From 2e5505f044e403ccaef8c43bdc66480c71dcf05a Mon Sep 17 00:00:00 2001
From: Martin Sukany <martin@sukany.cz>
Date: Sat, 28 Feb 2026 14:44:37 +0100
Subject: [PATCH] ns: fix overlay candidate detection (Fequal face comparison)

The previous ns_ax_selected_overlay_text matched ANY non-nil face,
but all Vertico lines have faces.  Fix: collect line boundaries,
compare each line's face against the first line's face via Fequal,
return the line with a DIFFERENT face (the selected candidate).

Also fix duplicate 'NSString *candidate' declaration.

* src/nsterm.m (ns_ax_selected_overlay_text): Rewrite to compare
faces line-by-line via Fequal instead of matching first non-nil face.
---
 src/nsterm.m | 94 +++++++++++++++++++++++++++-------------------------
 1 file changed, 48 insertions(+), 46 deletions(-)

diff --git a/src/nsterm.m b/src/nsterm.m
index 43d30f9..35edd39 100644
--- a/src/nsterm.m
+++ b/src/nsterm.m
@@ -6916,12 +6916,12 @@ ns_create_font_panel_buttons (id target, SEL select, SEL cancel_action)
 #define NS_AX_TEXT_CAP 100000
 
 /* Extract the currently selected candidate text from overlay display
-   strings in window W.  Completion frameworks (Vertico, Ivy, Icomplete)
-   highlight the current candidate by applying a face property to a
-   portion of the overlay's before-string or after-string.  We find
-   that highlighted portion and return it as an NSString.
+   strings.  Completion frameworks (Vertico, Ivy, Icomplete) highlight
+   the current candidate with a distinct face.  We find the line whose
+   face DIFFERS from the first line's face (the "normal" candidate
+   face) — that is the selected candidate.
 
-   Returns nil if no highlighted overlay text is found.  */
+   Returns nil if no distinctly-faced line is found.  */
 static NSString *
 ns_ax_selected_overlay_text (struct buffer *b,
 			     ptrdiff_t beg, ptrdiff_t end)
@@ -6942,57 +6942,60 @@ ns_ax_selected_overlay_text (struct buffer *b,
 	    continue;
 
 	  Lisp_Object str = strings[s];
-	  ptrdiff_t len = SCHARS (str);
-	  ptrdiff_t pos = 0;
+	  ptrdiff_t slen = SCHARS (str);
+	  if (slen == 0)
+	    continue;
+
+	  /* Collect line boundaries.  */
+	  ptrdiff_t line_starts[512];
+	  ptrdiff_t line_ends[512];
+	  int nlines = 0;
+	  ptrdiff_t lstart = 0;
 
-	  while (pos < len)
+	  for (ptrdiff_t i = 0; i <= slen && nlines < 512; i++)
 	    {
-	      Lisp_Object face
-		= Fget_text_property (make_fixnum (pos),
-				      Qface, str);
-	      if (!NILP (face))
+	      bool is_nl = false;
+	      if (i < slen)
+		{
+		  Lisp_Object ch = Faref (str, make_fixnum (i));
+		  is_nl = (FIXNUMP (ch) && XFIXNUM (ch) == '\n');
+		}
+	      if (is_nl || i == slen)
 		{
-		  /* Found highlighted text.  Extract the full line
-		     containing this position.  */
-		  ptrdiff_t line_start = pos;
-		  while (line_start > 0)
+		  if (i > lstart)
 		    {
-		      /* Check character before line_start.  */
-		      Lisp_Object ch
-			= Faref (str, make_fixnum (line_start - 1));
-		      if (FIXNUMP (ch) && XFIXNUM (ch) == '\n')
-			break;
-		      line_start--;
+		      line_starts[nlines] = lstart;
+		      line_ends[nlines] = i;
+		      nlines++;
 		    }
+		  lstart = i + 1;
+		}
+	    }
 
-		  ptrdiff_t line_end = pos;
-		  while (line_end < len)
-		    {
-		      Lisp_Object ch
-			= Faref (str, make_fixnum (line_end));
-		      if (FIXNUMP (ch) && XFIXNUM (ch) == '\n')
-			break;
-		      line_end++;
-		    }
+	  if (nlines < 2)
+	    continue;
 
+	  /* Get the face of the first line (the "normal" face).  */
+	  Lisp_Object normal_face
+	    = Fget_text_property (make_fixnum (line_starts[0]),
+				 Qface, str);
+
+	  /* Find the first line with a DIFFERENT face.  */
+	  for (int li = 0; li < nlines; li++)
+	    {
+	      Lisp_Object line_face
+		= Fget_text_property (make_fixnum (line_starts[li]),
+				      Qface, str);
+	      if (NILP (Fequal (line_face, normal_face)))
+		{
 		  Lisp_Object line
-		    = Fsubstring_no_properties (str,
-						make_fixnum (line_start),
-						make_fixnum (line_end));
+		    = Fsubstring_no_properties (
+			str,
+			make_fixnum (line_starts[li]),
+			make_fixnum (line_ends[li]));
 		  if (SCHARS (line) > 0)
 		    return [NSString stringWithLispString:line];
 		}
-
-	      /* Skip to next face change.  */
-	      Lisp_Object next
-		= Fnext_single_property_change (make_fixnum (pos),
-						Qface, str,
-						make_fixnum (len));
-	      ptrdiff_t npos
-		= FIXNUMP (next) ? XFIXNUM (next) : len;
-	      if (npos <= pos)
-		break;
-	      pos = npos;
 	    }
 	}
     }
@@ -8956,7 +8959,6 @@ ns_ax_completion_text_for_span (EmacsAccessibilityBuffer *elem,
 	 properties.  Completion frameworks highlight the current
 	 candidate with a text face (e.g. vertico-current,
 	 icomplete-selected-match).  */
-      NSString *candidate
       NSString *candidate
 	= ns_ax_selected_overlay_text (b, BUF_BEGV (b), BUF_ZV (b));
       if (candidate)
-- 
2.43.0