Merge branch 'ds/ahead-behind'

"git for-each-ref" learns '%(ahead-behind:<base>)' that computes the
distances from a single reference point in the history with bunch
of commits in bulk.

* ds/ahead-behind:
  commit-reach: add tips_reachable_from_bases()
  for-each-ref: add ahead-behind format atom
  commit-reach: implement ahead_behind() logic
  commit-graph: introduce `ensure_generations_valid()`
  commit-graph: return generation from memory
  commit-graph: simplify compute_generation_numbers()
  commit-graph: refactor compute_topological_levels()
  for-each-ref: explicitly test no matches
  for-each-ref: add --stdin option

7 files changed, 326 insertions, 1 deletions

diff --git a/t/perf/p1500-graph-walks.sh b/t/perf/p1500-graph-walks.sh
new file mode 100755
index 0000000000..e14e7620cc
--- /dev/null
+++ b/t/perf/p1500-graph-walks.sh
@@ -0,0 +1,50 @@
+#!/bin/sh
+
+test_description='Commit walk performance tests'
+. ./perf-lib.sh
+
+test_perf_large_repo
+
+test_expect_success 'setup' '
+	git for-each-ref --format="%(refname)" "refs/heads/*" "refs/tags/*" >allrefs &&
+	sort -r allrefs | head -n 50 >refs &&
+	for ref in $(cat refs)
+	do
+		git branch -f ref-$ref $ref &&
+		echo ref-$ref ||
+		return 1
+	done >branches &&
+	for ref in $(cat refs)
+	do
+		git tag -f tag-$ref $ref &&
+		echo tag-$ref ||
+		return 1
+	done >tags &&
+	git commit-graph write --reachable
+'
+
+test_perf 'ahead-behind counts: git for-each-ref' '
+	git for-each-ref --format="%(ahead-behind:HEAD)" --stdin <refs
+'
+
+test_perf 'ahead-behind counts: git branch' '
+	xargs git branch -l --format="%(ahead-behind:HEAD)" <branches
+'
+
+test_perf 'ahead-behind counts: git tag' '
+	xargs git tag -l --format="%(ahead-behind:HEAD)" <tags
+'
+
+test_perf 'contains: git for-each-ref --merged' '
+	git for-each-ref --merged=HEAD --stdin <refs
+'
+
+test_perf 'contains: git branch --merged' '
+	xargs git branch --merged=HEAD <branches
+'
+
+test_perf 'contains: git tag --merged' '
+	xargs git tag --merged=HEAD <tags
+'
+
+test_done
diff --git a/t/t3203-branch-output.sh b/t/t3203-branch-output.sh
index d34d77f893..1c0f7ea24e 100755
--- a/t/t3203-branch-output.sh
+++ b/t/t3203-branch-output.sh
@@ -337,6 +337,20 @@ test_expect_success 'git branch --format option' '
 	test_cmp expect actual
 '
 
+test_expect_success 'git branch --format with ahead-behind' '
+	cat >expect <<-\EOF &&
+	(HEAD detached from fromtag) 0 0
+	refs/heads/ambiguous 0 0
+	refs/heads/branch-one 1 0
+	refs/heads/branch-two 0 0
+	refs/heads/main 1 0
+	refs/heads/ref-to-branch 1 0
+	refs/heads/ref-to-remote 1 0
+	EOF
+	git branch --format="%(refname) %(ahead-behind:HEAD)" >actual &&
+	test_cmp expect actual
+'
+
 test_expect_success 'git branch with --format=%(rest) must fail' '
 	test_must_fail git branch --format="%(rest)" >actual
 '
diff --git a/t/t5318-commit-graph.sh b/t/t5318-commit-graph.sh
index 049c5fc8ea..b6e1211578 100755
--- a/t/t5318-commit-graph.sh
+++ b/t/t5318-commit-graph.sh
@@ -630,7 +630,7 @@ test_expect_success 'detect incorrect generation number' '
 
