QbsProjectManager: Fix infinite loop when "force probes" is checked

This happened for all projects with a Qt dependency, because the module
provider kept recreating the Qt modules, which in turn caused Qt Creator
to re-parse the project.

Change-Id: I77c5c8723c1d0bcd477db648692ddaf9e060ce99
Reviewed-by: Joerg Bornemann <joerg.bornemann@qt.io>

src/plugins/qbsprojectmanager/qbsproject.cpp

@@ -756,10 +756,16 @@ void QbsProject::updateDocuments(const QSet<QString> &files)
         }
     }
     QSet<IDocument *> toAdd;
-    foreach (const QString &f, filesToAdd)
-        toAdd.insert(new ProjectDocument(Constants::MIME_TYPE, FileName::fromString(f),
-                                         [this]() { delayParsing(); }));
-
+    const FileName buildDir = FileName::fromString(m_projectData.buildDirectory());
+    for (const QString &f : qAsConst(filesToAdd)) {
+        // A changed qbs file (project, module etc) should trigger a re-parse, but not if
+        // the file was generated by qbs itself, in which case that might cause an infinite loop.
+        const FileName fp = FileName::fromString(f);
+        static const ProjectDocument::ProjectCallback noOpCallback = []{};
+        const ProjectDocument::ProjectCallback reparseCallback = [this]() { delayParsing(); };
+        toAdd.insert(new ProjectDocument(Constants::MIME_TYPE, fp, fp.isChildOf(buildDir)
+                                         ? noOpCallback : reparseCallback));
+    }
     m_qbsDocuments.unite(toAdd);
 }