Add support for --input-file completions with spaces.

autoload/startuptime.vim

@@ -1431,36 +1431,50 @@ endfunction
 function! startuptime#CompleteOptions(arglead, cmdline, cursorpos) abort
   let l:args = []
   let l:cmdline = a:cmdline[:a:cursorpos - 1]
-  " WARN: The filename completion does not properly handle filenames with
-  " spaces. The two issues are:
-  " 1. The arglead that -complete-func bases its completion on includes no
-  "    spaces.
-  " 2. Even when backslash escaping spaces in the items returned by this
-  "    function, the spaces are completed without being backslash escaped.
-  let l:lead = trim(substitute(a:cmdline, a:arglead . '$', '', ''), ' ', 2)
-  if l:lead =~# '--input-file$'
-    let l:matches = glob(a:arglead .. '*', v:true, v:true)
-    call extend(l:args, l:matches)
-  elseif l:lead =~# '--tries$'
-    for l:digit in range(10)
-      let l:candidate = a:arglead .. l:digit
-      if str2nr(l:candidate) !=# 0
-        call add(l:args, l:candidate)
-      endif
-    endfor
-  else
-    call extend(l:args, [
-          \   '--help',
-          \   '--hidden',
-          \   '--input-file',
-          \   '--other-events', '--no-other-events',
-          \   '--save',
-          \   '--sourced', '--no-sourced',
-          \   '--sort', '--no-sort',
-          \   '--sourcing-events', '--no-sourcing-events',
-          \   '--tries',
-          \   '--',
-          \ ])
+  " First try to complete --input-file argument, with handling for paths with
+  " spaces.
+  let l:idx = stridx(l:cmdline, '--input-file')
+  if l:idx !=# -1
+    let l:offset = len('--input-file')
+    let l:str = l:cmdline[l:idx + l:offset:]
+    let l:str = substitute(l:str, '^ *', '', '')
+    " Don't proceed if there are spaces not preceded by backslash.
+    if l:str !~# '\\\@<! '
+      let l:str = substitute(l:str, '\\ ', ' ', 'g')
+      let l:matches = glob(l:str .. '*', v:true, v:true)
+      call map(l:matches, {_, x -> substitute(x, ' ', '\\ ', 'g')})
+      call extend(l:args, l:matches)
+    endif
+  endif
+  " If we couldn't complete an --input-file argument, try the other
+  " completions.
+  if empty(l:args)
+    let l:lead = trim(substitute(a:cmdline, a:arglead . '$', '', ''), ' ', 2)
+    if l:lead =~# '--tries$'
+      for l:digit in range(10)
+        let l:candidate = a:arglead .. l:digit
+        if str2nr(l:candidate) !=# 0
+          call add(l:args, l:candidate)
+        endif
+      endfor
+    elseif l:lead =~# '--input-file$'
+      " The handling above didn't have any completion. An argument is
+      " necessary for --input-file, so don't give the completions for other
+      " options.
+    else
+      call extend(l:args, [
+            \   '--help',
+            \   '--hidden',
+            \   '--input-file',
+            \   '--other-events', '--no-other-events',
+            \   '--save',
+            \   '--sourced', '--no-sourced',
+            \   '--sort', '--no-sort',
+            \   '--sourcing-events', '--no-sourcing-events',
+            \   '--tries',
+            \   '--',
+            \ ])
+    endif
   endif
   call sort(l:args)
   return join(l:args, "\n")