feature: add feature to increase/decrease size (#1048)

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