feat: add border prefix heading option

# Details

Request: #123

For heading borders some users use block characters. To improve the way
those look it would be nice if the color of the icon extended to the border.

Added the border_prefix option to do this. Highlights the border line
under the icon section with the foreground highlight group.

Minor bug fix for getting line below, did not update the if condition to
work correctly. Unnecessary virtual lines were being previously added.

Update CHANGELOG pre-release.

Author: MeanderingProgrammer

Diff for: CHANGELOG.md

@@ -2,6 +2,23 @@
 
 ## Pre-release
 
+### Features
+
+- min_width code block option [4b80b4f](https://github.com/MeanderingProgrammer/render-markdown.nvim/commit/4b80b4fb8f81dc39da23a13a0b4e971731c5f849)
+- left_pad bullet option [e455c4f](https://github.com/MeanderingProgrammer/render-markdown.nvim/commit/e455c4f4886d250bd610165a24524da2c6adce80)
+- preset option, obsidian & lazy [96988cc](https://github.com/MeanderingProgrammer/render-markdown.nvim/commit/96988cc76414a2f69a57c5dbaca7bf9336c9cb52)
+- left_pad, right_pad, & min_width heading options [#121](https://github.com/MeanderingProgrammer/render-markdown.nvim/issues/121)
+  [6392a5d](https://github.com/MeanderingProgrammer/render-markdown.nvim/commit/6392a5dfa10f367e10fe58ea9c2faf3179b145d5)
+- border heading option [#123](https://github.com/MeanderingProgrammer/render-markdown.nvim/issues/123)
+  [b700269](https://github.com/MeanderingProgrammer/render-markdown.nvim/commit/b7002694a7a794f8d8a6a0cc54769628cf1cf9d8)
+
+### Bug Fixes
+
+- same buffer in multiple windows [#122](https://github.com/MeanderingProgrammer/render-markdown.nvim/issues/122)
+  [1c7b5ee](https://github.com/MeanderingProgrammer/render-markdown.nvim/commit/1c7b5ee30d8cf6e52628862dbd06f2e23ecb888e)
+- link icon in headings [#124](https://github.com/MeanderingProgrammer/render-markdown.nvim/issues/124)
+  [f365cef](https://github.com/MeanderingProgrammer/render-markdown.nvim/commit/f365cef5c1d05fd2dd390e1830d5c41f2d1f2121)
+
 ## 6.0.0 (2024-08-05)
 
 ### ⚠ BREAKING CHANGES

Diff for: README.md

@@ -253,6 +253,8 @@ require('render-markdown').setup({
         min_width = 0,
         -- Determins if a border is added above and below headings
         border = false,
+        -- Highlight the start of the border using the foreground highlight
+        border_prefix = false,
         -- Used above heading for border
         above = '▄',
         -- Used below heading for border
@@ -546,6 +548,8 @@ require('render-markdown').setup({
         min_width = 0,
         -- Determins if a border is added above and below headings
         border = false,
+        -- Highlight the start of the border using the foreground highlight
+        border_prefix = false,
         -- Used above heading for border
         above = '▄',
         -- Used below heading for border

Diff for: doc/render-markdown.txt

@@ -281,6 +281,8 @@ Full Default Configuration ~
             min_width = 0,
             -- Determins if a border is added above and below headings
             border = false,
+            -- Highlight the start of the border using the foreground highlight
+            border_prefix = false,
             -- Used above heading for border
             above = '▄',
             -- Used below heading for border
@@ -573,6 +575,8 @@ HEADINGS                                      *render-markdown-setup-headings*
             min_width = 0,
             -- Determins if a border is added above and below headings
             border = false,
+            -- Highlight the start of the border using the foreground highlight
+            border_prefix = false,
             -- Used above heading for border
             above = '▄',
             -- Used below heading for border

Diff for: lua/render-markdown/handler/markdown.lua

@@ -101,7 +101,6 @@ function Handler:heading(info)
     })
 
