refactor(statusline)!: remove stop_when in favor of the more versatil…

…e pick_child.

add utility function `pick_child_on_condition` to cover general usecase of
selecting among multiple buffer-specific statuslines.

lua/heirline/statusline.lua

@@ -85,7 +85,6 @@ function StatusLine:nonlocal(attr)
     return getmetatable(self).__index(self, attr)
 end
 
-
 function StatusLine:local_(attr)
     local orig_mt = getmetatable(self)
     setmetatable(self, {})
@@ -146,9 +145,6 @@ function StatusLine:eval()
         local child = self[i]
         local out = child:eval()
         table.insert(stl, out)
-        if self.stop_when and self:stop_when(out, child) then
-            break
-        end
     end
 
     self.stl = table.concat(stl, "")

lua/heirline/utils.lua

@@ -201,6 +201,7 @@ function M.expand_or_contract_flexible_components(statusline, out)
                     saved_chars = saved_chars + (prev_len - cur_len)
                 end
             end
+
             if stl_len - saved_chars <= winw then
                 break
             end
@@ -232,4 +233,14 @@ function M.expand_or_contract_flexible_components(statusline, out)
     end
 end
 
+function M.pick_child_on_condition(self)
+    self.pick_child = {}
+    for i, child in ipairs(self) do
+        if not child.condition or child:condition() then
+            table.insert(self.pick_child, i)
+            break
+        end
+    end
+end
+
 return M