Support symbolic links on Windows

apply.c

@@ -3818,7 +3818,7 @@ static int check_preimage(struct apply_state *state,
 		if (*ce && !(*ce)->ce_mode)
 			BUG("ce_mode == 0 for path '%s'", old_name);
 
-		if (trust_executable_bit)
+		if (trust_executable_bit || !S_ISREG(st->st_mode))
 			st_mode = ce_mode_from_stat(*ce, st->st_mode);
 		else if (*ce)
 			st_mode = (*ce)->ce_mode;

compat/mingw.c

@@ -629,6 +629,7 @@ int mingw_open (const char *filename, int oflags, ...)
 	int fd, create = (oflags & (O_CREAT | O_EXCL)) == (O_CREAT | O_EXCL);
 	wchar_t wfilename[MAX_PATH];
 	open_fn_t open_fn;
+	WIN32_FILE_ATTRIBUTE_DATA fdata;
 
 	DECLARE_PROC_ADDR(ntdll.dll, NTSTATUS, NTAPI, RtlGetLastNtStatus, void);
 
@@ -653,6 +654,19 @@ int mingw_open (const char *filename, int oflags, ...)
 	else if (xutftowcs_path(wfilename, filename) < 0)
 		return -1;
 
+	/*
+	 * When `symlink` exists and is a symbolic link pointing to a
+	 * non-existing file, `_wopen(symlink, O_CREAT | O_EXCL)` would
+	 * create that file. Not what we want: Linux would say `EEXIST`
+	 * in that instance, which is therefore what Git expects.
+	 */
+	if (create &&
+	    GetFileAttributesExW(wfilename, GetFileExInfoStandard, &fdata) &&
+	    (fdata.dwFileAttributes & FILE_ATTRIBUTE_REPARSE_POINT)) {
+		errno = EEXIST;
+		return -1;
+	}
+
 	fd = open_fn(wfilename, oflags, mode);
 
 	/*
@@ -903,20 +917,22 @@ static int has_valid_directory_prefix(wchar_t *wfilename)
 	return 1;
 }
 
-/* We keep the do_lstat code in a separate function to avoid recursion.
- * When a path ends with a slash, the stat will fail with ENOENT. In
- * this case, we strip the trailing slashes and stat again.
- *
- * If follow is true then act like stat() and report on the link
- * target. Otherwise report on the link itself.
- */
-static int do_lstat(int follow, const char *file_name, struct stat *buf)
+int mingw_lstat(const char *file_name, struct stat *buf)
 {
 	WIN32_FILE_ATTRIBUTE_DATA fdata;
 	wchar_t wfilename[MAX_PATH];
-	if (xutftowcs_path(wfilename, file_name) < 0)
+	int wlen = xutftowcs_path(wfilename, file_name);
+	if (wlen < 0)
 		return -1;
 
+	/* strip trailing '/', or GetFileAttributes will fail */
+	while (wlen && is_dir_sep(wfilename[wlen - 1]))
+		wfilename[--wlen] = 0;
+	if (!wlen) {
+		errno = ENOENT;
+		return -1;
+	}
+
 	if (GetFileAttributesExW(wfilename, GetFileExInfoStandard, &fdata)) {
 		buf->st_ino = 0;
 		buf->st_gid = 0;
@@ -935,13 +951,7 @@ static int do_lstat(int follow, const char *file_name, struct stat *buf)
 			if (handle != INVALID_HANDLE_VALUE) {
 				if ((findbuf.dwFileAttributes & FILE_ATTRIBUTE_REPARSE_POINT) &&
 						(findbuf.dwReserved0 == IO_REPARSE_TAG_SYMLINK)) {
-					if (follow) {
-						char buffer[MAXIMUM_REPARSE_DATA_BUFFER_SIZE];
-						buf->st_size = readlink(file_name, buffer, MAXIMUM_REPARSE_DATA_BUFFER_SIZE);
-					} else {
-						buf->st_mode = S_IFLNK;
-					}
-					buf->st_mode |= S_IREAD;
+					buf->st_mode = S_IFLNK | S_IREAD;
 					if (!(findbuf.dwFileAttributes & FILE_ATTRIBUTE_READONLY))
 						buf->st_mode |= S_IWRITE;
 				}
@@ -976,39 +986,6 @@ static int do_lstat(int follow, const char *file_name, struct stat *buf)
 	return -1;
 }
 
