fix: background of indented code blocks in lists

## Details

Bug report: #133

For most code blocks we assumed a starting column of 0. This let us
handle multiline blocks with a single extmark. However for indented code
blocks this leads to jutting out background sections which do not line
up with the rest of the highlights.

To fix this apply background highlight for code blocks one line at a
time using the input starting column value.

Author: MeanderingProgrammer

Diff for: benches/readme_spec.lua

@@ -4,7 +4,7 @@ local util = require('benches.util')
 
 describe('README.md', function()
     it('default', function()
-        local base_marks = 45
+        local base_marks = 50
         util.less_than(util.setup('README.md'), 50)
         util.num_marks(base_marks)
 

Diff for: doc/render-markdown.txt

@@ -1,4 +1,4 @@
-*render-markdown.txt*          For 0.10.0          Last change: 2024 August 14
+*render-markdown.txt*          For 0.10.0          Last change: 2024 August 18
 
 ==============================================================================
 Table of Contents                          *render-markdown-table-of-contents*

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

@@ -350,18 +350,16 @@ function Handler:code_background(code_block, icon_added)
         end
     end
 
-    self:add(false, code_block.start_row, 0, {
-        end_row = code_block.end_row,
-        end_col = 0,
-        hl_group = code.highlight,
-        hl_eol = true,
-    })
-
-    if code.width == 'block' then
-        -- Overwrite anything beyond width with Normal
-        local padding = str.pad(vim.o.columns * 2)
-        for row = code_block.start_row, code_block.end_row - 1 do
-            self:add(false, row, 0, {
+    local padding = str.pad(vim.o.columns * 2)
+    for row = code_block.start_row, code_block.end_row - 1 do
+        self:add(false, row, code_block.col, {
+            end_row = row + 1,
+            hl_group = code.highlight,
+            hl_eol = true,
+        })
+        if code.width == 'block' then
+            -- Overwrite anything beyond width with Normal
+            self:add(false, row, code_block.col, {
                 priority = 0,
                 virt_text = { { padding, 'Normal' } },
                 virt_text_win_col = code_block.width,

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

@@ -5,7 +5,7 @@ local M = {}
 
 ---@private
 ---@type string
-M.version = '6.1.4'
+M.version = '6.1.5'
 
 function M.check()
     vim.health.start('render-markdown.nvim [version]')

Diff for: tests/callout_spec.lua

@@ -50,11 +50,12 @@ describe('callout.md', function()
             callout(tip_start + 2, 2, 8, '󰌶 Tip', ok), -- Callout text
             util.quote(tip_start + 3, '%s', ok), -- Quote continued
             util.quote(tip_start + 4, '%s ', ok),
-            util.code_block(tip_start + 4, tip_start + 6),
+            util.code_block_row(tip_start + 4, 2),
         })
-        vim.list_extend(expected, util.code_language(tip_start + 4, 5, 8, '󰢱 ', 'lua', 'MiniIconsAzure'))
+        vim.list_extend(expected, util.code_language(tip_start + 4, 5, 8, 'lua'))
         vim.list_extend(expected, {
             util.quote(tip_start + 5, '%s ', ok),
+            util.code_block_row(tip_start + 5, 2),
             util.quote(tip_start + 6, '%s ', ok),
             util.code_below(tip_start + 6, 2),
         })

Diff for: tests/heading_code_spec.lua

@@ -17,10 +17,13 @@ describe('heading_code.md', function()
 
         vim.list_extend(expected, {
             util.link(10, 0, 21, 'image'), -- Image link
-            util.code_block(12, 22), -- Code block
+            util.code_block_row(12, 0), -- Code block start
         })
-        vim.list_extend(expected, util.code_language(12, 3, 9, '󰌠 ', 'python', 'MiniIconsYellow'))
-        vim.list_extend(expected, { util.code_below(22, 0) })
+        vim.list_extend(expected, util.code_language(12, 3, 9, 'python'))
+        for i = 13, 21 do
+            table.insert(expected, util.code_block_row(i, 0))
+        end
+        table.insert(expected, util.code_below(22, 0))
 
         local actual = util.get_actual_marks()
         util.marks_are_equal(expected, actual)

Diff for: tests/util.lua

@@ -76,14 +76,14 @@ function M.inline_code(row, start_col, end_col)
     }
 end
 
----@param start_row integer
----@param end_row integer
+---@param row integer
+---@param col integer
 ---@return render.md.MarkInfo
-function M.code_block(start_row, end_row)
+function M.code_block_row(row, col)
     ---@type render.md.MarkInfo
     return {
-        row = { start_row, end_row },
-        col = { 0, 0 },
+        row = { row, row + 1 },
+        col = { col, 0 },
         hl_eol = true,
         hl_group = M.hl('Code'),
     }
@@ -92,11 +92,15 @@ end
 ---@param row integer
 ---@param start_col integer
 ---@param end_col integer
----@param icon string
----@param name string
----@param highlight string
+---@param name 'python'|'lua'
 ---@return render.md.MarkInfo[]
-function M.code_language(row, start_col, end_col, icon, name, highlight)
+function M.code_language(row, start_col, end_col, name)
+    local icon, highlight
+    if name == 'python' then
+        icon, highlight = '󰌠 ', 'MiniIconsYellow'
+    elseif name == 'lua' then
+        icon, highlight = '󰢱 ', 'MiniIconsAzure'
+    end
     ---@type render.md.MarkInfo
     local sign_mark = {
         row = { row, row },