terminal: 'scrollback'

Closes #2637

runtime/doc/nvim_terminal_emulator.txt

@@ -4,28 +4,19 @@
 		 NVIM REFERENCE MANUAL    by Thiago de Arruda
 
 
-Embedded terminal emulator				   *terminal-emulator*
+Terminal emulator					   *terminal-emulator*
 
-1. Introduction			|terminal-emulator-intro|
+Nvim embeds a VT220/xterm terminal emulator based on libvterm. The terminal is
-2. Spawning			|terminal-emulator-spawning|
+presented as a special buffer type, asynchronously updated from the virtual
-3. Input			|terminal-emulator-input|
+terminal as data is received from the program connected to it.
-4. Configuration		|terminal-emulator-configuration|
+
-5. Status Variables		|terminal-emulator-status|
+Terminal buffers behave mostly like normal 'nomodifiable' buffers, except:
+- Plugins can set 'modifiable' to modify text, but lines cannot be deleted.
+- 'scrollback' controls how many off-screen lines are kept.
+- Terminal output is followed if the cursor is on the last line.
 
 ==============================================================================
-1. Introduction					     *terminal-emulator-intro*
+Spawning					  *terminal-emulator-spawning*
-
-Nvim offers a mostly complete VT220/xterm terminal emulator. The terminal is
-presented as a special buffer type, asynchronously updated to mirror the
-virtual terminal display as data is received from the program connected to it.
-For most purposes, terminal buffers behave a lot like normal buffers with
-'nomodifiable' set.
-
-The implementation is powered by libvterm, a powerful abstract terminal
-emulation library. http://www.leonerd.org.uk/code/libvterm/
-
-==============================================================================
-2. Spawning					  *terminal-emulator-spawning*
 
 There are 3 ways to create a terminal buffer:
 
@@ -40,34 +31,27 @@ There are 3 ways to create a terminal buffer:
     Note: The "term://" pattern is handled by a BufReadCmd handler, so the
     |autocmd-nested| modifier is required to use it in an autocmd. >
         autocmd VimEnter * nested split term://sh
-<    This is only mentioned for reference; you should use the |:terminal|
+<    This is only mentioned for reference; use |:terminal| instead.
-    command instead.
 
 When the terminal spawns the program, the buffer will start to mirror the
-terminal display and change its name to `term://$CWD//$PID:$COMMAND`.
+terminal display and change its name to `term://{cwd}//{pid}:{cmd}`.
-Note that |:mksession| will "save" the terminal buffers by restarting all
+The "term://..." scheme enables |:mksession| to "restore" a terminal buffer by
-programs when the session is restored.
+restarting the {cmd} when the session is loaded.
 
 ==============================================================================
-3. Input					     *terminal-emulator-input*
+Input						     *terminal-emulator-input*
 
-Sending input is possible by entering terminal mode, which is achieved by
+To send input, enter terminal mode using any command that would enter "insert
-pressing any key that would enter insert mode in a normal buffer (|i| or |a|
+mode" in a normal buffer, such as |i| or |:startinsert|. In this mode all keys
-for example). The |:terminal| ex command will automatically enter terminal
+except <C-\><C-N> are sent to the underlying program. Use <C-\><C-N> to return
-mode once it's spawned. While in terminal mode, Nvim will forward all keys to
+to normal mode. |CTRL-\_CTRL-N|
-the underlying program. The only exception is the <C-\><C-n> key combo,
-which will exit back to normal mode.
 
-Terminal mode has its own namespace for mappings, which is accessed with the
+Terminal mode has its own |:tnoremap| namespace for mappings, this can be used
-"t" prefix. It's possible to use terminal mappings to customize interaction
+to automate any terminal interaction. To map <Esc> to exit terminal mode: >
-with the terminal. For example, here's how to map <Esc> to exit terminal mode:
->
     :tnoremap <Esc> <C-\><C-n>
 <
-Navigating to other windows is only possible by exiting to normal mode, which
+Navigating to other windows is only possible in normal mode. For convenience,
-can be cumbersome with <C-\><C-n> keys. To improve the navigation experience,
+you could use these mappings: >
-you could use the following mappings:
->
     :tnoremap <A-h> <C-\><C-n><C-w>h
     :tnoremap <A-j> <C-\><C-n><C-w>j
     :tnoremap <A-k> <C-\><C-n><C-w>k
@@ -77,11 +61,9 @@ you could use the following mappings:
     :nnoremap <A-k> <C-w>k
     :nnoremap <A-l> <C-w>l
 <
-This configuration allows using `Alt+{h,j,k,l}` to navigate between windows no
+Then you can use `Alt+{h,j,k,l}` to navigate between windows from any mode.
-matter if they are displaying a normal buffer or a terminal buffer in terminal
-mode.
 
