Merge branch 'master' of github.com:git/git

* 'master' of github.com:git/git: (51 commits)
  Hopefully the last batch of fixes before 2.44 final
  Git 2.43.2
  A few more fixes before -rc1
  write-or-die: fix the polarity of GIT_FLUSH environment variable
  A few more topics before -rc1
  completion: add and use __git_compute_second_level_config_vars_for_section
  completion: add and use __git_compute_first_level_config_vars_for_section
  completion: complete 'submodule.*' config variables
  completion: add space after config variable names also in Bash 3
  receive-pack: use find_commit_header() in check_nonce()
  ci(linux32): add a note about Actions that must not be updated
  ci: bump remaining outdated Actions versions
  unit-tests: do show relative file paths on non-Windows, too
  receive-pack: use find_commit_header() in check_cert_push_options()
  prune: mark rebase autostash and orig-head as reachable
  sequencer: unset GIT_CHERRY_PICK_HELP for 'exec' commands
  ref-filter.c: sort formatted dates by byte value
  ssh signing: signal an error with a negative return value
  bisect: document command line arguments for "bisect start"
  bisect: document "terms" subcommand more fully
  ...

10 files changed, 414 insertions, 65 deletions

diff --git a/t/t1400-update-ref.sh b/t/t1400-update-ref.sh
index f18843bf7a..78a09abc35 100755
--- a/t/t1400-update-ref.sh
+++ b/t/t1400-update-ref.sh
@@ -524,51 +524,51 @@ test_expect_success 'given old value for missing pseudoref, do not create' '
 
 test_expect_success 'create pseudoref' '
 	git update-ref PSEUDOREF $A &&
-	test $A = $(git rev-parse PSEUDOREF)
+	test $A = $(git show-ref -s --verify PSEUDOREF)
 '
 
 test_expect_success 'overwrite pseudoref with no old value given' '
 	git update-ref PSEUDOREF $B &&
-	test $B = $(git rev-parse PSEUDOREF)
+	test $B = $(git show-ref -s --verify PSEUDOREF)
 '
 
 test_expect_success 'overwrite pseudoref with correct old value' '
 	git update-ref PSEUDOREF $C $B &&
-	test $C = $(git rev-parse PSEUDOREF)
+	test $C = $(git show-ref -s --verify PSEUDOREF)
 '
 
 test_expect_success 'do not overwrite pseudoref with wrong old value' '
 	test_must_fail git update-ref PSEUDOREF $D $E 2>err &&
-	test $C = $(git rev-parse PSEUDOREF) &&
+	test $C = $(git show-ref -s --verify PSEUDOREF) &&
 	test_grep "cannot lock ref.*expected" err
 '
 
 test_expect_success 'delete pseudoref' '
 	git update-ref -d PSEUDOREF &&
-	test_must_fail git rev-parse PSEUDOREF
+	test_must_fail git show-ref -s --verify PSEUDOREF
 '
 
 test_expect_success 'do not delete pseudoref with wrong old value' '
 	git update-ref PSEUDOREF $A &&
 	test_must_fail git update-ref -d PSEUDOREF $B 2>err &&
-	test $A = $(git rev-parse PSEUDOREF) &&
+	test $A = $(git show-ref -s --verify PSEUDOREF) &&
 	test_grep "cannot lock ref.*expected" err
 '
 
 test_expect_success 'delete pseudoref with correct old value' '
 	git update-ref -d PSEUDOREF $A &&
-	test_must_fail git rev-parse PSEUDOREF
+	test_must_fail git show-ref -s --verify PSEUDOREF
 '
 
 test_expect_success 'create pseudoref with old OID zero' '
 	git update-ref PSEUDOREF $A $Z &&
-	test $A = $(git rev-parse PSEUDOREF)
+	test $A = $(git show-ref -s --verify PSEUDOREF)
 '
 
 test_expect_success 'do not overwrite pseudoref with old OID zero' '
 	test_when_finished git update-ref -d PSEUDOREF &&
 	test_must_fail git update-ref PSEUDOREF $B $Z 2>err &&
-	test $A = $(git rev-parse PSEUDOREF) &&
+	test $A = $(git show-ref -s --verify PSEUDOREF) &&
 	test_grep "already exists" err
 '
 
diff --git a/t/t1403-show-ref.sh b/t/t1403-show-ref.sh
index d0a8f7b121..33fb7a38ff 100755
--- a/t/t1403-show-ref.sh
+++ b/t/t1403-show-ref.sh
@@ -174,6 +174,14 @@ test_expect_success 'show-ref --verify HEAD' '
 	test_must_be_empty actual
 '
 
