Fix "qmake -spec foo" call for cross builds

In a cross built Qt, for example Qt for Android, calling "qmake -spec
android-clang" led to an error message:
    "Could not find qmake spec '-qtconf'."

This happened, because:
- the qmake in Qt for Android is a wrapper script that calls
  "qmake -qtconf qt_target.conf -spec android-clang"
- the first stage of command line argument handling in qmake garbled the
  call to "qmake -spec -qtconf qt_target.conf android-clang"

We do not modify the order of arguments anymore.

Instead, we skip the "-qtconf <file>" arguments in the first argument
handling stage that is supposed to determine qmake's modus
operandi (like -project or -query).

In addition, we need to fix the assignment of
QLibraryInfoPrivate::qtconfManualPath which was only done if
QMakeGlobals::addCommandLineArguments returned ArgumentsOk. However,
this function returns ArgumentUnknown, if it encounters an argument it
cannot handle - like the project name.
Now, we assign QLibraryInfoPrivate::qtconfManualPath if there was no
error detected.

Document the return values of addCommandLineArguments.

This amends commit 661b586a69.

Pick-to: 6.1 6.0
Fixes: QTBUG-93079
Task-number: QTBUG-85136
Change-Id: I12ec25b17d64c00be2a3904b7c4a975b781500a0
Reviewed-by: Alexandru Croitor <alexandru.croitor@qt.io>

qmake/library/qmakeglobals.cpp

@@ -103,6 +103,13 @@ QString QMakeGlobals::cleanSpec(QMakeCmdLineParserState &state, const QString &s
     return ret;
 }
 
+/*
+ * Return value meanings:
+ * ArgumentUnknown    The argument at *pos was not handled by this function.
+ *                    Leave it to the caller to handle this argument.
+ * ArgumentMalformed  There was an error detected.
+ * ArgumentsOk        All arguments were known. There are no arguments left to handle.
+ */
 QMakeGlobals::ArgumentReturn QMakeGlobals::addCommandLineArguments(
         QMakeCmdLineParserState &state, QStringList &args, int *pos)
 {

qmake/option.cpp

@@ -204,14 +204,13 @@ Option::parseCommandLine(QStringList &args, QMakeCmdLineParserState &state)
             continue;
         default:
             QMakeGlobals::ArgumentReturn cmdRet = globals->addCommandLineArguments(state, args, &x);
-            if (cmdRet == QMakeGlobals::ArgumentsOk) {
-                QLibraryInfoPrivate::qtconfManualPath = globals->qtconf;
-                break;
-            }
             if (cmdRet == QMakeGlobals::ArgumentMalformed) {
                 fprintf(stderr, "***Option %s requires a parameter\n", qPrintable(args.at(x - 1)));
                 return Option::QMAKE_CMDLINE_SHOW_USAGE | Option::QMAKE_CMDLINE_ERROR;
             }
+            QLibraryInfoPrivate::qtconfManualPath = globals->qtconf;
+            if (cmdRet == QMakeGlobals::ArgumentsOk)
+                break;
             Q_ASSERT(cmdRet == QMakeGlobals::ArgumentUnknown);
             QString arg = args.at(x);
             if (arg.startsWith(QLatin1Char('-'))) {
@@ -381,8 +380,9 @@ Option::init(int argc, char **argv)
         for (int i = 1; i < argc; i++)
             args << QString::fromLocal8Bit(argv[i]);
 
-        while (!args.isEmpty()) {
+        qsizetype idx = 0;
-            QString opt = args.at(0);
+        while (idx < args.size()) {
+            QString opt = args.at(idx);
             if (opt == "-project") {
                 Option::recursive = true;
                 Option::qmake_mode = Option::QMAKE_GENERATE_PROJECT;
@@ -399,15 +399,15 @@ Option::init(int argc, char **argv)
             } else if (opt == "-makefile") {
                 Option::qmake_mode = Option::QMAKE_GENERATE_MAKEFILE;
             } else if (opt == "-qtconf") {
-                if (args.length() >= 3) {
+                // Skip "-qtconf <file>" and proceed.
-                    // Move the argument following "-qtconf <file>" in front and check again.
+                ++idx;
-                    args.prepend(args.takeAt(2));
+                if (idx + 1 < args.length())
-                    continue;
+                    ++idx;
-                }
+                continue;
             } else {
                 break;
             }
-            args.takeFirst();
+            args.takeAt(idx);
             break;
         }