patch 9.1.1521: completion: pum does not reset scroll pos on reopen with 'noselect'

Problem:  When 'wildmode' is set to include "noselect", the popup menu (pum)
          incorrectly retained its scroll position when reopened. This
          meant that after scrolling down through the menu with `<C-n>`,
          reopening the menu (e.g., by retyping the command and
          triggering completion again) would show the menu starting from
          the previously scrolled position, rather than from the top.
          This could confuse users, as the first visible item would not
          be the first actual match in the list.

Solution: Ensure that the popup menu resets its scroll position to the
          top when reopened (Girish Palya).

closes: #17673

Signed-off-by: Girish Palya <girishji@gmail.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>

src/cmdexpand.c

@@ -411,6 +411,7 @@ cmdline_pum_create(
     // no default selection
     compl_selected = -1;
 
+    pum_clear();
     cmdline_pum_display();
 
     return EXPAND_OK;

src/testdir/dumps/Test_pum_scroll_noselect_1.dump

@@ -0,0 +1,10 @@
+| +0&#ffffff0@7| +0#0000001#ffd7ff255|a|1|5| @11| +0#0000000#a8a8a8255| +0&#ffffff0@49
+|~+0#4040ff13&| @6| +0#0000001#ffd7ff255|a|1|6| @11| +0#0000000#a8a8a8255| +0#4040ff13#ffffff0@49
+|~| @6| +0#0000001#ffd7ff255|a|1|7| @11| +0#0000000#a8a8a8255| +0#4040ff13#ffffff0@49
+|~| @6| +0#0000001#ffd7ff255|a|1|8| @11| +0#0000000#0000001| +0#4040ff13#ffffff0@49
+|~| @6| +0#0000001#ffd7ff255|a|1|9| @11| +0#0000000#a8a8a8255| +0#4040ff13#ffffff0@49
+|~| @6| +0#0000001#e0e0e08|a|2|0| @11| +0#0000000#a8a8a8255| +0#4040ff13#ffffff0@49
+|~| @6| +0#0000001#ffd7ff255|a|2|1| @11| +0#0000000#a8a8a8255| +0#4040ff13#ffffff0@49
+|~| @6| +0#0000001#ffd7ff255|a|2@1| @11| +0#0000000#a8a8a8255| +0#4040ff13#ffffff0@49
+|~| @6| +0#0000001#ffd7ff255|a|2|3| @11| +0#0000000#a8a8a8255| +0#4040ff13#ffffff0@49
+|:+0#0000000&|T|e|s|t|C|m|d| |a|2|0> @62

src/testdir/dumps/Test_pum_scroll_noselect_2.dump

@@ -0,0 +1,10 @@
+| +0&#ffffff0@7| +0#0000001#ffd7ff255|a|1| @12| +0#0000000#0000001| +0&#ffffff0@49
+|~+0#4040ff13&| @6| +0#0000001#ffd7ff255|a|2| @12| +0#0000000#a8a8a8255| +0#4040ff13#ffffff0@49
+|~| @6| +0#0000001#ffd7ff255|a|3| @12| +0#0000000#a8a8a8255| +0#4040ff13#ffffff0@49
+|~| @6| +0#0000001#ffd7ff255|a|4| @12| +0#0000000#a8a8a8255| +0#4040ff13#ffffff0@49
+|~| @6| +0#0000001#ffd7ff255|a|5| @12| +0#0000000#a8a8a8255| +0#4040ff13#ffffff0@49
+|~| @6| +0#0000001#ffd7ff255|a|6| @12| +0#0000000#a8a8a8255| +0#4040ff13#ffffff0@49
+|~| @6| +0#0000001#ffd7ff255|a|7| @12| +0#0000000#a8a8a8255| +0#4040ff13#ffffff0@49
+|~| @6| +0#0000001#ffd7ff255|a|8| @12| +0#0000000#a8a8a8255| +0#4040ff13#ffffff0@49
+|~| @6| +0#0000001#ffd7ff255|a|9| @12| +0#0000000#a8a8a8255| +0#4040ff13#ffffff0@49
+|:+0#0000000&|T|e|s|t|C|m|d| > @65

src/testdir/test_cmdline.vim

@@ -4622,4 +4622,35 @@ func Test_range_complete()
   set wildcharm=0
 endfunc
 
+" With 'noselect' in 'wildmode', ensure that the popup menu (pum) does not retain
+" its scroll position after reopening. The menu should open showing the top items,
+" regardless of previous scrolling.
+func Test_pum_scroll_noselect()
+  CheckScreendump
+
+  let lines =<< trim [SCRIPT]
+    command! -nargs=* -complete=customlist,TestFn TestCmd echo
+    func TestFn(a, b, c)
+      return map(range(1, 50), 'printf("a%d", v:val)')
+    endfunc
+    set wildmode=noselect,full
+    set wildoptions=pum
+    set wildmenu
+    set noruler
+  [SCRIPT]
+  call writefile(lines, 'XTest_pum_scroll', 'D')
+  let buf = RunVimInTerminal('-S XTest_pum_scroll', {'rows': 10})
+
+  call term_sendkeys(buf, ":TestCmd \<tab>" . repeat("\<c-n>", 20))
+  call TermWait(buf, 50)
+  call VerifyScreenDump(buf, 'Test_pum_scroll_noselect_1', {})
+
+  call term_sendkeys(buf, "\<esc>:TestCmd \<tab>")
+  call TermWait(buf, 50)
+  call VerifyScreenDump(buf, 'Test_pum_scroll_noselect_2', {})
+
+  call term_sendkeys(buf, "\<esc>")
+  call StopVimInTerminal(buf)
+endfunc
+
 " vim: shiftwidth=2 sts=2 expandtab

src/version.c

@@ -719,6 +719,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    1521,
 /**/
     1520,
 /**/