+test_expect_success 'show-ref --verify pseudorefs' '
+	git update-ref CHERRY_PICK_HEAD HEAD $ZERO_OID &&
+	test_when_finished "git update-ref -d CHERRY_PICK_HEAD" &&
+	git show-ref -s --verify HEAD >actual &&
+	git show-ref -s --verify CHERRY_PICK_HEAD >expect &&
+	test_cmp actual expect
+'
+
 test_expect_success 'show-ref --verify with dangling ref' '
 	sha1_file() {
 		echo "$*" | sed "s#..#.git/objects/&/#"
diff --git a/t/t3404-rebase-interactive.sh b/t/t3404-rebase-interactive.sh
index 64b641002e..d1bead61fa 100755
--- a/t/t3404-rebase-interactive.sh
+++ b/t/t3404-rebase-interactive.sh
@@ -153,6 +153,18 @@ test_expect_success 'rebase -i with the exec command checks tree cleanness' '
 	git rebase --continue
 '
 
+test_expect_success 'cherry-pick works with rebase --exec' '
+	test_when_finished "git cherry-pick --abort; \
+			    git rebase --abort; \
+			    git checkout primary" &&
+	echo "exec git cherry-pick G" >todo &&
+	(
+		set_replace_editor todo &&
+		test_must_fail git rebase -i D D
+	) &&
+	test_cmp_rev G CHERRY_PICK_HEAD
+'
+
 test_expect_success 'rebase -x with empty command fails' '
 	test_when_finished "git rebase --abort ||:" &&
 	test_must_fail env git rebase -x "" @ 2>actual &&
diff --git a/t/t3407-rebase-abort.sh b/t/t3407-rebase-abort.sh
index ebbaed147a..9f49c4228b 100755
--- a/t/t3407-rebase-abort.sh
+++ b/t/t3407-rebase-abort.sh
@@ -40,9 +40,24 @@ testrebase() {
 		test_path_is_missing "$state_dir"
 	'
 
+	test_expect_success "pre rebase$type head is marked as reachable" '
+		# Clean up the state from the previous one
+		git checkout -f --detach pre-rebase &&
+		test_tick &&
+		git commit --amend --only -m "reworded" &&
+		orig_head=$(git rev-parse HEAD) &&
+		test_must_fail git rebase$type main &&
+		# Stop ORIG_HEAD marking $state_dir/orig-head as reachable
+		git update-ref -d ORIG_HEAD &&
+		git reflog expire --expire="$GIT_COMMITTER_DATE" --all &&
+		git prune --expire=now &&
+		git rebase --abort &&
+		test_cmp_rev $orig_head HEAD
+	'
+
 	test_expect_success "rebase$type --abort after --skip" '
 		# Clean up the state from the previous one
-		git reset --hard pre-rebase &&
+		git checkout -B to-rebase pre-rebase &&
 		test_must_fail git rebase$type main &&
 		test_path_is_dir "$state_dir" &&
 		test_must_fail git rebase --skip &&
diff --git a/t/t3420-rebase-autostash.sh b/t/t3420-rebase-autostash.sh
index 693934ee8b..1a820f1481 100755
--- a/t/t3420-rebase-autostash.sh
+++ b/t/t3420-rebase-autostash.sh
@@ -333,4 +333,14 @@ test_expect_success 'never change active branch' '
 	test_cmp_rev not-the-feature-branch unrelated-onto-branch
 '
 