-Mouse input is also fully supported, and has the following behavior:
+Mouse input is supported, and has the following behavior:
 
 - If the program has enabled mouse events, the corresponding events will be
   forwarded to the program.
@@ -93,27 +75,23 @@ Mouse input is also fully supported, and has the following behavior:
   the terminal wont lose focus and the hovered window will be scrolled.
 
 ==============================================================================
-4. Configuration			     *terminal-emulator-configuration*
+Configuration				     *terminal-emulator-configuration*
 
-Terminal buffers can be customized through the following global/buffer-local
+Options:		'scrollback'
-variables (set via the |TermOpen| autocmd):
+Events:			|TermOpen|, |TermClose|
+Highlight groups:	|hl-TermCursor|, |hl-TermCursorNC|
+
+Terminal colors can be customized with these variables:
 
-- 'scrollback' option: Scrollback lines (output history) limit.
 - `{g,b}:terminal_color_$NUM`: The terminal color palette, where `$NUM` is the
   color index, between 0 and 255 inclusive. This setting only affects UIs with
   RGB capabilities; for normal terminals the color index is simply forwarded.
 
-The configuration variables are only processed when the terminal starts, which
+The `{g,b}:terminal_color_$NUM` variables are processed only when the terminal
-is why it needs to be done with the |TermOpen| autocmd or setting global
+starts (after |TermOpen|).
-variables before the terminal is started.
-
-There is also a corresponding |TermClose| event.
-
-The terminal cursor can be highlighted via |hl-TermCursor| and
-|hl-TermCursorNC|.
 
 ==============================================================================
-5. Status Variables				    *terminal-emulator-status*
+Status Variables				    *terminal-emulator-status*
 
 Terminal buffers maintain some information about the terminal in buffer-local
 variables:
@@ -126,11 +104,8 @@ variables:
 - *b:terminal_job_pid* The PID of the top-level process running in the
   terminal.
 
-These variables will have a value by the time the TermOpen autocmd runs, and
+These variables are initialized before TermOpen, so you can use them in
-will continue to have a value for the lifetime of the terminal buffer, making
+a local 'statusline'. Example: >
-them suitable for use in 'statusline'. For example, to show the terminal title
-as the status line:
->
     :autocmd TermOpen * setlocal statusline=%{b:term_title}
 <
 ==============================================================================

runtime/doc/options.txt

@@ -4949,9 +4949,15 @@ A jump table for the options with a short description can be found at |Q_op|.
 	be used as the new value for 'scroll'.  Reset to half the window
 	height with ":set scroll=0".
 
-			*'scrollback'* *'scbk'* *'noscrollback'* *'noscbk'*
+						*'scrollback'* *'scbk'*
-'scrollback' 'scbk'	boolean  (default: 1000)
+'scrollback' 'scbk'	number	(default: 1000
-			global or local to buffer |global-local|
+				 in normal buffers: -1)
+			local to buffer
+	Maximum number of lines kept beyond the visible screen. Lines at the
+	top are deleted if new lines exceed this limit.
+	Only in |terminal-emulator| buffers. 'buftype'
+	-1 means "unlimited" for normal buffers, 100000 otherwise.
+	Minimum is 1.
 
 			*'scrollbind'* *'scb'* *'noscrollbind'* *'noscb'*
 'scrollbind' 'scb'	boolean  (default off)

runtime/doc/various.txt

@@ -207,23 +207,15 @@ g8			Print the hex values of the bytes used in the
 :sh[ell]		Removed. |vim-differences| {Nvim}
 
 						  *:terminal* *:te*
-:te[rminal][!] {cmd}	Spawns {cmd} using the current value of 'shell' and
+:te[rminal][!] {cmd}	Execute {cmd} with 'shell' in a |terminal-emulator|
-			'shellcmdflag' in a new terminal buffer.  This is
+                        buffer.  Equivalent to: >
-			equivalent to: >
-
 			      :enew
 			      :call termopen('{cmd}')
 			      :startinsert
 <
-			If no {cmd} is given, 'shellcmdflag' will not be sent
+                        See |jobstart()|.
-			to |termopen()|.
 
-			Like |:enew|, it will fail if the current buffer is
+			To enter terminal mode automatically: >
-			modified, but can be forced with "!".  See |termopen()|
-			and |terminal-emulator|.
-
-			To switch to terminal mode automatically:
->
 			      autocmd BufEnter term://* startinsert
 <
 							*:!cmd* *:!* *E34*

src/.valgrind.supp

@@ -10,7 +10,7 @@
   Memcheck:Leak
   fun:malloc
   fun:uv_spawn
-  fun:pipe_process_spawn
+  fun:libuv_process_spawn
   fun:process_spawn
   fun:job_start
 }

src/nvim/eval.c

@@ -5845,8 +5845,8 @@ bool garbage_collect(bool testing)
     garbage_collect_at_exit = false;
   }
 
