@@ -195,6 +195,39 @@ For instance, if you configured the `diff.algorithm` variable to a
 non-default value and want to use the default one, then you
 have to use `--diff-algorithm=default` option.
 
+ifdef::git-diff[]
+ifdef::git-diff-index[]
+ifdef::git-diff-tree[]
+
+--scope=[sparse|all]::
+	Restrict or not restrict diff path scope in sparse specification.
+	The variants are as follows:
+
++
+--
+`sparse`;;
+	When using diff to compare commit history, restrict the
+	scope of file path comparisons to the sparse specification.
+	See sparse specification in link:technical/sparse-checkout.html
+	[the sparse-checkout design document] for more information.
+`all`;;
+	When using diff to compare commit history, the file comparison
+	scope is full-tree. This is consistent with the current default
+	behavior.
+--
++
+
+Note that `--scope` option only take effect if diff command specify
+`--cached` or `REVISION`.
+
+The behavior of this `--scope` option is experimental and may change
+in the future. See link:technical/sparse-checkout.html [the sparse-checkout
+design document] for more information.
+
+endif::git-diff-tree[]
+endif::git-diff-index[]
+endif::git-diff[]
+
 --stat[=<width>[,<name-width>[,<count>]]]::
 	Generate a diffstat. By default, as much space as necessary
 	will be used for the filename part, and the rest for the graph

@@ -20,6 +20,14 @@ int cmd_diff_index(int argc, const char **argv, const char *prefix)
 	unsigned int option = 0;
 	int i;
 	int result;
+	enum sparse_scope scope;
+
+	struct option sparse_scope_options[] = {
+		OPT_CALLBACK_F(0, "scope", &scope, N_("[sparse|all]"),
+				N_("restrict path scope in sparse specification"),
+				PARSE_OPT_NONEG, diff_opt_sparse_scope),
+		OPT_END()
+	};
 
 	if (argc == 2 && !strcmp(argv[1], "-h"))
 		usage(diff_cache_usage);

@@ -36,6 +44,15 @@ int cmd_diff_index(int argc, const char **argv, const char *prefix)
 	diff_merges_suppress_m_parsing();
 
 	argc = setup_revisions(argc, argv, &rev, NULL);
+
+	argc = parse_options(argc, argv, prefix, sparse_scope_options, NULL,
+			     PARSE_OPT_KEEP_DASHDASH |
+			     PARSE_OPT_KEEP_UNKNOWN_OPT |
+			     PARSE_OPT_KEEP_ARGV0 |
+			     PARSE_OPT_NO_INTERNAL_HELP);
+
+	rev.diffopt.scope = scope;
+
 	for (i = 1; i < argc; i++) {
 		const char *arg = argv[i];
 

@@ -66,9 +83,15 @@ int cmd_diff_index(int argc, const char **argv, const char *prefix)
 			perror("read_cache_preload");
 			return -1;
 		}
-	} else if (read_cache() < 0) {
-		perror("read_cache");
-		return -1;
+	} else {
+		if (read_cache() < 0) {
+			perror("read_cache");
+			return -1;
+		}
+		if (rev.diffopt.scope == SPARSE_SCOPE_SPARSE &&
+		    strcmp(rev.pending.objects[0].name, "HEAD"))
+			diff_collect_changes_index(&rev.diffopt.pathspec,
+						   &rev.diffopt.change_index_files);
 	}
 	result = run_diff_index(&rev, option);
 	result = diff_result_code(&rev.diffopt, result);

@@ -114,6 +114,14 @@ int cmd_diff_tree(int argc, const char **argv, const char *prefix)
 	struct userformat_want w;
 	int read_stdin = 0;
 	int merge_base = 0;
+	enum sparse_scope scope;
+
+	struct option sparse_scope_options[] = {
+		OPT_CALLBACK_F(0, "scope", &scope, N_("[sparse|all]"),
+				N_("restrict path scope in sparse specification"),
+				PARSE_OPT_NONEG, diff_opt_sparse_scope),
+		OPT_END()
+	};
 
 	if (argc == 2 && !strcmp(argv[1], "-h"))
 		usage(diff_tree_usage);