+test_expect_success 'autostash commit is marked as reachable' '
+	echo changed >file0 &&
+	git rebase --autostash --exec "git prune --expire=now" \
+		feature-branch^ feature-branch &&
+	# git rebase succeeds if the stash cannot be applied so we need to check
+	# the contents of file0
+	echo changed >expect &&
+	test_cmp expect file0
+'
+
 test_done
diff --git a/t/t3903-stash.sh b/t/t3903-stash.sh
index 3319240515..00db82fb24 100755
--- a/t/t3903-stash.sh
+++ b/t/t3903-stash.sh
@@ -1516,4 +1516,56 @@ test_expect_success 'restore untracked files even when we hit conflicts' '
 	)
 '
 
+test_expect_success 'stash create reports a locked index' '
+	test_when_finished "rm -rf repo" &&
+	git init repo &&
+	(
+		cd repo &&
+		test_commit A A.file &&
+		echo change >A.file &&
+		touch .git/index.lock &&
+
+		cat >expect <<-EOF &&
+		error: could not write index
+		EOF
+		test_must_fail git stash create 2>err &&
+		test_cmp expect err
+	)
+'
+
+test_expect_success 'stash push reports a locked index' '
+	test_when_finished "rm -rf repo" &&
+	git init repo &&
+	(
+		cd repo &&
+		test_commit A A.file &&
+		echo change >A.file &&
+		touch .git/index.lock &&
+
+		cat >expect <<-EOF &&
+		error: could not write index
+		EOF
+		test_must_fail git stash push 2>err &&
+		test_cmp expect err
+	)
+'
+
+test_expect_success 'stash apply reports a locked index' '
+	test_when_finished "rm -rf repo" &&
+	git init repo &&
+	(
+		cd repo &&
+		test_commit A A.file &&
+		echo change >A.file &&
+		git stash push &&
+		touch .git/index.lock &&
+
+		cat >expect <<-EOF &&
+		error: could not write index
+		EOF
+		test_must_fail git stash apply 2>err &&
+		test_cmp expect err
+	)
+'
+
 test_done
diff --git a/t/t5332-multi-pack-reuse.sh b/t/t5332-multi-pack-reuse.sh
index 99145327a6..3c20738bce 100755
--- a/t/t5332-multi-pack-reuse.sh
+++ b/t/t5332-multi-pack-reuse.sh
@@ -24,6 +24,27 @@ pack_position () {
 	grep "$1" objects | cut -d" " -f1
 }
 
+# test_pack_objects_reused_all <pack-reused> <packs-reused>
+test_pack_objects_reused_all () {
+	: >trace2.txt &&
+	GIT_TRACE2_EVENT="$PWD/trace2.txt" \
+		git pack-objects --stdout --revs --all --delta-base-offset \
+		>/dev/null &&
+
+	test_pack_reused "$1" <trace2.txt &&
+	test_packs_reused "$2" <trace2.txt
+}
+
+# test_pack_objects_reused <pack-reused> <packs-reused>
+test_pack_objects_reused () {
+	: >trace2.txt &&
+	GIT_TRACE2_EVENT="$PWD/trace2.txt" \
+		git pack-objects --stdout --revs >/dev/null &&
+
+	test_pack_reused "$1" <trace2.txt &&
+	test_packs_reused "$2" <trace2.txt
+}
+
 test_expect_success 'preferred pack is reused for single-pack reuse' '
 	test_config pack.allowPackReuse single &&
 
@@ -35,12 +56,24 @@ test_expect_success 'preferred pack is reused for single-pack reuse' '
 
 	git multi-pack-index write --bitmap &&
 
-	: >trace2.txt &&
-	GIT_TRACE2_EVENT="$PWD/trace2.txt" \
-		git pack-objects --stdout --revs --all >/dev/null &&
+	test_pack_objects_reused_all 3 1
+'
+
+test_expect_success 'multi-pack reuse is disabled by default' '
+	test_pack_objects_reused_all 3 1
+'
+
+test_expect_success 'feature.experimental implies multi-pack reuse' '
+	test_config feature.experimental true &&
+
+	test_pack_objects_reused_all 6 2
+'
+
+test_expect_success 'multi-pack reuse can be disabled with feature.experimental' '
+	test_config feature.experimental true &&
+	test_config pack.allowPackReuse single &&
 
