vim-patch:8.2.0131: command line is not cleared when switching tabs

Problem:    Command line is not cleared when switching tabs and the command
            line height differs.
Solution:   Set the "clear_cmdline" flag when needed. (Naruhiko Nishino,
            closes vim/vim#5495)
https://github.com/vim/vim/commit/479950f6c9aee4806f28a2b2fe5471e18a034cff

4 files changed, 100 insertions, 38 deletions

diff --git a/src/nvim/testdir/test_cmdline.vim b/src/nvim/testdir/test_cmdline.vim
index 871143699a..e3c42a4fe3 100644
--- a/src/nvim/testdir/test_cmdline.vim
+++ b/src/nvim/testdir/test_cmdline.vim
@@ -722,7 +722,7 @@ func Test_verbosefile()
 endfunc
 
 func Test_verbose_option()
-  " See test/functional/ui/cmdline_spec.lua
+  " See test/functional/legacy/cmdline_spec.lua
   CheckScreendump
 
   let lines =<< trim [SCRIPT]
@@ -842,6 +842,25 @@ func Test_buffers_lastused()
   bwipeout bufc
 endfunc
 
+func Test_cmdlineclear_tabenter()
+  " See test/functional/legacy/cmdline_spec.lua
+  CheckScreendump
+
+  let lines =<< trim [SCRIPT]
+    call setline(1, range(30))
+  [SCRIPT]
+
+  call writefile(lines, 'XtestCmdlineClearTabenter')
+  let buf = RunVimInTerminal('-S XtestCmdlineClearTabenter', #{rows: 10})
+  call term_wait(buf, 50)
+  " in one tab make the command line higher with CTRL-W -
+  call term_sendkeys(buf, ":tabnew\<cr>\<C-w>-\<C-w>-gtgt")
+  call VerifyScreenDump(buf, 'Test_cmdlineclear_tabenter', {})
+
+  call StopVimInTerminal(buf)
+  call delete('XtestCmdlineClearTabenter')
+endfunc
+
 " test that ";" works to find a match at the start of the first line
 func Test_zero_line_search()
   new
diff --git a/src/nvim/window.c b/src/nvim/window.c
index 4931221e7a..96409304ab 100644
--- a/src/nvim/window.c
+++ b/src/nvim/window.c
@@ -4049,7 +4049,7 @@ static void enter_tabpage(tabpage_T *tp, buf_T *old_curbuf, int trigger_enter_au
   prevwin = next_prevwin;
 
   last_status(false);  // status line may appear or disappear
-  (void)win_comp_pos();  // recompute w_winrow for all windows
+  const int row = win_comp_pos();  // recompute w_winrow for all windows
   diff_need_scrollbind = true;
 
   /* The tabpage line may have appeared or disappeared, may need to resize
@@ -4060,11 +4060,20 @@ static void enter_tabpage(tabpage_T *tp, buf_T *old_curbuf, int trigger_enter_au
     clear_cmdline = true;
   }
   p_ch = curtab->tp_ch_used;
-  if (curtab->tp_old_Rows != Rows || (old_off != firstwin->w_winrow
-                                      ))
+
+  // When cmdheight is changed in a tab page with '<C-w>-', cmdline_row is
+  // changed but p_ch and tp_ch_used are not changed. Thus we also need to
+  // check cmdline_row.
+  if ((row < cmdline_row) && (cmdline_row <= Rows - p_ch)) {
+    clear_cmdline = true;
+  }
+
+  if (curtab->tp_old_Rows != Rows || (old_off != firstwin->w_winrow)) {
     shell_new_rows();
-  if (curtab->tp_old_Columns != Columns && starting == 0)
-    shell_new_columns();        /* update window widths */
+  }
+  if (curtab->tp_old_Columns != Columns && starting == 0) {
+    shell_new_columns();  // update window widths
+  }
 
   lastused_tabpage = old_curtab;
 
