feat: add basic support for org-indent-mode like behavior

## Details

Request: #134

Adds a new top level configuration for `indent` which is disabled by default.

The effect of enabling it is to mimic org-indent-mode by adding
`per_level` * (level - 1) spaces to the start of each line. This is
accomplished by using the section nodes which nicely contain everything
within a header including nested headers. Since the sections themselves
are nested we don't even do the math for creating the padding we simply
add `per_level` for each line of each section and the fact they are
nested means the paddings stack.

We need to use inline virtual text to accomplish this since that is the
only way to shift text, meaining this only works for neovim >= 0.10.0.
Since virtual_lines are not impacted by inline text we need to manaully
pad them based on the level of the current object.

There are probably many edge cases that look weird or cause all sorts of
alignment problems. I'll work on them as they come up if they're not too
bad to handle, otherwise I will enumerate any non functional
configurations in the README.

Author: MeanderingProgrammer

README.md

@@ -158,6 +158,8 @@ require('render-markdown').setup({
     preset = 'none',
     -- Capture groups that get pulled from markdown
     markdown_query = [[
+        (section) @section
+
         (atx_heading [
             (atx_h1_marker)
             (atx_h2_marker)
@@ -489,6 +491,14 @@ require('render-markdown').setup({
         -- Applies to background of sign text
         highlight = 'RenderMarkdownSign',
     },
+    -- Mimic org-indent-mode behavior by indenting everything under a heading based on the
+    -- level of the heading. Indenting starts from level 2 headings onward.
+    indent = {
+        -- Turn on / off org-indent-mode
+        enabled = false,
+        -- Amount of additional padding added for each heading level
+        per_level = 2,
+    },
     -- Window options to use that change between rendered and raw view
     win_options = {
         -- See :h 'conceallevel'
@@ -510,7 +520,7 @@ require('render-markdown').setup({
     -- to have their own behavior. Values default to the top level configuration
     -- if no override is provided. Supports the following fields:
     --   enabled, max_file_size, debounce, render_modes, anti_conceal, heading, code,
-    --   dash, bullet, checkbox, quote, pipe_table, callout, link, sign, win_options
+    --   dash, bullet, checkbox, quote, pipe_table, callout, link, sign, indent, win_options
     overrides = {
         -- Overrides for different buftypes, see :h 'buftype'
         buftype = {
@@ -884,6 +894,23 @@ require('render-markdown').setup({
 })
 ```
 
+## Indent
+
+[Wiki Page](https://github.com/MeanderingProgrammer/render-markdown.nvim/wiki/Indent)
+
+```lua
+require('render-markdown').setup({
+    -- Mimic org-indent-mode behavior by indenting everything under a heading based on the
+    -- level of the heading. Indenting starts from level 2 headings onward.
+    indent = {
+        -- Turn on / off org-indent-mode
+        enabled = false,
+        -- Amount of additional padding added for each heading level
+        per_level = 2,
+    },
+})
+```
+
 # Colors
 
 The table below shows all the highlight groups with their default link

doc/render-markdown.txt

@@ -22,6 +22,7 @@ Table of Contents                          *render-markdown-table-of-contents*
   - Callouts                                  |render-markdown-setup-callouts|
   - Links                                        |render-markdown-setup-links|
   - Signs                                        |render-markdown-setup-signs|
+  - Indent                                      |render-markdown-setup-indent|
 7. Colors                                             |render-markdown-colors|
 8. Info                                                 |render-markdown-info|
   - vimwiki                                     |render-markdown-info-vimwiki|
@@ -188,6 +189,8 @@ Full Default Configuration ~
         preset = 'none',
         -- Capture groups that get pulled from markdown
