patch 9.1.1170: wildmenu highlighting in popup can be improved

Problem:  wildmenu highlighting in popup can be improved
Solution: Check if the completion items contain submatches of the
          entered text (Girish Palya).

This update enables highlighting in the popup menu even when the matched
fragment or pattern appears within an item (string) rather than only at the
beginning. This is especially useful for custom completion, where menu items
may not always start with the typed pattern.

For specific use cases, refer to the two examples in
https://github.com/vim/vim/pull/16759

A sliding window approach is used with direct string comparison. Performance
is not a concern, as highlighting is applied only to displayed lines, even if
the menu list is arbitrarily long.

closes: #16785

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

src/popupmenu.c

@@ -410,7 +410,7 @@ pum_compute_text_attrs(char_u *text, hlf_T hlf, int user_hlattr)
     int		*attrs = NULL;
     char_u	*leader = NULL;
     int		in_fuzzy;
-    int		matched_start = FALSE;
+    int		matched_len = -1;
     int_u	char_pos = 0;
     int		is_select = FALSE;
 
@@ -435,8 +435,6 @@ pum_compute_text_attrs(char_u *text, hlf_T hlf, int user_hlattr)
 
     if (in_fuzzy)
 	ga = fuzzy_match_str_with_pos(text, leader);
-    else
-	matched_start = MB_STRNICMP(text, leader, leader_len) == 0;
 
     while (*ptr != NUL)
     {
@@ -455,10 +453,16 @@ pum_compute_text_attrs(char_u *text, hlf_T hlf, int user_hlattr)
 		}
 	    }
 	}
-	else if (matched_start && ptr < text + leader_len)
+	else
+	{
+	    if (matched_len < 0 && MB_STRNICMP(ptr, leader, leader_len) == 0)
+		matched_len = leader_len;
+	    if (matched_len > 0)
 	    {
 		new_attr = highlight_attr[is_select ? HLF_PMSI : HLF_PMNI];
 		new_attr = hl_combine_attr(highlight_attr[hlf], new_attr);
+		matched_len--;
+	    }
 	}
 
 	new_attr = hl_combine_attr(highlight_attr[HLF_PNI], new_attr);

src/testdir/dumps/Test_wildmenu_pum_hl_match_nonf.dump

@@ -0,0 +1,10 @@
+| +0&#ffffff0@49
+|~+0#4040ff13&| @48
+|~| @48
+|~| @48
+|~| @48
+|~| @48
+|~| @4| +0#0000001#ffd7ff255|o|n+0#0000e05&|e|A+0#0000001&| @10| +0#4040ff13#ffffff0@27
+|~| @4| +0#0000001#ffd7ff255|o| |n+0#0000e05&|e|B+0#0000001&|n|e|B| @6| +0#4040ff13#ffffff0@27
+|~| @4| +0#0000001#ffd7ff255|a|o|n+0#0000e05&|e|C+0#0000001&| @9| +0#4040ff13#ffffff0@27
+|:+0#0000000&|M|y|C|m|d| |n|e> @40

src/testdir/test_cmdline.vim

@@ -2996,6 +2996,28 @@ func Test_wildmenu_pum_rightleft()
   call StopVimInTerminal(buf)
 endfunc
 
+" Test highlighting when pattern matches non-first character of item
+func Test_wildmenu_pum_hl_nonfirst()
+  CheckScreendump
+  let lines =<< trim END
+    set wildoptions=pum wildchar=<tab> wildmode=noselect,full
+    hi PmenuMatchSel  ctermfg=6 ctermbg=7
+    hi PmenuMatch     ctermfg=4 ctermbg=225
+    func T(a, c, p)
+      return ["oneA", "o neBneB", "aoneC"]
+    endfunc
+    command -nargs=1 -complete=customlist,T MyCmd
+  END
+
+  call writefile(lines, 'Xwildmenu_pum_hl_nonf', 'D')
+  let buf = RunVimInTerminal('-S Xwildmenu_pum_hl_nonf', #{rows: 10, cols: 50})
+
+  call term_sendkeys(buf, ":MyCmd ne\<tab>")
+  call VerifyScreenDump(buf, 'Test_wildmenu_pum_hl_match_nonf', {})
+  call term_sendkeys(buf, "\<Esc>")
+  call StopVimInTerminal(buf)
+endfunc
+
 " Test highlighting matched text in cmdline completion popup menu.
 func Test_wildmenu_pum_hl_match()
   CheckScreendump

src/version.c

@@ -704,6 +704,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    1170,
 /**/
     1169,
 /**/