make shellQuoteWin() be more sparing with circumflexes

... as newer versions of nmake (and jom, for compatibility) have botched
circumflex processing (they simply don't do it when shortcutting the shell
evaluation).

as a side effect, the output is also more readable if the string contains
quotes.

Change-Id: I0506b59ceecb70da258c482f9973156b2803066d
Reviewed-by: Joerg Bornemann <joerg.bornemann@theqtcompany.com>
(cherry picked from qtbase/cf38b12a27627161e6799a3883285d05bc6420e5)

src/shared/proparser/ioutils.cpp

@@ -100,12 +100,19 @@ QString IoUtils::resolvePath(const QString &baseDir, const QString &fileName)
     return QDir::cleanPath(baseDir + QLatin1Char('/') + fileName);
 }
 
+inline static
+bool isSpecialChar(ushort c, const uchar (&iqm)[16])
+{
+    if ((c < sizeof(iqm) * 8) && (iqm[c / 8] & (1 << (c & 7))))
+        return true;
+    return false;
+}
+
 inline static
 bool hasSpecialChars(const QString &arg, const uchar (&iqm)[16])
 {
     for (int x = arg.length() - 1; x >= 0; --x) {
-        ushort c = arg.unicode()[x].unicode();
-        if ((c < sizeof(iqm) * 8) && (iqm[c / 8] & (1 << (c & 7))))
+        if (isSpecialChar(arg.unicode()[x].unicode(), iqm))
             return true;
     }
     return false;
@@ -141,23 +148,38 @@ QString IoUtils::shellQuoteWin(const QString &arg)
         0xff, 0xff, 0xff, 0xff, 0x45, 0x13, 0x00, 0x78,
         0x00, 0x00, 0x00, 0x40, 0x00, 0x00, 0x00, 0x10
     };
+    // Shell meta chars that need escaping.
+    static const uchar ism[] = {
+        0x00, 0x00, 0x00, 0x00, 0x40, 0x03, 0x00, 0x50,
+        0x00, 0x00, 0x00, 0x40, 0x00, 0x00, 0x00, 0x10
+    }; // &()<>^|
 
     if (!arg.length())
         return QString::fromLatin1("\"\"");
 
     QString ret(arg);
     if (hasSpecialChars(ret, iqm)) {
-        // Quotes are escaped and their preceding backslashes are doubled.
-        // It's impossible to escape anything inside a quoted string on cmd
-        // level, so the outer quoting must be "suspended".
-        ret.replace(QRegExp(QLatin1String("(\\\\*)\"")), QLatin1String("\"\\1\\1\\^\"\""));
-        // The argument must not end with a \ since this would be interpreted
-        // as escaping the quote -- rather put the \ behind the quote: e.g.
-        // rather use "foo"\ than "foo\"
-        int i = ret.length();
-        while (i > 0 && ret.at(i - 1) == QLatin1Char('\\'))
-            --i;
-        ret.insert(i, QLatin1Char('"'));
+        // The process-level standard quoting allows escaping quotes with backslashes (note
+        // that backslashes don't escape themselves, unless they are followed by a quote).
+        // Consequently, quotes are escaped and their preceding backslashes are doubled.
+        ret.replace(QRegExp(QLatin1String("(\\\\*)\"")), QLatin1String("\\1\\1\\\""));
+        // Trailing backslashes must be doubled as well, as they are followed by a quote.
+        ret.replace(QRegExp(QLatin1String("(\\\\+)$")), QLatin1String("\\1\\1"));
+        // However, the shell also interprets the command, and no backslash-escaping exists
+        // there - a quote always toggles the quoting state, but is nonetheless passed down
+        // to the called process verbatim. In the unquoted state, the circumflex escapes
+        // meta chars (including itself and quotes), and is removed from the command.
+        bool quoted = true;
+        for (int i = 0; i < ret.length(); i++) {
+            QChar c = ret.unicode()[i];
+            if (c.unicode() == '"')
+                quoted = !quoted;
+            else if (!quoted && isSpecialChar(c.unicode(), ism))
+                ret.insert(i++, QLatin1Char('^'));
+        }
+        if (!quoted)
+            ret.append(QLatin1Char('^'));
+        ret.append(QLatin1Char('"'));
         ret.prepend(QLatin1Char('"'));
     }
     return ret;