better extmark inclusivity

lua/u/range.lua

@@ -382,6 +382,8 @@ function Range:save_to_extmark()
     end_col = 0
   end
   local id = vim.api.nvim_buf_set_extmark(r.start.bufnr, NS, r.start.lnum - 1, r.start.col - 1, {
+    right_gravity = false,
+    end_right_gravity = true,
     end_row = end_row,
     end_col = end_col,
   })

lua/u/renderer.lua

@@ -28,7 +28,6 @@ M.h = setmetatable({}, {
     }
   end,
   __index = function(_, name)
-    -- vim.print('dynamic hl ' .. name)
     return function(attributes, children)
       return M.h('text', vim.tbl_deep_extend('force', { hl = name }, attributes), children)
     end
@@ -324,6 +323,13 @@ function Renderer:_reconcile() -- {{{
         id = extmark.id,
         end_row = extmark.stop[1],
         end_col = extmark.stop[2],
+        -- If we change the text starting from the beginning (where the extmark
+        -- is), we don't want the extmark to move to the right.
+        right_gravity = false,
+        -- If we change the text starting from the end (where the end extmark
+        -- is), we don't want the extmark to move to stay stationary: we want
+        -- it to move to the right.
+        end_right_gravity = true,
       }, extmark.opts)
     )
   end
@@ -385,7 +391,7 @@ function Renderer:_on_text_changed()
       local end_row0, end_col0 = details.end_row, details.end_col
 
       if start_row0 == end_row0 and start_col0 == end_col0 then
-        -- Invalid extmark
+        on_change ''
       else
         local lines = vim.fn.getregion(
           { self.bufnr, start_row0 + 1, start_col0 + 1 },
@@ -405,9 +411,11 @@ end
 ---
 --- @private (private for now)
 --- @param pos0 [number; number]
+--- @param mode string?
 --- @return { extmark: u.renderer.RendererExtmark; tag: u.renderer.Tag; }[]
-function Renderer:get_pos_infos(pos0) -- {{{
+function Renderer:get_pos_infos(pos0, mode) -- {{{
   local cursor_line0, cursor_col0 = pos0[1], pos0[2]
+  if not mode then mode = vim.api.nvim_get_mode().mode end
 
   -- The cursor (block) occupies **two** extmark spaces: one for it's left
   -- edge, and one for it's right. We need to do our own intersection test,
@@ -437,10 +445,23 @@ function Renderer:get_pos_infos(pos0) -- {{{
     --- @param ext u.renderer.RendererExtmark
     :filter(function(ext)
       if ext.stop[1] ~= nil and ext.stop[2] ~= nil then
-        return cursor_line0 >= ext.start[1]
-          and cursor_col0 >= ext.start[2]
-          and cursor_line0 <= ext.stop[1]
-          and cursor_col0 < ext.stop[2]
+        -- If we've "ciw" and "collapsed" an extmark onto the cursor,
+        -- the cursor pos will equal the exmark's start AND end. In this
+        -- case, we want to include the extmark.
+        return (
+          cursor_line0 == ext.start[1]
+          and cursor_col0 == ext.start[2]
+          and cursor_line0 == ext.stop[1]
+          and cursor_col0 == ext.stop[2]
+        )
+          or (
+            cursor_line0 >= ext.start[1]
+            and cursor_col0 >= ext.start[2]
+            and cursor_line0 <= ext.stop[1]
+            -- In insert mode, the cursor is "thin", so <= to compensate:
+            -- In normal mode, the cursor is "wide", so < to compensate:
+            and (mode == 'i' and cursor_col0 <= ext.stop[2] or cursor_col0 < ext.stop[2])
+          )
       else
         return true
       end