 test_expect_success 'detect incorrect generation number' '
 	corrupt_graph_and_verify $GRAPH_BYTE_COMMIT_GENERATION "\01" \
-		"non-zero generation number"
+		"commit-graph generation for commit"
 '
 
 test_expect_success 'detect incorrect commit date' '
diff --git a/t/t6300-for-each-ref.sh b/t/t6300-for-each-ref.sh
index c466fd989f..6614469d2d 100755
--- a/t/t6300-for-each-ref.sh
+++ b/t/t6300-for-each-ref.sh
@@ -1464,4 +1464,54 @@ sig_crlf="$(printf "%s" "$sig" | append_cr; echo dummy)"
 sig_crlf=${sig_crlf%dummy}
 test_atom refs/tags/fake-sig-crlf contents:signature "$sig_crlf"
 
+test_expect_success 'git for-each-ref --stdin: empty' '
+	>in &&
+	git for-each-ref --format="%(refname)" --stdin <in >actual &&
+	git for-each-ref --format="%(refname)" >expect &&
+	test_cmp expect actual
+'
+
+test_expect_success 'git for-each-ref --stdin: fails if extra args' '
+	>in &&
+	test_must_fail git for-each-ref --format="%(refname)" \
+		--stdin refs/heads/extra <in 2>err &&
+	grep "unknown arguments supplied with --stdin" err
+'
+
+test_expect_success 'git for-each-ref --stdin: matches' '
+	cat >in <<-EOF &&
+	refs/tags/multi*
+	refs/heads/amb*
+	EOF
+
+	cat >expect <<-EOF &&
+	refs/heads/ambiguous
+	refs/tags/multi-ref1-100000-user1
+	refs/tags/multi-ref1-100000-user2
+	refs/tags/multi-ref1-200000-user1
+	refs/tags/multi-ref1-200000-user2
+	refs/tags/multi-ref2-100000-user1
+	refs/tags/multi-ref2-100000-user2
+	refs/tags/multi-ref2-200000-user1
+	refs/tags/multi-ref2-200000-user2
+	refs/tags/multiline
+	EOF
+
+	git for-each-ref --format="%(refname)" --stdin <in >actual &&
+	test_cmp expect actual
+'
+
+test_expect_success 'git for-each-ref with non-existing refs' '
+	cat >in <<-EOF &&
+	refs/heads/this-ref-does-not-exist
+	refs/tags/bogus
+	EOF
+
+	git for-each-ref --format="%(refname)" --stdin <in >actual &&
+	test_must_be_empty actual &&
+
+	xargs git for-each-ref --format="%(refname)" <in >actual &&
+	test_must_be_empty actual
+'
+
 test_done
diff --git a/t/t6301-for-each-ref-errors.sh b/t/t6301-for-each-ref-errors.sh
index bfda1f46ad..2667dd13fe 100755
--- a/t/t6301-for-each-ref-errors.sh
+++ b/t/t6301-for-each-ref-errors.sh
@@ -54,4 +54,18 @@ test_expect_success 'Missing objects are reported correctly' '
 	test_must_be_empty brief-err
 '
 
+test_expect_success 'ahead-behind requires an argument' '
+	test_must_fail git for-each-ref \
+		--format="%(ahead-behind)" 2>err &&
+	echo "fatal: expected format: %(ahead-behind:<committish>)" >expect &&
+	test_cmp expect err
+'
+
+test_expect_success 'missing ahead-behind base' '
+	test_must_fail git for-each-ref \
+		--format="%(ahead-behind:refs/heads/missing)" 2>err &&
+	echo "fatal: failed to find '\''refs/heads/missing'\''" >expect &&
+	test_cmp expect err
+'
+
 test_done
diff --git a/t/t6600-test-reach.sh b/t/t6600-test-reach.sh
index 338a9c46a2..b330945f49 100755
--- a/t/t6600-test-reach.sh
+++ b/t/t6600-test-reach.sh
@@ -443,4 +443,173 @@ test_expect_success 'get_reachable_subset:none' '
 	test_all_modes get_reachable_subset
 '
 