diff --git a/test/functional/legacy/cmdline_spec.lua b/test/functional/legacy/cmdline_spec.lua
new file mode 100644
index 0000000000..9ebe9aeb91
--- /dev/null
+++ b/test/functional/legacy/cmdline_spec.lua
@@ -0,0 +1,66 @@
+local helpers = require('test.functional.helpers')(after_each)
+local Screen = require('test.functional.ui.screen')
+local clear = helpers.clear
+local feed = helpers.feed
+local feed_command = helpers.feed_command
+local source = helpers.source
+
+describe('cmdline', function()
+  before_each(clear)
+
+  it('is cleared when switching tabs', function()
+    local screen = Screen.new(30, 10)
+    screen:attach()
+    feed_command([[call setline(1, range(30))]])
+    screen:expect([[
+      ^0                             |
+      1                             |
+      2                             |
+      3                             |
+      4                             |
+      5                             |
+      6                             |
+      7                             |
+      8                             |
+      :call setline(1, range(30))   |
+    ]])
+    feed([[:tabnew<cr><C-w>-<C-w>-gtgt]])
+    screen:expect([[
+       + [No Name]  [No Name]      X|
+      ^                              |
+      ~                             |
+      ~                             |
+      ~                             |
+      ~                             |
+      ~                             |
+      6                             |
+      7                             |
+                                    |
+    ]])
+  end)
+
+  it('prints every executed Ex command if verbose >= 16', function()
+    local screen = Screen.new(60, 12)
+    screen:attach()
+    source([[
+      command DoSomething echo 'hello' |set ts=4 |let v = '123' |echo v
+      call feedkeys("\r", 't') " for the hit-enter prompt
+      set verbose=20
+    ]])
+    feed_command('DoSomething')
+    screen:expect([[
+                                                                  |
+      ~                                                           |
+      ~                                                           |
+                                                                  |
+      Executing: DoSomething                                      |
+      Executing: echo 'hello' |set ts=4 |let v = '123' |echo v    |
+      hello                                                       |
+      Executing: set ts=4 |let v = '123' |echo v                  |
+      Executing: let v = '123' |echo v                            |
+      Executing: echo v                                           |
+      123                                                         |
+      Press ENTER or type command to continue^                     |
+    ]])
+  end)
+end)
diff --git a/test/functional/ui/cmdline_spec.lua b/test/functional/ui/cmdline_spec.lua
index 01f0d8a4d7..21c01b3458 100644
--- a/test/functional/ui/cmdline_spec.lua
+++ b/test/functional/ui/cmdline_spec.lua
@@ -3,7 +3,6 @@ local Screen = require('test.functional.ui.screen')
 local clear, feed = helpers.clear, helpers.feed
 local source = helpers.source
 local command = helpers.command
-local feed_command = helpers.feed_command
 
 local function new_screen(opt)
   local screen = Screen.new(25, 5)
@@ -843,34 +842,3 @@ describe('cmdline redraw', function()
     ]], unchanged=true}
   end)
 end)
-
-describe('cmdline', function()
-  before_each(function()
-    clear()
-  end)
-
-  it('prints every executed Ex command if verbose >= 16', function()
-    local screen = Screen.new(50, 12)
-    screen:attach()
-    source([[
-      command DoSomething echo 'hello' |set ts=4 |let v = '123' |echo v
-      call feedkeys("\r", 't') " for the hit-enter prompt
-      set verbose=20
-    ]])
-    feed_command('DoSomething')
-    screen:expect([[
-                                                        |
-      ~                                                 |
-                                                        |
-      Executing: DoSomething                            |
-      Executing: echo 'hello' |set ts=4 |let v = '123' ||
-      echo v                                            |
-      hello                                             |
-      Executing: set ts=4 |let v = '123' |echo v        |
-      Executing: let v = '123' |echo v                  |
-      Executing: echo v                                 |
-      123                                               |
-      Press ENTER or type command to continue^           |
-    ]])
-  end)
-end)