chore: Make arrow an optional dependency

haystack/components/builders/prompt_builder.py

@@ -160,8 +160,13 @@ def __init__(
         self._variables = variables
         self._required_variables = required_variables
         self.required_variables = required_variables or []
+        try:
+            # The Jinja2TimeExtension needs an optional dependency to be installed.
+            # If it's not available we can do without it and use the PromptBuilder as is.
+            self._env = SandboxedEnvironment(extensions=[Jinja2TimeExtension])
+        except ImportError:
+            self._env = SandboxedEnvironment()
 
-        self._env = SandboxedEnvironment(extensions=[Jinja2TimeExtension])
         self.template = self._env.from_string(template)
         if not variables:
             # infer variables from template

haystack/utils/jinja2_extensions.py

@@ -4,10 +4,14 @@
 
 from typing import Any, List, Optional, Union
 
-import arrow
 from jinja2 import Environment, nodes
 from jinja2.ext import Extension
 
+from haystack.lazy_imports import LazyImport
+
+with LazyImport(message='Run "pip install arrow>=1.3.0"') as arrow_import:
+    import arrow
+
 
 class Jinja2TimeExtension(Extension):
     # Syntax for current date
@@ -20,6 +24,7 @@ def __init__(self, environment: Environment):  # pylint: disable=useless-parent-
         :param environment: The Jinja2 environment to initialize the extension with.
             It provides the context where the extension will operate.
         """
+        arrow_import.check()
         super().__init__(environment)
 
     @staticmethod

pyproject.toml

@@ -57,7 +57,6 @@ dependencies = [
   "numpy<2",
   "python-dateutil",
   "haystack-experimental",
-  "arrow>=1.3.0"            # Jinja2TimeExtension
 ]
 
 [tool.hatch.envs.default]
@@ -86,6 +85,7 @@ extra-dependencies = [
   "sentence-transformers>=3.0.0",              # SentenceTransformersTextEmbedder and SentenceTransformersDocumentEmbedder
   "langdetect",                                # TextLanguageRouter and DocumentLanguageClassifier
   "openai-whisper>=20231106",                  # LocalWhisperTranscriber
+  "arrow>=1.3.0",                              # Jinja2TimeExtension
 
   # NamedEntityExtractor
   "spacy>=3.7,<3.8",

test/components/builders/test_prompt_builder.py

@@ -2,12 +2,14 @@
 #
 # SPDX-License-Identifier: Apache-2.0
 from typing import Any, Dict, List, Optional
-from jinja2 import TemplateSyntaxError
-import pytest
-from unittest.mock import patch, MagicMock
+from unittest.mock import patch
+
 import arrow
-from haystack.components.builders.prompt_builder import PromptBuilder
+import pytest
+from jinja2 import TemplateSyntaxError
+
 from haystack import component
+from haystack.components.builders.prompt_builder import PromptBuilder
 from haystack.core.pipeline.pipeline import Pipeline
 from haystack.dataclasses.document import Document
 
@@ -77,6 +79,14 @@ def test_init_with_custom_variables(self):
         assert set(outputs.keys()) == {"prompt"}
         assert outputs["prompt"].type == str
 
+    @patch("haystack.components.builders.prompt_builder.Jinja2TimeExtension")
+    def test_init_with_missing_extension_dependency(self, extension_mock):
+        extension_mock.side_effect = ImportError
+        builder = PromptBuilder(template="This is a {{ variable }}")
+        assert builder._env.extensions == {}
+        res = builder.run(variable="test")
+        assert res == {"prompt": "This is a test"}
+
     def test_to_dict(self):
         builder = PromptBuilder(
             template="This is a {{ variable }}", variables=["var1", "var2"], required_variables=["var1", "var3"]

test/utils/test_jinja2_extensions.py

@@ -2,6 +2,8 @@
 #
 # SPDX-License-Identifier: Apache-2.0
 
+from unittest.mock import patch
+
 import pytest
 from jinja2 import Environment
 import arrow
@@ -17,6 +19,12 @@ def jinja_env(self) -> Environment:
     def jinja_extension(self, jinja_env: Environment) -> Jinja2TimeExtension:
         return Jinja2TimeExtension(jinja_env)
 
+    @patch("haystack.utils.jinja2_extensions.arrow_import")
+    def test_init_fails_without_arrow(self, arrow_import_mock) -> None:
+        arrow_import_mock.check.side_effect = ImportError
+        with pytest.raises(ImportError):
+            Jinja2TimeExtension(Environment())
+
     def test_valid_datetime(self, jinja_extension: Jinja2TimeExtension) -> None:
         result = jinja_extension._get_datetime(
             "UTC", operator="+", offset="hours=2", datetime_format="%Y-%m-%d %H:%M:%S"