[core] Remove deprecated custom_components folder loading (#16679)

esphome/config.py

@@ -1005,7 +1005,6 @@ def validate_config(
     CORE.skip_external_update = skip_external_update
 
     loader.clear_component_meta_finders()
-    loader.install_custom_components_meta_finder()
 
     # 0. Load packages
     if CONF_PACKAGES in config:

esphome/loader.py

@@ -12,7 +12,6 @@ from types import ModuleType
 from typing import TYPE_CHECKING, Any
 
 from esphome.const import SOURCE_FILE_EXTENSIONS
-from esphome.core import CORE
 from esphome.types import ConfigType
 
 if TYPE_CHECKING:
@@ -206,18 +205,6 @@ def install_meta_finder(
     sys.meta_path.insert(0, ComponentMetaFinder(components_path, allowed_components))
 
 
-def install_custom_components_meta_finder():
-    # Remove before 2026.6.0
-    custom_components_dir = (Path(CORE.config_dir) / "custom_components").resolve()
-    if custom_components_dir.is_dir() and any(custom_components_dir.iterdir()):
-        _LOGGER.warning(
-            "The 'custom_components' folder is deprecated and will be removed in 2026.6.0. "
-            "Please use 'external_components' instead. "
-            "See https://esphome.io/components/external_components.html for more information."
-        )
-    install_meta_finder(custom_components_dir)
-
-
 def _lookup_module(domain: str, exception: bool) -> ComponentManifest | None:
     if domain in _COMPONENT_CACHE:
         return _COMPONENT_CACHE[domain]

esphome/writer.py

@@ -200,8 +200,8 @@ ESPHome automatically populates the build directory, and any
 changes to this directory will be removed the next time esphome is
 run.
 
-For modifying esphome's core files, please use a development esphome install,
+For modifying esphome's core files, please use a development esphome install
-the custom_components folder or the external_components feature.
+or the external_components feature.
 """