'inccommand': buftype=nofile, restore cursor/view

- Use a standard scratch buffer instead of a new 'buftype', functions
  like curbufIsChanged() already have special handling for scratch bufs.
- Cleanup some stuff from the previous merge.
- Add support for :smagic, :snomagic. Closes #5578

9 files changed, 73 insertions, 42 deletions

diff --git a/runtime/doc/options.txt b/runtime/doc/options.txt
index 94c5e2d11d..d13a245d87 100644
--- a/runtime/doc/options.txt
+++ b/runtime/doc/options.txt
@@ -1155,21 +1155,14 @@ A jump table for the options with a short description can be found at |Q_op|.
 						*'buftype'* *'bt'* *E382*
 'buftype' 'bt'		string (default: "")
 			local to buffer
-			{not available when compiled without the |+quickfix|
-			feature}
 	The value of this option specifies the type of a buffer:
 	  <empty>	normal buffer
-	  nofile	buffer which is not related to a file and will not be
-			written
-	  nowrite	buffer which will not be written
-	  acwrite	buffer which will always be written with BufWriteCmd
-			autocommands.
-	  quickfix	quickfix buffer, contains list of errors |:cwindow|
-			or list of locations |:lwindow|
-	  help		help buffer (you are not supposed to set this
-			manually)
-	  terminal	terminal buffer, this is set automatically when a 
-			terminal is created. |terminal-emulator|
+	  acwrite	buffer will always be written with |BufWriteCmd|s
+	  help		help buffer (do not set this manually)
+	  nofile	buffer is not related to a file, will not be written
+	  nowrite	buffer will not be written
+	  quickfix	list of errors |:cwindow| or locations |:lwindow|
+	  terminal	|terminal-emulator| buffer
 
 	This option is used together with 'bufhidden' and 'swapfile' to
 	specify special kinds of buffers.   See |special-buffers|.
@@ -3420,10 +3413,10 @@ A jump table for the options with a short description can be found at |Q_op|.
 'inccommand' 'icm'	string	(default "")
 			global
 			
-	"nosplit" : Shows the effects of a command incrementally, as you type.
-	"split"	  : Also shows partial off-screen results in a preview window.
+	"nosplit": Shows the effects of a command incrementally, as you type.
+	"split"	 : Also shows partial off-screen results in a preview window.
 
-	Currently only works for |:substitute|. |hl-Substitute|
+	Works for |:substitute|, |:smagic|, |:snomagic|. |hl-Substitute|
 
 						*'include'* *'inc'*
 'include' 'inc'		string	(default "^\s*#\s*include")
diff --git a/runtime/syntax/vim.vim b/runtime/syntax/vim.vim
index ae01c0f3ee..9c827b426e 100644
--- a/runtime/syntax/vim.vim
+++ b/runtime/syntax/vim.vim
@@ -56,7 +56,7 @@ syn keyword vimGroup contained	Comment Constant String Character Number Boolean
 syn keyword vimHLGroup contained	ColorColumn Cursor CursorColumn CursorIM CursorLine CursorLineNr DiffAdd DiffChange DiffDelete DiffText Directory ErrorMsg FoldColumn Folded IncSearch LineNr MatchParen Menu ModeMsg MoreMsg NonText Normal Pmenu PmenuSbar PmenuSel PmenuThumb Question Scrollbar Search SignColumn SpecialKey SpellBad SpellCap SpellLocal SpellRare StatusLine StatusLineNC TabLine TabLineFill TabLineSel Title Tooltip VertSplit Visual WarningMsg WildMenu
 syn match vimHLGroup contained	"Conceal"
 syn keyword vimOnlyHLGroup contained	VisualNOS
-syn keyword nvimHLGroup contained	EndOfBuffer IncSubstitute TermCursor TermCursorNC QuickFixLine
+syn keyword nvimHLGroup contained	EndOfBuffer Substitute TermCursor TermCursorNC QuickFixLine
 "}}}2
 syn case match
 " Special Vim Highlighting (not automatic) {{{1
diff --git a/src/nvim/buffer.c b/src/nvim/buffer.c
index 75caf2223b..8e6066453c 100644
--- a/src/nvim/buffer.c
+++ b/src/nvim/buffer.c
@@ -5273,14 +5273,20 @@ wipe_buffer (
   }
 }
 
