feat(search): add SearchTerm::exclude

Parenthesises both sides, as extend() does: unparenthesised, a
disjunction in the query bar binds so the exclusion covers only its last
term and leaves the excluded mail on screen, with nothing reporting an
error.

An empty existing query returns empty rather than the addition alone,
which is where this deliberately differs from extend(). Excluding from
nothing means the whole Maildir minus one value; the menus will grey the
entry out and this is the second layer.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

1 files changed, 39 insertions, 0 deletions

diff --git a/tests/test_searchterm.cpp b/tests/test_searchterm.cpp
index e0bdb60..53185f3 100644
--- a/tests/test_searchterm.cpp
+++ b/tests/test_searchterm.cpp
@@ -41,6 +41,9 @@ private slots:
     void tagIsNotQuoted();
     void extendParenthesisesBothSides();
     void extendOntoAnEmptyQueryIsAReplace();
+    void excludeParenthesisesBothSides();
+    void excludeFromAnEmptyQueryIsEmpty();
+    void excludeWithNothingToExcludeLeavesTheQuery();
 };
 
 void TestSearchTerm::quotesAPlainValue()
@@ -142,5 +145,41 @@ void TestSearchTerm::extendOntoAnEmptyQueryIsAReplace()
              QStringLiteral("tag:inbox"));
 }
 
+void TestSearchTerm::excludeParenthesisesBothSides()
+{
+    // The same trap as extendParenthesisesBothSides, and worse in this
+    // direction. Unparenthesised, `a or b AND NOT c` binds as
+    // `a or (b AND NOT c)`: the exclusion covers only the second term, so
+    // every message matching `a` stays on screen INCLUDING the ones the user
+    // asked to be rid of. notmuch reports no error for either form, so this
+    // assertion is the only thing that fails.
+    QCOMPARE(SearchTerm::exclude(QStringLiteral("tag:inbox or tag:flagged"),
+                                 QStringLiteral("from:foo@example.org")),
+             QStringLiteral(
+                 "(tag:inbox or tag:flagged) AND NOT (from:foo@example.org)"));
+}
+
+void TestSearchTerm::excludeFromAnEmptyQueryIsEmpty()
+{
+    // Deliberately NOT extend()'s behaviour. extend() returns the addition
+    // alone, because narrowing nothing by x sensibly means x. Excluding from
+    // nothing would mean the whole Maildir minus one value: a legitimate
+    // query, and an implausible thing to have meant by right-clicking a value
+    // in a fresh window. The menus grey the entry out; this is the second
+    // layer, against a caller that forgets the guard.
+    QVERIFY(SearchTerm::exclude(QString(), QStringLiteral("tag:inbox"))
+                .isEmpty());
+    QVERIFY(SearchTerm::exclude(QStringLiteral("   "),
+                                QStringLiteral("tag:inbox"))
+                .isEmpty());
+}
+
+void TestSearchTerm::excludeWithNothingToExcludeLeavesTheQuery()
+{
+    QCOMPARE(SearchTerm::exclude(QStringLiteral("tag:inbox"), QString()),
+             QStringLiteral("tag:inbox"));
+    QVERIFY(SearchTerm::exclude(QString(), QString()).isEmpty());
+}
+
 QTEST_MAIN(TestSearchTerm)
 #include "test_searchterm.moc"