Move engine-related functionality out of BuildGraph.

Change-Id: I5da16ea99bce3e6f737f37770fb0fe3e2e5c0214
Reviewed-by: Joerg Bornemann <joerg.bornemann@digia.com>

10 files changed, 320 insertions, 222 deletions

diff --git a/src/lib/api/internaljobs.cpp b/src/lib/api/internaljobs.cpp
index 67ff0deee..19543cc8f 100644
--- a/src/lib/api/internaljobs.cpp
+++ b/src/lib/api/internaljobs.cpp
@@ -31,9 +31,9 @@
 #include <buildgraph/artifactcleaner.h>
 #include <buildgraph/buildgraph.h>
 #include <buildgraph/executor.h>
+#include <buildgraph/rulesevaluationcontext.h>
 #include <language/language.h>
 #include <language/loader.h>
-#include <language/scriptengine.h>
 #include <logging/logger.h>
 #include <logging/translator.h>
 #include <tools/error.h>
@@ -143,25 +143,23 @@ void InternalSetupProjectJob::doResolve()
 
 void InternalSetupProjectJob::execute()
 {
-    ScriptEngine scriptEngine;
-    QScopedPointer<BuildGraph> buildGraph(new BuildGraph);
-    buildGraph->setEngine(&scriptEngine);
-    buildGraph->setProgressObserver(observer());
+    QScopedPointer<RulesEvaluationContext> evalContext(new RulesEvaluationContext);
+    evalContext->setObserver(observer());
     const QStringList searchPaths = Settings().searchPaths();
     const BuildProjectLoader::LoadResult loadResult = BuildProjectLoader().load(m_projectFilePath,
-            buildGraph.data(), m_buildRoot, m_buildConfig, searchPaths);
+            evalContext.data(), m_buildRoot, m_buildConfig, searchPaths);
 
     ResolvedProjectPtr rProject;
     if (!loadResult.discardLoadedProject)
         m_buildProject = loadResult.loadedProject;
     if (m_buildProject) {
-        buildGraph.take();
+        evalContext.take();
         rProject = m_buildProject->resolvedProject();
     } else {
         if (loadResult.changedResolvedProject) {
             rProject = loadResult.changedResolvedProject;
         } else {
-            Loader loader(&scriptEngine);
+            Loader loader(evalContext->engine());
             loader.setSearchPaths(searchPaths);
             loader.setProgressObserver(observer());
             rProject = loader.loadProject(m_projectFilePath, m_buildRoot, m_buildConfig);
@@ -188,10 +186,10 @@ void InternalSetupProjectJob::execute()
         return;
 
     TimedActivityLogger resolveLogger(QLatin1String("Resolving build project"));
-    m_buildProject = BuildProjectResolver().resolveProject(rProject, buildGraph.data(), observer());
+    m_buildProject = BuildProjectResolver().resolveProject(rProject, evalContext.data());
     if (loadResult.loadedProject)
         m_buildProject->rescueDependencies(loadResult.loadedProject);
-    buildGraph.take();
+    evalContext.take();
 }
 
 
@@ -237,7 +235,6 @@ void InternalBuildJob::start()
 {
     m_executor = new Executor(this);
     connect(m_executor, SIGNAL(finished()), SLOT(handleFinished()));
-    m_executor->setEngine(new ScriptEngine(this));
     m_executor->setBuildOptions(buildOptions());
     m_executor->setProgressObserver(observer());
     m_executor->build(products());
diff --git a/src/lib/buildgraph/automoc.cpp b/src/lib/buildgraph/automoc.cpp
index f6a9fffc8..070b75e17 100644
--- a/src/lib/buildgraph/automoc.cpp
+++ b/src/lib/buildgraph/automoc.cpp
@@ -51,8 +51,7 @@ void AutoMoc::setScanResultCache(ScanResultCache *scanResultCache)
     m_scanResultCache = scanResultCache;
 }
 