-/// Creates or switches to a special-purpose buffer.
+/// Creates or switches to a scratch buffer. :h special-buffers
+/// Scratch buffer is:
+///   - buftype=nofile bufhidden=hide noswapfile
+///   - Always considered 'nomodified'
 ///
 /// @param bufnr     Buffer to switch to, or 0 to create a new buffer.
-void buf_open_special(handle_T bufnr, char *bufname, char *buftype)
+///
+/// @see curbufIsChanged()
+void buf_open_scratch(handle_T bufnr, char *bufname)
 {
   (void)do_ecmd((int)bufnr, NULL, NULL, NULL, ECMD_ONE, ECMD_HIDE, NULL);
   (void)setfname(curbuf, (char_u *)bufname, NULL, true);
-  set_option_value((char_u *)"bt", 0L, (char_u *)buftype, OPT_LOCAL);
+  set_option_value((char_u *)"bh", 0L, (char_u *)"hide", OPT_LOCAL);
+  set_option_value((char_u *)"bt", 0L, (char_u *)"nofile", OPT_LOCAL);
   set_option_value((char_u *)"swf", 0L, NULL, OPT_LOCAL);
   RESET_BINDING(curwin);
 }
diff --git a/src/nvim/ex_cmds.c b/src/nvim/ex_cmds.c
index 13a0282b76..f9b8e995ed 100644
--- a/src/nvim/ex_cmds.c
+++ b/src/nvim/ex_cmds.c
@@ -2188,7 +2188,6 @@ int do_ecmd(
     if (fnum) {
       buf = buflist_findnr(fnum);
     } else {
-      ILOG("here");
       if (flags & ECMD_ADDBUF) {
         linenr_T tlnum = 1L;
 
@@ -3275,8 +3274,7 @@ buf_T *do_sub(exarg_T *eap)
     return NULL;
   }
 
-  int search_options = eap->is_live ? 0 : SEARCH_HIS;
-  if (search_regcomp(pat, RE_SUBST, which_pat, search_options,
+  if (search_regcomp(pat, RE_SUBST, which_pat, (eap->is_live ? 0 : SEARCH_HIS),
                      &regmatch) == FAIL) {
     if (subflags.do_error) {
       EMSG(_(e_invcmd));
@@ -3951,13 +3949,10 @@ skip:
 
   // Show 'inccommand' preview if there are matched lines.
   buf_T *preview_buf = NULL;
-  if (eap->is_live && matched_lines.size != 0 && pat != NULL && *p_icm != NUL) {
+  if (eap->is_live && *p_icm != NUL && matched_lines.size != 0 && pat != NULL) {
     curbuf->b_changed = save_b_changed;  // preserve 'modified' during preview
     preview_buf = show_sub(old_cursor, pat, sub, eap->line1, eap->line2,
                            &matched_lines);
-
-  } else if (*p_icm != NUL && eap->is_live) {
-    curwin->w_cursor = old_cursor;  // don't move the cursor
   }
 
   for (MatchedLine m; kv_size(matched_lines);) {
@@ -6058,10 +6053,9 @@ static buf_T *show_sub(pos_T old_cusr, char_u *pat, char_u *sub, linenr_T line1,
   }
 
   if (split && win_split((int)p_cwh, WSP_BOT) != FAIL) {
-    buf_open_special(preview_buf ? bufnr : 0, "[Preview]", "incsub");
+    buf_open_scratch(preview_buf ? bufnr : 0, "[Preview]");
     buf_clear();
     preview_buf = curbuf;
-    set_option_value((char_u *)"bufhidden", 0L, (char_u *)"hide", OPT_LOCAL);
     bufnr = preview_buf->handle;
     curbuf->b_p_bl = false;
     curbuf->b_p_ma = true;
@@ -6092,7 +6086,7 @@ static buf_T *show_sub(pos_T old_cusr, char_u *pat, char_u *sub, linenr_T line1,
         old_line_size = line_size;
       }
 
-      // put " | lnum|line" into str and append it to the preview buffer
+      // Put "|lnum| line" into `str` and append it to the preview buffer.
       snprintf(str, line_size, "|%*ld| %s", col_width - 3, mat.lnum, mat.line);
       ml_append(line, (char_u *)str, (colnr_T)line_size, false);
 
@@ -6155,6 +6149,7 @@ void ex_substitute(exarg_T *eap)
   buf_T *preview_buf = do_sub(eap);
 
   if (save_changedtick != curbuf->b_changedtick) {
+    // Undo invisibly. This also moves the cursor!
     if (!u_undo_and_forget(1)) { abort(); }
     // Restore newhead. It is meaningless when curhead is valid, but we must
     // restore it so that undotree() is identical before/after the preview.
diff --git a/src/nvim/ex_cmds.h b/src/nvim/ex_cmds.h
index ccb2202edb..243b11255e 100644
--- a/src/nvim/ex_cmds.h
+++ b/src/nvim/ex_cmds.h
@@ -14,7 +14,6 @@
 #define ECMD_OLDBUF          0x04    // use existing buffer if it exists
 #define ECMD_FORCEIT         0x08    // ! used in Ex command
 #define ECMD_ADDBUF          0x10    // don't edit, just add to buffer list
-#define ECMD_RESERVED_BUFNR  0x20    // bufnr argument is reserved bufnr
 
