[PATCH 2/2] merge-ours: integrate with sparse-index

From: Sam Bostock via GitGitGadget <gitgitgadget@gmail.com>
Date: Feb 6, 2026, 02:32 UTC
Message-ID: <20b9e0bf6e2b12eea1ff50b14d0d2809c601a943.1770345124.git.gitgitgadget@gmail.com>
In-Reply-To: <pull.2189.git.git.1770345124.gitgitgadget@gmail.com>

From: Sam Bostock <sam@sambostock.ca>

The merge-ours builtin reads the index only to compare it against HEAD via index_differs_from(), whose diff machinery (run_diff_index) is already sparse-aware.

Teach merge-ours to opt out of requiring a full index by setting command_requires_full_index to 0. Because merge-ours is invoked as a subprocess by "git merge -s ours" and never previously read config, the global variables core_apply_sparse_checkout and core_sparse_checkout_cone remained unset, causing is_sparse_index_allowed() to return false and the index to be expanded anyway. Add a repo_config() call with git_default_config to populate these globals.

Add tests to t1092 verifying that "git merge -s ours" produces identical results across full-checkout, sparse-checkout, and sparse-index modes, including verifying the resulting merge commit structure, and that the sparse index is not expanded during the operation.

Signed-off-by: Sam Bostock <sam@sambostock.ca>
---
 builtin/merge-ours.c                     |  6 ++++++
 t/t1092-sparse-checkout-compatibility.sh | 14 ++++++++++++++
 2 files changed, 20 insertions(+)

diff --git a/builtin/merge-ours.c b/builtin/merge-ours.c
index 2312e58ab3..405b2989f7 100644
--- a/builtin/merge-ours.c
+++ b/builtin/merge-ours.c
@@ -10,6 +10,8 @@
 
 #include "git-compat-util.h"
 #include "builtin.h"
+#include "config.h"
+#include "environment.h"
 #include "diff.h"
 
 static const char builtin_merge_ours_usage[] =
@@ -22,6 +24,10 @@ int cmd_merge_ours(int argc,
 {
 	show_usage_if_asked(argc, argv, builtin_merge_ours_usage);
 
+	repo_config(repo, git_default_config, NULL);
+	prepare_repo_settings(repo);
+	repo->settings.command_requires_full_index = 0;
+
 	/*
 	 * The contents of the current index becomes the tree we
 	 * commit.  The index must match HEAD, or this merge cannot go
diff --git a/t/t1092-sparse-checkout-compatibility.sh b/t/t1092-sparse-checkout-compatibility.sh
index b0f691c151..d98cb4ac11 100755
--- a/t/t1092-sparse-checkout-compatibility.sh
+++ b/t/t1092-sparse-checkout-compatibility.sh
@@ -2559,4 +2559,18 @@ test_expect_success 'cat-file --batch' '
 	ensure_expanded cat-file --batch <in
 '
 
+test_expect_success 'merge -s ours' '
+	init_repos &&
+
+	test_all_match git rev-parse HEAD^{tree} &&
+	test_all_match git merge -s ours merge-right &&
+	test_all_match git rev-parse HEAD^{tree} &&
+	test_all_match git rev-parse HEAD^2
+'
+
+test_expect_success 'sparse-index is not expanded: merge-ours' '
+	init_repos &&
+	ensure_not_expanded merge -s ours merge-right
+'
+
 test_done

-- 
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