-void AutoMoc::apply(const BuildProductPtr &product, ScriptEngine *engine,
-                    ProgressObserver *observer)
+void AutoMoc::apply(const BuildProductPtr &product)
 {
     if (scanners().isEmpty())
         throw Error("C++ scanner cannot be loaded.");
@@ -131,7 +130,7 @@ void AutoMoc::apply(const BuildProductPtr &product, ScriptEngine *engine,
         artifactsPerFileTag[QLatin1String("c++_pch")] += pchFile;
     if (!artifactsPerFileTag.isEmpty()) {
         qbsInfo() << DontPrintLogLevel << "Applying moc rules for '" << product->rProduct->name << "'.";
-        product->applyRules(artifactsPerFileTag, engine, observer);
+        product->applyRules(artifactsPerFileTag);
     }
     if (pluginHeaderFile && pluginMetaDataFile) {
         // Make every artifact that is dependent of the header file also
@@ -140,7 +139,7 @@ void AutoMoc::apply(const BuildProductPtr &product, ScriptEngine *engine,
             BuildGraph::loggedConnect(outputOfHeader, pluginMetaDataFile);
     }
 
-    product->project->updateNodesThatMustGetNewTransformer(engine, observer);
+    product->project->updateNodesThatMustGetNewTransformer();
 }
 
 QString AutoMoc::generateMocFileName(Artifact *artifact, FileType fileType)
diff --git a/src/lib/buildgraph/automoc.h b/src/lib/buildgraph/automoc.h
index 18c0089bc..89bcd7537 100644
--- a/src/lib/buildgraph/automoc.h
+++ b/src/lib/buildgraph/automoc.h
@@ -36,9 +36,7 @@ struct ScannerPlugin;
 
 namespace qbs {
 namespace Internal {
-class ProgressObserver;
 class ScanResultCache;
-class ScriptEngine;
 
 /**
   * Scans cpp and hpp files for the Q_OBJECT / Q_GADGET macro and
@@ -54,7 +52,7 @@ public:
     AutoMoc();
 
     void setScanResultCache(ScanResultCache *scanResultCache);
-    void apply(const BuildProductPtr &product, ScriptEngine *engine, ProgressObserver *observer);
+    void apply(const BuildProductPtr &product);
 
 private:
     enum FileType
diff --git a/src/lib/buildgraph/buildgraph.cpp b/src/lib/buildgraph/buildgraph.cpp
index 4f4db8498..4e79acd0f 100644
--- a/src/lib/buildgraph/buildgraph.cpp
+++ b/src/lib/buildgraph/buildgraph.cpp
@@ -33,6 +33,7 @@
 #include "cycledetector.h"
 #include "command.h"
 #include "rulegraph.h"
+#include "rulesevaluationcontext.h"
 #include "transformer.h"
 
 #include <language/language.h>
@@ -173,37 +174,17 @@ void BuildProduct::insertArtifact(Artifact *artifact)
         qbsTrace("[BG] insert artifact '%s'", qPrintable(artifact->filePath()));
 }
 
-void BuildProduct::applyRules(ArtifactsPerFileTagMap &artifactsPerFileTag, ScriptEngine *engine,
-                              ProgressObserver *observer)
+void BuildProduct::applyRules(ArtifactsPerFileTagMap &artifactsPerFileTag)
 {
-    BuildGraph::EngineInitializer engineInitializer(project->buildGraph());
-    RulesApplicator rulesApplier(this, artifactsPerFileTag, engine, observer);
+    RulesEvaluationContext::Scope s(project->evaluationContext());
+    RulesApplicator rulesApplier(this, artifactsPerFileTag);
     rulesApplier.applyAllRules();
 }
 
 
-BuildGraph::BuildGraph()
-    : m_progressObserver(0)
-    , m_engine(0)
-    , m_initEngineCalls(0)
-{
-}
-
-BuildGraph::~BuildGraph()
-{
-}
-
-void BuildGraph::setEngine(ScriptEngine *engine)
-{
-    m_engine = engine;
-    m_prepareScriptScope = m_engine->newObject();
-    ProcessCommand::setupForJavaScript(m_prepareScriptScope);
-    JavaScriptCommand::setupForJavaScript(m_prepareScriptScope);
-}
-
 void BuildGraph::setupScriptEngineForProduct(ScriptEngine *engine,
                                              const ResolvedProductConstPtr &product,
-                                             RuleConstPtr rule,
+                                             const RuleConstPtr &rule,
                                              QScriptValue targetObject)
 {
     const ResolvedProject *lastSetupProject = reinterpret_cast<ResolvedProject *>(engine->property("lastSetupProject").toULongLong());
@@ -241,11 +222,6 @@ void BuildGraph::setupScriptEngineForProduct(ScriptEngine *engine,
     engine->import(rule->jsImports, targetObject, targetObject);
 }
 