 
 /* for lnum argument in do_ecmd() */
diff --git a/src/nvim/ex_docmd.c b/src/nvim/ex_docmd.c
index 30347cbe85..07e0fa8844 100644
--- a/src/nvim/ex_docmd.c
+++ b/src/nvim/ex_docmd.c
@@ -7295,15 +7295,13 @@ void ex_may_print(exarg_T *eap)
   }
 }
 
-/*
- * ":smagic" and ":snomagic".
- */
+/// ":smagic" and ":snomagic".
 static void ex_submagic(exarg_T *eap)
 {
   int magic_save = p_magic;
 
   p_magic = (eap->cmdidx == CMD_smagic);
-  do_sub(eap);
+  ex_substitute(eap);
   p_magic = magic_save;
 }
 
@@ -9669,5 +9667,7 @@ bool cmd_is_live(char_u *cmd)
   }
   find_command(&ea, NULL);
 
-  return (ea.cmdidx == CMD_substitute);
+  return ea.cmdidx == CMD_substitute
+      || ea.cmdidx == CMD_smagic
+      || ea.cmdidx == CMD_snomagic;
 }
diff --git a/src/nvim/ex_getln.c b/src/nvim/ex_getln.c
index 17693ecfc8..8ddb1047c7 100644
--- a/src/nvim/ex_getln.c
+++ b/src/nvim/ex_getln.c
@@ -5147,7 +5147,9 @@ static int ex_window(void)
   cmdwin_type = get_cmdline_type();
 
   // Create empty command-line buffer.
-  buf_open_special(0, "[Command Line]", "nofile");
+  buf_open_scratch(0, "[Command Line]");
+  // Command-line buffer has bufhidden=wipe, unlike a true "scratch" buffer.
+  set_option_value((char_u *)"bh", 0L, (char_u *)"wipe", OPT_LOCAL);
   curwin->w_p_rl = cmdmsg_rl;
   cmdmsg_rl = false;
   curbuf->b_p_ma = true;
diff --git a/src/nvim/undo.c b/src/nvim/undo.c
index 2f4317980a..d6428d63f7 100644
--- a/src/nvim/undo.c
+++ b/src/nvim/undo.c
@@ -1685,7 +1685,8 @@ void u_redo(int count)
   u_doit(count, false);
 }
 
-/// undo, and remove the undo branch from the undo tree.
+/// Undo and remove the branch from the undo tree.
+/// Also moves the cursor (as a "normal" undo would).
 bool u_undo_and_forget(int count)
 {
   if (curbuf->b_u_synced == false) {
diff --git a/test/functional/ui/inccommand_spec.lua b/test/functional/ui/inccommand_spec.lua
index f2282e3fb8..de5f7411da 100644
--- a/test/functional/ui/inccommand_spec.lua
+++ b/test/functional/ui/inccommand_spec.lua
@@ -944,7 +944,7 @@ describe(":substitute, inccommand=split", function()
 
 end)
 
-describe(":substitute, inccommand=nosplit", function()
+describe("inccommand=nosplit", function()
   if helpers.pending_win32(pending) then return end
 
   local screen = Screen.new(20,10)
@@ -958,7 +958,42 @@ describe(":substitute, inccommand=nosplit", function()
     if screen then screen:detach() end
   end)
 
-  it('does not show a split window anytime', function()
+  it("works with :smagic, :snomagic", function()
+    execute("set hlsearch")
+    insert("Line *.3.* here")
+
+    feed(":%smagic/3.*/X")    -- start :smagic command
+    screen:expect([[
+      Inc substitution on |
+      two lines           |
+      Inc substitution on |
+      two lines           |
+      Line *.X            |
+      {15:~                   }|
+      {15:~                   }|
+      {15:~                   }|
+      {15:~                   }|
+      :%smagic/3.*/X^      |
+    ]])
+
+
+    feed([[<C-\><C-N>]])      -- cancel
+    feed(":%snomagic/3.*/X")  -- start :snomagic command
+    screen:expect([[
+      Inc substitution on |
+      two lines           |
+      Inc substitution on |
+      two lines           |
+      Line *.X here       |
+      {15:~                   }|
+      {15:~                   }|
+      {15:~                   }|
+      {15:~                   }|
+      :%snomagic/3.*/X^    |
+    ]])
+  end)
+
+  it('never shows preview buffer', function()
     execute("set hlsearch")
 
     feed(":%s/tw")
@@ -1163,7 +1198,7 @@ describe("'inccommand' and :cnoremap", function()
 
 end)
 
-describe("'inccommand': autocommands", function()
+describe("'inccommand' autocommands", function()
   before_each(clear)
 
   -- keys are events to be tested
@@ -1251,7 +1286,7 @@ describe("'inccommand': autocommands", function()
 
 end)
 
-describe("'inccommand': split windows", function()
+describe("'inccommand' split windows", function()
   if helpers.pending_win32(pending) then return end
 
   local screen