patch 8.1.2279: computation of highlight attributes is too complicated

Problem:    Computation of highlight attributes is too complicated.
Solution:   Simplify the attribute computation and make it more consistent.
            (closes #5190)  Fix that 'combine' set to zero doesn't work.

src/drawline.c

@@ -1470,6 +1470,16 @@ win_line(
 # endif
 		}
 	    }
+# ifdef FEAT_TEXT_PROP
+	    // Combine text property highlight into syntax highlight.
+	    if (text_prop_type != NULL)
+	    {
+		if (text_prop_combine)
+		    syntax_attr = hl_combine_attr(syntax_attr, text_prop_attr);
+		else
+		    syntax_attr = text_prop_attr;
+	    }
+# endif
 #endif
 
 	    // Decide which of the highlight attributes to use.
@@ -1479,28 +1489,16 @@ win_line(
 	    {
 		char_attr = hl_combine_attr(line_attr, area_attr);
 # ifdef FEAT_SYN_HL
-		if (syntax_attr != 0)
-		    char_attr = hl_combine_attr(syntax_attr, char_attr);
+		char_attr = hl_combine_attr(syntax_attr, char_attr);
 # endif
 	    }
 	    else if (search_attr != 0)
 	    {
 		char_attr = hl_combine_attr(line_attr, search_attr);
 # ifdef FEAT_SYN_HL
-		if (syntax_attr != 0)
-		    char_attr = hl_combine_attr(syntax_attr, char_attr);
+		char_attr = hl_combine_attr(syntax_attr, char_attr);
 # endif
 	    }
-# ifdef FEAT_TEXT_PROP
-	    else if (text_prop_type != NULL)
-	    {
-		char_attr = hl_combine_attr(line_attr != 0
-						? line_attr
-						: syntax_attr != 0
-						    ? syntax_attr
-						    : win_attr, text_prop_attr);
-	    }
-# endif
 	    else if (line_attr != 0 && ((fromcol == -10 && tocol == MAXCOL)
 				|| vcol < fromcol || vcol_prev < fromcol_prev
 				|| vcol >= tocol))
@@ -1508,11 +1506,10 @@ win_line(
 		// Use line_attr when not in the Visual or 'incsearch' area
 		// (area_attr may be 0 when "noinvcur" is set).
 # ifdef FEAT_SYN_HL
-		if (syntax_attr != 0)
-		    char_attr = hl_combine_attr(syntax_attr, line_attr);
-		else
+		char_attr = hl_combine_attr(syntax_attr, line_attr);
+# else
+		char_attr = line_attr;
 # endif
-		    char_attr = line_attr;
 		attr_pri = FALSE;
 	    }
 #else
@@ -1524,22 +1521,10 @@ win_line(
 	    else
 	    {
 		attr_pri = FALSE;
-#ifdef FEAT_TEXT_PROP
-		if (text_prop_type != NULL)
-		{
-		    if (text_prop_combine)
-			char_attr = hl_combine_attr(
-						  syntax_attr, text_prop_attr);
-		    else
-			char_attr = hl_combine_attr(
-						  win_attr, text_prop_attr);
-		}
-		else
-#endif
 #ifdef FEAT_SYN_HL
-		    char_attr = syntax_attr;
+		char_attr = syntax_attr;
 #else
-		    char_attr = 0;
+		char_attr = 0;
 #endif
 	    }
 	}

src/testdir/dumps/Test_textprop_01.dump

@@ -1,7 +1,7 @@
 | +0#af5f00255#ffffff0@1|1| |O+0#0000000&|n|e| +0&#ffff4012|t|w|o| +0&#ffffff0@63
 | +0#af5f00255&@1|2| |N+0#0000000#ffff4012|u|m|b|é|r| |1+0#4040ff13&|2|3| +0#0000000&|ä|n|d| |t|h|œ|n| |4+0#4040ff13&|¾|7|.+0#0000000&| +0&#ffffff0@46
 | +8#af5f00255&@1|3| >-+8#0000000#ffff4012|x+8&#ffffff0|a+8#4040ff13&@1|x+8#0000000&|-@1|x+8#4040ff13&|b@1|x+8#0000000&|-@1|x|c+8#4040ff13&@1|x|-+8#0000000&@1|x+8#4040ff13&|d@1|x|-+8#0000000&@1| @45
-| +0#af5f00255&@1|4| |/+0#40ff4011&@1| |c|o|m@1|e|n|t| |w+0&#e0e0e08|i|t|h| |e+8&&|r@1|o|r| +0&#ffffff0|i|n| |i|t| +0#0000000&@43
+| +0#af5f00255&@1|4| |/+0#40ff4011&@1| |c|o|m+0#0000000#e0e0e08@1|e|n+0#40ff4011#ffffff0|t| |w+0&#e0e0e08|i|t|h| |e+8&&|r@1|o|r| +0&#ffffff0|i|n| |i|t| +0#0000000&@43
 | +0#af5f00255&@1|5| |f+0#0000000&|i|r|s|t| |l+0&#ffff4012|i|n|e| @1|s|e|c|o|n|d| +0&#ffffff0|l|i|n|e| @1|t|h|i|r|d| |l|i|n|e| |f|o|u|r|t|h| |l+0&#ffff4012|i|n|e| +0&#ffffff0@23
 |~+0#4040ff13&| @73
 |~| @73

src/testdir/test_textprop.vim

@@ -678,8 +678,9 @@ func Test_textprop_screenshot_various()
 	\ "call prop_type_add('start', {'highlight': 'NumberProp', 'start_incl': 1})",
 	\ "call prop_type_add('end', {'highlight': 'NumberProp', 'end_incl': 1})",
 	\ "call prop_type_add('both', {'highlight': 'NumberProp', 'start_incl': 1, 'end_incl': 1})",
-	\ "call prop_type_add('background', {'highlight': 'NumberProp', 'combine': 1})",
-	\ "eval 'background'->prop_type_change({'highlight': 'BackgroundProp'})",
+	\ "call prop_type_add('background', {'highlight': 'BackgroundProp', 'combine': 0})",
+	\ "call prop_type_add('backgroundcomb', {'highlight': 'NumberProp', 'combine': 1})",
+	\ "eval 'backgroundcomb'->prop_type_change({'highlight': 'BackgroundProp'})",
 	\ "call prop_type_add('error', {'highlight': 'UnderlineProp', 'combine': 1})",
 	\ "call prop_add(1, 4, {'end_lnum': 3, 'end_col': 3, 'type': 'long'})",
 	\ "call prop_add(2, 9, {'length': 3, 'type': 'number'})",
@@ -688,7 +689,8 @@ func Test_textprop_screenshot_various()
 	\ "call prop_add(3, 7, {'length': 2, 'type': 'start'})",
 	\ "call prop_add(3, 11, {'length': 2, 'type': 'end'})",
 	\ "call prop_add(3, 15, {'length': 2, 'type': 'both'})",
-	\ "call prop_add(4, 12, {'length': 10, 'type': 'background'})",
+	\ "call prop_add(4, 6, {'length': 3, 'type': 'background'})",
+	\ "call prop_add(4, 12, {'length': 10, 'type': 'backgroundcomb'})",
 	\ "call prop_add(4, 17, {'length': 5, 'type': 'error'})",
 	\ "call prop_add(5, 7, {'length': 4, 'type': 'long'})",
 	\ "call prop_add(6, 1, {'length': 8, 'type': 'long'})",

src/version.c

@@ -741,6 +741,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    2279,
 /**/
     2278,
 /**/