revision.h: introduce blob/tree walking in order of the commits

The functionality to list tree objects in the order they were seen
while traversing the commits will be used in one of the next commits,
where we teach `git describe` to describe not only commits, but blobs, too.

The change in list-objects.c is rather minimal as we'll be re-using
the infrastructure put in place of the revision walking machinery. For
example one could expect that add_pending_tree is not called, but rather
commit->tree is directly passed to the tree traversal function. This
however requires a lot more code than just emptying the queue containing
trees after each commit.

Signed-off-by: Stefan Beller <sbeller@google.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Documentation/rev-list-options.txt

@@ -686,6 +686,11 @@ ifdef::git-rev-list[]
 	all object IDs which I need to download if I have the commit
 	object _bar_ but not _foo_''.
 
+--in-commit-order::
+	Print tree and blob ids in order of the commits. The tree
+	and blob ids are printed after they are first referenced
+	by a commit.
+
 --objects-edge::
 	Similar to `--objects`, but also print the IDs of excluded
 	commits prefixed with a ``-'' character.  This is used by

list-objects.c

@@ -239,6 +239,14 @@ void traverse_commit_list(struct rev_info *revs,
 		if (commit->tree)
 			add_pending_tree(revs, commit->tree);
 		show_commit(commit, data);
+
+		if (revs->tree_blobs_in_commit_order)
+			/*
+			 * NEEDSWORK: Adding the tree and then flushing it here
+			 * needs a reallocation for each commit. Can we pass the
+			 * tree directory without allocation churn?
+			 */
+			traverse_trees_and_blobs(revs, &csp, show_object, data);
 	}
 	traverse_trees_and_blobs(revs, &csp, show_object, data);
 

revision.c

@@ -1845,6 +1845,8 @@ static int handle_revision_opt(struct rev_info *revs, int argc, const char **arg
 		revs->dense = 0;
 	} else if (!strcmp(arg, "--show-all")) {
 		revs->show_all = 1;
+	} else if (!strcmp(arg, "--in-commit-order")) {
+		revs->tree_blobs_in_commit_order = 1;
 	} else if (!strcmp(arg, "--remove-empty")) {
 		revs->remove_empty_trees = 1;
 	} else if (!strcmp(arg, "--merges")) {

revision.h

@@ -121,7 +121,8 @@ struct rev_info {
 			bisect:1,
 			ancestry_path:1,
 			first_parent_only:1,
-			line_level_traverse:1;
+			line_level_traverse:1,
+			tree_blobs_in_commit_order:1;
 
 	/* Diff flags */
 	unsigned int	diff:1,

t/t6100-rev-list-in-order.sh

@@ -0,0 +1,77 @@
+#!/bin/sh
+
+test_description='rev-list testing in-commit-order'
+
+. ./test-lib.sh
+
+test_expect_success 'setup a commit history with trees, blobs' '
+	for x in one two three four
+	do
+		echo $x >$x &&
+		git add $x &&
+		git commit -m "add file $x" ||
+		return 1
+	done &&
+	for x in four three
+	do
+		git rm $x &&
+		git commit -m "remove $x" ||
+		return 1
+	done
+'
+
+test_expect_success 'rev-list --in-commit-order' '
+	git rev-list --in-commit-order --objects HEAD >actual.raw &&
+	cut -c 1-40 >actual <actual.raw &&
+
+	git cat-file --batch-check="%(objectname)" >expect.raw <<-\EOF &&
+		HEAD^{commit}
+		HEAD^{tree}
+		HEAD^{tree}:one
+		HEAD^{tree}:two
+		HEAD~1^{commit}
+		HEAD~1^{tree}
+		HEAD~1^{tree}:three
+		HEAD~2^{commit}
+		HEAD~2^{tree}
+		HEAD~2^{tree}:four
+		HEAD~3^{commit}
+		# HEAD~3^{tree} skipped, same as HEAD~1^{tree}
+		HEAD~4^{commit}
+		# HEAD~4^{tree} skipped, same as HEAD^{tree}
+		HEAD~5^{commit}
+		HEAD~5^{tree}
+	EOF
+	grep -v "#" >expect <expect.raw &&
+
+	test_cmp expect actual
+'
+
+test_expect_success 'rev-list lists blobs and trees after commits' '
+	git rev-list --objects HEAD >actual.raw &&
+	cut -c 1-40 >actual <actual.raw &&
+
+	git cat-file --batch-check="%(objectname)" >expect.raw <<-\EOF &&
+		HEAD^{commit}
+		HEAD~1^{commit}
+		HEAD~2^{commit}
+		HEAD~3^{commit}
+		HEAD~4^{commit}
+		HEAD~5^{commit}
+		HEAD^{tree}
+		HEAD^{tree}:one
+		HEAD^{tree}:two
+		HEAD~1^{tree}
+		HEAD~1^{tree}:three
+		HEAD~2^{tree}
+		HEAD~2^{tree}:four
+		# HEAD~3^{tree} skipped, same as HEAD~1^{tree}
+		# HEAD~4^{tree} skipped, same as HEAD^{tree}
+		HEAD~5^{tree}
+	EOF
+	grep -v "#" >expect <expect.raw &&
+
+	test_cmp expect actual
+'
+
+test_done