-	test_pack_reused 3 <trace2.txt &&
-	test_packs_reused 1 <trace2.txt
+	test_pack_objects_reused_all 3 1
 '
 
 test_expect_success 'enable multi-pack reuse' '
@@ -58,21 +91,11 @@ test_expect_success 'reuse all objects from subset of bitmapped packs' '
 	^$(git rev-parse A)
 	EOF
 
-	: >trace2.txt &&
-	GIT_TRACE2_EVENT="$PWD/trace2.txt" \
-		git pack-objects --stdout --revs <in >/dev/null &&
-
-	test_pack_reused 6 <trace2.txt &&
-	test_packs_reused 2 <trace2.txt
+	test_pack_objects_reused 6 2 <in
 '
 
 test_expect_success 'reuse all objects from all packs' '
-	: >trace2.txt &&
-	GIT_TRACE2_EVENT="$PWD/trace2.txt" \
-		git pack-objects --stdout --revs --all >/dev/null &&
-
-	test_pack_reused 9 <trace2.txt &&
-	test_packs_reused 3 <trace2.txt
+	test_pack_objects_reused_all 9 3
 '
 
 test_expect_success 'reuse objects from first pack with middle gap' '
@@ -105,12 +128,7 @@ test_expect_success 'reuse objects from first pack with middle gap' '
 	^$(git rev-parse D)
 	EOF
 
-	: >trace2.txt &&
-	GIT_TRACE2_EVENT="$PWD/trace2.txt" \
-		git pack-objects --stdout --delta-base-offset --revs <in >/dev/null &&
-
-	test_pack_reused 3 <trace2.txt &&
-	test_packs_reused 1 <trace2.txt
+	test_pack_objects_reused 3 1 <in
 '
 
 test_expect_success 'reuse objects from middle pack with middle gap' '
@@ -126,12 +144,7 @@ test_expect_success 'reuse objects from middle pack with middle gap' '
 	^$(git rev-parse D)
 	EOF
 
-	: >trace2.txt &&
-	GIT_TRACE2_EVENT="$PWD/trace2.txt" \
-		git pack-objects --stdout --delta-base-offset --revs <in >/dev/null &&
-
-	test_pack_reused 3 <trace2.txt &&
-	test_packs_reused 1 <trace2.txt
+	test_pack_objects_reused 3 1 <in
 '
 
 test_expect_success 'omit delta with uninteresting base (same pack)' '
@@ -161,10 +174,6 @@ test_expect_success 'omit delta with uninteresting base (same pack)' '
 	^$base
 	EOF
 
-	: >trace2.txt &&
-	GIT_TRACE2_EVENT="$PWD/trace2.txt" \
-		git pack-objects --stdout --delta-base-offset --revs <in >/dev/null &&
-
 	# We can only reuse the 3 objects corresponding to "other" from
 	# the latest pack.
 	#
@@ -176,8 +185,7 @@ test_expect_success 'omit delta with uninteresting base (same pack)' '
 	# The remaining objects from the other pack are similarly not
 	# reused because their objects are on the uninteresting side of
 	# the query.
-	test_pack_reused 3 <trace2.txt &&
-	test_packs_reused 1 <trace2.txt
+	test_pack_objects_reused 3 1 <in
 '
 
 test_expect_success 'omit delta from uninteresting base (cross pack)' '
@@ -190,15 +198,10 @@ test_expect_success 'omit delta from uninteresting base (cross pack)' '
 
 	git multi-pack-index write --bitmap --preferred-pack="pack-$P.idx" &&
 
-	: >trace2.txt &&
-	GIT_TRACE2_EVENT="$PWD/trace2.txt" \
-		git pack-objects --stdout --delta-base-offset --all >/dev/null &&
-
 	packs_nr="$(find $packdir -type f -name "pack-*.pack" | wc -l)" &&
 	objects_nr="$(git rev-list --count --all --objects)" &&
 