@@ -131,6 +139,13 @@ int cmd_diff_tree(int argc, const char **argv, const char *prefix)
 	prefix = precompose_argv_prefix(argc, argv, prefix);
 	argc = setup_revisions(argc, argv, opt, &s_r_opt);
 
+	argc = parse_options(argc, argv, prefix, sparse_scope_options, NULL,
+			     PARSE_OPT_KEEP_DASHDASH |
+			     PARSE_OPT_KEEP_UNKNOWN_OPT |
+			     PARSE_OPT_KEEP_ARGV0 |
+			     PARSE_OPT_NO_INTERNAL_HELP);
+	opt->diffopt.scope = scope;
+
 	memset(&w, 0, sizeof(w));
 	userformat_find_requirements(NULL, &w);
 

@@ -161,9 +161,15 @@ static int builtin_diff_index(struct rev_info *revs,
 			perror("read_cache_preload");
 			return -1;
 		}
-	} else if (read_cache() < 0) {
-		perror("read_cache");
-		return -1;
+	} else {
+		if (read_cache() < 0) {
+			perror("read_cache");
+			return -1;
+		}
+		if (revs->diffopt.scope == SPARSE_SCOPE_SPARSE &&
+		    strcmp(revs->pending.objects[0].name, "HEAD"))
+			diff_collect_changes_index(&revs->diffopt.pathspec,
+						   &revs->diffopt.change_index_files);
 	}
 	return run_diff_index(revs, option);
 }

@@ -388,6 +394,25 @@ static void symdiff_prepare(struct rev_info *rev, struct symdiff *sym)
 	sym->skip = map;
 }
 
+int diff_opt_sparse_scope(const struct option *option,
+				const char *optarg, int unset)
+{
+	enum sparse_scope *scope = option->value;
+
+	BUG_ON_OPT_NEG_NOARG(unset, optarg);
+
+	if (!core_apply_sparse_checkout)
+		return error(_("this git repository don't "
+			       "use sparse-checkout, --scope option cannot be used"));
+	if (!strcmp(optarg, "all"))
+		*scope = SPARSE_SCOPE_ALL;
+	else if (!strcmp(optarg, "sparse"))
+		*scope = SPARSE_SCOPE_SPARSE;
+	else
+		return error(_("invalid --scope value: %s"), optarg);
+	return 0;
+}
+
 int cmd_diff(int argc, const char **argv, const char *prefix)
 {
 	int i;

@@ -399,6 +424,14 @@ int cmd_diff(int argc, const char **argv, const char *prefix)
 	int nongit = 0, no_index = 0;
 	int result = 0;
 	struct symdiff sdiff;
+	enum sparse_scope scope;
+
+	struct option sparse_scope_options[] = {
+		OPT_CALLBACK_F(0, "scope", &scope, N_("[sparse|all]"),
+				N_("restrict path scope in sparse specification"),
+				PARSE_OPT_NONEG, diff_opt_sparse_scope),
+		OPT_END()
+	};
 
 	/*
 	 * We could get N tree-ish in the rev.pending_objects list.

@@ -504,6 +537,13 @@ int cmd_diff(int argc, const char **argv, const char *prefix)
 		diff_setup_done(&rev.diffopt);
 	}
 
+	argc = parse_options(argc, argv, prefix, sparse_scope_options, NULL,
+			     PARSE_OPT_KEEP_DASHDASH |
+			     PARSE_OPT_KEEP_UNKNOWN_OPT |
+			     PARSE_OPT_KEEP_ARGV0 |
+			     PARSE_OPT_NO_INTERNAL_HELP);
+
+	rev.diffopt.scope = scope;
 	rev.diffopt.flags.recursive = 1;
 	rev.diffopt.rotate_to_strict = 1;
 

@@ -1082,6 +1082,11 @@ extern int core_apply_sparse_checkout;
 extern int core_sparse_checkout_cone;
 extern int sparse_expect_files_outside_of_patterns;
 
