fix(path): don't remove trailing slash when getting absolute path (#20853)

Before Vim patch 8.2.3468 relative_directory is never used in the
resulting path name, so whether it has a trailing slash didn't matter.
Now path_full_dir_name() appends a non-existing relative directory to
the current directory name, so the trailing slash needs to be kept.

1 files changed, 10 insertions, 0 deletions

diff --git a/test/unit/path_spec.lua b/test/unit/path_spec.lua
index eb23a3cff1..3ed3a4aec9 100644
--- a/test/unit/path_spec.lua
+++ b/test/unit/path_spec.lua
@@ -504,6 +504,16 @@ describe('path.c', function()
       eq(OK, result)
     end)
 
+    itp('does not remove trailing slash from non-existing relative directory #20847', function()
+      local expected = lfs.currentdir() .. '/non_existing_dir/'
+      local filename = 'non_existing_dir/'
+      local buflen = get_buf_len(expected, filename)
+      local do_expand = 1
+      local buf, result = vim_FullName(filename, buflen, do_expand)
+      eq(expected, ffi.string(buf))
+      eq(OK, result)
+    end)
+
     itp('expands "./" to the current directory #7117', function()
       local expected = lfs.currentdir() .. '/unit-test-directory/test.file'
       local filename = './unit-test-directory/test.file'