-	test_pack_reused $(($objects_nr - 1)) <trace2.txt &&
-	test_packs_reused $packs_nr <trace2.txt
+	test_pack_objects_reused_all $(($objects_nr - 1)) $packs_nr
 '
 
 test_done
diff --git a/t/t6300-for-each-ref.sh b/t/t6300-for-each-ref.sh
index 843a7fe143..eb6c8204e8 100755
--- a/t/t6300-for-each-ref.sh
+++ b/t/t6300-for-each-ref.sh
@@ -1356,6 +1356,52 @@ test_expect_success '--no-sort without subsequent --sort prints expected refs' '
 	test_cmp expected actual
 '
 
+test_expect_success 'set up custom date sorting' '
+	# Dates:
+	# - Wed Feb 07 2024 21:34:20 +0000
+	# - Tue Dec 14 1999 00:05:22 +0000
+	# - Fri Jun 04 2021 11:26:51 +0000
+	# - Mon Jan 22 2007 16:44:01 GMT+0000
+	i=1 &&
+	for when in 1707341660 945129922 1622806011 1169484241
+	do
+		GIT_COMMITTER_DATE="@$when +0000" \
+		GIT_COMMITTER_EMAIL="user@example.com" \
+		git tag -m "tag $when" custom-dates-$i &&
+		i=$(($i+1)) || return 1
+	done
+'
+
+test_expect_success 'sort by date defaults to full timestamp' '
+	cat >expected <<-\EOF &&
+	945129922 refs/tags/custom-dates-2
+	1169484241 refs/tags/custom-dates-4
+	1622806011 refs/tags/custom-dates-3
+	1707341660 refs/tags/custom-dates-1
+	EOF
+
+	git for-each-ref \
+		--format="%(creatordate:unix) %(refname)" \
+		--sort=creatordate \
+		"refs/tags/custom-dates-*" >actual &&
+	test_cmp expected actual
+'
+
+test_expect_success 'sort by custom date format' '
+	cat >expected <<-\EOF &&
+	00:05:22 refs/tags/custom-dates-2
+	11:26:51 refs/tags/custom-dates-3
+	16:44:01 refs/tags/custom-dates-4
+	21:34:20 refs/tags/custom-dates-1
+	EOF
+
+	git for-each-ref \
+		--format="%(creatordate:format:%H:%M:%S) %(refname)" \
+		--sort="creatordate:format:%H:%M:%S" \
+		"refs/tags/custom-dates-*" >actual &&
+	test_cmp expected actual
+'
+
 test_expect_success 'do not dereference NULL upon %(HEAD) on unborn branch' '
 	test_when_finished "git checkout main" &&
 	git for-each-ref --format="%(HEAD) %(refname:short)" refs/heads/ >actual &&
diff --git a/t/t9902-completion.sh b/t/t9902-completion.sh
index 35eb534fdd..b16c284181 100755
--- a/t/t9902-completion.sh
+++ b/t/t9902-completion.sh
@@ -11,6 +11,11 @@ test_description='test bash completion'
 # untraceable with such ancient Bash versions.
 test_untraceable=UnfortunatelyYes
 
+# Override environment and always use master for the default initial branch
+# name for these tests, so that rev completion candidates are as expected.
+GIT_TEST_DEFAULT_INITIAL_BRANCH_NAME=master
+export GIT_TEST_DEFAULT_INITIAL_BRANCH_NAME
+
 . ./lib-bash.sh
 
 complete ()
@@ -1267,6 +1272,142 @@ test_expect_success 'git switch - with no options, complete local branches and u
 	EOF
 '
 