+enum sparse_scope {
+	SPARSE_SCOPE_ALL = 0,
+	SPARSE_SCOPE_SPARSE,
+};
+
 /*
  * Returns the boolean value of $GIT_OPTIONAL_LOCKS (or the default value).
  */

@@ -445,6 +445,13 @@ static void do_oneway_diff(struct unpack_trees_options *o,
 
 	match_missing = revs->match_missing;
 
+	if (revs->diffopt.scope == SPARSE_SCOPE_SPARSE &&
+	    ((o->index_only && revs->pending.objects[0].name &&
+	      strcmp(revs->pending.objects[0].name, "HEAD") &&
+	      !index_file_in_sparse_specification(idx ? idx : tree, &revs->diffopt.change_index_files)) ||
+	     (!o->index_only && !worktree_file_in_sparse_specification(idx))))
+		return;
+
 	if (cached && idx && ce_stage(idx)) {
 		struct diff_filepair *pair;
 		pair = diff_unmerge(&revs->diffopt, idx->name);

@@ -598,6 +605,43 @@ void diff_get_merge_base(const struct rev_info *revs, struct object_id *mb)
 	free_commit_list(merge_bases);
 }
 
+static void diff_collect_updated_cb(struct diff_queue_struct *q,
+					 struct diff_options *options,
+					 void *data) {
+	int i;
+	struct strset *change_index_files = (struct strset *)data;
+
+	for (i = 0; i < q->nr; i++) {
+		struct diff_filepair *p = q->queue[i];
+
+		strset_add(change_index_files, p->two->path);
+		if (p->status == DIFF_STATUS_RENAMED)
+			strset_add(change_index_files, p->one->path);
+	}
+}
+
+void diff_collect_changes_index(struct pathspec *pathspec, struct strset *change_index_files)
+{
+	struct rev_info rev;
+	struct setup_revision_opt opt;
+
+	repo_init_revisions(the_repository, &rev, NULL);
+	memset(&opt, 0, sizeof(opt));
+	opt.def = "HEAD";
+	setup_revisions(0, NULL, &rev, &opt);
+
+	rev.diffopt.ita_invisible_in_index = 1;
+	rev.diffopt.output_format |= DIFF_FORMAT_CALLBACK;
+	rev.diffopt.format_callback = diff_collect_updated_cb;
+	rev.diffopt.format_callback_data = change_index_files;
+	rev.diffopt.flags.recursive = 1;
+
+	copy_pathspec(&rev.prune_data, pathspec);
+	run_diff_index(&rev, 1);
+	release_revisions(&rev);
+}
+
+
 int run_diff_index(struct rev_info *revs, unsigned int option)
 {
 	struct object_array_entry *ent;

@@ -4663,6 +4663,7 @@ void repo_diff_setup(struct repository *r, struct diff_options *options)
 	options->color_moved = diff_color_moved_default;
 	options->color_moved_ws_handling = diff_color_moved_ws_default;
 
+	strset_init(&options->change_index_files);
 	prep_parse_options(options);
 }
 

@@ -6511,6 +6512,7 @@ void diff_free(struct diff_options *options)
 	diff_free_ignore_regex(options);
 	clear_pathspec(&options->pathspec);
 	FREE_AND_NULL(options->parseopts);
+	strset_clear(&options->change_index_files);
 }
 
 void diff_flush(struct diff_options *options)

@@ -8,6 +8,7 @@
 #include "pathspec.h"
 #include "object.h"
 #include "oidset.h"
+#include "strmap.h"
 
 /**
  * The diff API is for programs that compare two sets of files (e.g. two trees,

@@ -285,6 +286,9 @@ struct diff_options {
 	/* diff-filter bits */
 	unsigned int filter, filter_not;
 
+	/* diff sparse-checkout scope */
+	enum sparse_scope scope;
+
 	int use_color;
 
 	/* Number of context lines to generate in patch output. */

@@ -397,6 +401,7 @@ struct diff_options {
 	struct option *parseopts;
 	struct strmap *additional_path_headers;
 
