add folding based on fold expression

README.md

@@ -120,6 +120,10 @@ Any options that are not specified when calling `setup` will take on their defau
   -- Current options: "iron" for iron.nvim, "toggleterm" for toggleterm.nvim,
   -- or "auto" which checks which of the above are installed
   repl_provider = "auto",
+  -- If `true`, folding will be based on expression for buffers with a valid
+  -- cell marker and cells will be folded on entering the buffer
+  -- * NOTE: This will replace any previously set foldmethod for those buffers
+  cell_folding = true
 }
 ```
 

doc/NotebookNavigator.txt

@@ -120,6 +120,10 @@ Default values:
     -- Current options: "iron" for iron.nvim, "toggleterm" for toggleterm.nvim,
     -- or "auto" which checks which of the above are installed
     repl_provider = "auto",
+    -- If `true`, folding will be based on expression for buffers with a valid
+    -- cell marker and cells will be folded on entering the buffer
+    -- * NOTE: This will replace any previously set foldmethod for those buffers
+    cell_folding = true
   }
 <
 
@@ -138,4 +142,4 @@ Usage~
    any config parameter which you not pass will take on its default value.
 
 
- vim:tw=78:ts=8:noet:ft=help:norl:
+ vim:tw=78:ts=8:noet:ft=help:norl:

lua/notebook-navigator/init.lua

@@ -209,6 +209,10 @@ M.config = {
   -- Current options: "iron" for iron.nvim, "toggleterm" for toggleterm.nvim,
   -- or "auto" which checks which of the above are installed
   repl_provider = "auto",
+  -- If `true`, folding will be based on expression for buffers with a valid
+  -- cell marker and cells will be folded on entering the buffer
+  -- * NOTE: This will replace any previously set foldmethod for those buffers
+  cell_folding = true
 }
 --minidoc_afterlines_end
 
@@ -258,6 +262,24 @@ M.setup = function(config)
   if (M.config.activate_hydra_keys ~= nil) and got_hydra then
     activate_hydra(M.config)
   end
+
+  local cell_group = vim.api.nvim_create_augroup("Cells", {clear=true})
+  if M.config.cell_folding then
+    vim.api.nvim_create_autocmd("BufEnter", {
+      pattern = {"*"},
+      group = cell_group,
+      callback = function(ev)
+        local ft = vim.api.nvim_get_option_value("filetype", {buf = ev.buf})
+        if M.config.cell_markers[ft] then
+          local marker = M.config.cell_markers[ft]
+          local vim_marker = string.gsub(marker, " ", "\\ ")
+          vim.cmd[[setlocal foldmethod=expr]]
+          local expr = "setlocal foldexpr=(getline(v:lnum)=~'^"..vim_marker.."')==0"
+          vim.cmd(expr)
+        end
+      end
+    })
+  end
 end
 
 return M