vim-patch:8.2.0054: :diffget and :diffput don't have good completion

Problem:    :diffget and :diffput don't have good completion.
Solution:   Add proper completion. (Dominique Pelle, closes vim/vim#5409)
vim/vim@ae7dba8

runtime/doc/eval.txt

@@ -4454,6 +4454,7 @@ getcompletion({pat}, {type} [, {filtered}])		*getcompletion()*
 		command		Ex command (and arguments)
 		compiler	compilers
 		cscope		|:cscope| suboptions
+		diff_buffer     |:diffget| and |:diffput| completion
 		dir		directory names
 		environment	environment variable names
 		event		autocommand events

src/nvim/buffer.c

@@ -2345,6 +2345,15 @@ int ExpandBufnames(char_u *pat, int *num_file, char_u ***file, int options)
         if (!buf->b_p_bl) {             // skip unlisted buffers
           continue;
         }
+        if (options & BUF_DIFF_FILTER) {
+          // Skip buffers not suitable for
+          // :diffget or :diffput completion.
+          if (buf == curbuf
+              || !diff_mode_buf(curbuf)
+              || !diff_mode_buf(buf)) {
+            continue;
+          }
+        }
         p = buflist_match(&regmatch, buf, p_wic);
         if (p != NULL) {
           if (round == 1) {

src/nvim/ex_docmd.c

@@ -3512,6 +3512,13 @@ const char * set_one_cmd_context(
     xp->xp_context = EXPAND_BUFFERS;
     xp->xp_pattern = (char_u *)arg;
     break;
+  case CMD_diffget:
+  case CMD_diffput:
+    // If current buffer is in diff mode, complete buffer names
+    // which are in diff mode, and different than current buffer.
+    xp->xp_context = EXPAND_DIFF_BUFFERS;
+    xp->xp_pattern = (char_u *)arg;
+    break;
   case CMD_USER:
   case CMD_USER_BUF:
     if (context != EXPAND_NOTHING) {
@@ -5174,6 +5181,7 @@ static const char *command_complete[] =
   [EXPAND_CSCOPE] = "cscope",
   [EXPAND_USER_DEFINED] = "custom",
   [EXPAND_USER_LIST] = "customlist",
+  [EXPAND_DIFF_BUFFERS] = "diff_buffer",
   [EXPAND_DIRECTORIES] = "dir",
   [EXPAND_ENV_VARS] = "environment",
   [EXPAND_EVENTS] = "event",

src/nvim/ex_getln.c

@@ -5084,9 +5084,13 @@ ExpandFromContext (
   }
   if (xp->xp_context == EXPAND_BUFFERS)
     return ExpandBufnames(pat, num_file, file, options);
+  if (xp->xp_context == EXPAND_DIFF_BUFFERS) {
+    return ExpandBufnames(pat, num_file, file, options | BUF_DIFF_FILTER);
+  }
   if (xp->xp_context == EXPAND_TAGS
-      || xp->xp_context == EXPAND_TAGS_LISTFILES)
+      || xp->xp_context == EXPAND_TAGS_LISTFILES) {
     return expand_tags(xp->xp_context == EXPAND_TAGS, pat, num_file, file);
+  }
   if (xp->xp_context == EXPAND_COLORS) {
     char *directories[] = { "colors", NULL };
     return ExpandRTDir(pat, DIP_START + DIP_OPT, num_file, file, directories);

src/nvim/ex_getln.h

@@ -32,6 +32,7 @@
 #define WILD_IGNORE_COMPLETESLASH   0x400
 #define WILD_NOERROR            0x800  // sets EW_NOERROR
 #define WILD_BUFLASTUSED        0x1000
+#define BUF_DIFF_FILTER         0x2000
 
 /// Present history tables
 typedef enum {

src/nvim/testdir/test_diffmode.vim

@@ -242,6 +242,46 @@ func Test_diffput_two()
   bwipe! b
 endfunc
 
+func Test_diffget_diffput_completion()
+  new Xdiff1 | diffthis
+  new Xdiff2 | diffthis
+  new Xdiff3 | diffthis
+  new Xdiff4
+
+  " :diffput and :diffget completes names of buffers which
+  " are in diff mode and which are different then current buffer.
+  b Xdiff1
+  call feedkeys(":diffput \<C-A>\<C-B>\"\<CR>", 'tx')
+  call assert_equal('"diffput Xdiff2 Xdiff3', @:)
+  call feedkeys(":diffget \<C-A>\<C-B>\"\<CR>", 'tx')
+  call assert_equal('"diffget Xdiff2 Xdiff3', @:)
+  call assert_equal(['Xdiff2', 'Xdiff3'], getcompletion('', 'diff_buffer'))
+
+  b Xdiff2
+  call feedkeys(":diffput \<C-A>\<C-B>\"\<CR>", 'tx')
+  call assert_equal('"diffput Xdiff1 Xdiff3', @:)
+  call feedkeys(":diffget \<C-A>\<C-B>\"\<CR>", 'tx')
+  call assert_equal('"diffget Xdiff1 Xdiff3', @:)
+  call assert_equal(['Xdiff1', 'Xdiff3'], getcompletion('', 'diff_buffer'))
+
+  b Xdiff3
+  call feedkeys(":diffput \<C-A>\<C-B>\"\<CR>", 'tx')
+  call assert_equal('"diffput Xdiff1 Xdiff2', @:)
+  call feedkeys(":diffget \<C-A>\<C-B>\"\<CR>", 'tx')
+  call assert_equal('"diffget Xdiff1 Xdiff2', @:)
+  call assert_equal(['Xdiff1', 'Xdiff2'], getcompletion('', 'diff_buffer'))
+
+  " No completion when in Xdiff4, it's not in diff mode.
+  b Xdiff4
+  call feedkeys(":diffput \<C-A>\<C-B>\"\<CR>", 'tx')
+  call assert_equal('"diffput ', @:)
+  call feedkeys(":diffget \<C-A>\<C-B>\"\<CR>", 'tx')
+  call assert_equal('"diffget ', @:)
+  call assert_equal([], getcompletion('', 'diff_buffer'))
+
+  %bwipe
+endfunc
+
 func Test_dp_do_buffer()
   e! one
   let bn1=bufnr('%')

src/nvim/vim.h

@@ -158,6 +158,7 @@ enum {
   EXPAND_MESSAGES,
   EXPAND_MAPCLEAR,
   EXPAND_ARGLIST,
+  EXPAND_DIFF_BUFFERS,
   EXPAND_CHECKHEALTH,
   EXPAND_LUA,
 };