SNOW-902097 adding default_connection_name and default value to ConfigOption (#1718)

Author: sfc-gh-mkeller

DESCRIPTION.md

@@ -11,6 +11,8 @@ Source code is also available at: https://github.com/snowflakedb/snowflake-conne
 - v3.1.2(TBD)
 
   - Made the ``parser`` -> ``manager`` renaming more consistent in ``snowflake.connector.config_manager`` module.
+  - Added support for default values for ConfigOptions
+  - Added default_connection_name to config.toml file
 
 - v3.1.1(August 28,2023)
 

src/snowflake/connector/config_manager.py

@@ -62,6 +62,9 @@ class ConfigOption:
           supplied, we'll construct this. False disables reading from
           environmental variables, None uses the auto generated variable name
           and explicitly provided string overwrites the default one.
+        default: The value we should resolve to when the option is not defined
+          in any of the sources. When it's None we treat that as there's no
+          default value.
         _root_manager: Reference to the root manager. Used to efficiently
           refer to cached config file. Is supplied by the parent
           ConfigManager.
@@ -78,6 +81,7 @@ def __init__(
         parse_str: Callable[[str], _T] | None = None,
         choices: Iterable[Any] | None = None,
         env_name: str | None | Literal[False] = None,
+        default: Any | None = None,
         _root_manager: ConfigManager | None = None,
         _nest_path: list[str] | None,
     ) -> None:
@@ -91,6 +95,8 @@ def __init__(
               Providing a string will use that environment variable, False disables
               reading value from environmental variables and the default None generates
               an environmental variable name for it using the _nest_path and name.
+            default: Default value for the option. Used in case the value is
+              is not defined in any of the sources.
             _root_manager: Reference to the root manager. Should be supplied by
               the parent ConfigManager.
             _nest_path: The names of the ConfigManagers that this option is
@@ -106,6 +112,7 @@ def __init__(
         self._nest_path = _nest_path + [name]
         self._root_manager: ConfigManager = _root_manager
         self.env_name = env_name
+        self.default = default
 
     def value(self) -> Any:
         """Retrieve a value of option.
@@ -115,8 +122,15 @@ def value(self) -> Any:
         source = "environment variable"
         loaded_env, value = self._get_env()
         if not loaded_env:
-            source = "configuration file"
-            value = self._get_config()
+            try:
+                value = self._get_config()
+                source = "configuration file"
+            except MissingConfigOptionError:
+                if self.default:
+                    source = "default_value"
+                    value = self.default
+                else:
+                    raise
         if self.choices and value not in self.choices:
             raise ConfigSourceError(
                 f"The value of {self.option_name} read from "
@@ -436,6 +450,10 @@ def __getitem__(self, name: str) -> ConfigOption | ConfigManager:
     name="connections",
     parse_str=tomlkit.parse,
 )
+CONFIG_MANAGER.add_option(
+    name="default_connection_name",
+    default="default",
+)
 
 
 def __getattr__(name):

test/unit/test_configmanager.py

@@ -8,6 +8,7 @@
 import re
 import shutil
 import stat
+import string
 import warnings
 from pathlib import Path
 from test.randomize import random_string
@@ -22,6 +23,7 @@
 
 try:
     from snowflake.connector.config_manager import (
+        CONFIG_MANAGER,
         ConfigManager,
         ConfigOption,
         ConfigSlice,
@@ -653,3 +655,57 @@ def test_deprecationwarning_config_parser():
         == "CONFIG_PARSER has been deprecated, use CONFIG_MANAGER instead"
     )
     assert config_manager.CONFIG_MANAGER is config_manager.CONFIG_PARSER
+
+
+def test_configoption_default_value(tmp_path, monkeypatch):
+    env_name = random_string(
+        5,
+        "SF_TEST_OPTION_",
+        choices=string.ascii_uppercase,
+    )
+    conf_val = random_string(5)
+    cm = ConfigManager(
+        name="test_manager",
+        file_path=tmp_path / "config.toml",
+    )
+    cm.add_option(
+        name="test_option",
+        env_name=env_name,
+        default=conf_val,
+    )
+    assert cm["test_option"] == conf_val
+    env_value = random_string(5)
+    with monkeypatch.context() as c:
+        c.setenv(env_name, env_value)
+        assert cm["test_option"] == env_value
+
+
+def test_defaultconnectionname(tmp_path, monkeypatch):
+    c_file = tmp_path / "config.toml"
+    old_path = CONFIG_MANAGER.file_path
+    CONFIG_MANAGER.file_path = c_file
+    CONFIG_MANAGER.conf_file_cache = None
+    try:
+        with monkeypatch.context() as m:
+            m.delenv("SNOWFLAKE_DEFAULT_CONNECTION_NAME", raising=False)
+            assert CONFIG_MANAGER["default_connection_name"] == "default"
+        env_val = random_string(5, "DEF_CONN_")
+        with monkeypatch.context() as m:
+            m.setenv("SNOWFLAKE_DEFAULT_CONNECTION_NAME", env_val)
+            assert CONFIG_MANAGER["default_connection_name"] == env_val
+        assert CONFIG_MANAGER.file_path is not None
+        con_name = random_string(5, "conn_")
+        c_file.write_text(
+            dedent(
+                f"""\
+                default_connection_name = "{con_name}"
+                """
+            )
+        )
+        # re-cache config file from disk
+        CONFIG_MANAGER.file_path = c_file
+        CONFIG_MANAGER.conf_file_cache = None
+        assert CONFIG_MANAGER["default_connection_name"] == con_name
+    finally:
+        CONFIG_MANAGER.file_path = old_path
+        CONFIG_MANAGER.conf_file_cache = None