         markdown_query = [[
+            (section) @section
+    
             (atx_heading [
                 (atx_h1_marker)
                 (atx_h2_marker)
@@ -519,6 +522,14 @@ Full Default Configuration ~
             -- Applies to background of sign text
             highlight = 'RenderMarkdownSign',
         },
+        -- Mimic org-indent-mode behavior by indenting everything under a heading based on the
+        -- level of the heading. Indenting starts from level 2 headings onward.
+        indent = {
+            -- Turn on / off org-indent-mode
+            enabled = false,
+            -- Amount of additional padding added for each heading level
+            per_level = 2,
+        },
         -- Window options to use that change between rendered and raw view
         win_options = {
             -- See :h 'conceallevel'
@@ -540,7 +551,7 @@ Full Default Configuration ~
         -- to have their own behavior. Values default to the top level configuration
         -- if no override is provided. Supports the following fields:
         --   enabled, max_file_size, debounce, render_modes, anti_conceal, heading, code,
-        --   dash, bullet, checkbox, quote, pipe_table, callout, link, sign, win_options
+        --   dash, bullet, checkbox, quote, pipe_table, callout, link, sign, indent, win_options
         overrides = {
             -- Overrides for different buftypes, see :h 'buftype'
             buftype = {
@@ -933,6 +944,25 @@ Wiki Page
 <
 
 
+INDENT                                          *render-markdown-setup-indent*
+
+Wiki Page
+<https://github.com/MeanderingProgrammer/render-markdown.nvim/wiki/Indent>
+
+>lua
+    require('render-markdown').setup({
+        -- Mimic org-indent-mode behavior by indenting everything under a heading based on the
+        -- level of the heading. Indenting starts from level 2 headings onward.
+        indent = {
+            -- Turn on / off org-indent-mode
+            enabled = false,
+            -- Amount of additional padding added for each heading level
+            per_level = 2,
+        },
+    })
+<
+
+
 ==============================================================================
 7. Colors                                             *render-markdown-colors*
 

lua/render-markdown/handler/markdown.lua

@@ -37,7 +37,9 @@ function Handler:parse(root)
     self.context:query(root, state.markdown_query, function(capture, node)
         local info = NodeInfo.new(self.buf, node)
         logger.debug_node_info(capture, info)
-        if capture == 'heading' then
+        if capture == 'section' then
+            self:section(info)
+        elseif capture == 'heading' then
             self:heading(info)
         elseif capture == 'dash' then
             self:dash(info)
@@ -78,6 +80,31 @@ function Handler:add(conceal, start_row, start_col, opts)
     return list.add_mark(self.marks, conceal, start_row, start_col, opts)
 end
 
+---@private
+---@param info render.md.NodeInfo
+function Handler:section(info)
+    local indent = self.config.indent
+    if not indent.enabled then
+        return
+    end
+
+    -- Do not add any indentation on unknown or first level
+    local heading = info:child('atx_heading')
+    if heading == nil or heading:child('atx_h1_marker') ~= nil then
+        return
+    end
+
+    -- Each level stacks inline marks so we do not need to multiply spaces
+    -- However skipping a level, i.e. 2 -> 5, will only add one level of spaces
+    for row = info.start_row, info.end_row - 1 do
+        self:add(false, row, 0, {
+            priority = 0,
+            virt_text = { { str.spaces(indent.per_level), 'Normal' } },
+            virt_text_pos = 'inline',
+        })
+    end
+end
+
 ---@private
 ---@param info render.md.NodeInfo
 function Handler:heading(info)
@@ -209,7 +236,7 @@ function Handler:heading_border(info, level, foreground, background, width)
         })
     else
         self:add(false, info.start_row, 0, {
-            virt_lines = { line_above },
+            virt_lines = { self:indent_virt_line(info, line_above) },
             virt_lines_above = true,
