3 files changed, 118 insertions, 6 deletions

diff --git a/src/nvim/memline.c b/src/nvim/memline.c
index 1f601f0668..02a7e1f697 100644
--- a/src/nvim/memline.c
+++ b/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 +1540,28 @@ 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;
+    b0.b0_hname[B0_HNAME_SIZE - 1] = NUL;  // in case of corruption
+    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;
diff --git a/src/nvim/os/process.c b/src/nvim/os/process.c
index d9273e69da..f4d95e141b 100644
--- a/src/nvim/os/process.c
+++ b/src/nvim/os/process.c
@@ -264,5 +264,16 @@ Dictionary os_proc_info(int pid)
 /// Return true if process `pid` is running.
 bool os_proc_running(int pid)
 {
-  return uv_kill(pid, 0) == 0;
+  int err = uv_kill(pid, 0);
+  // If there is no error the process must be running.
+  if (err == 0) {
+    return true;
+  }
+  // If the error is ESRCH then the process is not running.
+  if (err == UV_ESRCH) {
+    return false;
+  }
+  // If the process is running and owned by another user we get EPERM.  With
+  // other errors the process might be running, assuming it is then.
+  return true;
 }
diff --git a/src/nvim/testdir/test_swap.vim b/src/nvim/testdir/test_swap.vim
index 34d1d585ce..284579b084 100644
--- a/src/nvim/testdir/test_swap.vim
+++ b/src/nvim/testdir/test_swap.vim
@@ -203,8 +203,8 @@ func Test_swapfile_delete()
   " This test won't work as root because root can successfully run kill(1, 0)
   if !IsRoot()
     " Write the swapfile with a modified PID, now it will be automatically
-    " deleted. Process one should never be Vim.
-    let swapfile_bytes[24:27] = 0z01000000
+    " deleted. Process 0x3fffffff most likely does not exist.
+    let swapfile_bytes[24:27] = 0zffffff3f
     call writefile(swapfile_bytes, swapfile_name)
     let s:swapname = ''
     split XswapfileText
@@ -421,6 +421,86 @@ func Test_swap_symlink()
   call delete('Xswapdir', 'rf')
 endfunc
 
+func s:get_unused_pid(base)
+  if has('job')
+    " Execute 'echo' as a temporary job, and return its pid as an unused pid.
+    if has('win32')
+      let cmd = 'cmd /c echo'
+    else
+      let cmd = 'echo'
+    endif
+    let j = job_start(cmd)
+    while job_status(j) ==# 'run'
+      sleep 10m
+    endwhile
+    if job_status(j) ==# 'dead'
+      return job_info(j).process
+    endif
+  endif
+  " Must add four for MS-Windows to see it as a different one.
+  return a:base + 4
+endfunc
+
+func s:blob_to_pid(b)
+  return a:b[3] * 16777216 + a:b[2] * 65536 + a:b[1] * 256 + a:b[0]
+endfunc
+
+func s:pid_to_blob(i)
+  let b = 0z
+  let b[0] = and(a:i, 0xff)
+  let b[1] = and(a:i / 256, 0xff)
+  let b[2] = and(a:i / 65536, 0xff)
+  let b[3] = and(a:i / 16777216, 0xff)
+  return b
+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[24:27] = s:pid_to_blob(s:get_unused_pid(
+        \ s:blob_to_pid(swapfile_bytes[24:27])))
+  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] = swapfile_bytes[28 + 40] + 2
+  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