[GSoC PATCH v2] backfill: add --[no-]progress option

[Trieu Huynh <vikingtc4@gmail.com>]

From: Trieu Huynh <vikingtc4@gmail.com>

'git backfill' does not show an overall progress bar across
batches, giving no cross-batch feedback during potentially
long-running operations on large repositories.  By contrast,
'git fetch', 'git gc', and 'git index-pack' all support
--[no-]progress.

Add a --[no-]progress option that tracks the total number of
missing blobs downloaded across all batches, defaulting to
showing progress when stderr is a terminal (matching the
behaviour of 'git fetch').

Add tests to verify that:
 - progress is shown by default on a TTY
 - --progress forces output regardless of TTY
 - --no-progress suppresses output

Signed-off-by: Trieu Huynh <vikingtc4@gmail.com>
---
 builtin/backfill.c  | 18 +++++++++++++++++-
 t/t5620-backfill.sh | 24 ++++++++++++++++++++++++
 2 files changed, 41 insertions(+), 1 deletion(-)

diff --git a/builtin/backfill.c b/builtin/backfill.c
index d794dd842f..e90c899071 100644
--- a/builtin/backfill.c
+++ b/builtin/backfill.c
@@ -26,7 +26,7 @@
 #include "path-walk.h"
 
 static const char * const builtin_backfill_usage[] = {
-	N_("git backfill [--min-batch-size=<n>] [--[no-]sparse]"),
+	N_("git backfill [--min-batch-size=<n>] [--[no-]sparse] [--[no-]progress]"),
 	NULL
 };
 
@@ -36,6 +36,9 @@ struct backfill_context {
 	size_t min_batch_size;
 	int sparse;
 	struct rev_info revs;
+	int show_progress;
+	size_t nr_downloaded;
+	struct progress *progress;
 };
 
 static void backfill_context_clear(struct backfill_context *ctx)
@@ -48,6 +51,7 @@ static void download_batch(struct backfill_context *ctx)
 	promisor_remote_get_direct(ctx->repo,
 				   ctx->current_batch.oid,
 				   ctx->current_batch.nr);
+	ctx->nr_downloaded += ctx->current_batch.nr;
 	oid_array_clear(&ctx->current_batch);
 
 	/*
@@ -55,6 +59,7 @@ static void download_batch(struct backfill_context *ctx)
 	 * avoid possible duplicate downloads of the same objects.
 	 */
 	odb_reprepare(ctx->repo->objects);
+	display_progress(ctx->progress, ctx->nr_downloaded);
 }
 
 static int fill_missing_blobs(const char *path UNUSED,
@@ -121,12 +126,16 @@ int cmd_backfill(int argc, const char **argv, const char *prefix, struct reposit
 		.min_batch_size = 50000,
 		.sparse = -1,
 		.revs = REV_INFO_INIT,
+		.nr_downloaded = 0,
+		.show_progress = -1,
 	};
 	struct option options[] = {
 		OPT_UNSIGNED(0, "min-batch-size", &ctx.min_batch_size,
 			     N_("Minimum number of objects to request at a time")),
 		OPT_BOOL(0, "sparse", &ctx.sparse,
 			 N_("Restrict the missing objects to the current sparse-checkout")),
+		OPT_BOOL(0, "progress", &ctx.show_progress,
+			 N_("show progress while downloading missing objects")),
 		OPT_END(),
 	};
 	struct repo_config_values *cfg = repo_config_values(the_repository);
@@ -150,7 +159,14 @@ int cmd_backfill(int argc, const char **argv, const char *prefix, struct reposit
 	if (ctx.sparse < 0)
 		ctx.sparse = cfg->apply_sparse_checkout;
 
+	if (ctx.show_progress < 0)
+		ctx.show_progress = isatty(2);
+
+	if (ctx.show_progress)
+		ctx.progress = start_progress(ctx.repo,
+					      _("Downloading missing blobs"), 0);
 	result = do_backfill(&ctx);
+	stop_progress(&ctx.progress);
 	backfill_context_clear(&ctx);
 	release_revisions(&ctx.revs);
 	return result;
diff --git a/t/t5620-backfill.sh b/t/t5620-backfill.sh
index f3b5e39493..a75b84d8ac 100755
--- a/t/t5620-backfill.sh
+++ b/t/t5620-backfill.sh
@@ -133,6 +133,30 @@ test_expect_success 'do partial clone 2, backfill min batch size' '
 	test_line_count = 0 revs2
 '
 
+test_expect_success TTY 'backfill shows progress on tty by default' '
+	git clone --no-checkout --filter=blob:none \
+		--single-branch --branch=main \
+		"file://$(pwd)/srv.bare" clone-tty &&
+	test_terminal env GIT_PROGRESS_DELAY=0 git -C clone-tty backfill 2>err &&
+	test_grep "Downloading missing blobs" err
+'
+
+test_expect_success 'backfill --progress shows progress' '
+	git clone --no-checkout --filter=blob:none \
+		--single-branch --branch=main \
+		"file://$(pwd)/srv.bare" clone-progress &&
+	git -C clone-progress backfill --progress 2>err &&
+	test_grep "Downloading missing blobs" err
+'
+
+test_expect_success 'backfill --no-progress suppresses progress' '
+	git clone --no-checkout --filter=blob:none \
+		--single-branch --branch=main \
+		"file://$(pwd)/srv.bare" clone-no-progress &&
+	git -C clone-no-progress backfill --no-progress 2>err &&
+	test_grep ! "Downloading missing blobs" err
+'
+
 test_expect_success 'backfill --sparse without sparse-checkout fails' '
 	git init not-sparse &&
 	test_must_fail git -C not-sparse backfill --sparse 2>err &&
-- 
2.43.0