     local width = self:heading_width(info, icon_width)
-
     if heading.width == 'block' then
         -- Overwrite anything beyond width with Normal
         self:add(true, info.start_row, 0, {
@@ -110,33 +109,8 @@ function Handler:heading(info)
             virt_text_win_col = width,
         })
     end
-
     if heading.border then
-        local text_above = { heading.above:rep(width), colors.inverse(background) }
-        if info:line('above') == '' and info.start_row - 1 ~= self.last_heading_border then
-            self:add(true, info.start_row - 1, 0, {
-                virt_text = { text_above },
-                virt_text_pos = 'overlay',
-            })
-        else
-            self:add(false, info.start_row, 0, {
-                virt_lines = { { text_above } },
-                virt_lines_above = true,
-            })
-        end
-
-        local text_below = { heading.below:rep(width), colors.inverse(background) }
-        if info:line('below') == '' then
-            self:add(true, info.end_row + 1, 0, {
-                virt_text = { text_below },
-                virt_text_pos = 'overlay',
-            })
-            self.last_heading_border = info.end_row + 1
-        else
-            self:add(false, info.end_row, 0, {
-                virt_lines = { { text_below } },
-            })
-        end
+        self:heading_border(info, level, foreground, colors.inverse(background), width)
     end
 
     if heading.left_pad > 0 then
@@ -205,6 +179,51 @@ function Handler:heading_width(info, icon_width)
     end
 end
 
+---@private
+---@param info render.md.NodeInfo
+---@param level integer
+---@param foreground string
+---@param background string
+---@param width integer
+function Handler:heading_border(info, level, foreground, background, width)
+    local heading = self.config.heading
+    local prefix = heading.border_prefix and level or 0
+
+    local line_above = {
+        { heading.above:rep(heading.left_pad), background },
+        { heading.above:rep(prefix), foreground },
+        { heading.above:rep(width - heading.left_pad - prefix), background },
+    }
+    if str.width(info:line('above')) == 0 and info.start_row - 1 ~= self.last_heading_border then
+        self:add(true, info.start_row - 1, 0, {
+            virt_text = line_above,
+            virt_text_pos = 'overlay',
+        })
+    else
+        self:add(false, info.start_row, 0, {
+            virt_lines = { line_above },
+            virt_lines_above = true,
+        })
+    end
+
+    local line_below = {
+        { heading.below:rep(heading.left_pad), background },
+        { heading.below:rep(prefix), foreground },
+        { heading.below:rep(width - heading.left_pad - prefix), background },
+    }
+    if str.width(info:line('below')) == 0 then
+        self:add(true, info.end_row + 1, 0, {
+            virt_text = line_below,
+            virt_text_pos = 'overlay',
+        })
+        self.last_heading_border = info.end_row + 1
+    else
+        self:add(false, info.end_row, 0, {
+            virt_lines = { line_below },
+        })
+    end
+end
+
 ---@private
 ---@param info render.md.NodeInfo
 function Handler:dash(info)

Diff for: lua/render-markdown/health.lua

@@ -5,7 +5,7 @@ local M = {}
 
 ---@private
 ---@type string
-M.version = '6.0.8'
+M.version = '6.0.9'
 
 function M.check()
     vim.health.start('render-markdown.nvim [version]')

Diff for: lua/render-markdown/init.lua

@@ -109,6 +109,7 @@ local M = {}
 ---@field public right_pad? integer
 ---@field public min_width? integer
 ---@field public border? boolean
+---@field public border_prefix? boolean
 ---@field public above? string
 ---@field public below? string
 ---@field public backgrounds? string[]
@@ -265,6 +266,8 @@ M.default_config = {
         min_width = 0,
         -- Determins if a border is added above and below headings
         border = false,
+        -- Highlight the start of the border using the foreground highlight
+        border_prefix = false,
         -- Used above heading for border
         above = '▄',
         -- Used below heading for border

Diff for: lua/render-markdown/node_info.lua

@@ -116,7 +116,7 @@ function NodeInfo:line(position)
     local start_row = nil
     if position == 'above' then
         start_row = self.start_row - 1
-    elseif position == 'above' then
+    elseif position == 'below' then
         start_row = self.end_row + 1
     else
         start_row = self.start_row

Diff for: lua/render-markdown/state.lua

@@ -173,6 +173,7 @@ function M.validate()
                 right_pad = { heading.right_pad, 'number', nilable },
                 min_width = { heading.min_width, 'number', nilable },
                 border = { heading.border, 'boolean', nilable },
+                border_prefix = { heading.border_prefix, 'boolean', nilable },
                 above = { heading.above, 'string', nilable },
                 below = { heading.below, 'string', nilable },
                 backgrounds = string_array(heading.backgrounds, nilable),

Diff for: lua/render-markdown/types.lua

@@ -98,6 +98,7 @@
 ---@field public right_pad integer
 ---@field public min_width integer
 ---@field public border boolean
+---@field public border_prefix boolean
 ---@field public above string
 ---@field public below string
 ---@field public backgrounds string[]