vim-patch:8.1.0542: shiftwidth() does not take 'vartabstop' into account

Problem:    shiftwidth() does not take 'vartabstop' into account.
Solution:   Use the cursor position or a position explicitly passed.
            Also make >> and << work better with 'vartabstop'. (Christian
            Brabandt)
https://github.com/vim/vim/commit/f951416a8396a54bbbe21de1a8b16716428549f2

9 files changed, 129 insertions, 12 deletions

diff --git a/runtime/doc/change.txt b/runtime/doc/change.txt
index ed40642d0c..310d244fbc 100644
--- a/runtime/doc/change.txt
+++ b/runtime/doc/change.txt
@@ -445,6 +445,9 @@ SHIFTING LINES LEFT OR RIGHT				*shift-left-right*
 							*<*
 <{motion}		Shift {motion} lines one 'shiftwidth' leftwards.
 
+			If the 'shiftwidth' option is set to zero, the amount
+			of indent is calculated at the first non-blank
+			character in the line.
 							*<<*
 <<			Shift [count] lines one 'shiftwidth' leftwards.
 
@@ -455,6 +458,9 @@ SHIFTING LINES LEFT OR RIGHT				*shift-left-right*
 							*>*
  >{motion}		Shift {motion} lines one 'shiftwidth' rightwards.
 
+			If the 'shiftwidth' option is set to zero, the amount
+			of indent is calculated at the first non-blank
+			character in the line.
 							*>>*
  >>			Shift [count] lines one 'shiftwidth' rightwards.
 
diff --git a/runtime/doc/eval.txt b/runtime/doc/eval.txt
index 164c6fb8e0..2911224de5 100644
--- a/runtime/doc/eval.txt
+++ b/runtime/doc/eval.txt
@@ -2308,7 +2308,6 @@ perleval({expr})		any	evaluate |perl| expression
 pow({x}, {y})			Float	{x} to the power of {y}
 prevnonblank({lnum})		Number	line nr of non-blank line <= {lnum}
 printf({fmt}, {expr1}...)	String	format text
-prompt_addtext({buf}, {expr})	none	add text to a prompt buffer
 prompt_setcallback({buf}, {expr}) none	set prompt callback function
 prompt_setinterrupt({buf}, {text}) none	set prompt interrupt function
 prompt_setprompt({buf}, {text}) none	set prompt text
@@ -2393,7 +2392,7 @@ sha256({string})		String	SHA256 checksum of {string}
 shellescape({string} [, {special}])
 				String	escape {string} for use as shell
 					command argument
-shiftwidth()			Number	effective value of 'shiftwidth'
+shiftwidth([{col}])		Number	effective value of 'shiftwidth'
 sign_define({name} [, {dict}])	Number	define or update a sign
 sign_getdefined([{name}])	List	get a list of defined signs
 sign_getplaced([{expr} [, {dict}]])
@@ -7899,7 +7898,7 @@ shellescape({string} [, {special}])			*shellescape()*
 <		See also |::S|.
 
