Merge defaults across successive tasks

src/dotbot/context.py

@@ -1,7 +1,7 @@
 import copy
 import os
 from argparse import Namespace
-from typing import TYPE_CHECKING, Any, Dict, List, Optional, Type
+from typing import TYPE_CHECKING, Any, Dict, List, Mapping, Optional, Type
 
 if TYPE_CHECKING:
     from dotbot.plugin import Plugin
@@ -33,7 +33,20 @@ def base_directory(self, canonical_path: bool = True) -> str:  # noqa: FBT001, F
         return base_directory
 
     def set_defaults(self, defaults: Dict[str, Any]) -> None:
-        self._defaults = defaults
+        self._defaults = self._merge_defaults(self._defaults, defaults)
+
+    @classmethod
+    def _merge_defaults(
+        cls, current: Mapping[str, Any], updates: Mapping[str, Any]
+    ) -> Dict[str, Any]:
+        """Merge default mappings recursively, with later values taking precedence."""
+        merged = copy.deepcopy(dict(current))
+        for key, value in updates.items():
+            if isinstance(value, Mapping) and isinstance(merged.get(key), Mapping):
+                merged[key] = cls._merge_defaults(merged[key], value)
+            else:
+                merged[key] = copy.deepcopy(value)
+        return merged
 
     def defaults(self) -> Dict[str, Any]:
         return copy.deepcopy(self._defaults)

tests/test_context.py

@@ -0,0 +1,54 @@
+from typing import Any, Dict
+
+from dotbot.context import Context
+
+
+def test_set_defaults_merges_nested_mappings() -> None:
+    """Verify that successive defaults preserve mappings from earlier tasks."""
+
+    context = Context(".")
+
+    context.set_defaults(
+        {
+            "shell": {"quiet": True},
+            "link": {"create": True, "relink": True},
+        }
+    )
+    context.set_defaults({"plugin": {"interactive": False}})
+
+    assert context.defaults() == {
+        "shell": {"quiet": True},
+        "link": {"create": True, "relink": True},
+        "plugin": {"interactive": False},
+    }
+
+
+def test_set_defaults_later_values_override_without_dropping_siblings() -> None:
+    """Verify that later nested defaults override only the selected value."""
+
+    context = Context(".")
+    context.set_defaults(
+        {
+            "link": {"create": True, "relink": False},
+            "options": ["--safe-links"],
+        }
+    )
+
+    context.set_defaults({"link": {"relink": True}})
+
+    assert context.defaults() == {
+        "link": {"create": True, "relink": True},
+        "options": ["--safe-links"],
+    }
+
+
+def test_defaults_are_copied_when_merged() -> None:
+    """Verify that mutating input defaults does not mutate the context."""
+
+    context = Context(".")
+    defaults: Dict[str, Any] = {"plugin": {"interactive": False}}
+
+    context.set_defaults(defaults)
+    defaults["plugin"]["interactive"] = True
+
+    assert context.defaults()["plugin"]["interactive"] is False