adjust and consolidate duplicated predicate code

data/core/command.lua

@@ -6,15 +6,33 @@ command.map = {}
 local always_true = function() return true end
 
 
-function command.add(predicate, map)
+---Used iternally by command.add, statusview, and contextmenu to generate a
+---function with a condition to evaluate returning the boolean result of this
+---evaluation.
+---
+---If a string predicate is given it is treated as a require import that should
+---return a valid object which is checked against the current active view, the
+---sames applies if a table is given. A function that returns a boolean can be
+---used instead to perform a custom evaluation, setting to nil means always
+---evaluates to true.
+---
+---@param predicate string | table | function
+---@return function
+function command.generate_predicate(predicate)
   predicate = predicate or always_true
   if type(predicate) == "string" then
     predicate = require(predicate)
   end
   if type(predicate) == "table" then
     local class = predicate
-    predicate = function() return core.active_view:is(class) end
+    predicate = function() return core.active_view:extends(class) end
   end
+  return predicate
+end
+
+
+function command.add(predicate, map)
+  predicate = command.generate_predicate(predicate)
   for name, fn in pairs(map) do
     assert(not command.map[name], "command already exists: " .. name)
     command.map[name] = { predicate = predicate, perform = fn }

data/core/contextmenu.lua

@@ -39,14 +39,7 @@ local function get_item_size(item)
 end
 
 function ContextMenu:register(predicate, items)
-  if type(predicate) == "string" then
-    predicate = require(predicate)
-  end
-  if type(predicate) == "table" then
-    local class = predicate
-    predicate = function() return core.active_view:is(class) end
-  end
-
+  predicate = command.generate_predicate(predicate)
   local width, height = 0, 0 --precalculate the size of context menu
   for i, item in ipairs(items) do
     if item ~= DIVIDER then

data/core/statusview.lua

@@ -113,9 +113,6 @@ function StatusView.Item:hide() self.visible = false end
 ---Show the item on the status bar.
 function StatusView.Item:show() self.visible = true end
 
----Function assiged by default when user provides a nil predicate.
-local function predicate_always_true() return true end
-
 ---A condition to evaluate if the item should be displayed. If a string
 ---is given it is treated as a require import that should return a valid object
 ---which is checked against the current active view, the sames applies if a
@@ -123,15 +120,7 @@ local function predicate_always_true() return true end
 ---perform a custom evaluation, setting to nil means always evaluates to true.
 ---@param predicate string | table | StatusView.Item.predicate
 function StatusView.Item:set_predicate(predicate)
-  predicate = predicate or predicate_always_true
-  if type(predicate) == "string" then
-    predicate = require(predicate)
-  end
-  if type(predicate) == "table" then
-    local class = predicate
-    predicate = function() return core.active_view:is(class) end
-  end
-  self.predicate = predicate
+  self.predicate = command.generate_predicate(predicate)
 end
 
 
@@ -655,14 +644,14 @@ local function merge_deprecated_items(destination, items, alignment)
   local position = alignment == StatusView.Item.LEFT and "left" or "right"
 
   local item_start = StatusView.Item(
-    predicate_always_true,
+    nil,
     "deprecated:"..position.."-start",
     alignment
   )
   item_start.get_item = items_start
 
   local item_end = StatusView.Item(
-    predicate_always_true,
+    nil,
     "deprecated:"..position.."-end",
     alignment
   )