-void BuildGraph::setProgressObserver(ProgressObserver *observer)
-{
-    m_progressObserver = observer;
-}
-
 bool BuildGraph::findPath(Artifact *u, Artifact *v, QList<Artifact*> &path)
 {
     if (u == v) {
@@ -329,32 +305,6 @@ void BuildGraph::disconnect(Artifact *u, Artifact *v)
     v->parents.remove(u);
 }
 
-void BuildGraph::initEngine()
-{
-    if (m_initEngineCalls++ > 0)
-        return;
-
-    m_engine->setProperty("lastSetupProject", QVariant());
-    m_engine->setProperty("lastSetupProduct", QVariant());
-
-    m_engine->clearImportsCache();
-    m_engine->pushContext();
-    m_scope = m_engine->newObject();
-    m_scope.setPrototype(m_prepareScriptScope);
-    m_engine->currentContext()->pushScope(m_scope);
-}
-
-void BuildGraph::cleanupEngine()
-{
-    Q_ASSERT(m_initEngineCalls > 0);
-    if (--m_initEngineCalls > 0)
-        return;
-
-    m_scope = QScriptValue();
-    m_engine->currentContext()->popScope();
-    m_engine->popContext();
-}
-
 void BuildGraph::removeGeneratedArtifactFromDisk(Artifact *artifact)
 {
     if (artifact->artifactType != Artifact::Generated)
@@ -473,15 +423,13 @@ void BuildProduct::store(PersistentPool &pool) const
     pool.storeContainer(dependencies);
 }
 
-BuildProject::BuildProject(BuildGraph *bg)
-    : m_buildGraph(bg)
-    , m_dirty(false)
+BuildProject::BuildProject() : m_evalContext(0), m_dirty(false)
 {
 }
 
 BuildProject::~BuildProject()
 {
-    delete m_buildGraph;
+    delete m_evalContext;
     qDeleteAll(m_dependencyArtifacts);
 }
 
@@ -529,6 +477,12 @@ QString BuildProject::buildGraphFilePath() const
     return deriveBuildGraphFilePath(resolvedProject()->buildDirectory, resolvedProject()->id());
 }
 
+void BuildProject::setEvaluationContext(RulesEvaluationContext *evalContext)
+{
+    delete m_evalContext;
+    m_evalContext = evalContext;
+}
+
 void BuildProject::load(PersistentPool &pool)
 {
     TimedActivityLogger logger(QLatin1String("Loading project from disk."));
@@ -587,11 +541,6 @@ void freeCFileTags(char **cFileTags, int numFileTags)
     delete[] cFileTags;
 }
 
-BuildGraph * BuildProject::buildGraph() const
-{
-    return m_buildGraph;
-}
-
 ResolvedProjectPtr BuildProject::resolvedProject() const
 {
     return m_resolvedProject;
@@ -717,17 +666,15 @@ void BuildProject::removeArtifact(Artifact *artifact)
     markDirty();
 }
 
-void BuildProject::updateNodesThatMustGetNewTransformer(ScriptEngine *engine,
-                                                        ProgressObserver *observer)
+void BuildProject::updateNodesThatMustGetNewTransformer()
 {
-    BuildGraph::EngineInitializer engineInitializer(buildGraph());
+    RulesEvaluationContext::Scope s(evaluationContext());
     foreach (Artifact *artifact, m_artifactsThatMustGetNewTransformers)
-        updateNodeThatMustGetNewTransformer(artifact, engine, observer);
+        updateNodeThatMustGetNewTransformer(artifact);
     m_artifactsThatMustGetNewTransformers.clear();
 }
 
-void BuildProject::updateNodeThatMustGetNewTransformer(Artifact *artifact, ScriptEngine *engine,
-                                                       ProgressObserver *observer)
+void BuildProject::updateNodeThatMustGetNewTransformer(Artifact *artifact)
 {
     Q_ASSERT(artifact->transformer);
 
@@ -745,7 +692,7 @@ void BuildProject::updateNodeThatMustGetNewTransformer(Artifact *artifact, Scrip
         foreach (const QString &fileTag, input->fileTags)
             artifactsPerFileTag[fileTag] += input;
     }
-    RulesApplicator rulesApplier(artifact->product, artifactsPerFileTag, engine, observer);
+    RulesApplicator rulesApplier(artifact->product, artifactsPerFileTag);
     rulesApplier.applyRule(rule);
 }
 