 
-shiftwidth()						*shiftwidth()*
+shiftwidth([{col}])						*shiftwidth()*
 		Returns the effective value of 'shiftwidth'. This is the
 		'shiftwidth' value unless it is zero, in which case it is the
 		'tabstop' value.  To be backwards compatible in indent
diff --git a/src/nvim/edit.c b/src/nvim/edit.c
index 90b5cfd8aa..20f31a478d 100644
--- a/src/nvim/edit.c
+++ b/src/nvim/edit.c
@@ -9156,10 +9156,16 @@ static void ins_try_si(int c)
  * Get the value that w_virtcol would have when 'list' is off.
  * Unless 'cpo' contains the 'L' flag.
  */
-static colnr_T get_nolist_virtcol(void)
+colnr_T get_nolist_virtcol(void)
 {
-  if (curwin->w_p_list && vim_strchr(p_cpo, CPO_LISTWM) == NULL)
+  // check validity of cursor in current buffer
+  if (curwin->w_buffer == NULL || curwin->w_buffer->b_ml.ml_mfp == NULL
+      || curwin->w_cursor.lnum > curwin->w_buffer->b_ml.ml_line_count) {
+    return 0;
+  }
+  if (curwin->w_p_list && vim_strchr(p_cpo, CPO_LISTWM) == NULL) {
     return getvcol_nolist(&curwin->w_cursor);
+  }
   validate_virtcol();
   return curwin->w_virtcol;
 }
diff --git a/src/nvim/eval.lua b/src/nvim/eval.lua
index d1a3ae3ff8..72168060cc 100644
--- a/src/nvim/eval.lua
+++ b/src/nvim/eval.lua
@@ -309,7 +309,7 @@ return {
     setwinvar={args=3},
     sha256={args=1},
     shellescape={args={1, 2}},
-    shiftwidth={},
+    shiftwidth={args={0, 1}},
     sign_define={args={1, 2}},
     sign_getdefined={args={0, 1}},
     sign_getplaced={args={0, 2}},
diff --git a/src/nvim/eval/funcs.c b/src/nvim/eval/funcs.c
index eeaaf7dbd1..0f2e904b1b 100644
--- a/src/nvim/eval/funcs.c
+++ b/src/nvim/eval/funcs.c
@@ -8849,6 +8849,18 @@ static void f_shellescape(typval_T *argvars, typval_T *rettv, FunPtr fptr)
  */
 static void f_shiftwidth(typval_T *argvars, typval_T *rettv, FunPtr fptr)
 {
+  rettv->vval.v_number = 0;
+
+  if (argvars[0].v_type != VAR_UNKNOWN) {
+    long col;
+
+    col = (long)tv_get_number_chk(argvars, NULL);
+    if (col < 0) {
+      return;  // type error; errmsg already given
+    }
+    rettv->vval.v_number = get_sw_value_col(curbuf, col);
+    return;
+  }
   rettv->vval.v_number = get_sw_value(curbuf);
 }
 
diff --git a/src/nvim/normal.c b/src/nvim/normal.c
index 0b4e2e1f23..3587b12277 100644
--- a/src/nvim/normal.c
+++ b/src/nvim/normal.c
@@ -6777,9 +6777,10 @@ static void nv_g_cmd(cmdarg_T *cap)
     }
     coladvance((colnr_T)i);
     if (flag) {
-      do
+      do {
         i = gchar_cursor();
-      while (ascii_iswhite(i) && oneright());
+      } while (ascii_iswhite(i) && oneright());
+      curwin->w_valid &= ~VALID_WCOL;
     }
     curwin->w_set_curswant = true;
     break;
diff --git a/src/nvim/ops.c b/src/nvim/ops.c
index ffa3e3d55f..e5de57ceaa 100644
--- a/src/nvim/ops.c
+++ b/src/nvim/ops.c
@@ -288,7 +288,7 @@ void shift_line(
 {
   int count;
   int i, j;
-  int p_sw = get_sw_value(curbuf);
+  int p_sw = (int)get_sw_value_indent(curbuf);
 
   count = get_indent();  // get current indent
 
@@ -332,9 +332,9 @@ static void shift_block(oparg_T *oap, int amount)
   const int oldstate = State;
   char_u *newp;
   const int oldcol = curwin->w_cursor.col;
-  const int p_sw = get_sw_value(curbuf);
-  const long p_ts = curbuf->b_p_ts;
+  int p_sw = (int)get_sw_value_indent(curbuf);
   long *p_vts = curbuf->b_p_vts_array;
+  const long p_ts = curbuf->b_p_ts;
   struct block_def bd;
   int incr;
   int i = 0, j = 0;
diff --git a/src/nvim/option.c b/src/nvim/option.c
index 67740e8d9f..7d21086fd4 100644
--- a/src/nvim/option.c
+++ b/src/nvim/option.c
@@ -7342,11 +7342,39 @@ int tabstop_first(long *ts)
 /// 'tabstop' value when 'shiftwidth' is zero.
 int get_sw_value(buf_T *buf)
 {
-  long result = buf->b_p_sw ? buf->b_p_sw : buf->b_p_ts;
+  long result = get_sw_value_col(buf, 0);
   assert(result >= 0 && result <= INT_MAX);
   return (int)result;
 }
 
