fix: Add error handling for provided runtime layer building

samcli/lib/build/app_builder.py

@@ -51,6 +51,7 @@
     BuildError,
     BuildInsideContainerError,
     UnsupportedBuilderLibraryVersionError,
+    MissingCompatibleRuntimesException,
 )
 from samcli.lib.build.workflow_config import (
     get_workflow_config,
@@ -62,6 +63,8 @@
 
 LOG = logging.getLogger(__name__)
 
+FIRST_COMPATIBLE_RUNTIME_INDEX = 0
+
 
 class ApplicationBuildResult(NamedTuple):
     """
@@ -546,7 +549,12 @@ def _build_layer(
                     )
                     # Only set to this value if specified workflow is makefile
                     # which will result in config language as provided
-                    build_runtime = compatible_runtimes[0]
+                    if not compatible_runtimes:
+                        raise MissingCompatibleRuntimesException(
+                            "The 'CompatibleRuntimes' field in the Layer Version configuration is "
+                            "missing and is required for building provided runtimes using a container."
+                        )
+                    build_runtime = compatible_runtimes[FIRST_COMPATIBLE_RUNTIME_INDEX]
                 global_image = self._build_images.get(None)
                 image = self._build_images.get(layer_name, global_image)
                 # pass to container only when specified workflow is supported to overwrite runtime to get image

samcli/lib/build/exceptions.py

@@ -42,6 +42,11 @@ def __init__(self, msg: str) -> None:
         BuildError.__init__(self, "MissingBuildMethodException", msg)
 
 
+class MissingCompatibleRuntimesException(BuildError):
+    def __init__(self, msg: str) -> None:
+        BuildError.__init__(self, "MissingCompatibleRuntimesException", msg)
+
+
 class InvalidBuildGraphException(Exception):
     def __init__(self, msg: str) -> None:
         Exception.__init__(self, msg)

tests/unit/lib/build_module/test_app_builder.py

@@ -11,6 +11,7 @@
 
 from parameterized import parameterized
 
+from samcli.lib.build.exceptions import MissingCompatibleRuntimesException
 from samcli.lib.build.workflow_config import UnsupportedRuntimeException
 from samcli.lib.providers.provider import ResourcesToBuildCollector, Function, FunctionBuildInfo
 from samcli.lib.build.app_builder import (
@@ -571,6 +572,30 @@ def test_must_build_layer_in_process(self, get_layer_subfolder_mock, osutils_moc
             is_building_layer=True,
         )
 
+    @parameterized.expand([([],), (None,)])
+    @patch("samcli.lib.build.app_builder.get_workflow_config")
+    @patch("samcli.lib.build.app_builder.get_layer_subfolder")
+    def test_must_handle_layer_build_compatible_runtimes_missing(
+        self, compatible_runtimes, get_layer_subfolder_mock, get_workflow_config_mock
+    ):
+        get_layer_subfolder_mock.return_value = "layer"
+        config_mock = Mock()
+        config_mock.manifest_name = "manifest_name"
+        config_mock.language = "provided"
+
+        get_workflow_config_mock.return_value = config_mock
+
+        self.builder._container_manager = Mock()
+
+        with self.assertRaises(MissingCompatibleRuntimesException) as ex:
+            self.builder._build_layer("layer_name", "code_uri", "provided", compatible_runtimes, ARM64, "full_path")
+
+        self.assertEqual(
+            str(ex.exception),
+            "The 'CompatibleRuntimes' field in the Layer Version configuration is "
+            "missing and is required for building provided runtimes using a container.",
+        )
+
     @patch("samcli.lib.build.app_builder.get_workflow_config")
     @patch("samcli.lib.build.app_builder.osutils")
     @patch("samcli.lib.build.app_builder.get_layer_subfolder")