vim-patch:8.0.0672: synconcealed() changes too often #7887

Problem:    Third item of synconcealed() changes too often. (Dominique Pelle)
Solution:   Reset the sequence number at the start of each line.
cc0750dc6e

closes #7589

runtime/doc/eval.txt

@@ -7610,12 +7610,21 @@ synconcealed({lnum}, {col})				*synconcealed()*
 		   is 1, the second item contains the text which will be
 		   displayed in place of the concealed text, depending on the
 		   current setting of 'conceallevel' and 'listchars'.
-		3. The third and final item in the list is a unique number
+		3. The third and final item in the list is a number
-		   representing the specific syntax region matched. This
+		   representing the specific syntax region matched in the
-		   allows detection of the beginning of a new concealable
+		   line. When the character is not concealed the value is
-		   region if there are two consecutive regions with the same
+		   zero. This allows detection of the beginning of a new
-		   replacement character.  For an example use see
+		   concealable region if there are two consecutive regions
-		   $VIMRUNTIME/syntax/2html.vim .
+		   with the same replacement character.  For an example, if
+		   the text is "123456" and both "23" and "45" are concealed
+		   and replace by the character "X", then:
+			call			returns ~
+		   	synconcealed(lnum, 1)   [0, '', 0]
+		   	synconcealed(lnum, 2)   [1, 'X', 1]
+		   	synconcealed(lnum, 3)   [1, 'X', 1]
+		   	synconcealed(lnum, 4)   [1, 'X', 2]
+		   	synconcealed(lnum, 5)   [1, 'X', 2]
+		   	synconcealed(lnum, 6)   [0, '', 0]
 
 
 synstack({lnum}, {col})					*synstack()*

src/nvim/syntax.c

@@ -881,7 +881,8 @@ static void syn_start_line(void)
   }
 
   next_match_idx = -1;
-  ++current_line_id;
+  current_line_id++;
+  next_seqnr = 1;
 }
 
 /*
@@ -1599,6 +1600,7 @@ get_syntax_attr (
     current_id = 0;
     current_trans_id = 0;
     current_flags = 0;
+    current_seqnr = 0;
     return 0;
   }
 
@@ -2042,6 +2044,7 @@ syn_current_attr (
   current_id = 0;
   current_trans_id = 0;
   current_flags = 0;
+  current_seqnr = 0;
   if (cur_si != NULL) {
     for (int idx = current_state.ga_len - 1; idx >= 0; --idx) {
       sip = &CUR_STATE(idx);

src/nvim/testdir/test_syntax.vim

@@ -356,24 +356,24 @@ func Test_conceal()
 
   set conceallevel=0
   call assert_equal('123456 ', ScreenLines(2, 7)[0])
-  call assert_equal([[0, ''], [0, ''], [0, ''], [0, ''], [0, ''], [0, '']], map(range(1, 6), 'synconcealed(2, v:val)[0:1]'))
+  call assert_equal([[0, '', 0], [0, '', 0], [0, '', 0], [0, '', 0], [0, '', 0], [0, '', 0]], map(range(1, 6), 'synconcealed(2, v:val)'))
 
   set conceallevel=1
   call assert_equal('1X 6   ', ScreenLines(2, 7)[0])
-  call assert_equal([[0, ''], [1, 'X'], [1, 'X'], [1, ' '], [1, ' '], [0, '']], map(range(1, 6), 'synconcealed(2, v:val)[0:1]'))
+  call assert_equal([[0, '', 0], [1, 'X', 1], [1, 'X', 1], [1, ' ', 2], [1, ' ', 2], [0, '', 0]], map(range(1, 6), 'synconcealed(2, v:val)'))
 
   set conceallevel=1
   set listchars=conceal:Y
-  call assert_equal([[0, ''], [1, 'X'], [1, 'X'], [1, 'Y'], [1, 'Y'], [0, '']], map(range(1, 6), 'synconcealed(2, v:val)[0:1]'))
+  call assert_equal([[0, '', 0], [1, 'X', 1], [1, 'X', 1], [1, 'Y', 2], [1, 'Y', 2], [0, '', 0]], map(range(1, 6), 'synconcealed(2, v:val)'))
   call assert_equal('1XY6   ', ScreenLines(2, 7)[0])
 
   set conceallevel=2
   call assert_match('1X6    ', ScreenLines(2, 7)[0])
-  call assert_equal([[0, ''], [1, 'X'], [1, 'X'], [1, ''], [1, ''], [0, '']], map(range(1, 6), 'synconcealed(2, v:val)[0:1]'))
+  call assert_equal([[0, '', 0], [1, 'X', 1], [1, 'X', 1], [1, '', 2], [1, '', 2], [0, '', 0]], map(range(1, 6), 'synconcealed(2, v:val)'))
 
   set conceallevel=3
   call assert_match('16     ', ScreenLines(2, 7)[0])
-  call assert_equal([[0, ''], [1, ''], [1, ''], [1, ''], [1, ''], [0, '']], map(range(1, 6), 'synconcealed(2, v:val)[0:1]'))
+  call assert_equal([[0, '', 0], [1, '', 1], [1, '', 1], [1, '', 2], [1, '', 2], [0, '', 0]], map(range(1, 6), 'synconcealed(2, v:val)'))
 
   syn clear
   set conceallevel&

src/nvim/version.c

@@ -825,7 +825,7 @@ static const int included_patches[] = {
   // 675,
   // 674,
   // 673,
-  // 672,
+  672,
   // 671,
   // 670,
   // 669,