-/* We provide our own lstat/fstat functions, since the provided
- * lstat/fstat functions are so slow. These stat functions are
- * tailored for Git's usage (read: fast), and are not meant to be
- * complete. Note that Git stat()s are redirected to mingw_lstat()
- * too, since Windows doesn't really handle symlinks that well.
- */
-static int do_stat_internal(int follow, const char *file_name, struct stat *buf)
-{
-	size_t namelen;
-	char alt_name[PATH_MAX];
-
-	if (!do_lstat(follow, file_name, buf))
-		return 0;
-
-	/* if file_name ended in a '/', Windows returned ENOENT;
-	 * try again without trailing slashes
-	 */
-	if (errno != ENOENT)
-		return -1;
-
-	namelen = strlen(file_name);
-	if (namelen && file_name[namelen-1] != '/')
-		return -1;
-	while (namelen && file_name[namelen-1] == '/')
-		--namelen;
-	if (!namelen || namelen >= PATH_MAX)
-		return -1;
-
-	memcpy(alt_name, file_name, namelen);
-	alt_name[namelen] = 0;
-	return do_lstat(follow, alt_name, buf);
-}
-
 static int get_file_info_by_handle(HANDLE hnd, struct stat *buf)
 {
 	BY_HANDLE_FILE_INFORMATION fdata;
@@ -1032,13 +1009,25 @@ static int get_file_info_by_handle(HANDLE hnd, struct stat *buf)
 	return 0;
 }
 
-int mingw_lstat(const char *file_name, struct stat *buf)
-{
-	return do_stat_internal(0, file_name, buf);
-}
 int mingw_stat(const char *file_name, struct stat *buf)
 {
-	return do_stat_internal(1, file_name, buf);
+	wchar_t wfile_name[MAX_PATH];
+	HANDLE hnd;
+	int result;
+
+	/* open the file and let Windows resolve the links */
+	if (xutftowcs_path(wfile_name, file_name) < 0)
+		return -1;
+	hnd = CreateFileW(wfile_name, 0,
+			FILE_SHARE_READ | FILE_SHARE_WRITE | FILE_SHARE_DELETE, NULL,
+			OPEN_EXISTING, FILE_FLAG_BACKUP_SEMANTICS, NULL);
+	if (hnd == INVALID_HANDLE_VALUE) {
+		errno = err_win_to_posix(GetLastError());
+		return -1;
+	}
+	result = get_file_info_by_handle(hnd, buf);
+	CloseHandle(hnd);
+	return result;
 }
 
 int mingw_fstat(int fd, struct stat *buf)
@@ -1225,18 +1214,16 @@ char *mingw_getcwd(char *pointer, int len)
 {
 	wchar_t cwd[MAX_PATH], wpointer[MAX_PATH];
 	DWORD ret = GetCurrentDirectoryW(ARRAY_SIZE(cwd), cwd);
+	HANDLE hnd;
 
 	if (!ret || ret >= ARRAY_SIZE(cwd)) {
 		errno = ret ? ENAMETOOLONG : err_win_to_posix(GetLastError());
 		return NULL;
 	}
-	ret = GetLongPathNameW(cwd, wpointer, ARRAY_SIZE(wpointer));
-	if (!ret && GetLastError() == ERROR_ACCESS_DENIED) {
-		HANDLE hnd = CreateFileW(cwd, 0,
-			FILE_SHARE_READ | FILE_SHARE_WRITE | FILE_SHARE_DELETE, NULL,
-			OPEN_EXISTING, FILE_FLAG_BACKUP_SEMANTICS, NULL);
-		if (hnd == INVALID_HANDLE_VALUE)
-			return NULL;
+	hnd = CreateFileW(cwd, 0,
+			  FILE_SHARE_READ | FILE_SHARE_WRITE | FILE_SHARE_DELETE, NULL,
+			  OPEN_EXISTING, FILE_FLAG_BACKUP_SEMANTICS, NULL);
+	if (hnd != INVALID_HANDLE_VALUE) {
 		ret = GetFinalPathNameByHandleW(hnd, wpointer, ARRAY_SIZE(wpointer), 0);
 		CloseHandle(hnd);
 		if (!ret || ret >= ARRAY_SIZE(wpointer))
@@ -1245,13 +1232,11 @@ char *mingw_getcwd(char *pointer, int len)
 			return NULL;
 		return pointer;
 	}
-	if (!ret || ret >= ARRAY_SIZE(wpointer))
-		return NULL;
-	if (GetFileAttributesW(wpointer) == INVALID_FILE_ATTRIBUTES) {
+	if (GetFileAttributesW(cwd) == INVALID_FILE_ATTRIBUTES) {
 		errno = ENOENT;
 		return NULL;
 	}
-	if (xwcstoutf(pointer, wpointer, len) < 0)
+	if (xwcstoutf(pointer, cwd, len) < 0)
 		return NULL;
 	convert_slashes(pointer);
 	return pointer;

environment.c

@@ -324,8 +324,8 @@ static enum fsync_component parse_fsync_components(const char *var, const char *
 	return (current & ~negative) | positive;
 }
 
