mouse: Implement horizontal scroll. #3450

- Code from Vim source.
- Removed the check for 'guioptions'
- mouse_spec.lua: test <ScrollWheelLeft> and <ScrollWheelRight>
- Move horizontal scroll logic to mouse.c
- Remove 'gui_' from the function names
- Renamed variables to be more specific (as opposed to generic p, w).
- Marked some functions as `static`

src/nvim/edit.c

@@ -7741,6 +7741,8 @@ static void ins_mousescroll(int dir)
             (long)(curwin->w_botline - curwin->w_topline));
       else
         scroll_redraw(dir, 3L);
+    } else {
+        mouse_scroll_horiz(dir);
     }
     did_scroll = TRUE;
   }

src/nvim/edit.h

@@ -36,12 +36,6 @@ typedef int (*IndentGetter)(void);
 #define INSCHAR_NO_FEX  8       /* don't use 'formatexpr' */
 #define INSCHAR_COM_LIST 16     /* format comments with list/2nd line indent */
 
-/* direction for nv_mousescroll() and ins_mousescroll() */
-#define MSCR_DOWN       0       /* DOWN must be FALSE */
-#define MSCR_UP         1
-#define MSCR_LEFT       -1
-#define MSCR_RIGHT      -2
-
 #ifdef INCLUDE_GENERATED_DECLARATIONS
 # include "edit.h.generated.h"
 #endif

src/nvim/mouse.c

@@ -14,6 +14,8 @@
 #include "nvim/misc1.h"
 #include "nvim/cursor.h"
 #include "nvim/buffer_defs.h"
+#include "nvim/memline.h"
+#include "nvim/charset.h"
 
 #ifdef INCLUDE_GENERATED_DECLARATIONS
 # include "mouse.c.generated.h"
@@ -503,3 +505,95 @@ void set_mouse_topline(win_T *wp)
   orig_topfill = wp->w_topfill;
 }
 
+///
+/// Return length of line "lnum" for horizontal scrolling.
+///
+static colnr_T scroll_line_len(linenr_T lnum)
+{
+  colnr_T col = 0;
+  char_u *line = ml_get(lnum);
+  if (*line != NUL) {
+    for (;;) {
+      int numchar = chartabsize(line, col);
+      mb_ptr_adv(line);
+      if (*line == NUL) {    // don't count the last character
+        break;
+      }
+      col += numchar;
+    }
+  }
+  return col;
+}
+
+///
+/// Find longest visible line number.
+///
+static linenr_T find_longest_lnum(void)
+{
+  linenr_T ret = 0;
+
+  // Calculate maximum for horizontal scrollbar.  Check for reasonable
+  // line numbers, topline and botline can be invalid when displaying is
+  // postponed.
+  if (curwin->w_topline <= curwin->w_cursor.lnum &&
+      curwin->w_botline > curwin->w_cursor.lnum &&
+      curwin->w_botline <= curbuf->b_ml.ml_line_count + 1) {
+    long max = 0;
+
+    // Use maximum of all visible lines.  Remember the lnum of the
+    // longest line, closest to the cursor line.  Used when scrolling
+    // below.
+    for (linenr_T lnum = curwin->w_topline; lnum < curwin->w_botline; lnum++) {
+      colnr_T len = scroll_line_len(lnum);
+      if (len > (colnr_T)max) {
+        max = len;
+        ret = lnum;
+      } else if (len == (colnr_T)max
+                 && abs((int)(lnum - curwin->w_cursor.lnum))
+                 < abs((int)(ret - curwin->w_cursor.lnum))) {
+        ret = lnum;
+      }
+    }
+  } else {
+    // Use cursor line only.
+    ret = curwin->w_cursor.lnum;
+  }
+
+  return ret;
+}
+
+///
+/// Do a horizontal scroll.  Return TRUE if the cursor moved, FALSE otherwise.
+///
+bool mouse_scroll_horiz(int dir)
+{
+  if (curwin->w_p_wrap) {
+      return false;
+  }
+
+  int step = 6;
+  if (mod_mask & (MOD_MASK_SHIFT | MOD_MASK_CTRL)) {
+      step = curwin->w_width;
+  }
+
+  int leftcol = curwin->w_leftcol + (dir == MSCR_RIGHT ? -step : +step);
+  if (leftcol < 0) {
+      leftcol = 0;
+  }
+
+  if (curwin->w_leftcol == leftcol) {
+      return false;
+  }
+
+  curwin->w_leftcol = (colnr_T)leftcol;
+
+  // When the line of the cursor is too short, move the cursor to the
+  // longest visible line.
+  if (!virtual_active()
+      && (colnr_T)leftcol > scroll_line_len(curwin->w_cursor.lnum)) {
+      curwin->w_cursor.lnum = find_longest_lnum();
+      curwin->w_cursor.col = 0;
+  }
+
+  return leftcol_changed();
+}

src/nvim/mouse.h

@@ -34,6 +34,12 @@
 #define MOUSE_X1       0x300  // Mouse-button X1 (6th)
 #define MOUSE_X2       0x400  // Mouse-button X2
 
+// Direction for nv_mousescroll() and ins_mousescroll()
+#define MSCR_DOWN       0     // DOWN must be FALSE
+#define MSCR_UP         1
+#define MSCR_LEFT       -1
+#define MSCR_RIGHT      -2
+
 
 #ifdef INCLUDE_GENERATED_DECLARATIONS
 # include "mouse.h.generated.h"

src/nvim/normal.c

@@ -3927,6 +3927,8 @@ static void nv_mousescroll(cmdarg_T *cap)
       cap->count0 = 3;
       nv_scroll_line(cap);
     }
+  } else {
+    mouse_scroll_horiz(cap->arg);
   }
 
   curwin->w_redr_status = true;

test/functional/ui/mouse_spec.lua

@@ -426,4 +426,35 @@ describe('Mouse input', function()
                                                            |
     ]])
   end)
+
+  it('horizontal scrolling', function()
+    feed("<esc>:set nowrap<cr>")
+
+    feed("a <esc>20Ab<esc>")
+    screen:expect([[
+                               |
+                               |
+      bbbbbbbbbbbbbbb^b         |
+      ~                        |
+                               |
+    ]])
+
+    feed("<ScrollWheelLeft><0,0>")
+    screen:expect([[
+                               |
+                               |
+      n bbbbbbbbbbbbbbbbbbb^b   |
+      ~                        |
+                               |
+    ]])
+
+    feed("^<ScrollWheelRight><0,0>")
+    screen:expect([[
+      g                        |
+                               |
+      ^t and selection bbbbbbbbb|
+      ~                        |
+                               |
+    ]])
+  end)
 end)