From daa56f1b4e784d6497ae4fdeaa664f3a1a7b5143 Mon Sep 17 00:00:00 2001
From: Mitch Curtis <mitch.curtis@digia.com>
Date: Wed, 11 Jun 2014 11:15:59 +0200
Subject: [PATCH] Suggest candidates when non-existent method passed to
 invokeMethod().
MIME-Version: 1.0
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Content-Transfer-Encoding: 8bit

QMetaObject::invokeMethod: No such method Object::someMethod(SomeType)

becomes:

QMetaObject::invokeMethod: No such method Object::someMethod(SomeType)
Candidates are:
    someMethod(SomeOtherType)
    someMethod(YetAnotherType)

Change-Id: I3566bca64423e2f8150d0d544fb4e35a5262b19e
Reviewed-by: Jędrzej Nowacki <jedrzej.nowacki@digia.com>
Reviewed-by: Olivier Goffart <ogoffart@woboq.com>
---
 src/corelib/kernel/qmetaobject.cpp            | 26 +++++++++++++++++--
 .../kernel/qmetaobject/tst_qmetaobject.cpp    | 12 ++++++---
 2 files changed, 32 insertions(+), 6 deletions(-)

diff --git a/src/corelib/kernel/qmetaobject.cpp b/src/corelib/kernel/qmetaobject.cpp
index accefb1ec4..cb63718680 100644
--- a/src/corelib/kernel/qmetaobject.cpp
+++ b/src/corelib/kernel/qmetaobject.cpp
@@ -1338,6 +1338,27 @@ QByteArray QMetaObject::normalizedSignature(const char *method)
 
 enum { MaximumParamCount = 11 }; // up to 10 arguments + 1 return value
 
+/*!
+    Returns the signatures of all methods whose name matches \a nonExistentMember,
+    or an empty QByteArray if there are no matches.
+*/
+static inline QByteArray findMethodCandidates(const QMetaObject *metaObject, const char *nonExistentMember)
+{
+    QByteArray candidateMessage;
+    // Prevent full string comparison in every iteration.
+    const QByteArray memberByteArray = nonExistentMember;
+    for (int i = 0; i < metaObject->methodCount(); ++i) {
+        const QMetaMethod method = metaObject->method(i);
+        if (method.name() == memberByteArray)
+            candidateMessage.append("    " + method.methodSignature() + '\n');
+    }
+    if (!candidateMessage.isEmpty()) {
+        candidateMessage.prepend("\nCandidates are:\n");
+        candidateMessage.chop(1);
+    }
+    return candidateMessage;
+}
+
 /*!
     Invokes the \a member (a signal or a slot name) on the object \a
     obj. Returns \c true if the member could be invoked. Returns \c false
@@ -1455,8 +1476,9 @@ bool QMetaObject::invokeMethod(QObject *obj,
     }
 
     if (idx < 0 || idx >= meta->methodCount()) {
-        qWarning("QMetaObject::invokeMethod: No such method %s::%s",
-                 meta->className(), sig.constData());
+        // This method doesn't belong to us; print out a nice warning with candidates.
+        qWarning("QMetaObject::invokeMethod: No such method %s::%s%s",
+                 meta->className(), sig.constData(), findMethodCandidates(meta, member).constData());
         return false;
     }
     QMetaMethod method = meta->method(idx);
diff --git a/tests/auto/corelib/kernel/qmetaobject/tst_qmetaobject.cpp b/tests/auto/corelib/kernel/qmetaobject/tst_qmetaobject.cpp
index 09084578ab..a920ea7a01 100644
--- a/tests/auto/corelib/kernel/qmetaobject/tst_qmetaobject.cpp
+++ b/tests/auto/corelib/kernel/qmetaobject/tst_qmetaobject.cpp
@@ -561,9 +561,11 @@ void tst_QMetaObject::invokeMetaMember()
     QVERIFY(!QMetaObject::invokeMethod(&obj, "doesNotExist"));
     QTest::ignoreMessage(QtWarningMsg, "QMetaObject::invokeMethod: No such method QtTestObject::sl1(QString)(QString)");
     QVERIFY(!QMetaObject::invokeMethod(&obj, "sl1(QString)", Q_ARG(QString, "arg")));
-    QTest::ignoreMessage(QtWarningMsg, "QMetaObject::invokeMethod: No such method QtTestObject::sl3(QString)");
+    QTest::ignoreMessage(QtWarningMsg, "QMetaObject::invokeMethod: No such method QtTestObject::sl3(QString)\n"
+                         "Candidates are:\n    sl3(QString,QString,QString)");
     QVERIFY(!QMetaObject::invokeMethod(&obj, "sl3", Q_ARG(QString, "arg")));
-    QTest::ignoreMessage(QtWarningMsg, "QMetaObject::invokeMethod: No such method QtTestObject::sl1(QString,QString,QString)");
+    QTest::ignoreMessage(QtWarningMsg, "QMetaObject::invokeMethod: No such method QtTestObject::sl1(QString,QString,QString)\n"
+                         "Candidates are:\n    sl1(QString)");
     QVERIFY(!QMetaObject::invokeMethod(&obj, "sl1", Q_ARG(QString, "arg"), Q_ARG(QString, "arg"), Q_ARG(QString, "arg")));
 
     //should not have changed since last test.
@@ -747,9 +749,11 @@ void tst_QMetaObject::invokeBlockingQueuedMetaMember()
     QVERIFY(!QMetaObject::invokeMethod(&obj, "doesNotExist", Qt::BlockingQueuedConnection));
     QTest::ignoreMessage(QtWarningMsg, "QMetaObject::invokeMethod: No such method QtTestObject::sl1(QString)(QString)");
     QVERIFY(!QMetaObject::invokeMethod(&obj, "sl1(QString)", Qt::BlockingQueuedConnection, Q_ARG(QString, "arg")));
-    QTest::ignoreMessage(QtWarningMsg, "QMetaObject::invokeMethod: No such method QtTestObject::sl3(QString)");
+    QTest::ignoreMessage(QtWarningMsg, "QMetaObject::invokeMethod: No such method QtTestObject::sl3(QString)\n"
+                         "Candidates are:\n    sl3(QString,QString,QString)");
     QVERIFY(!QMetaObject::invokeMethod(&obj, "sl3", Qt::BlockingQueuedConnection, Q_ARG(QString, "arg")));
-    QTest::ignoreMessage(QtWarningMsg, "QMetaObject::invokeMethod: No such method QtTestObject::sl1(QString,QString,QString)");
+    QTest::ignoreMessage(QtWarningMsg, "QMetaObject::invokeMethod: No such method QtTestObject::sl1(QString,QString,QString)\n"
+                         "Candidates are:\n    sl1(QString)");
     QVERIFY(!QMetaObject::invokeMethod(&obj, "sl1", Qt::BlockingQueuedConnection, Q_ARG(QString, "arg"), Q_ARG(QString, "arg"), Q_ARG(QString, "arg")));
 
     //should not have changed since last test.