base: Make --update more intuitive

Fix #45.

xbstrap/__init__.py

@@ -175,6 +175,8 @@ def handle_plan_args(cfg, plan, args):
         plan.reset = xbstrap.base.ResetMode.RESET
     if args.hard_reset:
         plan.reset = xbstrap.base.ResetMode.HARD_RESET
+    if args.restrict_updates:
+        plan.restrict_updates = True
     if args.only_wanted:
         plan.only_wanted = True
     if args.keep_going:
@@ -212,7 +214,7 @@ def handle_plan_args(cfg, plan, args):
     "-u", "--update", action="store_true", help="check for package updates"
 )
 handle_plan_args.parser.add_argument(
-    "--recursive", action="store_true", help="when updating: also update requirements"
+    "--recursive", action="store_true", help="recursively run build steps that are out of date"
 )
 handle_plan_args.parser.add_argument(
     "--paranoid",
@@ -229,6 +231,11 @@ def handle_plan_args(cfg, plan, args):
     action="store_true",
     help="clean and reset repository state; risks loss of local changes and commits!",
 )
+handle_plan_args.parser.add_argument(
+    "--restrict-updates",
+    action="store_true",
+    help="restrict updates to packages that are explicitly wanted on the command line",
+)
 handle_plan_args.parser.add_argument(
     "--only-wanted",
     action="store_true",

xbstrap/base.py

@@ -3318,6 +3318,7 @@ def __init__(self, cfg):
         self.explain = False
         self.check = False
         self.update = False
+        self.restrict_updates = False
         self.recursive = False
         self.paranoid = False
         self.wanted = set()
@@ -3657,32 +3658,33 @@ def activate(root_key):
                 dep_item = self._items[dep_pair]
                 dep_item.build_span = True
 
-        # Activate updatable items.
-        if self.update:
-
-            def is_outdated(item, dep_item):
-                ts = item.timestamp
-                dep_ts = dep_item.timestamp
-                if ts is None or dep_ts is None:
-                    return False
-                return dep_ts > ts
+        def is_outdated(item, dep_item):
+            ts = item.timestamp
+            dep_ts = dep_item.timestamp
+            if ts is None or dep_ts is None:
+                return False
+            return dep_ts > ts
 
+        # Handle --update and --recursive.
+        if self.update or self.recursive:
             for item in self._order:
-                # Unless we're doing a recursive update, we only follow check items
-                # that are reachable by build edges.
-                if not self.recursive and not item.build_span:
+                if self.restrict_updates and not item.build_span:
                     continue
+
+                # Both --update and --recursive activate missing/updatable items.
                 if item.is_missing or item.is_updatable:
                     activate(item.key)
 
-                # Activate items if their dependencies were activated.
+                # Both --update and --recursive activate on outdated build edges.
                 for dep_pair in item.build_edges:
                     dep_item = self._items[dep_pair]
                     if dep_item.active:
                         activate(item.key)
                     elif is_outdated(item, dep_item):
                         item.outdated = True
                         activate(item.key)
+
+                # Only --recursive activates on outdated requirements.
                 if self.recursive:
                     for dep_pair in item.require_edges:
                         dep_item = self._items[dep_pair]