-  // We advance by two because we add one for items referenced through
+  // We advance by two (COPYID_INC) because we add one for items referenced
-  // previous_funccal.
+  // through previous_funccal.
   const int copyID = get_copyID();
 
   // 1. Go through all accessible variables and mark all lists and dicts

src/nvim/normal.c

@@ -7420,21 +7420,19 @@ static void nv_esc(cmdarg_T *cap)
     restart_edit = 'a';
 }
 
-/*
+/// Handle "A", "a", "I", "i" and <Insert> commands.
- * Handle "A", "a", "I", "i" and <Insert> commands.
- */
 static void nv_edit(cmdarg_T *cap)
 {
-  /* <Insert> is equal to "i" */
+  // <Insert> is equal to "i"
-  if (cap->cmdchar == K_INS || cap->cmdchar == K_KINS)
+  if (cap->cmdchar == K_INS || cap->cmdchar == K_KINS) {
     cap->cmdchar = 'i';
+  }
 
-  /* in Visual mode "A" and "I" are an operator */
+  // in Visual mode "A" and "I" are an operator
-  if (VIsual_active && (cap->cmdchar == 'A' || cap->cmdchar == 'I'))
+  if (VIsual_active && (cap->cmdchar == 'A' || cap->cmdchar == 'I')) {
     v_visop(cap);
-
+  // in Visual mode and after an operator "a" and "i" are for text objects
-  /* in Visual mode and after an operator "a" and "i" are for text objects */
+  } else if ((cap->cmdchar == 'a' || cap->cmdchar == 'i')
-  else if ((cap->cmdchar == 'a' || cap->cmdchar == 'i')
              && (cap->oap->op_type != OP_NOP || VIsual_active)) {
     nv_object(cap);
   } else if (!curbuf->b_p_ma && !p_im && !curbuf->terminal) {

src/nvim/option.c

@@ -3994,16 +3994,7 @@ set_num_option (
   /*
    * Number options that need some action when changed
    */
-  if (pp == &p_scbk) {
+  if (pp == &p_wh || pp == &p_hh) {
-    // 'scrollback'
-    if (p_scbk < 1) {
-      errmsg = e_invarg;
-      p_scbk = 0;
-    } else if (p_scbk > 100000) {
-      errmsg = e_invarg;
-      p_scbk = 100000;
-    }
-  } else if (pp == &p_wh || pp == &p_hh) {
     if (p_wh < 1) {
       errmsg = e_positive;
       p_wh = 1;
@@ -4205,7 +4196,19 @@ set_num_option (
     FOR_ALL_TAB_WINDOWS(tp, wp) {
       check_colorcolumn(wp);
     }
-
+  } else if (pp == &curbuf->b_p_scbk) {
+    // 'scrollback'
+    if (!curbuf->terminal) {
+      errmsg = e_invarg;
+      curbuf->b_p_scbk = -1;
+    } else {
+      if (curbuf->b_p_scbk < -1 || curbuf->b_p_scbk > 100000) {
+        errmsg = e_invarg;
+        curbuf->b_p_scbk = 1000;
+      }
+      // Force the scrollback to take effect.
+      terminal_resize(curbuf->terminal, UINT16_MAX, UINT16_MAX);
+    }
   }
 
   /*
@@ -5641,7 +5644,7 @@ void buf_copy_options(buf_T *buf, int flags)
       buf->b_p_ai = p_ai;
       buf->b_p_ai_nopaste = p_ai_nopaste;
       buf->b_p_sw = p_sw;
-      buf->b_p_scbk = p_scbk;
+      buf->b_p_scbk = -1;
       buf->b_p_tw = p_tw;
       buf->b_p_tw_nopaste = p_tw_nopaste;
       buf->b_p_tw_nobin = p_tw_nobin;

src/nvim/options.lua

@@ -1918,7 +1918,7 @@ return {
       vi_def=true,
       varname='p_scbk',
       redraw={'current_buffer'},
-      defaults={if_true={vi=1000}}
+      defaults={if_true={vi=-1}}
     },
     {
       full_name='scrollbind', abbreviation='scb',

src/nvim/screen.c

@@ -7113,8 +7113,9 @@ void showruler(int always)
   }
   if ((*p_stl != NUL || *curwin->w_p_stl != NUL) && curwin->w_status_height) {
     redraw_custom_statusline(curwin);
-  } else
+  } else {
     win_redr_ruler(curwin, always);
+  }
 
   if (need_maketitle
       || (p_icon && (stl_syntax & STL_IN_ICON))

