feat: support collapse a single folder under cursor

doc/nvim-tree-lua.txt

@@ -1770,6 +1770,9 @@ tree.collapse_all({keep_buffers})          *nvim-tree-api.tree.collapse_all()*
     Parameters: ~
       • {keep_buffers} (boolean) do not collapse nodes with open buffers.
 
+tree.collapse()          *nvim-tree-api.tree.collapse()*
+    Collapse the folder under cursor.
+
 tree.expand_all()                            *nvim-tree-api.tree.expand_all()*
     Recursively expand all nodes in the tree.
     Folder: only the nodes underneath that folder.

lua/nvim-tree/actions/tree/modifiers/collapse.lua

@@ -0,0 +1,38 @@
+local renderer = require "nvim-tree.renderer"
+local utils = require "nvim-tree.utils"
+local core = require "nvim-tree.core"
+local lib = require "nvim-tree.lib"
+local Iterator = require "nvim-tree.iterators.node-iterator"
+
+local M = {}
+
+function M.fn()
+  local node = lib.get_node_at_cursor()
+  local explorer = core.get_explorer()
+
+  if explorer == nil then
+    return
+  end
+  if node == nil then
+    return
+  end
+  if node.nodes == nil then
+    return
+  end
+
+  Iterator.builder(node.nodes)
+    :hidden()
+    :applier(function(n)
+      n.open = false
+    end)
+    :recursor(function(n)
+      return n.group_next and { n.group_next } or n.nodes
+    end)
+    :iterate()
+
+  node.open = false
+  renderer.draw()
+  utils.focus_node_or_parent(node)
+end
+
+return M

lua/nvim-tree/actions/tree/modifiers/init.lua

@@ -1,6 +1,7 @@
 local M = {}
 
 M.collapse_all = require "nvim-tree.actions.tree.modifiers.collapse-all"
+M.collapse = require "nvim-tree.actions.tree.modifiers.collapse"
 M.expand_all = require "nvim-tree.actions.tree.modifiers.expand-all"
 M.toggles = require "nvim-tree.actions.tree.modifiers.toggles"
 

lua/nvim-tree/api.lua

@@ -161,6 +161,7 @@ Api.tree.get_nodes = wrap(lib.get_nodes)
 Api.tree.find_file = wrap(actions.tree.find_file.fn)
 Api.tree.search_node = wrap(actions.finders.search_node.fn)
 Api.tree.collapse_all = wrap(actions.tree.modifiers.collapse_all.fn)
+Api.tree.collapse = wrap(actions.tree.modifiers.collapse.fn)
 Api.tree.expand_all = wrap_node(actions.tree.modifiers.expand_all.fn)
 Api.tree.toggle_enable_filters = wrap(actions.tree.modifiers.toggles.enable)
 Api.tree.toggle_gitignore_filter = wrap(actions.tree.modifiers.toggles.git_ignored)