thodg/libgit2

diff --git a/include/git2/checkout.h b/include/git2/checkout.h
index 42d4700..ef3badb 100644
--- a/include/git2/checkout.h
+++ b/include/git2/checkout.h
@@ -36,6 +36,21 @@ typedef struct git_checkout_opts {
 	int file_mode; /* default is 0644 */
 	int file_open_flags; /* default is O_CREAT | O_TRUNC | O_WRONLY */
 
+	/* Optional callback to notify the consumer of files that
+	 * haven't be checked out because a modified version of them
+	 * exist in the working directory.
+	 *
+	 * When provided, this callback will be invoked when the flag
+	 * GIT_CHECKOUT_OVERWRITE_MODIFIED isn't part of the checkout strategy.
+	 */
+	int (* skipped_notify_cb)(
+		const char *skipped_file,
+		const git_oid *blob_oid,
+		int file_mode,
+		void *payload);
+
+	void *notify_payload;
+
 	/* when not NULL, arrays of fnmatch pattern specifying 
 	 * which paths should be taken into account
 	 */
diff --git a/src/checkout.c b/src/checkout.c
index 89f7354..ea5e79a 100644
--- a/src/checkout.c
+++ b/src/checkout.c
@@ -155,6 +155,7 @@ static int checkout_diff_fn(
 {
 	struct checkout_diff_data *data;
 	int error = -1;
+	git_checkout_opts *opts;
 
 	data = (struct checkout_diff_data *)cb_data;
 
@@ -164,9 +165,11 @@ static int checkout_diff_fn(
 	if (git_buf_joinpath(data->path, git_buf_cstr(data->path), delta->new_file.path) < 0)
 		return -1;
 
+	opts = data->checkout_opts;
+
 	switch (delta->status) {
 	case GIT_DELTA_UNTRACKED:
-		if (!(data->checkout_opts->checkout_strategy & GIT_CHECKOUT_REMOVE_UNTRACKED))
+		if (!(opts->checkout_strategy & GIT_CHECKOUT_REMOVE_UNTRACKED))
 			return 0;
 
 		if (!git__suffixcmp(delta->new_file.path, "/"))
@@ -176,8 +179,20 @@ static int checkout_diff_fn(
 		break;
 
 	case GIT_DELTA_MODIFIED:
-		if (!(data->checkout_opts->checkout_strategy & GIT_CHECKOUT_OVERWRITE_MODIFIED))
+		if (!(opts->checkout_strategy & GIT_CHECKOUT_OVERWRITE_MODIFIED)) {
+
+			if ((opts->skipped_notify_cb != NULL)
+				&& (opts->skipped_notify_cb(
+					delta->new_file.path,
+					&delta->old_file.oid,
+					delta->old_file.mode,
+					opts->notify_payload))) {
+						giterr_clear();
+						return GIT_EUSER;
+			}
+
 			return 0;
+		}
 
 		if (checkout_blob(
 				data->owner,
@@ -185,13 +200,13 @@ static int checkout_diff_fn(
 				git_buf_cstr(data->path),
 				delta->old_file.mode,
 				data->can_symlink,
-				data->checkout_opts) < 0)
+				opts) < 0)
 			goto cleanup;
 
 		break;
 
 	case GIT_DELTA_DELETED:
-		if (!(data->checkout_opts->checkout_strategy & GIT_CHECKOUT_CREATE_MISSING))
+		if (!(opts->checkout_strategy & GIT_CHECKOUT_CREATE_MISSING))
 			return 0;
 
 		if (checkout_blob(
@@ -200,7 +215,7 @@ static int checkout_diff_fn(
 				git_buf_cstr(data->path),
 				delta->old_file.mode,
 				data->can_symlink,
-				data->checkout_opts) < 0)
+				opts) < 0)
 			goto cleanup;
 
 		break;
@@ -378,4 +393,3 @@ int git_checkout_head(
 
 	return error;
 }
-
diff --git a/tests-clar/checkout/index.c b/tests-clar/checkout/index.c
index d1c59e3..f017a0f 100644
--- a/tests-clar/checkout/index.c
+++ b/tests-clar/checkout/index.c
@@ -287,3 +287,76 @@ void test_checkout_index__options_open_flags(void)
 
 	test_file_contents("./testrepo/new.txt", "hi\nmy new file\n");
 }
+
+struct notify_data {
+	const char *file;
+	const char *sha;
+};
+
+static int notify_cb(
+	const char *skipped_file,
+	const git_oid *blob_oid,
+	int file_mode,
+	void *payload)
+{
+	struct notify_data *expectations = (struct notify_data *)payload;
+
+	GIT_UNUSED(file_mode);
+
+	cl_assert_equal_s(expectations->file, skipped_file);
+	cl_assert_equal_i(0, git_oid_streq(blob_oid, expectations->sha));
+
+	return 0;
+}
+
+void test_checkout_index__can_notify_of_skipped_files(void)
+{
+	struct notify_data data;
+
+	cl_git_mkfile("./testrepo/new.txt", "This isn't what's stored!");
+
+	/*
+	 * $ git ls-tree HEAD
+	 * 100644 blob a8233120f6ad708f843d861ce2b7228ec4e3dec6    README
+	 * 100644 blob 3697d64be941a53d4ae8f6a271e4e3fa56b022cc    branch_file.txt
+	 * 100644 blob a71586c1dfe8a71c6cbf6c129f404c5642ff31bd    new.txt
+	 */
+	data.file = "new.txt";
+	data.sha = "a71586c1dfe8a71c6cbf6c129f404c5642ff31bd";
+
+	g_opts.checkout_strategy = GIT_CHECKOUT_CREATE_MISSING;
+	g_opts.skipped_notify_cb = notify_cb;
+	g_opts.notify_payload = &data;
+
+	cl_git_pass(git_checkout_index(g_repo, &g_opts, NULL));
+}
+
+static int dont_notify_cb(
+	const char *skipped_file,
+	const git_oid *blob_oid,
+	int file_mode,
+	void *payload)
+{
+	GIT_UNUSED(skipped_file);
+	GIT_UNUSED(blob_oid);
+	GIT_UNUSED(file_mode);
+	GIT_UNUSED(payload);
+
+	cl_assert(false);
+
+	return 0;
+}
+
+void test_checkout_index__wont_notify_of_expected_line_ending_changes(void)
+{
+	cl_git_pass(p_unlink("./testrepo/.gitattributes"));
+	set_core_autocrlf_to(true);
+	
+	cl_git_mkfile("./testrepo/new.txt", "my new file\r\n");
+
+	g_opts.checkout_strategy = GIT_CHECKOUT_CREATE_MISSING;
+	g_opts.skipped_notify_cb = dont_notify_cb;
+	g_opts.notify_payload = NULL;
+
+	cl_git_pass(git_checkout_index(g_repo, &g_opts, NULL));
+}