vim-patch:8.2.2236: 'scroll' option can change when setting the statusline

Problem:    'scroll' option can change when setting the statusline or tabline
            but the option context is not updated.
Solution:   Update the script context when the scroll option is changed as a
            side effect. (Christian Brabandt, closes vim/vim#7533)
746670604a

runtime/doc/options.txt

@@ -4856,7 +4856,9 @@ A jump table for the options with a short description can be found at |Q_op|.
 			local to window
 	Number of lines to scroll with CTRL-U and CTRL-D commands.  Will be
 	set to half the number of lines in the window when the window size
-	changes.  If you give a count to the CTRL-U or CTRL-D command it will
+	changes.  This may happen when enabling the |status-line| or
+	'tabline' option after setting the 'scroll' option.
+	If you give a count to the CTRL-U or CTRL-D command it will
 	be used as the new value for 'scroll'.  Reset to half the window
 	height with ":set scroll=0".
 

src/nvim/ex_cmds2.c

@@ -3024,6 +3024,7 @@ void scriptnames_slash_adjust(void)
 # endif
 
 /// Get a pointer to a script name.  Used for ":verbose set".
+/// Message appended to "Last set from "
 char_u *get_scriptname(LastSet last_set, bool *should_free)
 {
   *should_free = false;
@@ -3039,6 +3040,8 @@ char_u *get_scriptname(LastSet last_set, bool *should_free)
       return (char_u *)_("environment variable");
     case SID_ERROR:
       return (char_u *)_("error handler");
+    case SID_WINLAYOUT:
+      return (char_u *)_("changed window size");
     case SID_LUA:
       return (char_u *)_("Lua");
     case SID_API_CLIENT:

src/nvim/globals.h

@@ -333,9 +333,10 @@ EXTERN int garbage_collect_at_exit INIT(= false);
 #define SID_ENV         -4      // for sourcing environment variable
 #define SID_ERROR       -5      // option was reset because of an error
 #define SID_NONE        -6      // don't set scriptID
-#define SID_LUA         -7      // for Lua scripts/chunks
+#define SID_WINLAYOUT   -7      // changing window size
-#define SID_API_CLIENT  -8      // for API clients
+#define SID_LUA         -8      // for Lua scripts/chunks
-#define SID_STR         -9      // for sourcing a string
+#define SID_API_CLIENT  -9      // for API clients
+#define SID_STR         -10     // for sourcing a string
 
 // Script CTX being sourced or was sourced to define the current function.
 EXTERN sctx_T current_sctx INIT(= { 0 COMMA 0 COMMA 0 });

src/nvim/testdir/test_options.vim

@@ -636,4 +636,23 @@ func Test_isfname_with_options()
   setlocal keywordprg&
 endfunc
 
+" Test that resetting laststatus does change scroll option
+func Test_opt_reset_scroll()
+  " See test/functional/legacy/options_spec.lua
+  CheckRunVimInTerminal
+  let vimrc =<< trim [CODE]
+    set scroll=2
+    set laststatus=2
+  [CODE]
+  call writefile(vimrc, 'Xscroll')
+  let buf = RunVimInTerminal('-S Xscroll', {'rows': 16, 'cols': 45})
+  call term_sendkeys(buf, ":verbose set scroll?\n")
+  call WaitForAssert({-> assert_match('Last set.*window size', term_getline(buf, 15))})
+  call assert_match('^\s*scroll=7$', term_getline(buf, 14))
+  call StopVimInTerminal(buf)
+
+  " clean up
+  call delete('Xscroll')
+endfunc
+
 " vim: shiftwidth=2 sts=2 expandtab

src/nvim/window.c

@@ -5960,10 +5960,18 @@ void win_new_width(win_T *wp, int width)
 
 void win_comp_scroll(win_T *wp)
 {
+  const long old_w_p_scr = wp->w_p_scr;
+
   wp->w_p_scr = wp->w_height / 2;
-  if (wp->w_p_scr == 0)
+  if (wp->w_p_scr == 0) {
     wp->w_p_scr = 1;
   }
+  if (wp->w_p_scr != old_w_p_scr) {
+    // Used by "verbose set scroll".
+    wp->w_p_script_ctx[WV_SCROLL].script_ctx.sc_sid = SID_WINLAYOUT;
+    wp->w_p_script_ctx[WV_SCROLL].script_ctx.sc_lnum = 0;
+  }
+}
 
 /*
  * command_height: called whenever p_ch has been changed

test/functional/legacy/options_spec.lua

@@ -41,4 +41,32 @@ describe('set', function()
     ]])
     matches('E36: Not enough room', exc_exec('set wmh=1'))
   end)
+
+  it('scroll works', function()
+    local screen = Screen.new(42, 16)
+    screen:attach()
+    source([[
+      set scroll=2
+      set laststatus=2
+    ]])
+    command('verbose set scroll?')
+    screen:expect([[
+                                                |
+      ~                                         |
+      ~                                         |
+      ~                                         |
+      ~                                         |
+      ~                                         |
+      ~                                         |
+      ~                                         |
+      ~                                         |
+      ~                                         |
+      ~                                         |
+      ~                                         |
+                                                |
+        scroll=7                                |
+              Last set from changed window size |
+      Press ENTER or type command to continue^   |
+    ]])
+  end)
 end)