src/nvim/terminal.c

@@ -1,18 +1,17 @@
-// VT220/xterm-like terminal emulator implementation for nvim. Powered by
+// VT220/xterm-like terminal emulator.
-// libvterm (http://www.leonerd.org.uk/code/libvterm/).
+// Powered by libvterm http://www.leonerd.org.uk/code/libvterm
 //
 // libvterm is a pure C99 terminal emulation library with abstract input and
 // display. This means that the library needs to read data from the master fd
 // and feed VTerm instances, which will invoke user callbacks with screen
 // update instructions that must be mirrored to the real display.
 //
-// Keys are pressed in VTerm instances by calling
+// Keys are sent to VTerm instances by calling
 // vterm_keyboard_key/vterm_keyboard_unichar, which generates byte streams that
 // must be fed back to the master fd.
 //
-// This implementation uses nvim buffers as the display mechanism for both
+// Nvim buffers are used as the display mechanism for both the visible screen
-// the visible screen and the scrollback buffer. When focused, the window
+// and the scrollback buffer.
-// "pins" to the bottom of the buffer and mirrors libvterm screen state.
 //
 // When a line becomes invisible due to a decrease in screen height or because
 // a line was pushed up during normal terminal output, we store the line
@@ -23,18 +22,17 @@
 // scrollback buffer, which is mirrored in the nvim buffer displaying lines
 // that were previously invisible.
 //
-// The vterm->nvim synchronization is performed in intervals of 10
+// The vterm->nvim synchronization is performed in intervals of 10 milliseconds,
-// milliseconds. This is done to minimize screen updates when receiving large
+// to minimize screen updates when receiving large bursts of data.
-// bursts of data.
 //
 // This module is decoupled from the processes that normally feed it data, so
 // it's possible to use it as a general purpose console buffer (possibly as a
 // log/display mechanism for nvim in the future)
 //
-// Inspired by vimshell (http://www.wana.at/vimshell/) and
+// Inspired by: vimshell http://www.wana.at/vimshell
-// Conque (https://code.google.com/p/conque/). Libvterm usage instructions (plus
+//              Conque https://code.google.com/p/conque
-// some extra code) were taken from
+// Some code from pangoterm http://www.leonerd.org.uk/code/pangoterm
-// pangoterm (http://www.leonerd.org.uk/code/pangoterm/)
+
 #include <assert.h>
 #include <stdio.h>
 #include <stdint.h>
@@ -87,10 +85,10 @@ typedef struct terminal_state {
 # include "terminal.c.generated.h"
 #endif
 
-#define SCROLLBACK_BUFFER_DEFAULT_SIZE 1000
+#define SB_MAX 100000  // Maximum 'scrollback' value.
+
 // Delay for refreshing the terminal buffer after receiving updates from
-// libvterm. This is greatly improves performance when receiving large bursts
+// libvterm. Improves performance when receiving large bursts of data.
-// of data.
 #define REFRESH_DELAY 10
 
 static TimeWatcher refresh_timer;
@@ -102,27 +100,23 @@ typedef struct {
 } ScrollbackLine;
 
 struct terminal {
-  // options passed to terminal_open
+  TerminalOptions opts;  // options passed to terminal_open
-  TerminalOptions opts;
-  // libvterm structures
   VTerm *vt;
   VTermScreen *vts;
   // buffer used to:
   //  - convert VTermScreen cell arrays into utf8 strings
   //  - receive data from libvterm as a result of key presses.
   char textbuf[0x1fff];
-  // Scrollback buffer storage for libvterm.
+
-  // TODO(tarruda): Use a doubly-linked list
+  ScrollbackLine **sb_buffer;       // Scrollback buffer storage for libvterm
-  ScrollbackLine **sb_buffer;
+  size_t sb_current;                // number of rows pushed to sb_buffer
-  // number of rows pushed to sb_buffer
+  size_t sb_size;                   // sb_buffer size
-  size_t sb_current;
-  // sb_buffer size;
-  size_t sb_size;
   // "virtual index" that points to the first sb_buffer row that we need to
   // push to the terminal buffer when refreshing the scrollback. When negative,
   // it actually points to entries that are no longer in sb_buffer (because the
   // window height has increased) and must be deleted from the terminal buffer
   int sb_pending;
+
   // buf_T instance that acts as a "drawing surface" for libvterm
   // we can't store a direct reference to the buffer because the
   // refresh_timer_cb may be called after the buffer was freed, and there's
@@ -130,20 +124,18 @@ struct terminal {
   handle_T buf_handle;
   // program exited
   bool closed, destroy;
+
   // some vterm properties
   bool forward_mouse;
-  // invalid rows libvterm screen
+  int invalid_start, invalid_end;   // invalid rows in libvterm screen
-  int invalid_start, invalid_end;
   struct {
     int row, col;
     bool visible;
   } cursor;
-  // which mouse button is pressed
+  int pressed_button;               // which mouse button is pressed
-  int pressed_button;
+  bool pending_resize;              // pending width/height
-  // pending width/height
+
-  bool pending_resize;
+  size_t refcount;                  // reference count
-  // With a reference count of 0 the terminal can be freed.
-  size_t refcount;
 };
 
 static VTermScreenCallbacks vterm_screen_callbacks = {
@@ -238,28 +230,21 @@ Terminal *terminal_open(TerminalOptions opts)
   refresh_screen(rv, curbuf);
   set_option_value((uint8_t *)"buftype", 0, (uint8_t *)"terminal", OPT_LOCAL);
 