+	struct strset change_index_files;
 	int no_free;
 };
 

@@ -696,4 +701,7 @@ void print_stat_summary(FILE *fp, int files,
 			int insertions, int deletions);
 void setup_diff_pager(struct diff_options *);
 
+void diff_collect_changes_index(struct pathspec *pathspec, struct strset *files);
+int diff_opt_sparse_scope(const struct option *option, const char *optarg, int unset);
+
 #endif /* DIFF_H */

@@ -1503,6 +1503,26 @@ int path_in_cone_mode_sparse_checkout(const char *path,
 	return path_in_sparse_checkout_1(path, istate, 1);
 }
 
+int path_in_sparse_patterns(const char *path) {
+	return path_in_sparse_checkout_1(path, the_repository->index, core_sparse_checkout_cone);
+}
+
+/* Expand sparse-checkout specification (worktree) */
+int worktree_file_in_sparse_specification(const struct cache_entry *worktree_check_ce)
+{
+	return worktree_check_ce && !ce_skip_worktree(worktree_check_ce);
+}
+
+/* Expand sparse-checkout specification (index) */
+int index_file_in_sparse_specification(const struct cache_entry *ce, struct strset *change_index_files)
+{
+	if (!ce->ce_namelen)
+		return 0;
+	if (change_index_files && strset_contains(change_index_files, ce->name))
+		return 1;
+	return path_in_sparse_patterns(ce->name);
+}
+
 static struct path_pattern *last_matching_pattern_from_lists(
 		struct dir_struct *dir, struct index_state *istate,
 		const char *pathname, int pathlen,

@@ -4,6 +4,7 @@
 #include "cache.h"
 #include "hashmap.h"
 #include "strbuf.h"
+#include "strmap.h"
 
 /**
  * The directory listing API is used to enumerate paths in the work tree,

@@ -401,6 +402,9 @@ int path_in_sparse_checkout(const char *path,
 			    struct index_state *istate);
 int path_in_cone_mode_sparse_checkout(const char *path,
 				      struct index_state *istate);
+int path_in_sparse_patterns(const char *path);
+int index_file_in_sparse_specification(const struct cache_entry *ce, struct strset *change_index_files);
+int worktree_file_in_sparse_specification(const struct cache_entry *worktree_check_ce);
 
 struct dir_entry *dir_add_ignored(struct dir_struct *dir,
 				  struct index_state *istate,

