fileinfo: implement os_fileinfo_blocksize

src/nvim/memfile.c

@@ -123,10 +123,11 @@ memfile_T *mf_open(char_u *fname, int flags)
    */
   FileInfo file_info;
   if (mfp->mf_fd >= 0
-      && os_get_file_info_fd(mfp->mf_fd, &file_info)
-      && file_info.stat.st_blksize >= MIN_SWAP_PAGE_SIZE
-      && file_info.stat.st_blksize <= MAX_SWAP_PAGE_SIZE) {
-    mfp->mf_page_size = file_info.stat.st_blksize;
+      && os_get_file_info_fd(mfp->mf_fd, &file_info)) {
+    uint64_t blocksize = os_fileinfo_blocksize(&file_info);
+    if (blocksize >= MIN_SWAP_PAGE_SIZE && blocksize <= MAX_SWAP_PAGE_SIZE) {
+      mfp->mf_page_size = blocksize;
+    }
   }
 
   if (mfp->mf_fd < 0 || (flags & (O_TRUNC|O_EXCL))

src/nvim/os/fs.c

@@ -412,6 +412,15 @@ uint64_t os_fileinfo_hardlinks(const FileInfo *file_info)
   return file_info->stat.st_nlink;
 }
 
+/// Get the blocksize from a `FileInfo`.
+///
+/// @return blocksize in bytes.
+uint64_t os_fileinfo_blocksize(const FileInfo *file_info)
+  FUNC_ATTR_NONNULL_ALL
+{
+  return file_info->stat.st_blksize;
+}
+
 /// Get the `FileID` for a given path
 ///
 /// @param path Path to the file.

test/unit/os/fs_spec.lua

@@ -625,6 +625,27 @@ describe('fs function', function()
       end)
     end)
 
+    describe('os_fileinfo_blocksize', function()
+      it('returns the correct blocksize of a file', function()
+        local path = 'unit-test-directory/test.file'
+        -- there is a bug in luafilesystem where
+        -- `lfs.attributes path, 'blksize'` returns the worng value:
+        -- https://github.com/keplerproject/luafilesystem/pull/44
+        -- using this workaround for now:
+        local blksize = lfs.attributes(path).blksize
+        local file_info = file_info_new()
+        assert.is_true(fs.os_get_file_info(path, file_info))
+        if blksize then
+          eq(blksize, fs.os_fileinfo_blocksize(file_info))
+        else
+          -- luafs dosn't support blksize on windows
+          -- libuv on windows returns a constant value as blocksize
+          -- checking for this constant value should be enough
+          eq(2048, fs.os_fileinfo_blocksize(file_info))
+        end
+      end)
+    end)
+
     describe('os_get_file_id', function()
       it('returns false if given an non-existing file', function()
         local file_id = file_id_new()