chore: import upstream snapshot with attribution

haystack/lazy_imports.py

@@ -0,0 +1,53 @@
+# SPDX-FileCopyrightText: 2022-present deepset GmbH <info@deepset.ai>
+#
+# SPDX-License-Identifier: Apache-2.0
+
+from types import TracebackType
+
+from lazy_imports.try_import import _DeferredImportExceptionContextManager
+
+DEFAULT_IMPORT_ERROR_MSG = "Try 'pip install {}'"
+
+
+class LazyImport(_DeferredImportExceptionContextManager):
+    """
+    A context manager that provides controlled handling of import errors.
+
+    It adds the possibility to customize the error messages.
+
+    NOTE: Despite its name, this class does not delay the actual import operation.
+    For installed modules: executes the import immediately.
+    For uninstalled modules: captures the error and defers it until check() is called.
+    """
+
+    def __init__(self, message: str = DEFAULT_IMPORT_ERROR_MSG) -> None:
+        super().__init__()
+        self.import_error_msg = message
+
+    def __exit__(
+        self, exc_type: type[Exception] | None, exc_value: Exception | None, traceback: TracebackType | None
+    ) -> bool | None:
+        """
+        Exit the context manager.
+
+        Args:
+            exc_type:
+                Raised exception type. :obj:`None` if nothing is raised.
+            exc_value:
+                Raised exception object. :obj:`None` if nothing is raised.
+            traceback:
+                Associated traceback. :obj:`None` if nothing is raised.
+
+        Returns:
+            :obj:`None` if nothing is deferred, otherwise :obj:`True`.
+            :obj:`True` will suppress any exceptions avoiding them from propagating.
+
+        """
+        if isinstance(exc_value, ImportError):
+            message = (
+                f"Haystack failed to import the optional dependency '{exc_value.name}'. "
+                f"{self.import_error_msg.format(exc_value.name)}. Original error: {exc_value}"
+            )
+            self._deferred = (exc_value, message)
+            return True
+        return None