vim-patch:9.0.0342: ":wincmd =" equalizes in two directions

Problem:    ":wincmd =" equalizes in two directions.
Solution:   Make ":vertical wincmd =" equalize vertically only and
            ":horizontal wincmd =" equalize horizontally only.
https://github.com/vim/vim/commit/21c3a80a7fd6b7fc250ce5dc287963511f54b86f

5 files changed, 65 insertions, 12 deletions

diff --git a/src/nvim/ex_cmds.lua b/src/nvim/ex_cmds.lua
index 4bed1e94b9..04b8832428 100644
--- a/src/nvim/ex_cmds.lua
+++ b/src/nvim/ex_cmds.lua
@@ -1141,6 +1141,12 @@ module.cmds = {
     func='ex_history',
   },
   {
+    command='horizontal',
+    flags=bit.bor(NEEDARG, EXTRA, NOTRLCOM),
+    addr_type='ADDR_NONE',
+    func='ex_wrongmodifier',
+  },
+  {
     command='insert',
     flags=bit.bor(BANG, RANGE, TRLBAR, CMDWIN, LOCK_OK, MODIFY),
     addr_type='ADDR_LINES',
diff --git a/src/nvim/ex_docmd.c b/src/nvim/ex_docmd.c
index 0af737ff50..f99253ea75 100644
--- a/src/nvim/ex_docmd.c
+++ b/src/nvim/ex_docmd.c
@@ -2438,8 +2438,12 @@ int parse_command_modifiers(exarg_T *eap, char **errormsg, cmdmod_T *cmod, bool
       continue;
     }
 
-    // ":hide" and ":hide | cmd" are not modifiers
     case 'h':
+      if (checkforcmd(&eap->cmd, "horizontal", 3)) {
+        cmod->cmod_split |= WSP_HOR;
+        continue;
+      }
+      // ":hide" and ":hide | cmd" are not modifiers
       if (p != eap->cmd || !checkforcmd(&p, "hide", 3)
           || *p == NUL || ends_excmd(*p)) {
         break;
diff --git a/src/nvim/testdir/test_window_cmd.vim b/src/nvim/testdir/test_window_cmd.vim
index 83a3216534..1f4b9b77c6 100644
--- a/src/nvim/testdir/test_window_cmd.vim
+++ b/src/nvim/testdir/test_window_cmd.vim
@@ -343,6 +343,46 @@ func Test_window_height()
   bw Xa Xb Xc
 endfunc
 
+func Test_wincmd_equal()
+  edit Xone
+  below split Xtwo
+  rightbelow vsplit Xthree
+  call assert_equal('Xone', bufname(winbufnr(1)))
+  call assert_equal('Xtwo', bufname(winbufnr(2)))
+  call assert_equal('Xthree', bufname(winbufnr(3)))
+
+  " Xone and Xtwo should be about the same height
+  let [wh1, wh2] = [winheight(1), winheight(2)]
+  call assert_inrange(wh1 - 1, wh1 + 1, wh2)
+  " Xtwo and Xthree should be about the same width
+  let [ww2, ww3] = [winwidth(2), winwidth(3)]
+  call assert_inrange(ww2 - 1, ww2 + 1, ww3)
+
+  1wincmd w
+  10wincmd _
+  2wincmd w
+  20wincmd |
+  call assert_equal(10, winheight(1))
+  call assert_equal(20, winwidth(2))
+
+  " equalizing horizontally doesn't change the heights
+  hor wincmd =
+  call assert_equal(10, winheight(1))
+  let [ww2, ww3] = [winwidth(2), winwidth(3)]
+  call assert_inrange(ww2 - 1, ww2 + 1, ww3)
+
+  2wincmd w
+  20wincmd |
+  call assert_equal(20, winwidth(2))
+  " equalizing vertically doesn't change the widths
+  vert wincmd =
+  call assert_equal(20, winwidth(2))
+  let [wh1, wh2] = [winheight(1), winheight(2)]
+  call assert_inrange(wh1 - 1, wh1 + 1, wh2)
+
+  bwipe Xone Xtwo Xthree
+endfunc
+
 func Test_window_width()
   e Xa
   vsplit Xb
diff --git a/src/nvim/window.c b/src/nvim/window.c
index c11484d1b8..c0b73ff837 100644
--- a/src/nvim/window.c
+++ b/src/nvim/window.c
@@ -417,10 +417,12 @@ newwindow:
               | ((nchar == 'H' || nchar == 'K') ? WSP_TOP : WSP_BOT));
     break;
 
-  // make all windows the same height
-  case '=':
-    win_equal(NULL, false, 'b');
+  // make all windows the same width and/or height
+  case '=': {
+    int mod = cmdmod.cmod_split & (WSP_VERT | WSP_HOR);
+    win_equal(NULL, false, mod == WSP_VERT ? 'v' : mod == WSP_HOR ? 'h' : 'b');
     break;
+  }
 
   // increase current window height
   case '+':
diff --git a/src/nvim/window.h b/src/nvim/window.h
index b75b8abd9b..3137035b25 100644
--- a/src/nvim/window.h
+++ b/src/nvim/window.h
@@ -17,14 +17,15 @@
 #define FNAME_UNESC     32      // remove backslashes used for escaping
 
 // arguments for win_split()
-#define WSP_ROOM        1       // require enough room
-#define WSP_VERT        2       // split vertically
-#define WSP_TOP         4       // window at top-left of shell
-#define WSP_BOT         8       // window at bottom-right of shell
-#define WSP_HELP        16      // creating the help window
-#define WSP_BELOW       32      // put new window below/right
-#define WSP_ABOVE       64      // put new window above/left
-#define WSP_NEWLOC      128     // don't copy location list
+#define WSP_ROOM        0x01    // require enough room
+#define WSP_VERT        0x02    // split/equalize vertically
+#define WSP_HOR         0x04    // equalize horizontally
+#define WSP_TOP         0x08    // window at top-left of shell
+#define WSP_BOT         0x10    // window at bottom-right of shell
+#define WSP_HELP        0x20    // creating the help window
+#define WSP_BELOW       0x40    // put new window below/right
+#define WSP_ABOVE       0x80    // put new window above/left
+#define WSP_NEWLOC      0x100   // don't copy location list
 
 // Minimum screen size
 #define MIN_COLUMNS     12      // minimal columns for screen