Refactor indentexpr() to fix noindent indentation for lists.

Closes #473.

I tried doing small fixes to this code, but kept running into edge
cases. Hence, this complete rewrite. :) The important points:

- The queries in `indent.scm` no longer match on top-level (i.e
  un-nested) lists, but instead on list items of all levels.

- List item indentation no longer relies on the previous non-empty line.
  Each list item stores whether it's in a top-level or a nested list and
  calculates its indent based on that.

- The check whether we are in bulleted line or not no longer uses
  `str.match()`, since its pattern was buggy and forgot a few kinds of
  bullets. (namely, indented `*` bullets and `a.` ordered bullets)
  Instead, we compare the current line number to `match.line_nr`. We can
  do that because we query list items instead of lists now.

There is an edge case when the user is appending to a list. We want that
next line to be indented (see #472), but it's technically outside of the
list. At the same time, if an unindented line follows a list, it should
not become part of the list.

The best solution I found for this was to make the behavior of
`indentexpr()` depend on whether we are in insert mode. If yes, the line
after a list is part of the list. If not, it isn't.

The new code also correctly takes into account that two consecutive
empty lines always end a preceding list.

lua/orgmode/org/indent.lua

@@ -31,11 +31,24 @@ local get_matches = ts_utils.memoize_by_buf_tick(function(bufnr)
         matches[range.start.line + 1] = opts
       end
 
-      if type == 'list' then
-        local first_list_item = node:named_child(0)
-        local first_list_item_linenr = first_list_item:start()
-        local first_item_indent = vim.fn.indent(first_list_item_linenr + 1)
-        opts.indent = first_item_indent
+      if type == 'listitem' then
+        local content = node:named_child(1)
+        if content then
+          local content_linenr, content_indent = content:start()
+          if content_linenr == range.start.line then
+            opts.overhang = content_indent - opts.indent
+          end
+        end
+        if not opts.overhang then
+          local bullet = node:named_child(0)
+          opts.overhang = ts.get_node_text(bullet, bufnr):len() + 1
+        end
+
+        local parent = node:parent()
+        while parent and parent:type() ~= 'section' and parent:type() ~= 'listitem' do
+          parent = parent:parent()
+        end
+        opts.nesting_parent_linenr = parent and (parent:start() + 1)
 
         for i = range.start.line, range['end'].line - 1 do
           matches[i + 1] = opts
@@ -47,9 +60,6 @@ local get_matches = ts_utils.memoize_by_buf_tick(function(bufnr)
         local parent = node:parent()
         while parent and parent:type() ~= 'section' do
           parent = parent:parent()
-          if not parent then
-            break
-          end
         end
         if parent then
           local headline = parent:named_child('headline')
@@ -107,12 +117,6 @@ local function foldexpr()
   return '='
 end
 
-local function get_is_list_item(line)
-  local line_numbered_list_item = line:match('^%s*(%d+[%)%.]%s+)')
-  local line_unordered_list_item = line:match('^%s*([%+%-]%s+)')
-  return line_numbered_list_item or line_unordered_list_item
-end
-
 local function indentexpr(linenr, mode)
   linenr = linenr or vim.v.lnum
   mode = mode or vim.fn.mode()
@@ -143,26 +147,49 @@ local function indentexpr(linenr, mode)
     return 0
   end
 
-  if match.type == 'list' and prev_line_match.type == 'list' then
-    local prev_line_list_item = get_is_list_item(vim.fn.getline(prev_linenr))
-    local cur_line_list_item = get_is_list_item(vim.fn.getline(linenr))
-
-    if cur_line_list_item then
-      local diff = match.indent - vim.fn.indent(match.line_nr)
-      local indent = vim.fn.indent(linenr)
-      return indent - diff
+  if match.type == 'listitem' then
+    -- We first figure out the indent of the first line of a listitem. Then we
+    -- check if we're on the first line or a "hanging" line. In the latter
+    -- case, we add the overhang.
+    local first_line_indent
+    local parent_linenr = match.nesting_parent_linenr
+    if parent_linenr then
+      local parent_match = matches[parent_linenr]
+      if parent_match.type == 'listitem' then
+        -- Nested listitem. Because two listitems cannot start on the same line,
+        -- we simply fetch the parent's indentation and add its overhang.
+        -- Don't use parent_match.indent, it might be stale if the parent
+        -- already got reindented.
+        first_line_indent = vim.fn.indent(parent_linenr) + parent_match.overhang
+      elseif parent_match.type == 'headline' and not noindent_mode then
+        -- Un-nested list inside a section, indent according to section.
+        first_line_indent = parent_match.indent
+      else
+        -- Noindent mode.
+        first_line_indent = 0
+      end
+    else
+      -- Top-level list before the first headline.
+      first_line_indent = 0
     end
-
-    if prev_line_list_item then
-      return vim.fn.indent(prev_linenr) + prev_line_list_item:len()
+    -- Add overhang if this is a hanging line.
+    if linenr ~= match.line_nr then
+      return first_line_indent + match.overhang
     end
+    return first_line_indent
   end
 
