vim-patch:8.2.1970: it is easy to make mistakes when cleaning up swap files

Problem:    It is easy to make mistakes when cleaning up swap files after the
            system crashed.
Solution:   Warn for the process still running after recovery.  Do not
            automatically delete a swap file created on another system.
            (David Fries, closes vim/vim#7273)

f883508e36

src/nvim/memline.c

@@ -1138,7 +1138,14 @@ void ml_recover(bool checkext)
     } else {
       msg(_("Recovery completed. Buffer contents equals file contents."));
     }
-    msg_puts(_("\nYou may want to delete the .swp file now.\n\n"));
+    msg_puts(_("\nYou may want to delete the .swp file now."));
+    if (os_proc_running((int)char_to_long(b0p->b0_pid))) {
+      // Warn there could be an active Vim on the same file, the user may
+      // want to kill it.
+      msg_puts(_("\nNote: process STILL RUNNING: "));
+      msg_outnum(char_to_long(b0p->b0_pid));
+    }
+    msg_puts("\n\n");
     cmdline_row = msg_row;
   }
   redraw_curbuf_later(UPD_NOT_VALID);
@@ -1533,14 +1540,27 @@ static bool swapfile_unchanged(char *fname)
     ret = false;
   }
 
+  // Host name must be known and must equal the current host name, otherwise
+  // comparing pid is meaningless.
+  if (*(b0.b0_hname) == NUL) {
+    ret = false;
+  } else {
+    char hostname[B0_HNAME_SIZE];
+    os_get_hostname(hostname, B0_HNAME_SIZE);
+    hostname[B0_HNAME_SIZE - 1] = NUL;
+    if (STRICMP(b0.b0_hname, hostname) != 0) {
+      ret = false;
+    }
+  }
+
   // process must be known and not running.
   long pid = char_to_long(b0.b0_pid);
   if (pid == 0L || os_proc_running((int)pid)) {
     ret = false;
   }
 
-  // TODO(bram): Should we check if the swap file was created on the current
-  // system?  And the current user?
+  // We do not check the user, it should be irrelevant for whether the swap
+  // file is still useful.
 
   close(fd);
   return ret;

src/nvim/testdir/test_swap.vim

@@ -421,6 +421,52 @@ func Test_swap_symlink()
   call delete('Xswapdir', 'rf')
 endfunc
 
+func Test_swap_auto_delete()
+  " Create a valid swapfile by editing a file with a special extension.
+  split Xtest.scr
+  call setline(1, ['one', 'two', 'three'])
+  write  " file is written, not modified
+  write  " write again to make sure the swapfile is created
+  " read the swapfile as a Blob
+  let swapfile_name = swapname('%')
+  let swapfile_bytes = readfile(swapfile_name, 'B')
+
+  " Forget about the file, recreate the swap file, then edit it again.  The
+  " swap file should be automatically deleted.
+  bwipe!
+  " change the process ID to avoid the "still running" warning
+  let swapfile_bytes[24] = 0x99
+  call writefile(swapfile_bytes, swapfile_name)
+  edit Xtest.scr
+  " will end up using the same swap file after deleting the existing one
+  call assert_equal(swapfile_name, swapname('%'))
+  bwipe!
+
+  " create the swap file again, but change the host name so that it won't be
+  " deleted
+  autocmd! SwapExists
+  augroup test_swap_recover_ext
+    autocmd!
+    autocmd SwapExists * let v:swapchoice = 'e'
+  augroup END
+
+  " change the host name
+  let swapfile_bytes[28 + 40] = 0x89
+  call writefile(swapfile_bytes, swapfile_name)
+  edit Xtest.scr
+  call assert_equal(1, filereadable(swapfile_name))
+  " will use another same swap file name
+  call assert_notequal(swapfile_name, swapname('%'))
+  bwipe!
+
+  call delete('Xtest.scr')
+  call delete(swapfile_name)
+  augroup test_swap_recover_ext
+    autocmd!
+  augroup END
+  augroup! test_swap_recover_ext
+endfunc
+
 func Test_no_swap_file()
   call assert_equal("\nNo swap file", execute('swapname'))
 endfunc