Retain ".pragma library" when reformatting JavaScript files

For ".pragma library" there is a special flag in QmlJS::Directives.
We just need to actually set the flag and query it when re-emitting the
code.

Change-Id: Ia3455fda18aba3219b02ecf092bb28987a6ccef5
Fixes: QTCREATORBUG-22326
Reviewed-by: Thomas Hartmann <thomas.hartmann@qt.io>

src/libs/qmljs/qmljsdocument.cpp

@@ -265,6 +265,11 @@ public:
         addLocation(line, column);
     }
 
+    void pragmaLibrary() override
+    {
+        isLibrary = true;
+    }
+
     virtual QList<SourceLocation> locations() { return _locations; }
 
     const QString documentPath;

src/libs/qmljs/qmljsreformatter.cpp

@@ -24,8 +24,9 @@
 ****************************************************************************/
 
 #include "qmljsreformatter.h"
-
 #include "qmljscodeformatter.h"
+#include "qmljsbind.h"
+
 #include "parser/qmljsast_p.h"
 #include "parser/qmljsastvisitor_p.h"
 #include "parser/qmljsengine_p.h"
@@ -122,6 +123,10 @@ public:
 
 
         // emit directives
+        if (_doc->bind()->isJsLibrary()) {
+            out(QLatin1String(".pragma library"));
+            newLine();
+        }
         const QList<SourceLocation> &directives = _doc->jsDirectives();
         for (const auto &d: directives) {
             quint32 line = 1;

tests/auto/qml/reformatter/pragmalibrary.js

@@ -0,0 +1,3 @@
+.pragma library
+
+function foo() {}