@@ -761,23 +708,9 @@ QString fileName(Artifact *n)
     return str;
 }
 
-BuildGraph::EngineInitializer::EngineInitializer(BuildGraph *bg)
-    : buildGraph(bg)
-{
-    buildGraph->initEngine();
-}
-
-BuildGraph::EngineInitializer::~EngineInitializer()
-{
-    buildGraph->cleanupEngine();
-}
-
-RulesApplicator::RulesApplicator(BuildProduct *product, ArtifactsPerFileTagMap &artifactsPerFileTag,
-                                 ScriptEngine *engine, ProgressObserver *observer)
+RulesApplicator::RulesApplicator(BuildProduct *product, ArtifactsPerFileTagMap &artifactsPerFileTag)
     : m_buildProduct(product)
     , m_artifactsPerFileTag(artifactsPerFileTag)
-    , m_engine(engine)
-    , m_observer(observer)
 {
 }
 
@@ -790,8 +723,8 @@ void RulesApplicator::applyAllRules()
 void RulesApplicator::applyRule(const RuleConstPtr &rule)
 {
     m_rule = rule;
-    BuildGraph::setupScriptEngineForProduct(m_engine, m_buildProduct->rProduct, m_rule, scope());
-    Q_ASSERT_X(scope().property("product").strictlyEquals(m_engine->evaluate("product")),
+    BuildGraph::setupScriptEngineForProduct(engine(), m_buildProduct->rProduct, m_rule, scope());
+    Q_ASSERT_X(scope().property("product").strictlyEquals(engine()->evaluate("product")),
                "BG", "Product object is not in current scope.");
 
     ArtifactList inputArtifacts;
@@ -813,8 +746,7 @@ void RulesApplicator::applyRule(const RuleConstPtr &rule)
 
 void RulesApplicator::doApply(const ArtifactList &inputArtifacts)
 {
-    if (m_observer && m_observer->canceled())
-        throw Error(Tr::tr("Build canceled."));
+    evalContext()->checkForCancelation();
 
     if (qbsLogLevel(LoggerDebug))
         qbsDebug() << "[BG] apply rule " << m_rule->toString() << " "
@@ -870,7 +802,7 @@ void RulesApplicator::doApply(const ArtifactList &inputArtifacts)
         m_buildProduct->project->removeFromArtifactsThatMustGetNewTransformers(outputArtifact);
     }
 
-    m_transformer->setupInputs(m_engine, scope());
+    m_transformer->setupInputs(engine(), scope());
 
     // change the transformer outputs according to the bindings in Artifact
     QScriptValue scriptValue;
@@ -883,13 +815,13 @@ void RulesApplicator::doApply(const ArtifactList &inputArtifacts)
         Artifact *outputArtifact = ruleArtifactArtifactMap.at(i).second;
         outputArtifact->properties = outputArtifact->properties->clone();
 
-        scope().setProperty("fileName", m_engine->toScriptValue(outputArtifact->filePath()));
-        scope().setProperty("fileTags", toScriptValue(m_engine, outputArtifact->fileTags));
+        scope().setProperty("fileName", engine()->toScriptValue(outputArtifact->filePath()));
+        scope().setProperty("fileTags", toScriptValue(engine(), outputArtifact->fileTags));
 
         QVariantMap artifactModulesCfg = outputArtifact->properties->value().value("modules").toMap();
         for (int i=0; i < ra->bindings.count(); ++i) {
             const RuleArtifact::Binding &binding = ra->bindings.at(i);
-            scriptValue = m_engine->evaluate(binding.code);
+            scriptValue = engine()->evaluate(binding.code);
             if (scriptValue.isError()) {
                 QString msg = QLatin1String("evaluating rule binding '%1': %2");
                 throw Error(msg.arg(binding.name.join(QLatin1String(".")), scriptValue.toString()), binding.location);
@@ -901,8 +833,8 @@ void RulesApplicator::doApply(const ArtifactList &inputArtifacts)
         outputArtifact->properties->setValue(outputArtifactConfig);
     }
 
