advice.h: add advise_on_moving_dirty_path()

Add an advice.

When the user use `git mv --sparse <dirty-path> <destination>`, Git
will warn the user to use `git add --sparse <paths>` then use
`git sparse-checkout reapply` to apply the sparsity rules.

Add a few lines to previous "move dirty path" tests so we can test
this new advice is working.

Suggested-by: Derrick Stolee <derrickstolee@github.com>
Signed-off-by: Shaoxuan Yuan <shaoxuan.yuan02@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

advice.c

@@ -261,3 +261,22 @@ void detach_advice(const char *new_name)
 
 	fprintf(stderr, fmt, new_name);
 }
+
+void advise_on_moving_dirty_path(struct string_list *pathspec_list)
+{
+	struct string_list_item *item;
+
+	if (!pathspec_list->nr)
+		return;
+
+	fprintf(stderr, _("The following paths have been moved outside the\n"
+			  "sparse-checkout definition but are not sparse due to local\n"
+			  "modifications.\n"));
+	for_each_string_list_item(item, pathspec_list)
+		fprintf(stderr, "%s\n", item->string);
+
+	advise_if_enabled(ADVICE_UPDATE_SPARSE_PATH,
+			  _("To correct the sparsity of these paths, do the following:\n"
+			    "* Use \"git add --sparse <paths>\" to update the index\n"
+			    "* Use \"git sparse-checkout reapply\" to apply the sparsity rules"));
+}

advice.h

@@ -74,5 +74,6 @@ void NORETURN die_conclude_merge(void);
 void NORETURN die_ff_impossible(void);
 void advise_on_updating_sparse_paths(struct string_list *pathspec_list);
 void detach_advice(const char *new_name);
+void advise_on_moving_dirty_path(struct string_list *pathspec_list);
 
 #endif /* ADVICE_H */

builtin/mv.c

@@ -532,6 +532,9 @@ remove_entry:
 	strbuf_release(&a_src_dir);
 	free(src_dir);
 
+	if (dirty_paths.nr)
+		advise_on_moving_dirty_path(&dirty_paths);
+
 	if (gitmodules_modified)
 		stage_updated_gitmodules(&the_index);
 

t/t7002-mv-sparse-checkout.sh

@@ -28,12 +28,25 @@ test_expect_success 'setup' "
 	updated in the index:
 	EOF
 
-	cat >sparse_hint <<-EOF
+	cat >sparse_hint <<-EOF &&
 	hint: If you intend to update such entries, try one of the following:
 	hint: * Use the --sparse option.
 	hint: * Disable or modify the sparsity rules.
 	hint: Disable this message with \"git config advice.updateSparsePath false\"
 	EOF
+
+	cat >dirty_error_header <<-EOF &&
+	The following paths have been moved outside the
+	sparse-checkout definition but are not sparse due to local
+	modifications.
+	EOF
+
+	cat >dirty_hint <<-EOF
+	hint: To correct the sparsity of these paths, do the following:
+	hint: * Use \"git add --sparse <paths>\" to update the index
+	hint: * Use \"git sparse-checkout reapply\" to apply the sparsity rules
+	hint: Disable this message with \"git config advice.updateSparsePath false\"
+	EOF
 "
 
 test_expect_success 'mv refuses to move sparse-to-sparse' '
@@ -431,6 +444,10 @@ test_expect_success 'move dirty path from in-cone to out-of-cone' '
 	test_cmp expect stderr &&
 
 	git mv --sparse sub/d folder1 2>stderr &&
+	cat dirty_error_header >expect &&
+	echo "folder1/d" >>expect &&
+	cat dirty_hint >>expect &&
+	test_cmp expect stderr &&
 
 	test_path_is_missing sub/d &&
 	test_path_is_file folder1/d &&
@@ -478,6 +495,11 @@ test_expect_success 'move partially-dirty dir from in-cone to out-of-cone' '
 	test_cmp expect stderr &&
 
 	git mv --sparse sub/dir folder1 2>stderr &&
+	cat dirty_error_header >expect &&
+	echo "folder1/dir/e2" >>expect &&
+	echo "folder1/dir/e3" >>expect &&
+	cat dirty_hint >>expect &&
+	test_cmp expect stderr &&
 
 	test_path_is_missing sub/dir &&
 	test_path_is_missing folder1/dir/e &&