-  // some sane settings for terminal buffers
+  // Default settings for terminal buffers
   curbuf->b_p_ma = false;   // 'nomodifiable'
   curbuf->b_p_ul = -1;      // disable undo
+  curbuf->b_p_scbk = 1000;  // 'scrollback'
   set_option_value((uint8_t *)"wrap", false, NULL, OPT_LOCAL);
   set_option_value((uint8_t *)"number", false, NULL, OPT_LOCAL);
   set_option_value((uint8_t *)"relativenumber", false, NULL, OPT_LOCAL);
   buf_set_term_title(curbuf, (char *)curbuf->b_ffname);
   RESET_BINDING(curwin);
 
-  // Apply TermOpen autocmds so the user can configure the terminal
+  // Apply TermOpen autocmds _before_ configuring the scrollback buffer.
   apply_autocmds(EVENT_TERMOPEN, NULL, NULL, false, curbuf);
 
-  // Configure the scrollback buffer. Try to get the size from:
+  // Configure the scrollback buffer.
-  //
+  rv->sb_size = curbuf->b_p_scbk < 0 ? SB_MAX : (size_t)curbuf->b_p_scbk;;
-  // - b:terminal_scrollback_buffer_size
-  // - g:terminal_scrollback_buffer_size
-  // - SCROLLBACK_BUFFER_DEFAULT_SIZE
-  //
-  // but limit to 100k.
-  int size = get_config_int("terminal_scrollback_buffer_size");
-  rv->sb_size = size > 0 ? (size_t)size : SCROLLBACK_BUFFER_DEFAULT_SIZE;
-  rv->sb_size = MIN(rv->sb_size, 100000);
   rv->sb_buffer = xmalloc(sizeof(ScrollbackLine *) * rv->sb_size);
 
   if (!true_color) {
@@ -338,22 +323,22 @@ void terminal_close(Terminal *term, char *msg)
 void terminal_resize(Terminal *term, uint16_t width, uint16_t height)
 {
   if (term->closed) {
-    // will be called after exited if two windows display the same terminal and
+    // If two windows display the same terminal and one is closed by keypress.
-    // one of the is closed as a consequence of pressing a key.
     return;
   }
+  bool force = width == UINT16_MAX || height == UINT16_MAX;
   int curwidth, curheight;
   vterm_get_size(term->vt, &curheight, &curwidth);
 
-  if (!width) {
+  if (force || !width) {
     width = (uint16_t)curwidth;
   }
 
-  if (!height) {
+  if (force || !height) {
     height = (uint16_t)curheight;
   }
 
-  if (curheight == height && curwidth == width) {
+  if (!force && curheight == height && curwidth == width) {
     return;
   }
 
@@ -671,10 +656,15 @@ static int term_bell(void *data)
   return 1;
 }
 
-// the scrollback push/pop handlers were copied almost verbatim from pangoterm
+// Scrollback push handler (from pangoterm).
 static int term_sb_push(int cols, const VTermScreenCell *cells, void *data)
 {
   Terminal *term = data;
+
+  if (!term->sb_size) {
+    return 0;
+  }
+
   // copy vterm cells into sb_buffer
   size_t c = (size_t)cols;
   ScrollbackLine *sbrow = NULL;
@@ -686,10 +676,12 @@ static int term_sb_push(int cols, const VTermScreenCell *cells, void *data)
       xfree(term->sb_buffer[term->sb_current - 1]);
     }
 
+    // Make room at the start by shifting to the right.
     memmove(term->sb_buffer + 1, term->sb_buffer,
         sizeof(term->sb_buffer[0]) * (term->sb_current - 1));
 
   } else if (term->sb_current > 0) {
+    // Make room at the start by shifting to the right.
     memmove(term->sb_buffer + 1, term->sb_buffer,
         sizeof(term->sb_buffer[0]) * term->sb_current);
   }
@@ -699,6 +691,7 @@ static int term_sb_push(int cols, const VTermScreenCell *cells, void *data)
     sbrow->cols = c;
   }
 
+  // New row is added at the start of the storage buffer.
   term->sb_buffer[0] = sbrow;
   if (term->sb_current < term->sb_size) {
     term->sb_current++;
@@ -714,6 +707,11 @@ static int term_sb_push(int cols, const VTermScreenCell *cells, void *data)
   return 1;
 }
 
