patch 8.1.1471: 'background' not correctly set for 2-digit rgb termresponse

Problem:    'background' not correctly set for 2-digit rgb termresponse.
Solution:   Adjust what digit to use. (closes #4495)

src/term.c

@@ -4994,17 +4994,20 @@ check_termcode(
 			    && (is_4digit
 				   || (tp[j + 9] == '/' && tp[i + 12 == '/'])))
 			{
+			    char_u *tp_r = tp + j + 7;
+			    char_u *tp_g = tp + j + (is_4digit ? 12 : 10);
+			    char_u *tp_b = tp + j + (is_4digit ? 17 : 13);
 # ifdef FEAT_TERMINAL
 			    int rval, gval, bval;
 
-			    rval = hexhex2nr(tp + j + 7);
+			    rval = hexhex2nr(tp_r);
-			    gval = hexhex2nr(tp + j + (is_4digit ? 12 : 10));
+			    gval = hexhex2nr(tp_b);
-			    bval = hexhex2nr(tp + j + (is_4digit ? 17 : 13));
+			    bval = hexhex2nr(tp_g);
 # endif
 			    if (is_bg)
 			    {
-				char *newval = (3 * '6' < tp[j+7] + tp[j+12]
+				char *new_bg_val = (3 * '6' < *tp_r + *tp_g +
-						+ tp[j+17]) ? "light" : "dark";
+						     *tp_b) ? "light" : "dark";
 
 				LOG_TR(("Received RBG response: %s", tp));
 				rbg_status.tr_progress = STATUS_GOT;
@@ -5014,11 +5017,11 @@ check_termcode(
 				bg_b = bval;
 # endif
 				if (!option_was_set((char_u *)"bg")
-						  && STRCMP(p_bg, newval) != 0)
+					      && STRCMP(p_bg, new_bg_val) != 0)
 				{
 				    /* value differs, apply it */
 				    set_option_value((char_u *)"bg", 0L,
-							  (char_u *)newval, 0);
+						      (char_u *)new_bg_val, 0);
 				    reset_option_was_set((char_u *)"bg");
 				    redraw_asap(CLEAR);
 				}

src/testdir/test_termcodes.vim

@@ -647,21 +647,49 @@ func Test_term_rgb_response()
   call feedkeys(seq, 'Lx!')
   call assert_equal(seq, v:termrfgresp)
 
-  " response to t_RB, 4 digits
+  " response to t_RB, 4 digits, dark
-  let red = 0x21
+  set background=light
-  let green = 0x43
+  call test_option_not_set('background')
+  let red = 0x29
+  let green = 0x4a
+  let blue = 0x6b
+  let seq = printf("\<Esc>]11;rgb:%02x00/%02x00/%02x00\x07", red, green, blue)
+  call feedkeys(seq, 'Lx!')
+  call assert_equal(seq, v:termrbgresp)
+  call assert_equal('dark', &background)
+
+  " response to t_RB, 4 digits, light
+  set background=dark
+  call test_option_not_set('background')
+  let red = 0x81
+  let green = 0x63
   let blue = 0x65
   let seq = printf("\<Esc>]11;rgb:%02x00/%02x00/%02x00\x07", red, green, blue)
   call feedkeys(seq, 'Lx!')
   call assert_equal(seq, v:termrbgresp)
+  call assert_equal('light', &background)
 
-  " response to t_RB, 2 digits
+  " response to t_RB, 2 digits, dark
-  let red = 0x87
+  set background=light
-  let green = 0xa9
+  call test_option_not_set('background')
-  let blue = 0xcb
+  let red = 0x47
+  let green = 0x59
+  let blue = 0x5b
   let seq = printf("\<Esc>]11;rgb:%02x/%02x/%02x\x07", red, green, blue)
   call feedkeys(seq, 'Lx!')
   call assert_equal(seq, v:termrbgresp)
+  call assert_equal('dark', &background)
+  
+  " response to t_RB, 2 digits, light
+  set background=dark
+  call test_option_not_set('background')
+  let red = 0x83
+  let green = 0xa4
+  let blue = 0xc2
+  let seq = printf("\<Esc>]11;rgb:%02x/%02x/%02x\x07", red, green, blue)
+  call feedkeys(seq, 'Lx!')
+  call assert_equal(seq, v:termrbgresp)
+  call assert_equal('light', &background)
   
   set t_RF= t_RB=
 endfunc

src/version.c

@@ -767,6 +767,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    1471,
 /**/
     1470,
 /**/