-  if prev_line_match.type == 'list' and match.type ~= 'list' then
-    local prev_line_list_item = get_is_list_item(vim.fn.getline(prev_linenr))
-    if prev_line_list_item then
-      return vim.fn.indent(prev_linenr) + prev_line_list_item:len()
+  -- In indent mode, we also count the non-listem line *after* a listitem as
+  -- part of the listitem. Keep in mind that double empty lines end a list as
+  -- per Orgmode syntax.
+  if mode:match('^[iR]') and prev_line_match.type == 'listitem' and linenr - prev_linenr < 3 then
+    -- After the first line of a listitem, we have to add the overhang to the
+    -- listitem's own base indent. After all further lines, we can simply copy
+    -- the indentation.
+    if prev_linenr == prev_line_match.line_nr then
+      return vim.fn.indent(prev_linenr) + prev_line_match.overhang
     end
+    return vim.fn.indent(prev_linenr)
   end
 
   if noindent_mode then

queries/org/org_indent.scm

@@ -1,5 +1,5 @@
 (headline) @OrgIndentHeadline
-(body (list) @OrgList)
+(listitem) @OrgListItem
 (body (paragraph) @OrgParagraph)
 (body (drawer) @OrgDrawer)
 (section (property_drawer) @OrgPropertyDrawer)

tests/minimal_init.vim

@@ -3,6 +3,7 @@ set rtp+=./plenary.nvim
 set rtp+=./nvim-treesitter
 set termguicolors
 set noswapfile
+set expandtab  " Accommodates some deep nesting in indent_spec.lua
 language en_US.utf-8
 runtime plugin/plenary.vim
 runtime plugin/nvim-treesitter.lua

tests/plenary/org/indent_spec.lua

@@ -51,12 +51,12 @@ local function test_full_reindent()
       '',
       '  1. Ordered list',
       '     a) nested list',
-      '     over-indented',
-      '     over-indented',
+      '        over-indented',
+      '        over-indented',
       '     b) nested list',
-      '     under-indented',
+      '        under-indented',
       '  2. Ordered list',
-      '     Not part of the list',
+      '  Not part of the list',
       '',
       '** Second task',
       '   DEADLINE: <1970-01-01 Thu>',
@@ -68,10 +68,10 @@ local function test_full_reindent()
       '     + nested list',
       '       under-indented',
       '   - unordered list',
-      '    + nested list',
-      '      * triple nested list',
-      '      continuation',
-      '      part of the first-level list',
+      '     + nested list',
+      '       * triple nested list',
+      '         continuation',
+      '     part of the first-level list',
       '   Not part of the list',
     }
   elseif config.org_indent_mode == 'noindent' then
@@ -81,27 +81,27 @@ local function test_full_reindent()
       '',
       '1. Ordered list',
       '   a) nested list',
-      'over-indented',
-      'over-indented',
-      'b) nested list',
-      'under-indented',
+      '      over-indented',
+      '      over-indented',
+      '   b) nested list',
+      '      under-indented',
       '2. Ordered list',
-      '   Not part of the list',
+      'Not part of the list',
       '',
       '** Second task',
       'DEADLINE: <1970-01-01 Thu>',
       '',
       '- Unordered list',
       '  + nested list',
       '    over-indented',
-      'over-indented',
+      '    over-indented',
       '  + nested list',
       '    under-indented',
       '- unordered list',
-      ' + nested list',
-      '   * triple nested list',
-      'continuation',
-      'part of the first-level list',
+      '  + nested list',
+      '    * triple nested list',
+      '      continuation',
+      '  part of the first-level list',
       'Not part of the list',
     }
   end
@@ -123,7 +123,7 @@ local function test_newly_written_list()
     expected = {
       '- new item',
       '  second line',
-      'third line',
+      '  third line',
     }
   end
   expect_whole_buffer(expected)
@@ -148,7 +148,7 @@ local function test_insertion_to_an_existing_list()
       '- first item',
       '- new item',
       '  second line',
-      'third line',
+      '  third line',
       '- third item',
     }
   end