patch 8.0.0659: no test for conceal mode

Problem:    No test for conceal mode.
Solution:   Add a conceal mode test. (Dominique Pelle, closes #1783)

runtime/doc/eval.txt

@@ -7655,17 +7655,20 @@ synIDtrans({synID})					*synIDtrans()*
 		":highlight link" are followed.
 
 synconcealed({lnum}, {col})				*synconcealed()*
-		The result is a List. The first item in the list is 0 if the
-		character at the position {lnum} and {col} is not part of a
-		concealable region, 1 if it is. The second item in the list is
-		a string. If the first item 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'. The third
-		and final item in the list is a unique number representing the
-		specific syntax region matched. This allows detection of the
-		beginning of a new concealable region if there are two
-		consecutive regions with the same replacement character.
-		For an example use see $VIMRUNTIME/syntax/2html.vim .
+		The result is a List with currently three items:
+		1. The first item in the list is 0 if the character at the
+		   position {lnum} and {col} is not part of a concealable
+		   region, 1 if it is.
+		2. The second item in the list is a string. If the first item
+		   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
+		   representing the specific syntax region matched. This
+		   allows detection of the beginning of a new concealable
+		   region if there are two consecutive regions with the same
+		   replacement character.  For an example use see
+		   $VIMRUNTIME/syntax/2html.vim .
 
 
 synstack({lnum}, {col})					*synstack()*

src/evalfunc.c

@@ -11841,8 +11841,8 @@ f_synconcealed(typval_T *argvars UNUSED, typval_T *rettv)
 	    if ((syntax_flags & HL_CONCEAL) && curwin->w_p_cole < 3)
 	    {
 		cchar = syn_get_sub_char();
-		if (cchar == NUL && curwin->w_p_cole == 1 && lcs_conceal != NUL)
-		    cchar = lcs_conceal;
+		if (cchar == NUL && curwin->w_p_cole == 1)
+		    cchar = (lcs_conceal == NUL) ? ' ' : lcs_conceal;
 		if (cchar != NUL)
 		{
 # ifdef FEAT_MBYTE

src/testdir/test_syntax.vim

@@ -4,6 +4,8 @@ if !has("syntax")
   finish
 endif
 
+source view_util.vim
+
 func GetSyntaxItem(pat)
   let c = ''
   let a = ['a', getreg('a'), getregtype('a')]
@@ -458,3 +460,46 @@ func Test_syntax_hangs()
   set redrawtime&
   bwipe!
 endfunc
+
+
+func Test_conceal()
+  if !has('conceal')
+    return
+  endif
+
+  new
+  call setline(1, ['', '123456'])
+  syn match test23 "23" conceal cchar=X
+  syn match test45 "45" 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]'))
+
+  set conceallevel=1
+  call assert_equal('1X 6   ', ScreenLines(2, 7)[0])
+  " FIXME: with conceallevel=1, I would expect that the portion "45" of
+  " the line to be replaced with a space since ":help 'conceallevel'
+  " states that if listchars is not set, then the default replacement
+  " should be a space. But synconcealed() gives an empty string in
+  " the 2nd value of the returned list. Bug?
+  " So for now, the following line is commented out:
+  call assert_equal([[0, ''], [1, 'X'], [1, 'X'], [1, ' '], [1, ' '], [0, '']], map(range(1, 6), 'synconcealed(2, v:val)[0:1]'))
+
+  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('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]'))
+
+  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]'))
+
+  syn clear
+  set conceallevel&
+  bw!
+endfunc

src/version.c

@@ -764,6 +764,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    659,
 /**/
     658,
 /**/