+test_expect_success 'git bisect - when not bisecting, complete only replay and start subcommands' '
+	test_completion "git bisect " <<-\EOF
+	replay Z
+	start Z
+	EOF
+'
+
+test_expect_success 'git bisect - complete options to start subcommand' '
+	test_completion "git bisect start --" <<-\EOF
+	--term-new Z
+	--term-bad Z
+	--term-old Z
+	--term-good Z
+	--no-checkout Z
+	--first-parent Z
+	EOF
+'
+
+test_expect_success 'setup for git-bisect tests requiring a repo' '
+	git init git-bisect &&
+	(
+		cd git-bisect &&
+		echo "initial contents" >file &&
+		git add file &&
+		git commit -am "Initial commit" &&
+		git tag initial &&
+		echo "new line" >>file &&
+		git commit -am "First change" &&
+		echo "another new line" >>file &&
+		git commit -am "Second change" &&
+		git tag final
+	)
+'
+
+test_expect_success 'git bisect - start subcommand arguments before double-dash are completed as revs' '
+	(
+		cd git-bisect &&
+		test_completion "git bisect start " <<-\EOF
+		HEAD Z
+		final Z
+		initial Z
+		master Z
+		EOF
+	)
+'
+
+# Note that these arguments are <pathspec>s, which in practice the fallback
+# completion (not the git completion) later ends up completing as paths.
+test_expect_success 'git bisect - start subcommand arguments after double-dash are not completed' '
+	(
+		cd git-bisect &&
+		test_completion "git bisect start final initial -- " ""
+	)
+'
+
+test_expect_success 'setup for git-bisect tests requiring ongoing bisection' '
+	(
+		cd git-bisect &&
+		git bisect start --term-new=custom_new --term-old=custom_old final initial
+	)
+'
+
+test_expect_success 'git-bisect - when bisecting all subcommands are candidates' '
+	(
+		cd git-bisect &&
+		test_completion "git bisect " <<-\EOF
+		start Z
+		bad Z
+		custom_new Z
+		custom_old Z
+		new Z
+		good Z
+		old Z
+		terms Z
+		skip Z
+		reset Z
+		visualize Z
+		replay Z
+		log Z
+		run Z
+		help Z
+		EOF
+	)
+'
+
+test_expect_success 'git-bisect - options to terms subcommand are candidates' '
+	(
+		cd git-bisect &&
+		test_completion "git bisect terms --" <<-\EOF
+		--term-bad Z
+		--term-good Z
+		--term-new Z
+		--term-old Z
+		EOF
+	)
+'
+
+test_expect_success 'git-bisect - git-log options to visualize subcommand are candidates' '
+	(
+		cd git-bisect &&
+		# The completion used for git-log and here does not complete
+		# every git-log option, so rather than hope to stay in sync
+		# with exactly what it does we will just spot-test here.
+		test_completion "git bisect visualize --sta" <<-\EOF &&
+		--stat Z
+		EOF
+		test_completion "git bisect visualize --summar" <<-\EOF
+		--summary Z
+		EOF
+	)
+'
+
+test_expect_success 'git-bisect - view subcommand is not a candidate' '
+	(
+		cd git-bisect &&
+		test_completion "git bisect vi" <<-\EOF
+		visualize Z
+		EOF
+	)
+'
+
+test_expect_success 'git-bisect - existing view subcommand is recognized and enables completion of git-log options' '
+	(
+		cd git-bisect &&
+		# The completion used for git-log and here does not complete
+		# every git-log option, so rather than hope to stay in sync
+		# with exactly what it does we will just spot-test here.
+		test_completion "git bisect view --sta" <<-\EOF &&
+		--stat Z
+		EOF
+		test_completion "git bisect view --summar" <<-\EOF
+		--summary Z
+		EOF
+	)
+'
+
 test_expect_success 'git checkout - completes refs and unique remote branches for DWIM' '
 	test_completion "git checkout " <<-\EOF
 	HEAD Z
@@ -2583,6 +2724,35 @@ test_expect_success 'git config - variable name include' '
 	EOF
 '
 
