os/path: Fix path_get_absolute_path for top-level paths

Close #2833

2 files changed, 17 insertions, 2 deletions

diff --git a/src/nvim/path.c b/src/nvim/path.c
index 1a1f15e8f3..45ae12b78a 100644
--- a/src/nvim/path.c
+++ b/src/nvim/path.c
@@ -2089,8 +2089,15 @@ static int path_get_absolute_path(const char_u *fname, char_u *buf, int len, int
   // expand it if forced or not an absolute path
   if (force || !path_is_absolute_path(fname)) {
     if ((p = vim_strrchr(fname, '/')) != NULL) {
-      STRNCPY(relative_directory, fname, p-fname);
-      relative_directory[p-fname] = NUL;
+      // relative to root
+      if (p == fname) {
+        // only one path component
+        relative_directory[0] = '/';
+        relative_directory[1] = NUL;
+      } else {
+        STRNCPY(relative_directory, fname, p-fname);
+        relative_directory[p-fname] = NUL;
+      }
       end_of_path = (char *) (p + 1);
     } else {
       relative_directory[0] = NUL;
diff --git a/test/unit/path_spec.lua b/test/unit/path_spec.lua
index 261d797624..239a255151 100644
--- a/test/unit/path_spec.lua
+++ b/test/unit/path_spec.lua
@@ -416,6 +416,14 @@ describe('more path function', function()
       eq('unit-test-directory/test.file', (ffi.string(filename)))
       eq(OK, result)
     end)
+
+    it('works with directories that have one path component', function()
+      local force_expansion = 1
+      local filename = to_cstr('/tmp')
+      local result = path.vim_FullName(filename, buffer, len, force_expansion)
+      eq('/tmp', ffi.string(buffer))
+      eq(OK, result)
+    end)
   end)
 
   describe('path_fix_case', function()