-    m_transformer->setupOutputs(m_engine, scope());
-    m_transformer->createCommands(m_rule->script, m_engine);
+    m_transformer->setupOutputs(engine(), scope());
+    m_transformer->createCommands(m_rule->script, engine());
     if (m_transformer->commands.isEmpty())
         throw Error(QString("There's a rule without commands: %1.").arg(m_rule->toString()), m_rule->script->location);
 }
@@ -922,11 +854,11 @@ void RulesApplicator::setupScriptEngineForArtifact(Artifact *artifact)
         basedir = FileInfo::path(buildDir.relativeFilePath(artifact->filePath()));
     }
 
-    QScriptValue modulesScriptValue = artifact->properties->toScriptValue(m_engine);
+    QScriptValue modulesScriptValue = artifact->properties->toScriptValue(engine());
     modulesScriptValue = modulesScriptValue.property("modules");
 
     // expose per file properties we want to use in an Artifact within a Rule
-    QScriptValue scriptValue = m_engine->newObject();
+    QScriptValue scriptValue = engine()->newObject();
     scriptValue.setProperty("fileName", inFileName);
     scriptValue.setProperty("baseName", inBaseName);
     scriptValue.setProperty("completeBaseName", inCompleteBaseName);
@@ -934,15 +866,15 @@ void RulesApplicator::setupScriptEngineForArtifact(Artifact *artifact)
     scriptValue.setProperty("modules", modulesScriptValue);
 
     scope().setProperty("input", scriptValue);
-    Q_ASSERT_X(scriptValue.strictlyEquals(m_engine->evaluate("input")),
+    Q_ASSERT_X(scriptValue.strictlyEquals(engine()->evaluate("input")),
                "BG", "The input object is not in current scope.");
 }
 
 Artifact *RulesApplicator::createOutputArtifact(const RuleArtifactConstPtr &ruleArtifact,
         const ArtifactList &inputArtifacts)
 {
-    QScriptValue scriptValue = m_engine->evaluate(ruleArtifact->fileName);
-    if (scriptValue.isError() || m_engine->hasUncaughtException())
+    QScriptValue scriptValue = engine()->evaluate(ruleArtifact->fileName);
+    if (scriptValue.isError() || engine()->hasUncaughtException())
         throw Error("Error in Rule.Artifact fileName: " + scriptValue.toString());
     QString outputPath = scriptValue.toString();
     outputPath.replace("..", "dotdot");     // don't let the output artifact "escape" its build dir
@@ -1020,25 +952,33 @@ QString RulesApplicator::resolveOutPath(const QString &path) const
     return result;
 }
 
+RulesEvaluationContext *RulesApplicator::evalContext() const
+{
+    return m_buildProduct->project->evaluationContext();
+}
+
+ScriptEngine *RulesApplicator::engine() const
+{
+    return evalContext()->engine();
+}
+
 QScriptValue RulesApplicator::scope() const
 {
-    return m_engine->currentContext()->scopeChain().first();
+    return evalContext()->scope();
 }
 
 
 BuildProjectPtr BuildProjectResolver::resolveProject(const ResolvedProjectPtr &resolvedProject,
-        BuildGraph *buildgraph, ProgressObserver *observer)
+                                                     RulesEvaluationContext *evalContext)
 {
     m_productCache.clear();
-    m_observer = observer;
-    m_project = BuildProjectPtr(new BuildProject(buildgraph));
+    m_project = BuildProjectPtr(new BuildProject);
+    m_project->setEvaluationContext(evalContext);
     m_project->setResolvedProject(resolvedProject);
-    if (m_observer)
-        m_observer->initialize(Tr::tr("Resolving project"), resolvedProject->products.count());
+    evalContext->initializeObserver(Tr::tr("Resolving project"), resolvedProject->products.count());
     foreach (ResolvedProductPtr rProduct, resolvedProject->products) {
         resolveProduct(rProduct);
-        if (m_observer)
-            m_observer->incrementProgressValue();
+        evalContext->incrementProgressValue();
     }
     CycleDetector().visitProject(m_project);
     return m_project;
@@ -1050,8 +990,7 @@ BuildProductPtr BuildProjectResolver::resolveProduct(const ResolvedProductPtr &r
     if (product)
         return product;
 