         })
     end
@@ -227,7 +254,7 @@ function Handler:heading_border(info, level, foreground, background, width)
         self.last_heading_border = info.end_row + 1
     else
         self:add(false, info.end_row, 0, {
-            virt_lines = { line_below },
+            virt_lines = { self:indent_virt_line(info, line_below) },
         })
     end
 end
@@ -653,19 +680,41 @@ function Handler:table_full(parsed_table)
         return border[11]:rep(column.width)
     end, delim.columns)
 
-    local line_above = border[1] .. table.concat(sections, border[2]) .. border[3]
+    local line_above = {
+        { border[1] .. table.concat(sections, border[2]) .. border[3], pipe_table.head },
+    }
     self:add(false, first.info.start_row, first.info.start_col, {
         virt_lines_above = true,
-        virt_lines = { { { line_above, pipe_table.head } } },
+        virt_lines = { self:indent_virt_line(parsed_table.info, line_above) },
     })
 
-    local line_below = border[7] .. table.concat(sections, border[8]) .. border[9]
+    local line_below = {
+        { border[7] .. table.concat(sections, border[8]) .. border[9], pipe_table.row },
+    }
     self:add(false, last.info.start_row, last.info.start_col, {
         virt_lines_above = false,
-        virt_lines = { { { line_below, pipe_table.row } } },
+        virt_lines = { self:indent_virt_line(parsed_table.info, line_below) },
     })
 end
 
+---@private
+---@param info render.md.NodeInfo
+---@param line { [1]: string, [2]: string }[]
+---@return { [1]: string, [2]: string }[]
+function Handler:indent_virt_line(info, line)
+    local indent = self.config.indent
+    if not indent.enabled then
+        return line
+    end
+    local level = info:level() - 1
+    if level <= 0 then
+        return line
+    end
+    local indent_line = { str.spaces(indent.per_level * level), 'Normal' }
+    table.insert(line, 1, indent_line)
+    return line
+end
+
 ---@class render.md.handler.Markdown: render.md.Handler
 local M = {}
 

lua/render-markdown/health.lua

@@ -5,7 +5,7 @@ local M = {}
 
 ---@private
 ---@type string
-M.version = '6.1.11'
+M.version = '6.1.12'
 
 function M.check()
     vim.health.start('render-markdown.nvim [version]')

lua/render-markdown/init.lua

@@ -22,6 +22,10 @@ local M = {}
 ---@field public default? number|string|boolean
 ---@field public rendered? number|string|boolean
 
+---@class (exact) render.md.UserIndent
+---@field public enabled? boolean
+---@field public per_level? integer
+
 ---@class (exact) render.md.UserSign
 ---@field public enabled? boolean
 ---@field public highlight? string
@@ -157,6 +161,7 @@ local M = {}
 ---@field public callout? table<string, render.md.UserCustomComponent>
 ---@field public link? render.md.UserLink
 ---@field public sign? render.md.UserSign
+---@field public indent? render.md.UserIndent
 ---@field public win_options? table<string, render.md.UserWindowOption>
 
 ---@alias render.md.config.Preset 'none'|'lazy'|'obsidian'
@@ -193,6 +198,8 @@ M.default_config = {
     preset = 'none',
     -- Capture groups that get pulled from markdown
     markdown_query = [[
+        (section) @section
+
         (atx_heading [
             (atx_h1_marker)
             (atx_h2_marker)
@@ -524,6 +531,14 @@ M.default_config = {
         -- Applies to background of sign text
         highlight = 'RenderMarkdownSign',
     },
+    -- Mimic org-indent-mode behavior by indenting everything under a heading based on the
+    -- level of the heading. Indenting starts from level 2 headings onward.
+    indent = {
+        -- Turn on / off org-indent-mode
+        enabled = false,
+        -- Amount of additional padding added for each heading level
+        per_level = 2,
+    },
     -- Window options to use that change between rendered and raw view
     win_options = {
         -- See :h 'conceallevel'
@@ -545,7 +560,7 @@ M.default_config = {
     -- to have their own behavior. Values default to the top level configuration
     -- if no override is provided. Supports the following fields:
     --   enabled, max_file_size, debounce, render_modes, anti_conceal, heading, code,
