[esp32] Add framework migration warning for upcoming ESP-IDF default change (#10030)

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

esphome/components/esp32/__init__.py

@@ -680,6 +680,64 @@ ESP_IDF_FRAMEWORK_SCHEMA = cv.All(
 )
 
 
+class _FrameworkMigrationWarning:
+    shown = False
+
+
+def _show_framework_migration_message(name: str, variant: str) -> None:
+    """Show a friendly message about framework migration when defaulting to Arduino."""
+    if _FrameworkMigrationWarning.shown:
+        return
+    _FrameworkMigrationWarning.shown = True
+
+    from esphome.log import AnsiFore, color
+
+    message = (
+        color(
+            AnsiFore.BOLD_CYAN,
+            f"💡 IMPORTANT: {name} doesn't have a framework specified!",
+        )
+        + "\n\n"
+        + f"Currently, {variant} defaults to the Arduino framework.\n"
+        + color(AnsiFore.YELLOW, "This will change to ESP-IDF in ESPHome 2026.1.0.\n")
+        + "\n"
+        + "Note: Newer ESP32 variants (C6, H2, P4, etc.) already use ESP-IDF by default.\n"
+        + "\n"
+        + "Why change? ESP-IDF offers:\n"
+        + color(AnsiFore.GREEN, "  ✨ Up to 40% smaller binaries\n")
+        + color(AnsiFore.GREEN, "  🚀 Better performance and optimization\n")
+        + color(AnsiFore.GREEN, "  📦 Custom-built firmware for your exact needs\n")
+        + color(
+            AnsiFore.GREEN,
+            "  🔧 Active development and testing by ESPHome developers\n",
+        )
+        + "\n"
+        + "Trade-offs:\n"
+        + color(AnsiFore.YELLOW, "  ⏱️  Compile times are ~25% longer\n")
+        + color(AnsiFore.YELLOW, "  🔄 Some components need migration\n")
+        + "\n"
+        + "What should I do?\n"
+        + color(AnsiFore.CYAN, "  Option 1")
+        + ": Migrate to ESP-IDF (recommended)\n"
+        + "    Add this to your YAML under 'esp32:':\n"
+        + color(AnsiFore.WHITE, "      framework:\n")
+        + color(AnsiFore.WHITE, "        type: esp-idf\n")
+        + "\n"
+        + color(AnsiFore.CYAN, "  Option 2")
+        + ": Keep using Arduino (still supported)\n"
+        + "    Add this to your YAML under 'esp32:':\n"
+        + color(AnsiFore.WHITE, "      framework:\n")
+        + color(AnsiFore.WHITE, "        type: arduino\n")
+        + "\n"
+        + "Need help? Check out the migration guide:\n"
+        + color(
+            AnsiFore.BLUE,
+            "https://esphome.io/guides/esp32_arduino_to_idf.html",
+        )
+    )
+    _LOGGER.warning(message)
+
+
 def _set_default_framework(config):
     if CONF_FRAMEWORK not in config:
         config = config.copy()
@@ -688,6 +746,10 @@ def _set_default_framework(config):
         if variant in ARDUINO_ALLOWED_VARIANTS:
             config[CONF_FRAMEWORK] = ARDUINO_FRAMEWORK_SCHEMA({})
             config[CONF_FRAMEWORK][CONF_TYPE] = FRAMEWORK_ARDUINO
+            # Show the migration message
+            _show_framework_migration_message(
+                config.get(CONF_NAME, "This device"), variant
+            )
         else:
             config[CONF_FRAMEWORK] = ESP_IDF_FRAMEWORK_SCHEMA({})
             config[CONF_FRAMEWORK][CONF_TYPE] = FRAMEWORK_ESP_IDF

esphome/util.py

@@ -345,5 +345,11 @@ def get_esp32_arduino_flash_error_help() -> str | None:
         + "2. Clean build files and compile again\n"
         + "\n"
         + "Note: ESP-IDF uses less flash space and provides better performance.\n"
-        + "Some Arduino-specific libraries may need alternatives.\n\n"
+        + "Some Arduino-specific libraries may need alternatives.\n"
+        + "\n"
+        + "For detailed migration instructions, see:\n"
+        + color(
+            AnsiFore.BLUE,
+            "https://esphome.io/guides/esp32_arduino_to_idf.html\n\n",
+        )
     )