+test_expect_success 'for-each-ref ahead-behind:linear' '
+	cat >input <<-\EOF &&
+	refs/heads/commit-1-1
+	refs/heads/commit-1-3
+	refs/heads/commit-1-5
+	refs/heads/commit-1-8
+	EOF
+	cat >expect <<-\EOF &&
+	refs/heads/commit-1-1 0 8
+	refs/heads/commit-1-3 0 6
+	refs/heads/commit-1-5 0 4
+	refs/heads/commit-1-8 0 1
+	EOF
+	run_all_modes git for-each-ref \
+		--format="%(refname) %(ahead-behind:commit-1-9)" --stdin
+'
+
+test_expect_success 'for-each-ref ahead-behind:all' '
+	cat >input <<-\EOF &&
+	refs/heads/commit-1-1
+	refs/heads/commit-2-4
+	refs/heads/commit-4-2
+	refs/heads/commit-4-4
+	EOF
+	cat >expect <<-\EOF &&
+	refs/heads/commit-1-1 0 24
+	refs/heads/commit-2-4 0 17
+	refs/heads/commit-4-2 0 17
+	refs/heads/commit-4-4 0 9
+	EOF
+	run_all_modes git for-each-ref \
+		--format="%(refname) %(ahead-behind:commit-5-5)" --stdin
+'
+
+test_expect_success 'for-each-ref ahead-behind:some' '
+	cat >input <<-\EOF &&
+	refs/heads/commit-1-1
+	refs/heads/commit-5-3
+	refs/heads/commit-4-8
+	refs/heads/commit-9-9
+	EOF
+	cat >expect <<-\EOF &&
+	refs/heads/commit-1-1 0 53
+	refs/heads/commit-4-8 8 30
+	refs/heads/commit-5-3 0 39
+	refs/heads/commit-9-9 27 0
+	EOF
+	run_all_modes git for-each-ref \
+		--format="%(refname) %(ahead-behind:commit-9-6)" --stdin
+'
+
+test_expect_success 'for-each-ref ahead-behind:some, multibase' '
+	cat >input <<-\EOF &&
+	refs/heads/commit-1-1
+	refs/heads/commit-5-3
+	refs/heads/commit-7-8
+	refs/heads/commit-4-8
+	refs/heads/commit-9-9
+	EOF
+	cat >expect <<-\EOF &&
+	refs/heads/commit-1-1 0 53 0 53
+	refs/heads/commit-4-8 8 30 0 22
+	refs/heads/commit-5-3 0 39 0 39
+	refs/heads/commit-7-8 14 12 8 6
+	refs/heads/commit-9-9 27 0 27 0
+	EOF
+	run_all_modes git for-each-ref \
+		--format="%(refname) %(ahead-behind:commit-9-6) %(ahead-behind:commit-6-9)" \
+		--stdin
+'
+
+test_expect_success 'for-each-ref ahead-behind:none' '
+	cat >input <<-\EOF &&
+	refs/heads/commit-7-5
+	refs/heads/commit-4-8
+	refs/heads/commit-9-9
+	EOF
+	cat >expect <<-\EOF &&
+	refs/heads/commit-4-8 16 16
+	refs/heads/commit-7-5 7 4
+	refs/heads/commit-9-9 49 0
+	EOF
+	run_all_modes git for-each-ref \
+		--format="%(refname) %(ahead-behind:commit-8-4)" --stdin
+'
+
+test_expect_success 'for-each-ref merged:linear' '
+	cat >input <<-\EOF &&
+	refs/heads/commit-1-1
+	refs/heads/commit-1-3
+	refs/heads/commit-1-5
+	refs/heads/commit-1-8
+	refs/heads/commit-2-1
+	refs/heads/commit-5-1
+	refs/heads/commit-9-1
+	EOF
+	cat >expect <<-\EOF &&
+	refs/heads/commit-1-1
+	refs/heads/commit-1-3
+	refs/heads/commit-1-5
+	refs/heads/commit-1-8
+	EOF
+	run_all_modes git for-each-ref --merged=commit-1-9 \
+		--format="%(refname)" --stdin
+'
+
+test_expect_success 'for-each-ref merged:all' '
+	cat >input <<-\EOF &&
+	refs/heads/commit-1-1
+	refs/heads/commit-2-4
+	refs/heads/commit-4-2
+	refs/heads/commit-4-4
+	EOF
+	cat >expect <<-\EOF &&
+	refs/heads/commit-1-1
+	refs/heads/commit-2-4
+	refs/heads/commit-4-2
+	refs/heads/commit-4-4
+	EOF
+	run_all_modes git for-each-ref --merged=commit-5-5 \
+		--format="%(refname)" --stdin
+'
+
+test_expect_success 'for-each-ref ahead-behind:some' '
+	cat >input <<-\EOF &&
+	refs/heads/commit-1-1
+	refs/heads/commit-5-3
+	refs/heads/commit-4-8
+	refs/heads/commit-9-9
+	EOF
+	cat >expect <<-\EOF &&
+	refs/heads/commit-1-1
+	refs/heads/commit-5-3
+	EOF
+	run_all_modes git for-each-ref --merged=commit-9-6 \
+		--format="%(refname)" --stdin
+'
+
+test_expect_success 'for-each-ref merged:some, multibase' '
+	cat >input <<-\EOF &&
+	refs/heads/commit-1-1
+	refs/heads/commit-5-3
+	refs/heads/commit-7-8
+	refs/heads/commit-4-8
+	refs/heads/commit-9-9
+	EOF
+	cat >expect <<-\EOF &&
+	refs/heads/commit-1-1
+	refs/heads/commit-4-8
+	refs/heads/commit-5-3
+	EOF
+	run_all_modes git for-each-ref \
+		--merged=commit-5-8 \
+		--merged=commit-8-5 \
+		--format="%(refname)" \
+		--stdin
+'
+
+test_expect_success 'for-each-ref merged:none' '
+	cat >input <<-\EOF &&
+	refs/heads/commit-7-5
+	refs/heads/commit-4-8
+	refs/heads/commit-9-9
+	EOF
+	>expect &&
+	run_all_modes git for-each-ref --merged=commit-8-4 \
+		--format="%(refname)" --stdin
+'
+
 test_done
diff --git a/t/t7004-tag.sh b/t/t7004-tag.sh
index 9aa1660651..04a4b44183 100755
--- a/t/t7004-tag.sh
+++ b/t/t7004-tag.sh
@@ -792,6 +792,34 @@ test_expect_success 'annotations for blobs are empty' '
 	test_cmp expect actual
 '
 
