feat(pack): add built-in plugin manager vim.pack

Problem: No built-in plugin manager

Solution: Add built-in plugin manager

Co-authored-by: Lewis Russell <lewis6991@gmail.com>

runtime/ftplugin/nvim-pack.lua

@@ -0,0 +1,47 @@
+local ns = vim.api.nvim_create_namespace('nvim.pack.confirm')
+vim.api.nvim_buf_clear_namespace(0, ns, 0, -1)
+
+local priority = 100
+local hi_range = function(lnum, start_col, end_col, hl, pr)
+  --- @type vim.api.keyset.set_extmark
+  local opts = { end_row = lnum - 1, end_col = end_col, hl_group = hl, priority = pr or priority }
+  vim.api.nvim_buf_set_extmark(0, ns, lnum - 1, start_col, opts)
+end
+
+local header_hl_groups =
+  { Error = 'DiagnosticError', Update = 'DiagnosticWarn', Same = 'DiagnosticHint' }
+local cur_header_hl_group = nil
+
+local lines = vim.api.nvim_buf_get_lines(0, 0, -1, false)
+for i, l in ipairs(lines) do
+  local cur_group = l:match('^# (%S+)')
+  local cur_info = l:match('^Path: +') or l:match('^Source: +') or l:match('^State[^:]*: +')
+  if cur_group ~= nil then
+    --- @cast cur_group string
+    -- Header 1
+    cur_header_hl_group = header_hl_groups[cur_group]
+    hi_range(i, 0, l:len(), cur_header_hl_group)
+  elseif l:find('^## (.+)$') ~= nil then
+    -- Header 2
+    hi_range(i, 0, l:len(), cur_header_hl_group)
+  elseif cur_info ~= nil then
+    -- Plugin info
+    local end_col = l:match('(). +%b()$') or l:len()
+    hi_range(i, cur_info:len(), end_col, 'DiagnosticInfo')
+
+    -- Plugin state after update
+    local col = l:match('() %b()$') or l:len()
+    hi_range(i, col, l:len(), 'DiagnosticHint')
+  elseif l:match('^> ') then
+    -- Added change with possibly "breaking message"
+    hi_range(i, 0, l:len(), 'Added')
+    local col = l:match('│() %S+!:') or l:match('│() %S+%b()!:') or l:len()
+    hi_range(i, col, l:len(), 'DiagnosticWarn', priority + 1)
+  elseif l:match('^< ') then
+    -- Removed change
+    hi_range(i, 0, l:len(), 'Removed')
+  elseif l:match('^• ') then
+    -- Available newer tags
+    hi_range(i, 4, l:len(), 'DiagnosticHint')
+  end
+end