fix(path): avoid chdir() when resolving path (#28799)

Use uv_fs_realpath() instead.

It seems that uv_fs_realpath() has some problems on non-Linux platforms:
- macOS and other BSDs: this function will fail with UV_ELOOP if more
  than 32 symlinks are found while resolving the given path.  This limit
  is hardcoded and cannot be sidestepped.
- Windows: while this function works in the common case, there are a
  number of corner cases where it doesn't:
  - Paths in ramdisk volumes created by tools which sidestep the Volume
    Manager (such as ImDisk) cannot be resolved.
  - Inconsistent casing when using drive letters.
  - Resolved path bypasses subst'd drives.

Ref: https://docs.libuv.org/en/v1.x/fs.html#c.uv_fs_realpath

I don't know if the old implementation that uses uv_chdir() and uv_cwd()
also suffers from the same problems.
- For the ELOOP case, chdir() seems to have the same limitations.
- On Windows, Vim doesn't use anything like chdir() either. It uses
  _wfullpath(), while libuv uses GetFinalPathNameByHandleW().

1 files changed, 7 insertions, 7 deletions

diff --git a/src/nvim/os/fs.c b/src/nvim/os/fs.c
index 2eca906d4e..19bdf30311 100644
--- a/src/nvim/os/fs.c
+++ b/src/nvim/os/fs.c
@@ -1320,22 +1320,22 @@ bool os_fileid_equal_fileinfo(const FileID *file_id, const FileInfo *file_info)
 /// Return the canonicalized absolute pathname.
 ///
 /// @param[in] name Filename to be canonicalized.
-/// @param[out] buf Buffer to store the canonicalized values. A minimum length
-//                  of MAXPATHL+1 is required. If it is NULL, memory is
-//                  allocated. In that case, the caller should deallocate this
-//                  buffer.
+/// @param[out] buf Buffer to store the canonicalized values.
+///                 If it is NULL, memory is allocated. In that case, the caller
+///                 should deallocate this buffer.
+/// @param[in] len  The length of the buffer.
 ///
 /// @return pointer to the buf on success, or NULL.
-char *os_realpath(const char *name, char *buf)
+char *os_realpath(const char *name, char *buf, size_t len)
   FUNC_ATTR_NONNULL_ARG(1)
 {
   uv_fs_t request;
   int result = uv_fs_realpath(NULL, &request, name, NULL);
   if (result == kLibuvSuccess) {
     if (buf == NULL) {
-      buf = xmallocz(MAXPATHL);
+      buf = xmalloc(len);
     }
-    xstrlcpy(buf, request.ptr, MAXPATHL + 1);
+    xstrlcpy(buf, request.ptr, len);
   }
   uv_fs_req_cleanup(&request);
   return result == kLibuvSuccess ? buf : NULL;