-static int git_default_core_config(const char *var, const char *value,
-				   const struct config_context *ctx, void *cb)
+int git_default_core_config(const char *var, const char *value,
+			    const struct config_context *ctx, void *cb)
 {
 	/* This needs a better name */
 	if (!strcmp(var, "core.filemode")) {

environment.h

@@ -106,6 +106,8 @@ const char *strip_namespace(const char *namespaced_ref);
 
 int git_default_config(const char *, const char *,
 		       const struct config_context *, void *);
+int git_default_core_config(const char *var, const char *value,
+			    const struct config_context *ctx, void *cb);
 
 /*
  * TODO: All the below state either explicitly or implicitly relies on

lockfile.c

@@ -19,14 +19,14 @@ static void trim_last_path_component(struct strbuf *path)
 	int i = path->len;
 
 	/* back up past trailing slashes, if any */
-	while (i && path->buf[i - 1] == '/')
+	while (i && is_dir_sep(path->buf[i - 1]))
 		i--;
 
 	/*
 	 * then go backwards until a slash, or the beginning of the
 	 * string
 	 */
-	while (i && path->buf[i - 1] != '/')
+	while (i && !is_dir_sep(path->buf[i - 1]))
 		i--;
 
 	strbuf_setlen(path, i);

setup.c

@@ -2693,7 +2693,7 @@ int init_db(const char *git_dir, const char *real_git_dir,
 	 * have set up the repository format such that we can evaluate
 	 * includeIf conditions correctly in the case of re-initialization.
 	 */
-	repo_config(the_repository, platform_core_config, NULL);
+	repo_config(the_repository, git_default_core_config, NULL);
 
 	safe_create_dir(the_repository, git_dir, 0);
 

strbuf.c

@@ -566,24 +566,22 @@ ssize_t strbuf_write(struct strbuf *sb, FILE *f)
 	return sb->len ? fwrite(sb->buf, 1, sb->len, f) : 0;
 }
 
-#define STRBUF_MAXLINK (2*PATH_MAX)
-
 int strbuf_readlink(struct strbuf *sb, const char *path, size_t hint)
 {
 	size_t oldalloc = sb->alloc;
 
 	if (hint < 32)
 		hint = 32;
 
-	while (hint < STRBUF_MAXLINK) {
+	for (;;) {
 		ssize_t len;
 
-		strbuf_grow(sb, hint);
-		len = readlink(path, sb->buf, hint);
+		strbuf_grow(sb, hint + 1);
+		len = readlink(path, sb->buf, hint + 1);
 		if (len < 0) {
 			if (errno != ERANGE)
 				break;
-		} else if (len < hint) {
+		} else if (len <= hint) {
 			strbuf_setlen(sb, len);
 			return 0;
 		}

t/t0001-init.sh

@@ -425,7 +425,11 @@ test_expect_success SYMLINKS 're-init to move gitdir symlink' '
 	git init --separate-git-dir ../realgitdir
 	) &&
 	echo "gitdir: $(pwd)/realgitdir" >expected &&
-	test_cmp expected newdir/.git &&
+	case "$GIT_TEST_CMP" in
+	# `git diff --no-index` does not resolve symlinks
+	*--no-index*) cmp expected newdir/.git;;
+	*) test_cmp expected newdir/.git;;
+	esac &&
 	test_cmp expected newdir/here &&
 	test_path_is_dir realgitdir/refs
 '

t/t0301-credential-cache.sh

@@ -123,7 +123,8 @@ test_expect_success SYMLINKS 'use user socket if user directory is a symlink to
 		rmdir \"\$HOME/dir/\" &&
 		rm \"\$HOME/.git-credential-cache\"
 	" &&
-	mkdir -p -m 700 "$HOME/dir/" &&
+	mkdir -p "$HOME/dir/" &&
+	chmod 700 "$HOME/dir/" &&
 	ln -s "$HOME/dir" "$HOME/.git-credential-cache" &&
 	check approve cache <<-\EOF &&
 	protocol=https

t/t0600-reffiles-backend.sh

@@ -467,7 +467,7 @@ test_expect_success POSIXPERM 'git reflog expire honors core.sharedRepository' '
 	esac
 '
 