+test_expect_success 'setup for git config submodule tests' '
+	test_create_repo sub &&
+	test_commit -C sub initial &&
+	git submodule add ./sub
+'
+
+test_expect_success 'git config - variable name - submodule and __git_compute_first_level_config_vars_for_section' '
+	test_completion "git config submodule." <<-\EOF
+	submodule.active Z
+	submodule.alternateErrorStrategy Z
+	submodule.alternateLocation Z
+	submodule.fetchJobs Z
+	submodule.propagateBranches Z
+	submodule.recurse Z
+	submodule.sub.Z
+	EOF
+'
+
+test_expect_success 'git config - variable name - __git_compute_second_level_config_vars_for_section' '
+	test_completion "git config submodule.sub." <<-\EOF
+	submodule.sub.url Z
+	submodule.sub.update Z
+	submodule.sub.branch Z
+	submodule.sub.fetchRecurseSubmodules Z
+	submodule.sub.ignore Z
+	submodule.sub.active Z
+	EOF
+'
+
 test_expect_success 'git config - value' '
 	test_completion "git config color.pager " <<-\EOF
 	false Z
diff --git a/t/unit-tests/test-lib.c b/t/unit-tests/test-lib.c
index 7bf9dfdb95..66d6980ffb 100644
--- a/t/unit-tests/test-lib.c
+++ b/t/unit-tests/test-lib.c
@@ -21,12 +21,11 @@ static struct {
 	.result = RESULT_NONE,
 };
 
-#ifndef _MSC_VER
-#define make_relative(location) location
-#else
 /*
  * Visual C interpolates the absolute Windows path for `__FILE__`,
  * but we want to see relative paths, as verified by t0080.
+ * There are other compilers that do the same, and are not for
+ * Windows.
  */
 #include "dir.h"
 
@@ -34,32 +33,66 @@ static const char *make_relative(const char *location)
 {
 	static char prefix[] = __FILE__, buf[PATH_MAX], *p;
 	static size_t prefix_len;
+	static int need_bs_to_fs = -1;
 
-	if (!prefix_len) {
+	/* one-time preparation */
+	if (need_bs_to_fs < 0) {
 		size_t len = strlen(prefix);
-		const char *needle = "\\t\\unit-tests\\test-lib.c";
+		char needle[] = "t\\unit-tests\\test-lib.c";
 		size_t needle_len = strlen(needle);
 
-		if (len < needle_len || strcmp(needle, prefix + len - needle_len))
-			die("unexpected suffix of '%s'", prefix);
+		if (len < needle_len)
+			die("unexpected prefix '%s'", prefix);
+
+		/*
+		 * The path could be relative (t/unit-tests/test-lib.c)
+		 * or full (/home/user/git/t/unit-tests/test-lib.c).
+		 * Check the slash between "t" and "unit-tests".
+		 */
+		prefix_len = len - needle_len;
+		if (prefix[prefix_len + 1] == '/') {
+			/* Oh, we're not Windows */
+			for (size_t i = 0; i < needle_len; i++)
+				if (needle[i] == '\\')
+					needle[i] = '/';
+			need_bs_to_fs = 0;
+		} else {
+			need_bs_to_fs = 1;
+		}
 
-		/* let it end in a directory separator */
-		prefix_len = len - needle_len + 1;
+		/*
+		 * prefix_len == 0 if the compiler gives paths relative
+		 * to the root of the working tree.  Otherwise, we want
+		 * to see that we did find the needle[] at a directory
+		 * boundary.  Again we rely on that needle[] begins with
+		 * "t" followed by the directory separator.
+		 */
+		if (fspathcmp(needle, prefix + prefix_len) ||
+		    (prefix_len && prefix[prefix_len - 1] != needle[1]))
+			die("unexpected suffix of '%s'", prefix);
 	}
 
-	/* Does it not start with the expected prefix? */
-	if (fspathncmp(location, prefix, prefix_len))
+	/*
+	 * Does it not start with the expected prefix?
+	 * Return it as-is without making it worse.
+	 */
+	if (prefix_len && fspathncmp(location, prefix, prefix_len))
 		return location;
 
-	strlcpy(buf, location + prefix_len, sizeof(buf));
+	/*
+	 * If we do not need to munge directory separator, we can return
+	 * the substring at the tail of the location.
+	 */
+	if (!need_bs_to_fs)
+		return location + prefix_len;
+
 	/* convert backslashes to forward slashes */
+	strlcpy(buf, location + prefix_len, sizeof(buf));
 	for (p = buf; *p; p++)
 		if (*p == '\\')
 			*p = '/';
-
 	return buf;
 }
-#endif
 
 static void msg_with_prefix(const char *prefix, const char *format, va_list ap)
 {