vim-patch:9.1.1473: inconsistent range arg for :diffget/diffput (#34588)

Problem:  inconsistent range arg for :diffget/diffput
Solution: fix the range specification, place the cursor for :diffput and
          :diffget consistently on the last line (Yee Cheng Chin)

Previously, `:<range>diffget` only allowed using 1 or above in the range
value, making it impossible to use the command for a diff block at the
beginning of the file. Fix the range specification so the user can now
use 0 to specify the space before the first line. This allows
`:0,$+1diffget` to work to retrieve all the changes from the other file
instead of missing the first diff block. Also do this for `:diffput`.

Also, make `:diffput` work more similar to `:diffget`. Make it so that
if the cursor is on the last line and a new line is inserted in the
other file, doing `:diffput` will select that diff block below the line,
just like `:diffget` would.

Also clean up the logic a little bit for edge cases and for handling
line matched diff blocks better.

closes: vim/vim#17579

d75ab0cbf5

Co-authored-by: Yee Cheng Chin <ychin.git@gmail.com>

runtime/doc/diff.txt

@@ -292,18 +292,20 @@ that the buffers will be equal within the specified range.
 
 
 When no [range] is given, the diff at the cursor position or just above it is
-affected.  When [range] is used, Vim tries to only put or get the specified
+affected.  There can be deleted lines below the last line of the buffer.  When
-lines.  When there are deleted lines, this may not always be possible.
+the cursor is on the last line in the buffer and there is no diff above this
+line, and no [range] is given, the diff below the cursor position will be used
+instead.
 
-There can be deleted lines below the last line of the buffer.  When the cursor
+When [range] is used, Vim tries to only put or get the specified lines.  When
-is on the last line in the buffer and there is no diff above this line, the
+there are deleted lines, they will be used if they are between the lines
-":diffget" and "do" commands will obtain lines from the other buffer.
+specified by [range].
 
-To be able to get those lines from another buffer in a [range] it's allowed to
+To be able to put or get those lines to/from another buffer in a [range] it's
-use the last line number plus one.  This command gets all diffs from the other
+allowed to use 0 and the last line number plus one.  This command gets all
-buffer: >
+diffs from the other buffer: >
 
-	:1,$+1diffget
+	:0,$+1diffget
 
 Note that deleted lines are displayed, but not counted as text lines.  You
 can't move the cursor into them.  To fill the deleted lines with the lines

src/nvim/diff.c

@@ -3492,10 +3492,13 @@ void ex_diffgetput(exarg_T *eap)
   if (eap->addr_count == 0) {
     // Make it possible that ":diffget" on the last line gets line below
     // the cursor line when there is no difference above the cursor.
-    if ((eap->cmdidx == CMD_diffget)
+    int linestatus = 0;
-        && (eap->line1 == curbuf->b_ml.ml_line_count)
+    if (eap->line1 == curbuf->b_ml.ml_line_count
-        && (diff_check(curwin, eap->line1) == 0)
+        && (diff_check_with_linestatus(curwin, eap->line1, &linestatus) == 0
-        && ((eap->line1 == 1) || (diff_check(curwin, eap->line1 - 1) == 0))) {
+            && linestatus == 0)
+        && (eap->line1 == 1
+            || (diff_check_with_linestatus(curwin, eap->line1 - 1, &linestatus) >= 0
+                && linestatus == 0))) {
       eap->line2++;
     } else if (eap->line1 > 0) {
       eap->line1--;

src/nvim/ex_cmds.lua

@@ -752,7 +752,7 @@ M.cmds = {
   },
   {
     command = 'diffget',
-    flags = bit.bor(RANGE, EXTRA, TRLBAR, MODIFY),
+    flags = bit.bor(RANGE, ZEROR, EXTRA, TRLBAR, MODIFY),
     addr_type = 'ADDR_LINES',
     func = 'ex_diffgetput',
   },
@@ -770,7 +770,7 @@ M.cmds = {
   },
   {
     command = 'diffput',
-    flags = bit.bor(RANGE, EXTRA, TRLBAR),
+    flags = bit.bor(RANGE, ZEROR, EXTRA, TRLBAR),
     addr_type = 'ADDR_LINES',
     func = 'ex_diffgetput',
   },

src/nvim/ex_docmd.c

@@ -3728,8 +3728,9 @@ char *invalid_range(exarg_T *eap)
   if (eap->argt & EX_RANGE) {
     switch (eap->addr_type) {
     case ADDR_LINES:
-      if (eap->line2 > (curbuf->b_ml.ml_line_count
+      if (eap->line2 >
-                        + (eap->cmdidx == CMD_diffget))) {
+          (curbuf->b_ml.ml_line_count
+           + (eap->cmdidx == CMD_diffget || eap->cmdidx == CMD_diffput))) {
         return _(e_invrange);
       }
       break;

test/old/testdir/test_diffmode.vim

@@ -288,6 +288,63 @@ func Test_diffget_diffput_range()
   %bw!
 endfunc
 
+" Test :diffget/:diffput handling of added/deleted lines
+func Test_diffget_diffput_deleted_lines()
+  call setline(1, ['2','4','6'])
+  diffthis
+  new
+  call setline(1, range(1,7))
+  diffthis
+  wincmd w
+
+  3,3diffget " get nothing
+  call assert_equal(['2', '4', '6'], getline(1, '$'))
+  3,4diffget " get the last insertion past the end of file
+  call assert_equal(['2', '4', '6', '7'], getline(1, '$'))
+  0,1diffget " get the first insertion above first line
+  call assert_equal(['1', '2', '4', '6', '7'], getline(1, '$'))
+
+  " When using non-range diffget on the last line, it should get the
+  " change above or at the line as usual, but if the only change is below the
+  " last line, diffget should get that instead.
+  1,$delete
+  call setline(1, ['2','4','6'])
+  diffupdate
+  norm Gdo
+  call assert_equal(['2', '4', '5', '6'], getline(1, '$'))
+  norm Gdo
+  call assert_equal(['2', '4', '5', '6', '7'], getline(1, '$'))
+
+  " Test non-range diffput on last line with the same logic
+  1,$delete
+  call setline(1, ['2','4','6'])
+  diffupdate
+  norm Gdp
+  wincmd w
+  call assert_equal(['1', '2', '3', '4', '6', '7'], getline(1, '$'))
+  wincmd w
+  norm Gdp
+  wincmd w
+  call assert_equal(['1', '2', '3', '4', '6'], getline(1, '$'))
+  call setline(1, range(1,7))
+  diffupdate
+  wincmd w
+
+  " Test that 0,$+1 will get/put all changes from/to the other buffer
+  1,$delete
+  call setline(1, ['2','4','6'])
+  diffupdate
+  0,$+1diffget
+  call assert_equal(['1', '2', '3', '4', '5', '6', '7'], getline(1, '$'))
+  1,$delete
+  call setline(1, ['2','4','6'])
+  diffupdate
+  0,$+1diffput
+  wincmd w
+  call assert_equal(['2', '4', '6'], getline(1, '$'))
+  %bw!
+endfunc
+
 " Test for :diffget/:diffput with an empty buffer and a non-empty buffer
 func Test_diffget_diffput_empty_buffer()
   %d _