Git branch component: Add option to limit the length

Added a new function that truncates git branch name if the max_length
option is set. It also attempts to strip the last incomplete word after
the last word separator (i.e. "-", "_")

README.md

@@ -490,6 +490,21 @@ These are options that are available on specific components.
 For example, you have option on `diagnostics` component to
 specify what your diagnostic sources will be.
 
+#### branch component options
+
+```lua
+sections = {
+  lualine_a = {
+    {
+      'branch',
+      max_length = 0, -- Maximum displayed characters of the branch name.
+                      -- Takes effect, if the value is larger than 0.
+                      -- Recommended setting: 30.
+    }
+  }
+}
+```
+
 #### buffers component options
 
 ```lua
@@ -608,6 +623,20 @@ sections = {
 }
 ```
 
+#### encoding component options
+
+```lua
+sections = {
+  lualine_a = {
+    {
+      'encoding',
+      -- Show '[BOM]' when the file has a byte-order mark
+        show_bomb = false,
+    }
+  }
+}
+```
+
 #### fileformat component options
 
 ```lua
@@ -670,20 +699,6 @@ sections = {
 }
 ```
 
-#### encoding component options
-
-```lua
-sections = {
-  lualine_a = {
-    {
-      'encoding',
-      -- Show '[BOM]' when the file has a byte-order mark
-        show_bomb = false,
-    }
-  }
-}
-```
-
 #### searchcount component options
 
 ```lua

lua/lualine/components/branch/git_branch.lua

@@ -15,6 +15,21 @@ local sep = package.config:sub(1, 1)
 -- Windows doesn't like file watch for some reason.
 local file_changed = sep ~= '\\' and vim.loop.new_fs_event() or vim.loop.new_fs_poll()
 local git_dir_cache = {} -- Stores git paths that we already know of
+local options = {max_length = 0}
+
+---truncates git branch name based on options.max_length.
+---also attempts to strip the last incomplete word after the last word separator (i.e. "-", "_")
+local function truncate_git_branch()
+  current_git_branch = current_git_branch:sub(1, options.max_length)
+  if not current_git_branch:find("[-_]") then
+    current_git_branch = current_git_branch .. '…'
+    return
+  end
+
+  -- make the truncated output nicer by cutting off the last incomplete word
+  local last_word_separator_idx = current_git_branch:len() - current_git_branch:reverse():find("[-_]")
+  current_git_branch = current_git_branch:sub(1, last_word_separator_idx) .. '…'
+end
 
 ---sets git_branch variable to branch name or commit hash if not on branch
 ---@param head_file string full path of .git/HEAD file
@@ -26,6 +41,9 @@ local function get_git_head(head_file)
     local branch = HEAD:match('ref: refs/heads/(.+)$')
     if branch then
       current_git_branch = branch
+      if options.max_length ~= 0 and current_git_branch:len() > options.max_length then
+        truncate_git_branch()
+      end
     else
       current_git_branch = HEAD:sub(1, 6)
     end
@@ -135,12 +153,17 @@ function M.find_git_dir(dir_path)
 end
 
 ---initializes git_branch module
-function M.init()
+function M.init(opts)
+  if opts.max_length then
+    options.max_length = opts.max_length
+  end
+
   -- run watch head on load so branch is present when component is loaded
   M.find_git_dir()
   -- update branch state of BufEnter as different Buffer may be on different repos
   utils.define_autocmd('BufEnter', "lua require'lualine.components.branch.git_branch'.find_git_dir()")
 end
+
 function M.get_branch(bufnr)
   if vim.g.actual_curbuf ~= nil and active_bufnr ~= vim.g.actual_curbuf then
     -- Workaround for https://github.com/nvim-lualine/lualine.nvim/issues/286

lua/lualine/components/branch/init.lua

@@ -13,7 +13,7 @@ M.init = function(self, options)
   if not self.options.icon then
     self.options.icon = '' -- e0a0
   end
-  modules.git_branch.init()
+  modules.git_branch.init(options)
 end
 
 M.update_status = function(_, is_focused)

tests/spec/component_spec.lua

@@ -871,4 +871,31 @@ describe('Branch component', function()
     local rev = git('rev-parse --short=6 HEAD'):sub(1, 6)
     assert_component('branch', opts, rev)
   end)
+
+  it('works with max_length option', function()
+    local opts = build_component_opts {
+      component_separators = { left = '', right = '' },
+      icons_enabled = false,
+      padding = 0,
+      max_length = 10,
+    }
+    local branch_comp = helpers.init_component('branch', opts)
+
+    local test = {
+      noseparator = "noseparato…",
+      separated_name = "separated…",
+      separatorafter_threshold = "separatora…",
+      short_name = "short_name",
+    }
+    -- hack to add a hyphenated key
+    test["other-sep-character"] = "other-sep…"
+
+    for input, expected in pairs(test) do
+      git('checkout -b ' .. input)
+      vim.cmd('e k')
+      vim.cmd('bd')
+      vim.cmd('e ' .. file)
+      assert_comp_ins(branch_comp, expected)
+    end
+  end)
 end)