-    --   dash, bullet, checkbox, quote, pipe_table, callout, link, sign, win_options
+    --   dash, bullet, checkbox, quote, pipe_table, callout, link, sign, indent, win_options
     overrides = {
         -- Overrides for different buftypes, see :h 'buftype'
         buftype = {

lua/render-markdown/node_info.lua

@@ -45,6 +45,19 @@ function NodeInfo.sort_inplace(infos)
     end)
 end
 
+---@return integer
+function NodeInfo:level()
+    local level = 0
+    local parent = self.node:parent()
+    while parent ~= nil and parent:type() ~= 'document' do
+        if parent:type() == 'section' then
+            level = level + 1
+        end
+        parent = parent:parent()
+    end
+    return level
+end
+
 ---Walk through parent nodes, count the number of target nodes
 ---@param target string
 ---@return integer

lua/render-markdown/parser/pipe_table.lua

@@ -22,6 +22,7 @@ local str = require('render-markdown.str')
 ---@field columns render.md.parsed.table.Column[]
 
 ---@class render.md.parsed.PipeTable
+---@field info render.md.NodeInfo
 ---@field delim render.md.parsed.table.DelimRow
 ---@field rows render.md.parsed.table.Row[]
 
@@ -72,7 +73,7 @@ function M.parse(context, info)
     end
 
     ---@type render.md.parsed.PipeTable
-    return { delim = delim, rows = rows }
+    return { info = info, delim = delim, rows = rows }
 end
 
 ---@private

lua/render-markdown/state.lua

@@ -85,7 +85,7 @@ end
 function M.default_buffer_config()
     local config = M.config
     ---@type render.md.BufferConfig
-    return vim.deepcopy({
+    local buffer_config = {
         enabled = true,
         max_file_size = config.max_file_size,
         debounce = config.debounce,
@@ -101,8 +101,10 @@ function M.default_buffer_config()
         callout = config.callout,
         link = config.link,
         sign = config.sign,
+        indent = config.indent,
         win_options = config.win_options,
-    })
+    }
+    return vim.deepcopy(buffer_config)
 end
 
 ---@return string[]
@@ -374,6 +376,14 @@ function M.validate()
             })
         end
 
+        local indent = config.indent
+        if indent ~= nil then
+            append_errors(path .. '.indent', indent, {
+                enabled = { indent.enabled, 'boolean', nilable },
+                per_level = { indent.per_level, 'number', nilable },
+            })
+        end
+
         if config.win_options ~= nil then
             for name, win_option in pairs(config.win_options) do
                 append_errors(path .. '.win_options.' .. name, win_option, {
@@ -401,6 +411,7 @@ function M.validate()
         callout = { config.callout, 'table' },
         link = { config.link, 'table' },
         sign = { config.sign, 'table' },
+        indent = { config.indent, 'table' },
         win_options = { config.win_options, 'table' },
         preset = one_of(config.preset, { 'none', 'lazy', 'obsidian' }, {}, false),
         markdown_query = { config.markdown_query, 'string' },
@@ -449,6 +460,7 @@ function M.validate()
                 callout = { override.callout, 'table', true },
                 link = { override.link, 'table', true },
                 sign = { override.sign, 'table', true },
+                indent = { override.indent, 'table', true },
                 win_options = { override.win_options, 'table', true },
             })
             validate_buffer_config(path, override, true)

lua/render-markdown/types.lua

@@ -11,6 +11,10 @@
 ---@field public default number|string|boolean
 ---@field public rendered number|string|boolean
 
+---@class (exact) render.md.Indent
+---@field public enabled boolean
+---@field public per_level integer
+
 ---@class (exact) render.md.Sign
 ---@field public enabled boolean
 ---@field public highlight string
@@ -132,6 +136,7 @@
 ---@field public callout table<string, render.md.CustomComponent>
 ---@field public link render.md.Link
 ---@field public sign render.md.Sign
+---@field public indent render.md.Indent
 ---@field public win_options table<string, render.md.WindowOption>
 
 ---@class (exact) render.md.Config: render.md.BufferConfig