fix(build): ensure the main component exists when MINIMAL_BUILD is enabled

The minimal build property is simply a shorthand for `set(COMPONENTS
main)`. The issue is that there is currently no check to verify whether
the `main` component actually exists or is known to the build system.
If the `main` component is not present, print an error message along
with suggestions on how to fix this inconsistency.

Closes https://github.com/espressif/esp-idf/issues/18219

Signed-off-by: Frantisek Hrbata <frantisek.hrbata@espressif.com>

tools/test_build_system/test_components.py

@@ -1,4 +1,4 @@
-# SPDX-FileCopyrightText: 2023-2025 Espressif Systems (Shanghai) CO LTD
+# SPDX-FileCopyrightText: 2023-2026 Espressif Systems (Shanghai) CO LTD
 # SPDX-License-Identifier: Apache-2.0
 import json
 import logging
@@ -579,3 +579,25 @@ def test_component_validation_with_common_platform_example(idf_py: IdfPyFunc, te
     assert re_source.search(ret.stderr) is None, (
         f'Unexpected source file ownership warning for common path: {ret.stderr}'
     )
+
+
+@pytest.mark.buildv2_skip('Build system v2 does not support MINIMAL_BUILD')
+def test_minimal_build_without_main_component(idf_py: IdfPyFunc, test_app_copy: Path) -> None:
+    logging.info('Verify that the build fails when using `MINIMAL_BUILD` without main component')
+
+    # Rename main to no_main
+    shutil.move(test_app_copy / 'main', test_app_copy / 'no_main')
+
+    # Set minimal build property
+    replace_in_file(
+        (test_app_copy / 'CMakeLists.txt'),
+        '# placeholder_after_include_project_cmake',
+        'idf_build_set_property(MINIMAL_BUILD ON)',
+    )
+
+    # Reconfigure should fail
+    ret = idf_py('reconfigure', check=False)
+
+    assert 'MINIMAL_BUILD is enabled but component main was not found.' in ret.stderr, (
+        'Reconfiguration should fail with missing main component and MINIMAL_BUILD ON'
+    )