feature: add feature to increase/decrease size

README.md

@@ -90,7 +90,12 @@ let g:nvim_tree_icons = {
 nnoremap <C-n> :NvimTreeToggle<CR>
 nnoremap <leader>r :NvimTreeRefresh<CR>
 nnoremap <leader>n :NvimTreeFindFile<CR>
-" NvimTreeOpen, NvimTreeClose, NvimTreeFocus, NvimTreeFindFileToggle, and NvimTreeResize are also available if you need them
+" More available functions:
+" NvimTreeOpen
+" NvimTreeClose
+" NvimTreeFocus
+" NvimTreeFindFileToggle
+" NvimTreeResize
 
 set termguicolors " this variable must be enabled for colors to be applied properly
 

doc/nvim-tree-lua.txt

@@ -61,7 +61,11 @@ Print clipboard content for both cut and copy
 |:NvimTreeResize|			          *:NvimTreeResize*
 
 Resize the NvimTree window to the given size. Example: `:NvimTreeResize 50`
-resizes the window to the width of 50.
+resizes the window to the width of 50. If the size starts with "+" or "-" it
+adds or removes the given value to the current window width.
+Example `:NvimTreeResize -20` removes the value 20 from the current width. And
+`:NvimTreeResize +20` adds the value 20 to the current width.
+
 
 ==============================================================================
 SETUP                                *nvim-tree.setup*

lua/nvim-tree.lua

@@ -276,7 +276,7 @@ local function setup_vim_commands()
     command! NvimTreeClipboard lua require'nvim-tree.actions.copy-paste'.print_clipboard()
     command! NvimTreeFindFile lua require'nvim-tree'.find_file(true)
     command! NvimTreeFindFileToggle lua require'nvim-tree'.toggle(true)
-    command! -nargs=1 NvimTreeResize lua require'nvim-tree'.resize(<args>)
+    command! -nargs=1 NvimTreeResize lua require'nvim-tree'.resize("<args>")
   ]]
 end
 

lua/nvim-tree/view.lua

@@ -175,6 +175,24 @@ function M.open(options)
 end
 
 function M.resize(size)
+  if type(size) == "string" then
+    size = vim.trim(size)
+    local first_char = size:sub(1, 1)
+    size = tonumber(size)
+
+    if first_char == "+" or first_char == "-" then
+      size = M.View.width + size
+    end
+  end
+
+  if type(size) ~= "number" then
+    return
+  end
+
+  if size <= 0 then
+    return
+  end
+
   if size then
     M.View.width = size
     M.View.height = size