+/// Scrollback pop handler (from pangoterm).
+///
+/// @param cols
+/// @param cells  VTerm state to update.
+/// @param data   Terminal
 static int term_sb_pop(int cols, VTermScreenCell *cells, void *data)
 {
   Terminal *term = data;
@@ -726,24 +724,24 @@ static int term_sb_pop(int cols, VTermScreenCell *cells, void *data)
     term->sb_pending--;
   }
 
-  // restore vterm state
-  size_t c = (size_t)cols;
   ScrollbackLine *sbrow = term->sb_buffer[0];
   term->sb_current--;
+  // Forget the "popped" row by shifting the rest onto it.
   memmove(term->sb_buffer, term->sb_buffer + 1,
       sizeof(term->sb_buffer[0]) * (term->sb_current));
 
-  size_t cols_to_copy = c;
+  size_t cols_to_copy = (size_t)cols;
   if (cols_to_copy > sbrow->cols) {
     cols_to_copy = sbrow->cols;
   }
 
   // copy to vterm state
   memcpy(cells, sbrow->cells, sizeof(cells[0]) * cols_to_copy);
-  for (size_t col = cols_to_copy; col < c; col++) {
+  for (size_t col = cols_to_copy; col < (size_t)cols; col++) {
     cells[col].chars[0] = 0;
     cells[col].width = 1;
   }
+
   xfree(sbrow);
   pmap_put(ptr_t)(invalidated_terminals, term, NULL);
 
@@ -889,7 +887,7 @@ static bool send_mouse_event(Terminal *term, int c)
 // terminal buffer refresh & misc {{{
 
 
-void fetch_row(Terminal *term, int row, int end_col)
+static void fetch_row(Terminal *term, int row, int end_col)
 {
   int col = 0;
   size_t line_len = 0;
@@ -977,8 +975,7 @@ static void refresh_terminal(Terminal *term)
   });
   adjust_topline(term, buf, pending_resize);
 }
-// libuv timer callback. This will enqueue on_refresh to be processed as an
+// Calls refresh_terminal() on all invalidated_terminals.
-// event.
 static void refresh_timer_cb(TimeWatcher *watcher, void *data)
 {
   if (exiting) {  // Cannot redraw (requires event loop) during teardown/exit.
@@ -1012,7 +1009,37 @@ static void refresh_size(Terminal *term, buf_T *buf)
   term->opts.resize_cb((uint16_t)width, (uint16_t)height, term->opts.data);
 }
 
-// Refresh the scrollback of a invalidated terminal
+/// Adjusts scrollback storage after 'scrollback' option changed.
+static void on_scrollback_option_changed(Terminal *term, buf_T *buf)
+{
+  const size_t scbk = curbuf->b_p_scbk < 0
+                      ? SB_MAX : (size_t)MAX(1, curbuf->b_p_scbk);
+  assert(term->sb_current < SIZE_MAX);
+  if (term->sb_pending > 0) {  // Pending rows must be processed first.
+    abort();
+  }
+
+  // Delete lines exceeding the new 'scrollback' limit.
+  if (scbk < term->sb_current) {
+    size_t diff = term->sb_current - scbk;
+    for (size_t i = 0; i < diff; i++) {
+      ml_delete(1, false);
+      term->sb_current--;
+      xfree(term->sb_buffer[term->sb_current]);
+    }
+    deleted_lines(1, (long)diff);
+  }
+
+  // Resize the scrollback storage.
+  size_t sb_region = sizeof(ScrollbackLine *) * scbk;
+  if (scbk != term->sb_size) {
+    term->sb_buffer = xrealloc(term->sb_buffer, sb_region);
+  }
+
+  term->sb_size = scbk;
+}
+
+// Refresh the scrollback of an invalidated terminal.
 static void refresh_scrollback(Terminal *term, buf_T *buf)
 {
   int width, height;
@@ -1041,6 +1068,8 @@ static void refresh_scrollback(Terminal *term, buf_T *buf)
     ml_delete(buf->b_ml.ml_line_count, false);
     deleted_lines(buf->b_ml.ml_line_count, 1);
   }
+
+  on_scrollback_option_changed(term, buf);
 }
 
 // Refresh the screen (visible part of the buffer when the terminal is
@@ -1052,8 +1081,7 @@ static void refresh_screen(Terminal *term, buf_T *buf)
   int height;
   int width;
   vterm_get_size(term->vt, &height, &width);
-  // It's possible that the terminal height decreased and `term->invalid_end`
+  // Terminal height may have decreased before `invalid_end` reflects it.
-  // doesn't reflect it yet
   term->invalid_end = MIN(term->invalid_end, height);
 
   for (int r = term->invalid_start, linenr = row_to_linenr(term, r);
@@ -1182,17 +1210,6 @@ static char *get_config_string(char *key)
   return NULL;
 }
 
