fix(tags): complete every tag in the list, not only the first

Reported by the user: in the Edit tags fields, the first tag suggested
existing tags and the second did not. Typing a comma, a space and a
letter offered nothing.

QLineEdit::setCompleter hands completion to the line edit, which
overwrites the completer's prefix with the widget's ENTIRE text on every
keystroke. These fields hold a comma-separated list, so once one reads
"unread, fl" that whole string is matched against the tag names, nothing
matches, and completion silently stops after the first tag. Confirmed
with a probe: the prefix really is "unread, fl" and the completion count
really is zero.

Attach with setWidget instead, which keeps the popup anchored without
ceding control of the prefix, and drive it from the token under the
cursor on every edit. Setting the prefix from a textEdited handler while
leaving setCompleter in place does NOT work, which was the first attempt:
the line edit sets it again afterwards.

Accepting a candidate needed the same treatment, and is the other half of
the fix. QCompleter's own insertion replaces the whole field, so taking
"flagged" from the popup would have discarded every tag already typed.
replaceCurrentToken() overwrites only the token under the cursor and
keeps the separator's spacing, so the result is "unread, flagged" rather
than "unread,flagged".

This is the same defect QueryCompleter hit in c98b179. Having now cost
two debugging rounds, it is written into CLAUDE.md as a Qt trap rather
than a property of either class, together with the reason a test using
setText() passes against it: setText does not drive a completer at all,
so the keys have to be typed.

Both new tests were confirmed to fail against setCompleter before the fix
was kept.

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

1 files changed, 80 insertions, 0 deletions

diff --git a/tests/test_tagdialog.cpp b/tests/test_tagdialog.cpp
index f41850e..df0fece 100644
--- a/tests/test_tagdialog.cpp
+++ b/tests/test_tagdialog.cpp
@@ -19,6 +19,7 @@
 #include <QtTest>
 
 #include <QCheckBox>
+#include <QCompleter>
 #include <QLineEdit>
 #include <QListWidget>
 
@@ -42,6 +43,8 @@ private slots:
     void aPartialTagLeftAloneChangesNothing();
     void aPartialTagCheckedIsAddedEverywhere();
     void nothingTouchedYieldsNoChange();
+    void completionFollowsTheTagAfterAComma();
+    void acceptingACandidateKeepsTheOtherTags();
 };
 
 void TestTagDialog::validNamesAreAccepted()
@@ -239,5 +242,82 @@ void TestTagDialog::nothingTouchedYieldsNoChange()
     QVERIFY(dialog.tagsToRemove().isEmpty());
 }
 
+void TestTagDialog::completionFollowsTheTagAfterAComma()
+{
+    // Reported by the user: the first tag completes, the second does not.
+    //
+    // QLineEdit::setCompleter matches against the widget's ENTIRE text, so once
+    // the field reads "unread, fl" that whole string becomes the completion
+    // prefix and nothing matches. The completer has to be driven on the token
+    // under the cursor instead. This is the same defect QueryCompleter hit in
+    // 01ba356, in a second place.
+    //
+    // Typed rather than setText(): setText does not drive a completer at all,
+    // so a test using it passes against the broken code.
+    TagDialog dialog({ QStringLiteral("inbox"), QStringLiteral("unread"),
+                       QStringLiteral("flagged") }, {}, 1);
+    dialog.show();
+    QVERIFY(QTest::qWaitForWindowExposed(&dialog));
+
+    const QList<QLineEdit *> edits = dialog.findChildren<QLineEdit *>();
+    QVERIFY(edits.size() >= 2);
+    QLineEdit *addEdit = edits.at(0);
+    addEdit->setFocus();
+    QTRY_COMPARE(QApplication::focusWidget(), addEdit);
+
+    // findChild, not QLineEdit::completer(): the completer is attached with
+    // setWidget() rather than setCompleter(), for the reason the fix documents,
+    // so the line edit does not report one. It is parented to the edit, which
+    // is what makes it reachable here.
+    QCompleter *completer = addEdit->findChild<QCompleter *>();
+    QVERIFY(completer);
+
+    // First tag: this much always worked.
+    QTest::keyClicks(addEdit, QStringLiteral("un"));
+    QCOMPARE(completer->completionPrefix(), QStringLiteral("un"));
+    QVERIFY(completer->completionCount() > 0);
+
+    // Second tag, after a comma and a space. The prefix must be the new token,
+    // not the whole line.
+    QTest::keyClicks(addEdit, QStringLiteral("read, fl"));
+    QCOMPARE(addEdit->text(), QStringLiteral("unread, fl"));
+
+    QCOMPARE(completer->completionPrefix(), QStringLiteral("fl"));
+    QVERIFY2(completer->completionCount() > 0,
+             "no candidate for the tag after the comma: the completer is "
+             "matching against the whole line");
+}
+
+void TestTagDialog::acceptingACandidateKeepsTheOtherTags()
+{
+    // Driving the prefix per token is only half the fix. Accepting a candidate
+    // has to overwrite that token too: QCompleter's own insertion replaces the
+    // whole field, so taking "flagged" here would discard "unread" with it.
+    TagDialog dialog({ QStringLiteral("inbox"), QStringLiteral("unread"),
+                       QStringLiteral("flagged") }, {}, 1);
+    dialog.show();
+    QVERIFY(QTest::qWaitForWindowExposed(&dialog));
+
+    const QList<QLineEdit *> edits = dialog.findChildren<QLineEdit *>();
+    QVERIFY(edits.size() >= 2);
+    QLineEdit *addEdit = edits.at(0);
+    addEdit->setFocus();
+    QTRY_COMPARE(QApplication::focusWidget(), addEdit);
+
+    QCompleter *completer = addEdit->findChild<QCompleter *>();
+    QVERIFY(completer);
+
+    QTest::keyClicks(addEdit, QStringLiteral("unread, fl"));
+    QCOMPARE(completer->completionPrefix(), QStringLiteral("fl"));
+
+    // What clicking a row emits.
+    emit completer->activated(QStringLiteral("flagged"));
+
+    QCOMPARE(addEdit->text(), QStringLiteral("unread, flagged"));
+    // And the separator's spacing survives: replacing from the comma itself
+    // would have produced "unread,flagged".
+    QVERIFY(addEdit->text().contains(QStringLiteral(", ")));
+}
+
 QTEST_MAIN(TestTagDialog)
 #include "test_tagdialog.moc"