+// Idem, using the first non-black in the current line.
+long get_sw_value_indent(buf_T *buf)
+{
+  pos_T pos = curwin->w_cursor;
+
+  pos.col = (colnr_T)getwhitecols_curline();
+  return get_sw_value_pos(buf, &pos);
+}
+
+// Idem, using "pos".
+long get_sw_value_pos(buf_T *buf, pos_T *pos)
+{
+  pos_T save_cursor = curwin->w_cursor;
+  long sw_value;
+
+  curwin->w_cursor = *pos;
+  sw_value = get_sw_value_col(buf, get_nolist_virtcol());
+  curwin->w_cursor = save_cursor;
+  return sw_value;
+}
+
+// Idem, using virtual column "col".
+long get_sw_value_col(buf_T *buf, colnr_T col)
+{
+  return buf->b_p_sw ? buf->b_p_sw
+                     : tabstop_at(col, buf->b_p_ts, buf->b_p_vts_array);
+}
+
 /// Return the effective softtabstop value for the current buffer,
 /// using the shiftwidth  value when 'softtabstop' is negative.
 int get_sts_value(void)
diff --git a/src/nvim/testdir/test_vartabs.vim b/src/nvim/testdir/test_vartabs.vim
index c8470952d1..81e81b7fbe 100644
--- a/src/nvim/testdir/test_vartabs.vim
+++ b/src/nvim/testdir/test_vartabs.vim
@@ -297,6 +297,71 @@ func Test_vartabs_linebreak()
   set nolist listchars&vim
 endfunc
 
+func Test_vartabs_shiftwidth()
+  "return
+  if winwidth(0) < 40
+    return
+  endif
+  new
+  40vnew
+  %d
+"  setl varsofttabstop=10,20,30,40
+  setl shiftwidth=0 vartabstop=10,20,30,40
+  call setline(1, "x")
+
+  " Check without any change.
+  let expect = ['x                                       ']
+  let lines = ScreenLines(1, winwidth(0))
+  call s:compare_lines(expect, lines)
+  " Test 1:
+  " shiftwidth depends on the indent, first check with cursor at the end of the
+  " line (which is the same as the start of the line, since there is only one
+  " character).
+  norm! $>>
+  let expect1 = ['          x                             ']
+  let lines = ScreenLines(1, winwidth(0))
+  call s:compare_lines(expect1, lines)
+  call assert_equal(10, shiftwidth())
+  call assert_equal(10, shiftwidth(1))
+  call assert_equal(20, shiftwidth(virtcol('.')))
+  norm! $>>
+  let expect2 = ['                              x         ', '~                                       ']
+  let lines = ScreenLines([1, 2], winwidth(0))
+  call s:compare_lines(expect2, lines)
+  call assert_equal(20, shiftwidth(virtcol('.')-2))
+  call assert_equal(30, shiftwidth(virtcol('.')))
+  norm! $>>
+  let expect3 = ['                                        ', '                    x                   ', '~                                       ']
+  let lines = ScreenLines([1, 3], winwidth(0))
+  call s:compare_lines(expect3, lines)
+  call assert_equal(30, shiftwidth(virtcol('.')-2))
+  call assert_equal(40, shiftwidth(virtcol('.')))
+  norm! $>>
+  let expect4 = ['                                        ', '                                        ', '                    x                   ']
+  let lines = ScreenLines([1, 3], winwidth(0))
+  call assert_equal(40, shiftwidth(virtcol('.')))
+  call s:compare_lines(expect4, lines)
+
+  " Test 2: Put the cursor at the first column, result should be the same
+  call setline(1, "x")
+  norm! 0>>
+  let lines = ScreenLines(1, winwidth(0))
+  call s:compare_lines(expect1, lines)
+  norm! 0>>
+  let lines = ScreenLines([1, 2], winwidth(0))
+  call s:compare_lines(expect2, lines)
+  norm! 0>>
+  let lines = ScreenLines([1, 3], winwidth(0))
+  call s:compare_lines(expect3, lines)
+  norm! 0>>
+  let lines = ScreenLines([1, 3], winwidth(0))
+  call s:compare_lines(expect4, lines)
+
+  " cleanup
+  bw!
+  bw!
+endfunc
+
 func Test_vartabs_failures()
   call assert_fails('set vts=8,')
   call assert_fails('set vsts=8,')