revision: drop early output option

We added the --early-output feature long ago in cdcefbc971 (Add
"--early-output" log flag for interactive GUI use, 2007-11-03). The idea
was that GUIs could use it to progressively render a history view,
showing something quick-and-inaccurate at first and then enhancing it
later.

But we never documented it, and it appears never to have been used, even
by the projects which initially expressed interest. There was an RFC
patch for gitk to use it:

  http://public-inbox.org/git/18221.2285.259487.655684@cargo.ozlabs.ibm.com/

but it was never merged. Likewise QGit had a patch in:

  https://lore.kernel.org/git/e5bfff550711040225ne67c907r2023b1354c35f35@mail.gmail.com/

but it was never fully merged (to this day, QGit has a commented-out line to
add "--early-output" to the "log" invocation). Searching for other
mentions on the web or forges like github.com turns up nothing.

Meanwhile, the feature has been broken off and on over the years without
anybody noticing (and naturally, there are no tests, either). From 2011
to 2017 the option didn't even turn on via "--early-output"; this was
fixed in e35b6ac56f (revision.h: turn rev_info.early_output back into an
unsigned int, 2017-06-10).

It worked for a while then, but it does not interact well at all with
commit-graphs (which are turned on by default these days). The main
logic to count early commits is triggered by limit_list(), which we
traditionally invoked when showing output in topo-order (and
--early-output always enables --topo-order). But that changed in
f0d9cc4196 (revision.c: begin refactoring --topo-order logic,
2018-11-01). Now when we have generation numbers, we skip limit_list()
entirely, and the early-output code shows no commits, and just the final
header "Final output: 1 done". Which is syntactically OK, but
semantically wrong: that message should give the total number of commits
we're about to show.

So let's drop the feature. It is extra code that is untested and
undocumented, and makes working on the revision machinery more brittle.

Given the history above, it seems unlikely that anybody is using it (or
has used it), and we can drop it without the usual deprecation period.

A gentler option might be to "soft" drop it: keep accepting the option,
have it imply --topo-order as it does now, print "Final output: 1 done",
and then do our regular traversal. That would keep any hypothetical
caller working. But it doesn't seem worth the hassle to me.

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 0 insertions, 17 deletions

diff --git a/revision.c b/revision.c
index 2c36a9c179..edbf027843 100644
--- a/revision.c
+++ b/revision.c
@@ -50,8 +50,6 @@
 #include "parse-options.h"
 #include "wildmatch.h"
 
-volatile show_early_output_fn_t show_early_output;
-
 static char *term_bad;
 static char *term_good;
 
@@ -1479,7 +1477,6 @@ static int limit_list(struct rev_info *revs)
 	while (original_list) {
 		struct commit *commit = pop_commit(&original_list);
 		struct object *obj = &commit->object;
-		show_early_output_fn_t show;
 
 		if (commit == interesting_cache)
 			interesting_cache = NULL;
@@ -1503,13 +1500,6 @@ static int limit_list(struct rev_info *revs)
 			continue;
 		date = commit->date;
 		p = &commit_list_insert(commit, p)->next;
-
-		show = show_early_output;
-		if (!show)
-			continue;
-
-		show(revs, newlist);
-		show_early_output = NULL;
 	}
 	if (revs->cherry_pick || revs->cherry_mark)
 		cherry_pick_list(newlist, revs);
@@ -2441,13 +2431,6 @@ static int handle_revision_opt(struct rev_info *revs, int argc, const char **arg
 	} else if (!strcmp(arg, "--author-date-order")) {
 		revs->sort_order = REV_SORT_BY_AUTHOR_DATE;
 		revs->topo_order = 1;
-	} else if (!strcmp(arg, "--early-output")) {
-		revs->early_output = 100;
-		revs->topo_order = 1;
-	} else if (skip_prefix(arg, "--early-output=", &optarg)) {
-		if (strtoul_ui(optarg, 10, &revs->early_output) < 0)
-			die("'%s': not a non-negative integer", optarg);
-		revs->topo_order = 1;
 	} else if (!strcmp(arg, "--parents")) {
 		revs->rewrite_parents = 1;
 		revs->print_parents = 1;