-test_expect_success SYMLINKS 'symref transaction supports symlinks' '
+test_expect_success SYMLINKS,!MINGW 'symref transaction supports symlinks' '
 	test_when_finished "git symbolic-ref -d TEST_SYMREF_HEAD" &&
 	git update-ref refs/heads/new @ &&
 	test_config core.prefersymlinkrefs true &&

t/t1006-cat-file.sh

@@ -1048,18 +1048,28 @@ test_expect_success 'git cat-file --batch-check --follow-symlinks works for out-
 	echo .. >>expect &&
 	echo HEAD:dir/subdir/out-of-repo-link-dir | git cat-file --batch-check --follow-symlinks >actual &&
 	test_cmp expect actual &&
-	echo symlink 3 >expect &&
-	echo ../ >>expect &&
+	if test_have_prereq MINGW,SYMLINKS
+	then
+		test_write_lines "symlink 2" ..
+	else
+		test_write_lines "symlink 3" ../
+	fi >expect &&
 	echo HEAD:dir/subdir/out-of-repo-link-dir-trailing | git cat-file --batch-check --follow-symlinks >actual &&
 	test_cmp expect actual
 '
 
 test_expect_success 'git cat-file --batch-check --follow-symlinks works for symlinks with internal ..' '
-	echo HEAD: | git cat-file --batch-check >expect &&
-	echo HEAD:up-down | git cat-file --batch-check --follow-symlinks >actual &&
-	test_cmp expect actual &&
-	echo HEAD:up-down-trailing | git cat-file --batch-check --follow-symlinks >actual &&
-	test_cmp expect actual &&
+	if test_have_prereq !MINGW
+	then
+		# The `up-down` and `up-down-trailing` symlinks are normalized
+		# in MSYS in `winsymlinks` mode and are therefore in a
+		# different shape than Git expects them.
+		echo HEAD: | git cat-file --batch-check >expect &&
+		echo HEAD:up-down | git cat-file --batch-check --follow-symlinks >actual &&
+		test_cmp expect actual &&
+		echo HEAD:up-down-trailing | git cat-file --batch-check --follow-symlinks >actual &&
+		test_cmp expect actual
+	fi &&
 	echo HEAD:up-down-file | git cat-file --batch-check --follow-symlinks >actual &&
 	test_cmp found actual &&
 	echo symlink 7 >expect &&

t/t1305-config-include.sh

@@ -286,7 +286,7 @@ test_expect_success SYMLINKS 'conditional include, relative path with symlinks'
 	)
 '
 
-test_expect_success SYMLINKS 'conditional include, gitdir matching symlink' '
+test_expect_success SYMLINKS,!MINGW 'conditional include, gitdir matching symlink' '
 	ln -s foo bar &&
 	(
 		cd bar &&
@@ -298,7 +298,7 @@ test_expect_success SYMLINKS 'conditional include, gitdir matching symlink' '
 	)
 '
 
-test_expect_success SYMLINKS 'conditional include, gitdir matching symlink, icase' '
+test_expect_success SYMLINKS,!MINGW 'conditional include, gitdir matching symlink, icase' '
 	(
 		cd bar &&
 		echo "[includeIf \"gitdir/i:BAR/\"]path=bar8" >>.git/config &&

t/t6423-merge-rename-directories.sh

@@ -5158,13 +5158,18 @@ test_setup_12m () {
 		git switch B &&
 		git rm dir/subdir/file &&
 		mkdir dir &&
-		ln -s /dev/null dir/subdir &&
+		if test_have_prereq MINGW
+		then
+			cmd //c 'mklink dir\subdir NUL'
+		else
+			ln -s /dev/null dir/subdir
+		fi &&
 		git add . &&
 		git commit -m "B"
 	)
 }
 
-test_expect_success '12m: Change parent of renamed-dir to symlink on other side' '
+test_expect_success SYMLINKS '12m: Change parent of renamed-dir to symlink on other side' '
 	test_setup_12m &&
 	(
 		cd 12m &&