+# Run this before doing any signing, so the test has the same results
+# regardless of the GPG prereq.
+test_expect_success 'git tag --format with ahead-behind' '
+	test_when_finished git reset --hard tag-one-line &&
+	git commit --allow-empty -m "left" &&
+	git tag -a -m left tag-left &&
+	git reset --hard HEAD~1 &&
+	git commit --allow-empty -m "right" &&
+	git tag -a -m left tag-right &&
+
+	# Use " !" at the end to demonstrate whitespace
+	# around empty ahead-behind token for tag-blob.
+	cat >expect <<-EOF &&
+	refs/tags/tag-blob  !
+	refs/tags/tag-left 1 1 !
+	refs/tags/tag-lines 0 1 !
+	refs/tags/tag-one-line 0 1 !
+	refs/tags/tag-right 0 0 !
+	refs/tags/tag-zero-lines 0 1 !
+	EOF
+	git tag -l --format="%(refname) %(ahead-behind:HEAD) !" >actual 2>err &&
+	grep "refs/tags/tag" actual >actual.focus &&
+	test_cmp expect actual.focus &&
+
+	# Error reported for tags that point to non-commits.
+	grep "error: object [0-9a-f]* is a blob, not a commit" err
+'
+
 # trying to verify annotated non-signed tags:
 
 test_expect_success GPG \