feat: left padding for checkboxes

## Details

Adds `checkbox.left_pad` option, makes things consistent as all other
configurations that support one side also support the other.

Required a bit of refactoring due to wanting to use `overlay` text when
possible as `inline` does not behave super well with the cursor.

To make this happen added `sub` function to the `Line` class which can
get a subset of a line while correctly using utf code points rather than
byte widths. Added a similar function to the `str` helper module which
functions on individual strings and is what the `Line` class relies on.
Currently only used for checkboxes but made available through helpers as
the pattern is likely to come up again.

Author: MeanderingProgrammer

README.md

@@ -594,6 +594,8 @@ require('render-markdown').setup({
         render_modes = false,
         -- Render the bullet point before the checkbox.
         bullet = false,
+        -- Padding to add to the left of checkboxes.
+        left_pad = 0,
         -- Padding to add to the right of checkboxes.
         right_pad = 1,
         unchecked = {
@@ -1268,6 +1270,8 @@ require('render-markdown').setup({
         render_modes = false,
         -- Render the bullet point before the checkbox.
         bullet = false,
+        -- Padding to add to the left of checkboxes.
+        left_pad = 0,
         -- Padding to add to the right of checkboxes.
         right_pad = 1,
         unchecked = {

doc/render-markdown.txt

@@ -1,4 +1,4 @@
-*render-markdown.txt*       For NVIM v0.11.4      Last change: 2025 October 06
+*render-markdown.txt*       For NVIM v0.11.4      Last change: 2025 October 07
 
 ==============================================================================
 Table of Contents                          *render-markdown-table-of-contents*
@@ -656,6 +656,8 @@ Default Configuration ~
             render_modes = false,
             -- Render the bullet point before the checkbox.
             bullet = false,
+            -- Padding to add to the left of checkboxes.
+            left_pad = 0,
             -- Padding to add to the right of checkboxes.
             right_pad = 1,
             unchecked = {
@@ -1318,6 +1320,8 @@ Checkbox Configuration ~
             render_modes = false,
             -- Render the bullet point before the checkbox.
             bullet = false,
+            -- Padding to add to the left of checkboxes.
+            left_pad = 0,
             -- Padding to add to the right of checkboxes.
             right_pad = 1,
             unchecked = {

lua/render-markdown/health.lua

@@ -6,7 +6,7 @@ local state = require('render-markdown.state')
 local M = {}
 
 ---@private
-M.version = '8.9.0'
+M.version = '8.9.1'
 
 function M.check()
     M.start('versions')

lua/render-markdown/lib/config.lua

@@ -56,7 +56,7 @@ end
 
 ---@return render.md.Line
 function Config:line()
-    return Line.new(self)
+    return Line.new(self.padding.highlight)
 end
 
 ---@param destination string

lua/render-markdown/lib/line.lua

@@ -1,3 +1,4 @@
+local interval = require('render-markdown.lib.interval')
 local str = require('render-markdown.lib.str')
 
 ---@class render.md.Line
@@ -6,11 +7,11 @@ local str = require('render-markdown.lib.str')
 local Line = {}
 Line.__index = Line
 
----@param config render.md.buf.Config
+---@param highlight string
 ---@return render.md.Line
-function Line.new(config)
+function Line.new(highlight)
     local self = setmetatable({}, Line)
-    self.highlight = config.padding.highlight
+    self.highlight = highlight
     self.line = {}
     return self
 end
@@ -39,9 +40,24 @@ end
 
 ---@return render.md.Line
 function Line:copy()
-    local result = setmetatable({}, Line)
-    result.highlight = self.highlight
-    result.line = vim.list_extend({}, self.line)
+    return Line.new(self.highlight):extend(self)
+end
+
+---@param i integer 1-based inclusive
+---@param j integer 1-based inclusive
+---@return render.md.Line
+function Line:sub(i, j)
+    local result = Line.new(self.highlight)
+    local position = 0
+    for _, text in ipairs(self.line) do
+        local length = str.width(text[1])
+        local range = { i - position, j - position } ---@type render.md.Range
+        local overlap = interval.overlap({ 1, length }, range)
+        if overlap then
+            result:add(str.sub(text[1], overlap[1], overlap[2]), text[2])
+        end
+        position = position + length
+    end
     return result
 end
 

lua/render-markdown/lib/str.lua

@@ -9,6 +9,17 @@ function M.split(s, sep, trimempty)
     return vim.split(s, sep, { plain = true, trimempty = trimempty })
 end
 
+---@param s string
+---@param i integer 1-based inclusive
+---@param j integer 1-based inclusive
+---@return string
+function M.sub(s, i, j)
+    local bytes = vim.str_utf_pos(s)
+    local start_byte = bytes[i]
+    local end_byte = j < #bytes and bytes[j + 1] - 1 or #s
+    return s:sub(start_byte, end_byte)
+end
+
 ---number of hashtags at the start of the string
 ---@param s string
 ---@return integer

lua/render-markdown/render/markdown/checkbox.lua

@@ -79,49 +79,40 @@ end
 
 ---@private
 function Render:checkbox()
+    -- add 1 to end to account for space after checkbox
     local node = self.data.checkbox
-    local right = self.config.right_pad
-
-    -- add 1 to account for space after checkbox
+    local row = node.start_row
+    local start_col = node.start_col
+    local end_col = node.end_col + 1
     local width = self.context:width(node) + 1
-    local space = width - str.width(self.data.icon)
 
