feat(rules): build the scoped query in one place

A rule stores no scope. The hook supplies tag:new, a dry run supplies
nothing. The parentheses around the rule's own query are what stop a
disjunction of senders from escaping the scope and matching everything.

1 files changed, 29 insertions, 0 deletions

diff --git a/test_mailrules.py b/test_mailrules.py
index a3faa5e..b1f31c9 100755
--- a/test_mailrules.py
+++ b/test_mailrules.py
@@ -237,6 +237,35 @@ def test_save_creates_the_directory():
         assert json.loads(path.read_text()) == {"version": 1, "rules": []}
 
 
+def test_scoped_query_parenthesises_the_rule():
+    """Without the parentheses `tag:new and a or b` binds as
+    `(tag:new and a) or b`, and the rule matches every message in the corpus
+    satisfying b rather than only new arrivals. Several real rules are a
+    disjunction of senders, so this is the difference between tagging four
+    messages and tagging four thousand."""
+    rule = mailrules.Rule(
+        id="disjunction",
+        query="from:a@example.com or from:b@example.com",
+        add=["promo"])
+    assert mailrules.scoped_query(rule, "tag:new") == (
+        "tag:new and (from:a@example.com or from:b@example.com)")
+
+
+def test_scoped_query_with_no_scope_is_the_bare_query():
+    """A dry run counts against the whole corpus, which is what makes the
+    same rule answer 'what would this tag on arrival' and 'what does this
+    match in all my mail'."""
+    rule = mailrules.Rule(id="x", query="from:a@example.com", add=["y"])
+    assert mailrules.scoped_query(rule, None) == "from:a@example.com"
+    assert mailrules.scoped_query(rule, "") == "from:a@example.com"
+
+
+def test_tag_arguments():
+    rule = mailrules.Rule(id="x", query="from:a@example.com",
+                          add=["one", "two"], remove=["three"])
+    assert mailrules.tag_arguments(rule) == ["+one", "+two", "-three"]
+
+
 def run_all():
     for name, fn in sorted(globals().items()):
         if name.startswith("test_") and callable(fn):