Only query the requested path in the file API

autoload/fugitive.vim

@@ -2069,14 +2069,57 @@ function! s:TreeInfo(dir, commit) abort
   return [{}, -1]
 endfunction
 
+let s:index_info = {}
+function! s:IndexInfo(dir, commit_stage, path) abort
+  let cache_key = 'cache://' . a:dir . '//' . a:path
+  let index = get(s:index_info, cache_key, [])
+  let newftime = getftime(fugitive#Find('.git/index', a:dir))
+
+  if get(index, 0, -1) == newftime
+    return get(get(index, 1, {}), a:commit_stage, [])
+  endif
+
+  let indexes = {'0': [], '1': [], '2': [], '3': []}
+  let s:index_info[cache_key] = [newftime, indexes]
+
+  let result = fugitive#Execute(['--literal-pathspecs', 'ls-files', '--stage', '--', a:path])
+  if result.exit_status
+    return []
+  endif
+  for line in result.stdout[:2]
+    " Inspect up to the first three lines to find the correct stage
+    if empty(line)
+      break
+    endif
+    let [info, filename] = split(line, "\t")
+    let [mode, sha, stage] = split(info, '\s\+')
+    if filename ==# a:path
+      let indexes[stage] = [newftime, mode, 'blob', sha, -2]
+    else
+      " Only support stage '0' for tree objects
+      let indexes['0'] = [newftime, '040000', 'tree', '', 0]
+    endif
+  endfor
+  return get(indexes, a:commit_stage, [])
+endfunction
+
 function! s:PathInfo(url) abort
   let [dir, commit, file] = s:DirCommitFile(a:url)
   if empty(dir) || !get(g:, 'fugitive_file_api', 1)
     return [-1, '000000', '', '', -1]
   endif
   let path = substitute(file[1:-1], '/*$', '', '')
-  let [tree, ftime] = s:TreeInfo(dir, commit)
-  let entry = empty(path) ? [ftime, '040000', 'tree', '', -1] : get(tree, path, [])
+
+  if empty(path)
+    let [_, ftime] = s:TreeInfo(dir, commit)
+    let entry = [ftime, '040000', 'tree', '', -1]
+  elseif commit =~# '^:\=[0-3]$'
+    let entry = s:IndexInfo(dir, commit[-1:-1], path)
+  else
+    let [tree, ftime] = s:TreeInfo(dir, commit)
+    let entry = get(tree, path, [])
+  endif
+
   if empty(entry) || file =~# '/$' && entry[2] !=# 'tree'
     return [-1, '000000', '', '', -1]
   else