Always use temp file for :Git diff and :Git log

You can use :Git -p log to get a terminal instead.

autoload/fugitive.vim

@@ -2104,7 +2104,7 @@ function! s:GitCommand(line1, line2, range, count, bang, mods, reg, arg, args) a
     let cmd = s:StatusCommand(a:line1, a:line2, a:range, a:count, a:bang, a:mods, a:reg, '', [])
     return (empty(cmd) ? 'exe' : cmd) . after
   endif
-  if a:bang || args[0] =~# '^-P$\|^--no-pager$'
+  if a:bang || args[0] =~# '^-P$\|^--no-pager$\|diff\%(tool\)\@!\|log'
     return s:OpenExec((a:count > 0 ? a:count : '') . (a:count ? 'split' : 'edit'), a:mods, args, dir) . after
   endif
   let git = s:UserCommandList(dir)

doc/fugitive.txt

@@ -26,7 +26,8 @@ that are part of Git repositories).
                                                 *fugitive-:Git!*
 :Git! {args}            Like |:Git|, but capture the output into a temp file,
 :Git --no-pager {args}  and |:split| that that temp file.  Use :0Git to
-:Git -P {args}          |:edit| the temp file instead.
+:Git -P {args}          |:edit| the temp file instead.  A temp file is always
+                        used for diff and log commands.
 
                                                 *fugitive-:Gcd*
 :Gcd [directory]        |:cd| relative to the repository.