patch 9.1.1473: inconsistent range arg for :diffget/diffput

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: #17579

Signed-off-by: Yee Cheng Chin <ychin.git@gmail.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>

runtime/doc/diff.txt

@@ -1,4 +1,4 @@
-*diff.txt*      For Vim version 9.1.  Last change: 2025 Mar 28
+*diff.txt*      For Vim version 9.1.  Last change: 2025 Jun 20
 
 
 		  VIM REFERENCE MANUAL    by Bram Moolenaar
@@ -304,18 +304,20 @@ 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
-lines.  When there are deleted lines, this may not always be possible.
+affected.  There can be deleted lines below the last line of the buffer.  When
+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
-is on the last line in the buffer and there is no diff above this line, the
-":diffget" and "do" commands will obtain lines from the other buffer.
+When [range] is used, Vim tries to only put or get the specified lines.  When
+there are deleted lines, they will be used if they are between the lines
+specified by [range].
 
-To be able to get those lines from another buffer in a [range] it's allowed to
-use the last line number plus one.  This command gets all diffs from the other
-buffer: >
+To be able to put or get those lines to/from another buffer in a [range] it's
+allowed to use 0 and the last line number plus one.  This command gets all
+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/diff.c

@@ -3874,10 +3874,13 @@ ex_diffgetput(exarg_T *eap)
     {
 	// 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
-		&& eap->line1 == curbuf->b_ml.ml_line_count
-		&& diff_check(curwin, eap->line1) == 0
-		&& (eap->line1 == 1 || diff_check(curwin, eap->line1 - 1) == 0))
+	int linestatus = 0;
+	if (eap->line1 == curbuf->b_ml.ml_line_count
+		&& (diff_check_with_linestatus(curwin, eap->line1, &linestatus) == 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/ex_cmds.h

@@ -486,7 +486,7 @@ EXCMD(CMD_diffupdate,	"diffupdate",	ex_diffupdate,
 	EX_BANG|EX_TRLBAR,
 	ADDR_NONE),
 EXCMD(CMD_diffget,	"diffget",	ex_diffgetput,
-	EX_RANGE|EX_EXTRA|EX_TRLBAR|EX_MODIFY,
+	EX_RANGE|EX_ZEROR|EX_EXTRA|EX_TRLBAR|EX_MODIFY,
 	ADDR_LINES),
 EXCMD(CMD_diffoff,	"diffoff",	ex_diffoff,
 	EX_BANG|EX_TRLBAR,
@@ -495,7 +495,7 @@ EXCMD(CMD_diffpatch,	"diffpatch",	ex_diffpatch,
 	EX_EXTRA|EX_FILE1|EX_TRLBAR|EX_MODIFY,
 	ADDR_NONE),
 EXCMD(CMD_diffput,	"diffput",	ex_diffgetput,
-	EX_RANGE|EX_EXTRA|EX_TRLBAR,
+	EX_RANGE|EX_ZEROR|EX_EXTRA|EX_TRLBAR,
 	ADDR_LINES),
 EXCMD(CMD_diffsplit,	"diffsplit",	ex_diffsplit,
 	EX_EXTRA|EX_FILE1|EX_TRLBAR,

src/ex_docmd.c

@@ -4850,7 +4850,8 @@ invalid_range(exarg_T *eap)
 	    case ADDR_LINES:
 		if (eap->line2 > curbuf->b_ml.ml_line_count
 #ifdef FEAT_DIFF
-			    + (eap->cmdidx == CMD_diffget)
+			    + (eap->cmdidx == CMD_diffget ||
+				eap->cmdidx == CMD_diffput)
 #endif
 		   )
 		    return _(e_invalid_range);

src/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 _

src/version.c

@@ -709,6 +709,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    1473,
 /**/
     1472,
 /**/