-static int get_config_int(char *key)
-{
-  Object obj;
-  GET_CONFIG_VALUE(key, obj);
-  if (obj.type == kObjectTypeInteger) {
-    return (int)obj.data.integer;
-  }
-  api_free_object(obj);
-  return 0;
-}
-
 // }}}
 
 // vim: foldmethod=marker

src/nvim/undo.c

@@ -308,8 +308,9 @@ bool undo_allowed(void)
 /// Get the 'undolevels' value for the current buffer.
 static long get_undolevel(void)
 {
-  if (curbuf->b_p_ul == NO_LOCAL_UNDOLEVEL)
+  if (curbuf->b_p_ul == NO_LOCAL_UNDOLEVEL) {
     return p_ul;
+  }
   return curbuf->b_p_ul;
 }
 

test/functional/terminal/edit_spec.lua

@@ -31,45 +31,40 @@ describe(':edit term://*', function()
     eq(termopen_runs[1], termopen_runs[1]:match('^term://.//%d+:$'))
   end)
 
-  it('runs TermOpen early enough to respect terminal_scrollback_buffer_size', function()
+  it("runs TermOpen early enough to set buffer-local 'scrollback'", function()
     local columns, lines = 20, 4
     local scr = get_screen(columns, lines)
     local rep = 'a'
     meths.set_option('shellcmdflag', 'REP ' .. rep)
-    local rep_size = rep:byte()
+    local rep_size = rep:byte()  -- 'a' => 97
     local sb = 10
-    local gsb = 20
+    command('autocmd TermOpen * :setlocal scrollback='..tostring(sb))
-    meths.set_var('terminal_scrollback_buffer_size', gsb)
-    command('autocmd TermOpen * :let b:terminal_scrollback_buffer_size = '
-            .. tostring(sb))
     command('edit term://foobar')
+
     local bufcontents = {}
     local winheight = curwinmeths.get_height()
-    -- I have no idea why there is + 4 needed. But otherwise it works fine with
+    local buf_cont_start = rep_size - sb - winheight + 2
-    -- different scrollbacks.
+    local function bufline (i)
-    local shift = -4
+      return ('%d: foobar'):format(i)
-    local buf_cont_start = rep_size - 1 - sb - winheight - shift
+    end
-    local bufline = function(i) return ('%d: foobar'):format(i) end
     for i = buf_cont_start,(rep_size - 1) do
       bufcontents[#bufcontents + 1] = bufline(i)
     end
     bufcontents[#bufcontents + 1] = ''
     bufcontents[#bufcontents + 1] = '[Process exited 0]'
-    -- Do not ask me why displayed screen is one line *before* buffer
+
-    -- contents: buffer starts with 87:, screen with 86:.
     local exp_screen = '\n'
-    local did_cursor = false
+    for i = 1,(winheight - 1) do
-    for i = 0,(winheight - 1) do
+      local line = bufcontents[#bufcontents - winheight + i]
-      local line = bufline(buf_cont_start + i - 1)
       exp_screen = (exp_screen
-                    .. (did_cursor and '' or '^')
                     .. line
                     .. (' '):rep(columns - #line)
                     .. '|\n')
-      did_cursor = true
     end
-    exp_screen = exp_screen .. (' '):rep(columns) .. '|\n'
+    exp_screen = exp_screen..'^[Process exited 0]  |\n'
+
+    exp_screen = exp_screen..(' '):rep(columns)..'|\n'
     scr:expect(exp_screen)
-    eq(bufcontents, curbufmeths.get_lines(1, -1, true))
+    eq(bufcontents, curbufmeths.get_lines(0, -1, true))
   end)
 end)

test/functional/terminal/ex_terminal_spec.lua

@@ -20,22 +20,18 @@ describe(':terminal', function()
     source([[
       echomsg "msg1"
       echomsg "msg2"
+      echomsg "msg3"
     ]])
     -- Invoke a command that emits frequent terminal activity.
     execute([[terminal while true; do echo X; done]])
     helpers.feed([[<C-\><C-N>]])
-    screen:expect([[
+    wait()
-      X                                                 |
-      X                                                 |
-      ^X                                                 |
-                                                        |
-    ]])
     helpers.sleep(10)  -- Let some terminal activity happen.
     execute("messages")
     screen:expect([[
-      X                                                 |
       msg1                                              |
       msg2                                              |
+      msg3                                              |
       Press ENTER or type command to continue^           |
     ]])
   end)

