Handle git add <file> where <file> traverses an NTFS junction

abspath.c

@@ -95,6 +95,9 @@ char *strbuf_realpath(struct strbuf *resolved, const char *path,
 			goto error_out;
 	}
 
+	if (platform_strbuf_realpath(resolved, path))
+		return resolved->buf;
+
 	strbuf_addstr(&remaining, path);
 	get_root_part(resolved, &remaining);
 

compat/mingw.c

@@ -1256,6 +1256,37 @@ struct tm *localtime_r(const time_t *timep, struct tm *result)
 	return NULL;
 }
 
+char *mingw_strbuf_realpath(struct strbuf *resolved, const char *path)
+{
+	wchar_t wpath[MAX_PATH];
+	HANDLE h;
+	DWORD ret;
+	int len;
+
+	if (xutftowcs_path(wpath, path) < 0)
+		return NULL;
+
+	h = CreateFileW(wpath, 0,
+			FILE_SHARE_READ | FILE_SHARE_WRITE | FILE_SHARE_DELETE, NULL,
+			OPEN_EXISTING, FILE_FLAG_BACKUP_SEMANTICS, NULL);
+	if (h == INVALID_HANDLE_VALUE)
+		return NULL;
+
+	ret = GetFinalPathNameByHandleW(h, wpath, ARRAY_SIZE(wpath), 0);
+	CloseHandle(h);
+	if (!ret || ret >= ARRAY_SIZE(wpath))
+		return NULL;
+
+	len = wcslen(wpath) * 3;
+	strbuf_grow(resolved, len);
+	len = xwcstoutf(resolved->buf, normalize_ntpath(wpath), len);
+	if (len < 0)
+		return NULL;
+	resolved->len = len;
+	return resolved->buf;
+
+}
+
 char *mingw_getcwd(char *pointer, int len)
 {
 	wchar_t cwd[MAX_PATH], wpointer[MAX_PATH];

compat/mingw.h

@@ -471,6 +471,8 @@ extern int (*win32_is_mount_point)(struct strbuf *path);
 #define PATH_SEP ';'
 char *mingw_query_user_email(void);
 #define query_user_email mingw_query_user_email
+char *mingw_strbuf_realpath(struct strbuf *resolved, const char *path);
+#define platform_strbuf_realpath mingw_strbuf_realpath
 #if !defined(__MINGW64_VERSION_MAJOR) && (!defined(_MSC_VER) || _MSC_VER < 1800)
 #define PRIuMAX "I64u"
 #define PRId64 "I64d"

git-compat-util.h

@@ -408,6 +408,10 @@ static inline int git_create_symlink(struct index_state *index, const char *targ
 #define query_user_email() NULL
 #endif
 
+#ifndef platform_strbuf_realpath
+#define platform_strbuf_realpath(resolved, path) NULL
+#endif
+
 #ifdef __TANDEM
 #include <floss.h(floss_execl,floss_execlp,floss_execv,floss_execvp)>
 #include <floss.h(floss_getpwuid)>

t/t3700-add.sh

@@ -421,4 +421,15 @@ test_expect_success CASE_INSENSITIVE_FS 'path is case-insensitive' '
 	git add "$downcased"
 '
 
+test_expect_success MINGW 'can add files via NTFS junctions' '
+	test_when_finished "cmd //c rmdir junction && rm -rf target" &&
+	test_create_repo target &&
+	cmd //c "mklink /j junction target" &&
+	>target/via-junction &&
+	git -C junction add "$(pwd)/junction/via-junction" &&
+	echo via-junction >expect &&
+	git -C target diff --cached --name-only >actual &&
+	test_cmp expect actual
+'
+
 test_done