feat: Add type option to hint what type of component is the string

String values for component are way too overloaded . This means lualine
has to make lots of checks to understand how to load a string value
as a component . With type option users can specify exactly what they
want.

README.md

@@ -284,7 +284,14 @@ sections = {
       -- color = {fg = '#rrggbb', bg= '#rrggbb', gui='style'}
       -- or highlight group
       -- color = "WarningMsg"
-      color = nil
+      color = nil,
+      -- Type option specifies what type a component is.
+      -- When type is omitted lualine will guess it.
+      -- Available types [format: type_name(example)]
+      -- mod(branch/filename), stl(%f/%m), var(g:coc_status/bo:modifiable),
+      -- luae(lua expressions), vimf(viml function name)
+      -- luae is short for lua-expression and vimf is short fror vim-function
+      type = nil,
     }
   }
 }

doc/lualine.txt

@@ -220,7 +220,15 @@ Local options~
         -- color = {fg = '#rrggbb', bg= '#rrggbb', gui='style'}
         -- or highlight group
         -- color = "WarningMsg"
-        color = nil
+        color = nil,
+        -- Type option specifies what type a component is.
+        -- When type is omitted lualine will guess it.
+        -- Available types [format: type_name(example)]
+        -- mod(branch/filename), stl(%f/%m), var(g:coc_status/bo:modifiable),
+        -- luae(lua expressions), vimf(viml function name)
+        -- luae is short for lua-expression and vimf is short fror vim-function
+        -- vim_function(viml function name)
+        type = nil,
       }
     }
   }

lua/lualine/components/special/eval_func_component.lua

@@ -2,12 +2,22 @@ local EvalFuncComponent = require('lualine.component'):new()
 
 EvalFuncComponent.update_status = function(self)
   local component = self.options[1]
-  local ok, status = pcall(EvalFuncComponent.eval_lua, component)
-  if not ok then status = EvalFuncComponent.vim_function(component) end
+  local ok, status
+  if self.options.type == nil then
+    ok, status = pcall(EvalFuncComponent.lua_eval, component)
+    if not ok then status = EvalFuncComponent.vim_function(component) end
+  else
+    if self.options.type == 'luae' then
+      ok, status = pcall(EvalFuncComponent.lua_eval, component)
+      if not ok then status = nil end
+    elseif self.options.type == 'vimf' then
+      status = EvalFuncComponent.vim_function(component)
+    end
+  end
   return status
 end
 
-EvalFuncComponent.eval_lua = function(code)
+EvalFuncComponent.lua_eval = function(code)
   local result = loadstring('return ' .. code)()
   assert(result, 'String expected got nil')
   return tostring(result)
@@ -18,11 +28,7 @@ EvalFuncComponent.vim_function = function(name)
   local ok, return_val = pcall(vim.fn[name])
   if not ok then return '' end -- function call failed
   ok, return_val = pcall(tostring, return_val)
-  if ok then
-    return return_val
-  else
-    return ''
-  end
+  return ok and return_val or ''
 end
 
 return EvalFuncComponent

lua/lualine/components/special/vim_var_component.lua

@@ -8,12 +8,12 @@ VarComponent.update_status = function(self)
   -- filters var portion from g:var
   local var_name = component:sub(#scope + 2, #component)
   -- Displays nothing when veriable aren't present
+  if not (scope and var_name) then return '' end
   local return_val = vim[scope][var_name]
   if return_val == nil then return '' end
   local ok
   ok, return_val = pcall(tostring, return_val)
-  if ok then return return_val end
-  return ''
+  return ok and return_val or ''
 end
 
 return VarComponent

lua/lualine/utils/loader.lua

@@ -60,31 +60,64 @@ local function lualine_load(patern, use_cache)
   return retval
 end
 
-local function component_loader(component)
-  if type(component[1]) == 'function' then
+local component_types = {
+  luaf = function(component)
     return
       lualine_load({'lua', 'lualine', 'components', 'special', 'function_component'}, true):new(component)
-  end
-  if type(component[1]) == 'string' then
-    -- load the component
+  end,
+  mod = function(component)
     local ok, loaded_component = pcall(lualine_load,
-                          {'lua', 'lualine', 'components', component[1]}, true)
+                            {'lua', 'lualine', 'components', component[1]}, true)
     if ok then
       component.component_name = component[1]
       loaded_component = loaded_component:new(component)
-    elseif string.char(component[1]:byte(1)) == '%' then
-      local stl_expr = component[1] -- Vim's %p %l statusline elements
-      component[1] = function() return stl_expr end
-      loaded_component =
-        lualine_load({'lua', 'lualine', 'components', 'special', 'function_component'}, true):new(component)
-    elseif component[1]:find('[gvtwb]?o?:') == 1 then
-      loaded_component =
-        lualine_load({'lua', 'lualine', 'components', 'special', 'vim_var_component'}, true):new(component)
-    else
-      loaded_component =
-        lualine_load({'lua', 'lualine', 'components', 'special', 'eval_func_component'}, true):new(component)
+      return loaded_component
+    end
+  end,
+  stl = function(component)
+    local stl_expr = component[1] -- Vim's %p %l statusline elements
+    component[1] = function() return stl_expr end
+    return
+      lualine_load({'lua', 'lualine', 'components', 'special', 'function_component'}, true):new(component)
+  end,
+  var = function(component)
+    return
+        lualine_load({'lua', 'lualine', 'components', 'special', 'vim_var_component'}, true):new(component)
+  end,
+  ['_'] = function(component)
+    return
+        lualine_load({'lua', 'lualine', 'components', 'special', 'eval_func_component'}, true):new(component)
+  end
+}
+
+local function component_loader(component)
+  if type(component[1]) == 'function' then
+    return component_types.luaf(component)
+  end
+  if type(component[1]) == 'string' then
+    -- load the component
+    if component.type ~= nil then
+      if component_types[component.type] and component.type ~= 'luaf' then
+        return component_types[component.type](component)
+      elseif component.type == 'vimf' or component.type == 'luae' then
+        return component_types['_'](component)
+      else
+        notice.add_notice(string.format([[
+### component.type
+
+component type '%s' isn't recognised. Check if spelling is correct.]], component.type))
+      end
+    end
+    local loaded_component = component_types.mod(component)
+    if loaded_component then
+      return loaded_component
+    elseif string.char(component[1]:byte(1)) == '%' then
+      return component_types.stl(component)
+    elseif component[1]:find('[gvtwb]?o?:') == 1 then
+      return component_types.var(component)
+    else
+      return component_types['_'](component)
     end
-    return loaded_component
   end
 end