Avoid raising errors on database passwords that contain a $ charact…

…er (#14876)

src/prefect/settings.py

@@ -323,7 +323,11 @@ def templater(settings, value):
             setting.name: setting.value_from(settings) for setting in upstream_settings
         }
         template = string.Template(str(value))
-        return original_type(template.substitute(template_values))
+        # Note the use of `safe_substitute` to avoid raising an exception if a
+        # template value is missing. In this case, template values will be left
+        # as-is in the string. Using `safe_substitute` prevents us raising when
+        # the DB password contains a `$` character.
+        return original_type(template.safe_substitute(template_values))
 
     return templater
 

tests/test_settings.py

@@ -569,6 +569,31 @@ def test_unknown_driver_raises(self):
             ):
                 pass
 
+    def test_connection_string_with_dollar_sign(self):
+        """
+        Regression test for https://github.com/PrefectHQ/prefect/issues/11067.
+
+        This test ensures that passwords with dollar signs do not cause issues when
+        templating the connection string.
+        """
+        with temporary_settings(
+            {
+                PREFECT_API_DATABASE_CONNECTION_URL: (
+                    "postgresql+asyncpg://"
+                    "the-user:the-$password@"
+                    "the-database-server.example.com:5432"
+                    "/the-database"
+                ),
+                PREFECT_API_DATABASE_USER: "the-user",
+            }
+        ):
+            assert PREFECT_API_DATABASE_CONNECTION_URL.value() == (
+                "postgresql+asyncpg://"
+                "the-user:the-$password@"
+                "the-database-server.example.com:5432"
+                "/the-database"
+            )
+
 
 class TestTemporarySettings:
     def test_temporary_settings(self):