test/functional/terminal/helpers.lua

@@ -37,7 +37,6 @@ local default_command = '["'..nvim_dir..'/tty-test'..'"]'
 local function screen_setup(extra_height, command)
   nvim('command', 'highlight TermCursor cterm=reverse')
   nvim('command', 'highlight TermCursorNC ctermbg=11')
-  nvim('set_var', 'terminal_scrollback_buffer_size', 10)
   if not extra_height then extra_height = 0 end
   if not command then command = default_command end
   local screen = Screen.new(50, 7 + extra_height)
@@ -58,7 +57,9 @@ local function screen_setup(extra_height, command)
   -- tty-test puts the terminal into raw mode and echoes all input. tests are
   -- done by feeding it with terminfo codes to control the display and
   -- verifying output with screen:expect.
-  execute('enew | call termopen('..command..') | startinsert')
+  execute('enew | call termopen('..command..')')
+  execute('setlocal scrollback=10')
+  execute('startinsert')
   if command == default_command then
     -- wait for "tty ready" to be printed before each test or the terminal may
     -- still be in canonical mode(will echo characters for example)

test/functional/terminal/scrollback_spec.lua

@@ -3,7 +3,11 @@ local helpers = require('test.functional.helpers')(after_each)
 local thelpers = require('test.functional.terminal.helpers')
 local clear, eq, curbuf = helpers.clear, helpers.eq, helpers.curbuf
 local feed, nvim_dir, execute = helpers.feed, helpers.nvim_dir, helpers.execute
+local eval = helpers.eval
+local command = helpers.command
 local wait = helpers.wait
+local retry = helpers.retry
+local curbufmeths = helpers.curbufmeths
 local feed_data = thelpers.feed_data
 
 if helpers.pending_win32(pending) then return end
@@ -20,7 +24,7 @@ describe('terminal scrollback', function()
     screen:detach()
   end)
 
-  describe('when the limit is crossed', function()
+  describe('when the limit is exceeded', function()
     before_each(function()
       local lines = {}
       for i = 1, 30 do
@@ -359,3 +363,88 @@ describe('terminal prints more lines than the screen height and exits', function
   end)
 end)
 
+describe("'scrollback' option", function()
+  before_each(function()
+    clear()
+  end)
+
+  local function expect_lines(expected)
+    local actual = eval("line('$')")
+    if expected ~= actual then
+    error('expected: '..expected..', actual: '..tostring(actual))
+    end
+  end
+
+  it('set to 0 behaves as 1', function()
+    local screen = thelpers.screen_setup(nil, "['sh']", 30)
+
+    curbufmeths.set_option('scrollback', 0)
+    feed_data('for i in $(seq 1 30); do echo "line$i"; done\n')
+    screen:expect('line30                        ', nil, nil, nil, true)
+    retry(nil, nil, function() expect_lines(7) end)
+
+    screen:detach()
+  end)
+
+  it('deletes lines (only) if necessary', function()
+    local screen = thelpers.screen_setup(nil, "['sh']", 30)
+
+    curbufmeths.set_option('scrollback', 200)
+
+    -- Wait for prompt.
+    screen:expect('$', nil, nil, nil, true)
+
+    wait()
+    feed_data('for i in $(seq 1 30); do echo "line$i"; done\n')
+
+    screen:expect('line30                        ', nil, nil, nil, true)
+
+    retry(nil, nil, function() expect_lines(33) end)
+    curbufmeths.set_option('scrollback', 10)
+    wait()
+    retry(nil, nil, function() expect_lines(16) end)
+    curbufmeths.set_option('scrollback', 10000)
+    eq(16, eval("line('$')"))
+    -- Terminal job data is received asynchronously, may happen before the
+    -- 'scrollback' option is synchronized with the internal sb_buffer.
+    command('sleep 100m')
+    feed_data('for i in $(seq 1 40); do echo "line$i"; done\n')
+
+    screen:expect('line40                        ', nil, nil, nil, true)
+
+    retry(nil, nil, function() expect_lines(58) end)
+    -- Verify off-screen state
+    eq('line35', eval("getline(line('w0') - 1)"))
+    eq('line26', eval("getline(line('w0') - 10)"))
+
+    screen:detach()
+  end)
+
+  it('defaults to 1000', function()
+    execute('terminal')
+    eq(1000, curbufmeths.get_option('scrollback'))
+  end)
+
+  it('error if set to invalid values', function()
+    local status, rv = pcall(command, 'set scrollback=-2')
+    eq(false, status)  -- assert failure
+    eq('E474:', string.match(rv, "E%d*:"))
+
+    status, rv = pcall(command, 'set scrollback=100001')
+    eq(false, status)  -- assert failure
+    eq('E474:', string.match(rv, "E%d*:"))
+  end)
+
+  it('defaults to -1 on normal buffers', function()
+    execute('new')
+    eq(-1, curbufmeths.get_option('scrollback'))
+  end)
+
+  it('error if set on a normal buffer', function()
+    command('new')
+    execute('set scrollback=42')
+    feed('<CR>')
+    eq('E474:', string.match(eval("v:errmsg"), "E%d*:"))
+  end)
+
+end)