-    local line = self:line():text(self.data.icon, self.data.highlight)
-    if space < 0 then
-        -- not enough space to fit the icon in-place
-        self.marks:over(self.config, 'check_icon', node, {
-            virt_text = line:pad(right):get(),
-            virt_text_pos = 'inline',
-            conceal = '',
-        }, { 0, 0, 0, 1 })
-    else
-        local fits = math.min(space, right) ---@type integer
-        space = space - fits
-        right = right - fits
-
-        local row = node.start_row
-        local start_col = node.start_col
-        local end_col = node.end_col + 1
+    local line = self:line()
+        :pad(self.config.left_pad)
+        :text(self.data.icon, self.data.highlight)
+        :pad(self.config.right_pad)
 
+    local overlay = line:sub(1, width)
+    if not overlay:empty() then
         self.marks:add(self.config, 'check_icon', row, start_col, {
-            end_col = end_col - space,
-            virt_text = line:pad(fits):get(),
+            virt_text = overlay:get(),
             virt_text_pos = 'overlay',
         })
-        if space > 0 then
-            -- remove extra space after the icon
-            self.marks:add(self.config, 'check_icon', row, end_col - space, {
-                end_col = end_col,
-                conceal = '',
-            })
-        end
-        if right > 0 then
-            -- add padding
-            self.marks:add(self.config, 'check_icon', row, end_col, {
-                virt_text = self:line():pad(right):get(),
-                virt_text_pos = 'inline',
-            })
-        end
+    end
+
+    local inline = line:sub(width + 1, line:width())
+    if not inline:empty() then
+        self.marks:add(self.config, 'check_icon', row, end_col, {
+            virt_text = inline:get(),
+            virt_text_pos = 'inline',
+        })
+    end
+
+    local space = width - overlay:width()
+    if space > 0 then
+        self.marks:add(self.config, 'check_icon', row, end_col - space, {
+            end_col = end_col,
+            conceal = '',
+        })
     end
 end
 

lua/render-markdown/settings.lua

@@ -275,6 +275,7 @@ M.checkbox = {}
 
 ---@class (exact) render.md.checkbox.Config: render.md.base.Config
 ---@field bullet boolean
+---@field left_pad number
 ---@field right_pad integer
 ---@field unchecked render.md.checkbox.component.Config
 ---@field checked render.md.checkbox.component.Config
@@ -302,6 +303,8 @@ M.checkbox.default = {
     render_modes = false,
     -- Render the bullet point before the checkbox.
     bullet = false,
+    -- Padding to add to the left of checkboxes.
+    left_pad = 0,
     -- Padding to add to the right of checkboxes.
     right_pad = 1,
     unchecked = {
@@ -354,6 +357,7 @@ function M.checkbox.schema()
     }
     return M.base.schema({
         bullet = { type = 'boolean' },
+        left_pad = { type = 'number' },
         right_pad = { type = 'number' },
         unchecked = component,
         checked = component,

lua/render-markdown/types.lua

@@ -70,6 +70,7 @@
 
 ---@class (exact) render.md.checkbox.UserConfig: render.md.base.UserConfig
 ---@field bullet? boolean
+---@field left_pad? number
 ---@field right_pad? integer
 ---@field unchecked? render.md.checkbox.component.UserConfig
 ---@field checked? render.md.checkbox.component.UserConfig

tests/demo/box_dash_quote_spec.lua

@@ -13,19 +13,19 @@ describe('demo/box_dash_quote.md', function()
         marks:add(row:get(0, 1), { 0, 0 }, util.heading.bg(1))
 
         marks:add(row:get(1, 0), { 0, 2 }, util.conceal())
-        marks:add(row:get(0, 0), { 2, 5 }, {
+        marks:add(row:get(0), 2, {
             virt_text = { { '󰄱 ', 'RmUnchecked' }, { ' ', 'Normal' } },
             virt_text_pos = 'overlay',
         })
         marks:add(row:get(0, 0), { 5, 6 }, util.conceal())
         marks:add(row:get(1, 0), { 0, 2 }, util.conceal())
-        marks:add(row:get(0, 0), { 2, 5 }, {
+        marks:add(row:get(0), 2, {
             virt_text = { { '󰱒 ', 'RmChecked' }, { ' ', 'Normal' } },
             virt_text_pos = 'overlay',
         })
         marks:add(row:get(0, 0), { 5, 6 }, util.conceal())
         marks:add(row:get(1, 0), { 0, 2 }, util.conceal())
-        marks:add(row:get(0, 0), { 2, 6 }, {
+        marks:add(row:get(0), 2, {
             virt_text = { { '󰥔 ', 'RmTodo' } },
             virt_text_pos = 'overlay',
         })