@@ -0,0 +1,286 @@
+#!/bin/sh
+
+test_description='diff sparse-checkout scope'
+
+GIT_TEST_DEFAULT_INITIAL_BRANCH_NAME=main
+export GIT_TEST_DEFAULT_INITIAL_BRANCH_NAME
+
+. ./test-lib.sh
+
+test_expect_success 'setup' '
+	git init repo &&
+	(
+		cd repo &&
+		mkdir in out1 out2 &&
+		for i in $(test_seq 6)
+		do
+			echo "in $i" >in/"$i" &&
+			echo "out1 $i" >out1/"$i" &&
+			echo "out2 $i" >out2/"$i" || return 1
+		done &&
+		git add in out1 out2 &&
+		git commit -m init &&
+		for i in $(test_seq 6)
+		do
+			echo "in $i" >>in/"$i" &&
+			echo "out1 $i" >>out1/"$i" || return 1
+		done &&
+		git add in out1 &&
+		git commit -m change &&
+		git sparse-checkout set "in"
+	)
+'
+
+reset_sparse_checkout_state() {
+	git -C repo reset --hard HEAD &&
+	git -C repo sparse-checkout reapply
+}
+
+reset_and_change_index() {
+	reset_sparse_checkout_state &&
+	# add new ce
+	oid=$(echo "new thing" | git -C repo hash-object --stdin -w) &&
+	git -C repo update-index --add --cacheinfo 100644 $oid in/7 &&
+	git -C repo update-index --add --cacheinfo 100644 $oid out1/7 &&
+	# rm ce
+	git -C repo update-index --remove in/6 &&
+	git -C repo update-index --remove out1/6 &&
+	# modify ce
+	git -C repo update-index --cacheinfo 100644 $oid out1/5 &&
+	# mv ce1 -> ce2
+	oid=$(git -C repo ls-files --format="%(objectname)" in/4) &&
+	git -C repo update-index --add --cacheinfo 100644 $oid in/8 &&
+	git -C repo update-index --remove in/4 &&
+	oid=$(git -C repo ls-files --format="%(objectname)" out1/4) &&
+	git -C repo update-index --add --cacheinfo 100644 $oid out1/8 &&
+	git -C repo update-index --remove out1/4 &&
+	# chmod ce
+	git -C repo update-index --chmod +x in/3 &&
+	git -C repo update-index --chmod +x out1/3
+}
+
+reset_and_change_worktree() {
+	reset_sparse_checkout_state &&
+	rm -rf repo/out1 repo/out2 &&
+	mkdir repo/out1 repo/out2 &&
+	# add new file
+	echo "in 7" >repo/in/7 &&
+	echo "out1 7" >repo/out1/7 &&
+	git -C repo add --sparse in/7 out1/7 &&
+	# create out old file
+	>repo/out1/6 &&
+	# rm file
+	rm repo/in/6 &&
+	# modify file
+	echo "out1 x" >repo/out1/5 &&
+	# mv file1 -> file2
+	mv repo/in/4 repo/in/3 &&
+	# chmod file
+	chmod +x repo/in/2 &&
+	# add new file, mark skipworktree
+	echo "in 8" >repo/in/8 &&
+	echo "out1 8" >repo/out1/8 &&
+	echo "out2 8" >repo/out2/8 &&
+	git -C repo add --sparse in/8 out1/8 out2/8 &&
+	git -C repo update-index --skip-worktree in/8 &&
+	git -C repo update-index --skip-worktree out1/8 &&
+	git -C repo update-index --skip-worktree out2/8 &&
+	rm repo/in/8 repo/out1/8
+}
+
+# git diff --cached REV
+
+test_expect_success 'git diff --cached --scope=all' '
+	reset_and_change_index &&
+	cat >expected <<-EOF &&
+M	in/1
+M	in/2
+M	in/3
+M	in/4
+M	in/5
+M	in/6
+A	in/7
+A	in/8
+M	out1/1
+M	out1/2
+M	out1/3
+M	out1/5
+D	out1/6
+A	out1/7
+R050	out1/4	out1/8
+	EOF
+	git -C repo diff --name-status --cached --scope=all HEAD~ >actual &&
+	test_cmp expected actual
+'
+
+test_expect_success 'git diff --cached --scope=sparse' '
+	reset_and_change_index &&
+	cat >expected <<-EOF &&
+M	in/1
+M	in/2
+M	in/3
+M	in/4
+M	in/5
+M	in/6
+A	in/7
+A	in/8
+M	out1/3
+M	out1/5
+D	out1/6
+A	out1/7
+R050	out1/4	out1/8
+	EOF
+	git -C repo diff --name-status --cached --scope=sparse HEAD~ >actual &&
+	test_cmp expected actual
+'
+
+# git diff REV
+
