fix: take into count of multi-width characters on offset of highlight…

…s and jump (#125)

* feat: take into count of multi-width characters on offset of highlights and jump

* fix: wrong jump position on operator pending mode

This also let offset_pos() receive and return (1,0)-indexed position.
Formerly it received (1,0)-based index and returned (0,0)-based index

* refactor: simplify util.offset_pos

* refactor: let offset_pos use (1,0)-indexed positions with internal variables

to be consistent with parameter and return values

lua/flash/highlight.lua

@@ -113,8 +113,8 @@ function M.update(state)
   local function label(match, pos, offset, is_after)
     local buf = vim.api.nvim_win_get_buf(match.win)
     local cursor = vim.api.nvim_win_get_cursor(match.win)
-    local row = pos[1] - 1 + offset[1]
-    local col = math.max(pos[2] + offset[2], 0)
+    local pos2 = require('flash.util').offset_pos(buf, pos, offset)
+    local row, col = pos2[1] - 1, pos2[2]
     -- dont show the label if the cursor is on the same position
     -- in the same window
     -- and the label is not a range

lua/flash/jump.lua

@@ -190,8 +190,7 @@ function M._jump(match, state, opts)
         offset = 1
       end
 
-      pos = pos + Pos({ 0, offset or 0 })
-      ---@cast pos Pos
+      pos = Pos(require('flash.util').offset_pos(vim.api.nvim_win_get_buf(match.win), pos, { 0, offset or 0}))
       pos[2] = math.max(0, pos[2])
     end
 

lua/flash/util.lua

@@ -13,6 +13,25 @@ M.BS = M.t("<bs>")
 M.LUA_CALLBACK = "\x80\253g"
 M.CMD = "\x80\253h"
 
+---@param buf number
+---@param pos number[] (1,0)-indexed position
+---@param offset number[]
+---@return number[] (1,0)-indexed position
+function M.offset_pos(buf, pos, offset)
+  local row = pos[1] + offset[1]
+  local ok, lines = pcall(vim.api.nvim_buf_get_lines, buf, row - 1, row, true)
+  if not ok or lines == nil then
+    -- fallback to old behavior if anything wrong happens
+    return {row, math.max(pos[2] + offset[2], 0)}
+  end
+
+  local line = lines[1]
+  local charidx = vim.fn.charidx(line, pos[2])
+  local col = vim.fn.byteidx(line, charidx + offset[2])
+
+  return {row, math.max(col, 0)}
+end
+
 function M.get_char()
   Hacks.setcursor()
   vim.cmd.redraw()