testlib: Don't print QCOMPARE values if they lack string representation

Before 0681a2dd5a8095baddb5905fb21a58ce19b958c5, QCOMPARE'ing types
for which no QTest::toString specialization exists did not output
Actual and Expected lines on failure, as that would only print <null>
for both values (which then look like the same value, confusingly).

Commit 0681a2dd5a8095baddb5905fb21a58ce19b958c5 changed that behavior,
and started printing the confusing <null> values.

Take care of the logic in the formatFailMessage function: if both values
are nullptr, then print only the variable names, but not the confusing
<null> text representation of the values.

Remove dead and duplicated code related to the formatting logic, add a
self-test function, and update the expected_cmptest files.

Fixes: QTBUG-104867
Pick-to: 6.4
Change-Id: I4be98e79f91196b14690a2cc0a68ffd50b431a45
Reviewed-by: Tor Arne Vestbø <tor.arne.vestbo@qt.io>
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>

1 files changed, 27 insertions, 23 deletions

diff --git a/src/testlib/qtestresult.cpp b/src/testlib/qtestresult.cpp
index 14d344f381..556cafd4d4 100644
--- a/src/testlib/qtestresult.cpp
+++ b/src/testlib/qtestresult.cpp
@@ -321,43 +321,47 @@ static const char *rightArgNameForOp(QTest::ComparisonOperation op)
     return op == QTest::ComparisonOperation::CustomCompare ? "Expected " : "Right  ";
 }
 
-// Format failures using the toString() template
-template <class Actual, class Expected>
+// Overload to format failures for "const char *" - no need to strdup().
 void formatFailMessage(char *msg, size_t maxMsgLen,
                        const char *failureMsg,
-                       const Actual &val1, const Expected &val2,
+                       const char *val1, const char *val2,
                        const char *actual, const char *expected,
                        QTest::ComparisonOperation op)
 {
-    auto val1S = QTest::toString(val1);
-    auto val2S = QTest::toString(val2);
-
     size_t len1 = mbstowcs(nullptr, actual, maxMsgLen);    // Last parameter is not ignored on QNX
     size_t len2 = mbstowcs(nullptr, expected, maxMsgLen);  // (result is never larger than this).
-    qsnprintf(msg, maxMsgLen, "%s\n   %s(%s)%*s %s\n   %s(%s)%*s %s", failureMsg,
-              leftArgNameForOp(op), actual, qMax(len1, len2) - len1 + 1, ":",
-              val1S ? val1S : "<null>",
-              rightArgNameForOp(op), expected, qMax(len1, len2) - len2 + 1, ":",
-              val2S ? val2S : "<null>");
-
-    delete [] val1S;
-    delete [] val2S;
+    const int written = qsnprintf(msg, maxMsgLen, "%s\n", failureMsg);
+    msg += written;
+    maxMsgLen -= written;
+
+    if (val1 || val2) {
+        qsnprintf(msg, maxMsgLen, "   %s(%s)%*s %s\n   %s(%s)%*s %s",
+                    leftArgNameForOp(op), actual, qMax(len1, len2) - len1 + 1, ":",
+                    val1 ? val1 : "<null>",
+                    rightArgNameForOp(op), expected, qMax(len1, len2) - len2 + 1, ":",
+                    val2 ? val2 : "<null>");
+    } else {
+        // only print variable names if neither value can be represented as a string
+        qsnprintf(msg, maxMsgLen, "   %s: %s\n   %s: %s",
+                    leftArgNameForOp(op), actual, rightArgNameForOp(op), expected);
+    }
 }
 
-// Overload to format failures for "const char *" - no need to strdup().
+// Format failures using the toString() template
+template <class Actual, class Expected>
 void formatFailMessage(char *msg, size_t maxMsgLen,
                        const char *failureMsg,
-                       const char *val1, const char *val2,
+                       const Actual &val1, const Expected &val2,
                        const char *actual, const char *expected,
                        QTest::ComparisonOperation op)
 {
-    size_t len1 = mbstowcs(nullptr, actual, maxMsgLen);    // Last parameter is not ignored on QNX
-    size_t len2 = mbstowcs(nullptr, expected, maxMsgLen);  // (result is never larger than this).
-    qsnprintf(msg, maxMsgLen, "%s\n   %s(%s)%*s %s\n   %s(%s)%*s %s", failureMsg,
-              leftArgNameForOp(op), actual, qMax(len1, len2) - len1 + 1, ":",
-              val1 ? val1 : "<null>",
-              rightArgNameForOp(op), expected, qMax(len1, len2) - len2 + 1, ":",
-              val2 ? val2 : "<null>");
+    const char *val1S = QTest::toString(val1);
+    const char *val2S = QTest::toString(val2);
+
+    formatFailMessage(msg, maxMsgLen, failureMsg, val1S, val2S, actual, expected, op);
+
+    delete [] val1S;
+    delete [] val2S;
 }
 
 template <class Actual, class Expected>