+test_expect_success 'git diff REVISION --scope=all' '
+	reset_and_change_worktree &&
+	cat >expected <<-EOF &&
+M	in/1
+M	in/2
+M	in/3
+D	in/4
+M	in/5
+D	in/6
+A	in/7
+M	out1/1
+M	out1/2
+M	out1/3
+M	out1/4
+M	out1/5
+M	out1/6
+A	out1/7
+A	out2/8
+	EOF
+	git -C repo diff --name-status --scope=all HEAD~ >actual &&
+	test_cmp expected actual
+'
+
+test_expect_success 'git diff REVISION --scope=sparse' '
+	reset_and_change_worktree &&
+	cat >expected <<-EOF &&
+M	in/1
+M	in/2
+M	in/3
+D	in/4
+M	in/5
+D	in/6
+A	in/7
+M	out1/5
+M	out1/6
+A	out1/7
+A	out2/8
+	EOF
+	git -C repo diff --name-status --scope=sparse HEAD~ >actual &&
+	test_cmp expected actual
+'
+
+# git diff REV1 REV2
+
+test_expect_success 'git diff two REVISION --scope=all' '
+	reset_sparse_checkout_state &&
+	cat >expected <<-EOF &&
+M	in/1
+M	in/2
+M	in/3
+M	in/4
+M	in/5
+M	in/6
+M	out1/1
+M	out1/2
+M	out1/3
+M	out1/4
+M	out1/5
+M	out1/6
+	EOF
+	git -C repo diff --name-status --scope=all HEAD~ HEAD >actual &&
+	test_cmp expected actual
+'
+
+test_expect_success 'git diff two REVISION --scope=sparse' '
+	reset_sparse_checkout_state &&
+	cat >expected <<-EOF &&
+M	in/1
+M	in/2
+M	in/3
+M	in/4
+M	in/5
+M	in/6
+	EOF
+	git -C repo diff --name-status --scope=sparse HEAD~ HEAD >actual &&
+	test_cmp expected actual
+'
+
+# git diff-index
+
+test_expect_success 'git diff-index --cached --scope=all' '
+	reset_and_change_index &&
+	cat >expected <<-EOF &&
+M	in/1
+M	in/2
+M	in/3
+M	in/4
+M	in/5
+M	in/6
+A	in/7
+A	in/8
+M	out1/1
+M	out1/2
+M	out1/3
+D	out1/4
+M	out1/5
+D	out1/6
+A	out1/7
+A	out1/8
+	EOF
+	git -C repo diff-index --name-status --cached --scope=all HEAD~ >actual &&
+	test_cmp expected actual
+'
+
+test_expect_success 'git diff-index --cached --scope=sparse' '
+	reset_and_change_index &&
+	cat >expected <<-EOF &&
+M	in/1
+M	in/2
+M	in/3
+M	in/4
+M	in/5
+M	in/6
+A	in/7
+A	in/8
+M	out1/3
+D	out1/4
+M	out1/5
+D	out1/6
+A	out1/7
+A	out1/8
+	EOF
+	git -C repo diff-index --name-status --cached --scope=sparse HEAD~ >actual &&
+	test_cmp expected actual
+'
+
+# git diff-tree
+
+test_expect_success 'git diff-tree --scope=all' '
+	reset_sparse_checkout_state &&
+	cat >expected <<-EOF &&
+M	in
+M	out1
+	EOF
+	git -C repo diff-tree --name-status --scope=all HEAD~ HEAD >actual &&
+	test_cmp expected actual
+'
+
+test_expect_success 'git diff-tree --scope=sparse' '
+	reset_sparse_checkout_state &&
+	cat >expected <<-EOF &&
+M	in
+	EOF
+	git -C repo diff-tree --name-status --scope=sparse HEAD~ HEAD >actual &&
+	test_cmp expected actual
+'
+
+test_done

@@ -5,6 +5,7 @@
 #include "diff.h"
 #include "diffcore.h"
 #include "tree.h"
+#include "dir.h"
 
 /*
  * internal mode marker, saying a tree entry != entry of tp[imin]

@@ -76,6 +77,16 @@ static int tree_entry_pathcmp(struct tree_desc *t1, struct tree_desc *t2)
 static int emit_diff_first_parent_only(struct diff_options *opt, struct combine_diff_path *p)
 {
 	struct combine_diff_parent *p0 = &p->parent[0];
+
+	if (opt->scope == SPARSE_SCOPE_SPARSE) {
+		struct strbuf sb = STRBUF_INIT;
+
+		strbuf_addstr(&sb, p->path);
+		if (S_ISDIR(p->mode) || S_ISDIR(p0->mode))
+			strbuf_addch(&sb, '/');
+		if (!path_in_sparse_patterns(sb.buf))
+			return 0;
+	}
 	if (p->mode && p0->mode) {
 		opt->change(opt, p0->mode, p->mode, &p0->oid, &p->oid,
 			1, 1, p->path, 0, 0);