid))
+				die("not an object name '%s'", line + 10);
+			register_shallow(the_repository, &oid);
+			use_bitmap_index = 0;
+			return REV_INFO_STDIN_LINE_CONTINUE;
+		}
+		die(_("not a rev '%s'"), line);
+	}
+	if (handle_revision_arg(line, revs, *flags, REVARG_CANNOT_BE_FILENAME))
+			die(_("bad revision '%s'"), line);
+	return REV_INFO_STDIN_LINE_CONTINUE;
+}
+
 static void get_object_list(int ac, const char **av)
 {
 	struct rev_info revs;
 	struct setup_revision_opt s_r_opt = {
 		.allow_exclude_promisor_objects = 1,
 	};
-	char line[1000];
 	int flags = 0;
-	int save_warning;
 
 	repo_init_revisions(the_repository, &revs, NULL);
 	save_commit_buffer = 0;
@@ -3761,39 +3789,11 @@ static void get_object_list(int ac, const char **av)
 	/* make sure shallows are read */
 	is_repository_shallow(the_repository);
 
+	revs.stdin_handling = REV_INFO_STDIN_ALWAYS_READ;
+	revs.handle_stdin_line = get_object_list_handle_stdin_line;
+	revs.stdin_line_priv = &flags;
 	setup_revisions(ac, av, &revs, &s_r_opt);
 
-	save_warning = warn_on_object_refname_ambiguity;
-	warn_on_object_refname_ambiguity = 0;
-
-	while (fgets(line, sizeof(line), stdin) != NULL) {
-		int len = strlen(line);
-		if (len && line[len - 1] == '\n')
-			line[--len] = 0;
-		if (!len)
-			break;
-		if (*line == '-') {
-			if (!strcmp(line, "--not")) {
-				flags ^= UNINTERESTING;
-				write_bitmap_index = 0;
-				continue;
-			}
-			if (starts_with(line, "--shallow ")) {
-				struct object_id oid;
-				if (get_oid_hex(line + 10, &oid))
-					die("not an object name '%s'", line + 10);
-				register_shallow(the_repository, &oid);
-				use_bitmap_index = 0;
-				continue;
-			}
-			die(_("not a rev '%s'"), line);
-		}
-		if (handle_revision_arg(line, &revs, flags, REVARG_CANNOT_BE_FILENAME))
-			die(_("bad revision '%s'"), line);
-	}
-
-	warn_on_object_refname_ambiguity = save_warning;
-
 	if (use_bitmap_index && !get_object_list_from_bitmap(&revs))
 		return;
 
diff --git a/revision.c b/revision.c
index 69b3812093..878eb51032 100644
--- a/revision.c
+++ b/revision.c
@@ -2119,6 +2119,25 @@ static void read_revisions_from_stdin(struct rev_info *revs,
 		int len = sb.len;
 		if (!len)
 			break;
+
+		if (revs->handle_stdin_line) {
+			int do_break = 0;
+			enum rev_info_stdin_line ret = revs->handle_stdin_line(
+				revs, &sb, revs->stdin_line_priv);
+	
+			switch (ret) {
+			case REV_INFO_STDIN_LINE_PROCESS:
+				break;
+			case REV_INFO_STDIN_LINE_BREAK:
+				do_break = 1;
+				break;
+			case REV_INFO_STDIN_LINE_CONTINUE:
+				continue;
+			}
+			if (do_break)
+				break;
+		}
+
 		if (sb.buf[0] == '-') {
 			if (len == 2 && sb.buf[1] == '-') {
 				seen_dashdash = 1;
@@ -2787,6 +2806,14 @@ int setup_revisions(int argc, const char **argv, struct rev_info *revs, struct s
 		}
 	}
 
+	/*
+	 * We've got always_read_from_stdin but no --stdin (or
+	 * "consumed_stdin_per_option" would be set).
+	 */
+	if (revs->stdin_handling == REV_INFO_STDIN_ALWAYS_READ &&
+	    !revs->consumed_stdin_per_option)
+		read_revisions_from_stdin(revs, &prune_data);
+
 	if (prune_data.nr) {
 		/*
 		 * If we need to introduce the magic "a lone ':' means no
diff --git a/revision.h b/revision.h
index 03231f089f..9d977cd3cc 100644
--- a/revision.h
+++ b/revision.h
@@ -89,8 +89,18 @@ struct topo_walk_info;
 enum rev_info_stdin {
 	REV_INFO_STDIN_CONSUME_ON_OPTION = 0,
 	REV_INFO_STDIN_IGNORE,
+	REV_INFO_STDIN_ALWAYS_READ,
 };
 
+enum rev_info_stdin_line {
+	REV_INFO_STDIN_LINE_PROCESS,
+	REV_INFO_STDIN_LINE_BREAK,
+	REV_INFO_STDIN_LINE_CONTINUE,
+};
+
+typedef enum rev_info_stdin_line (*rev_info_stdin_line_func)(
+	struct rev_info *revs, struct strbuf *line, void *stdin_line_priv);
+
 struct rev_info {
 	/* Starting list */
 	struct commit_list *commits;
@@ -126,6 +136,9 @@ struct rev_info {
 	 *
 	 * Can be set to REV_INFO_STDIN_IGNORE to ignore any provided
 	 * --stdin option.
+	 *
+	 * Set it to REV_INFO_STDIN_ALWAYS_READ if there's always data
+	 * on stdin to be read, even if no --stdin option is provided.
 	 */
 	enum rev_info_stdin stdin_handling;
 
@@ -136,6 +149,24 @@ struct rev_info {
 	 */
 	int consumed_stdin_per_option;
 
+	/*
+	 * When reading from stdin (see "stdin_handling" above) define
+	 * a handle_stdin_line function to consume the lines.
+	 *
+	 * - Return 0 to continue revision.c's normal processing of the
+	 *   line (after possibly munging the provided strbuf).
+	 *
+	 * - Return 1 to indicate that the line is fully processed,
+         *   moving onto the next line (if any)
+	 *
+	 * - Return 2 to process no further lines.
+	 *
+	 * Use the "stdin_line_priv" to optionally pass your own data
+	 * around.
+	 */
+	rev_info_stdin_line_func handle_stdin_line;
+	void *stdin_line_priv;
+
 	/* topo-sort */
 	enum rev_sort_order sort_order;
 
-- 
2.32.0.rc3.434.gd8aed1f08a7