-    if (m_observer && m_observer->canceled())
-        throw Error(Tr::tr("Build canceled."));
+    evalContext()->checkForCancelation();
 
     product = BuildProduct::create();
     m_productCache.insert(rProduct, product);
@@ -1114,7 +1053,7 @@ BuildProductPtr BuildProjectResolver::resolveProduct(const ResolvedProductPtr &r
             transformer->outputs += outputArtifact;
             product->targetArtifacts += outputArtifact;
             foreach (Artifact *inputArtifact, inputArtifacts)
-                buildGraph()->safeConnect(outputArtifact, inputArtifact);
+                BuildGraph::safeConnect(outputArtifact, inputArtifact);
             foreach (const QString &fileTag, outputArtifact->fileTags)
                 artifactsPerFileTag[fileTag].insert(outputArtifact);
 
@@ -1125,16 +1064,16 @@ BuildProductPtr BuildProjectResolver::resolveProduct(const ResolvedProductPtr &r
         }
         transformer->rule = rule;
 
-        BuildGraph::EngineInitializer initializer(buildGraph());
-        buildGraph()->setupScriptEngineForProduct(engine(), rProduct, transformer->rule, scope());
+        RulesEvaluationContext::Scope s(evalContext());
+        BuildGraph::setupScriptEngineForProduct(engine(), rProduct, transformer->rule, scope());
         transformer->setupInputs(engine(), scope());
         transformer->setupOutputs(engine(), scope());
-        transformer->createCommands(rtrafo->transform, buildGraph()->engine());
+        transformer->createCommands(rtrafo->transform, engine());
         if (transformer->commands.isEmpty())
             throw Error(QString("There's a transformer without commands."), rtrafo->transform->location);
     }
 
-    product->applyRules(artifactsPerFileTag, buildGraph()->engine(), m_observer);
+    product->applyRules(artifactsPerFileTag);
 
     QSet<Artifact *> productArtifactCandidates;
     for (int i = 0; i < product->rProduct->fileTags.count(); ++i)
@@ -1152,18 +1091,27 @@ BuildProductPtr BuildProjectResolver::resolveProduct(const ResolvedProductPtr &r
     return product;
 }
 
+RulesEvaluationContext *BuildProjectResolver::evalContext() const
+{
+    return m_project->evaluationContext();
+}
+
+ScriptEngine *BuildProjectResolver::engine() const
+{
+    return evalContext()->engine();
+}
+
 QScriptValue BuildProjectResolver::scope() const
 {
-    return engine()->currentContext()->scopeChain().first();
+    return evalContext()->scope();
 }
 
 BuildProjectLoader::LoadResult BuildProjectLoader::load(const QString &projectFilePath,
-        BuildGraph *bg, const QString &buildRoot, const QVariantMap &cfg,
+        RulesEvaluationContext *evalContext, const QString &buildRoot, const QVariantMap &cfg,
         const QStringList &loaderSearchPaths)
 {
     m_result = LoadResult();
-    m_engine = bg->engine();
-    m_observer = bg->observer();
+    m_evalContext = evalContext;
 
     const QString projectId = ResolvedProject::deriveId(cfg);
     const QString buildDir = ResolvedProject::deriveBuildDirectory(buildRoot, projectId);
@@ -1178,7 +1126,8 @@ BuildProjectLoader::LoadResult BuildProjectLoader::load(const QString &projectFi
         return m_result;
     }
 
-    const BuildProjectPtr project = BuildProjectPtr(new BuildProject(bg));
+    const BuildProjectPtr project = BuildProjectPtr(new BuildProject);
+    project->setEvaluationContext(evalContext);
     TimedActivityLogger loadLogger(QLatin1String("Loading build graph"), QLatin1String("[BG] "));
     project->load(pool);
     foreach (const BuildProductPtr &bp, project->buildProducts())
@@ -1219,7 +1168,7 @@ BuildProjectLoader::LoadResult BuildProjectLoader::load(const QString &projectFi
     }
 
     if (projectFileChanged || referencedProductRemoved || !changedProducts.isEmpty()) {
-        Loader ldr(bg->engine());
+        Loader ldr(evalContext->engine());
         ldr.setSearchPaths(loaderSearchPaths);
         const ResolvedProjectPtr changedProject
                 = ldr.loadProject(project->resolvedProject()->location.fileName, buildRoot, cfg);
@@ -1349,13 +1298,13 @@ void BuildProjectLoader::onProductChanged(const BuildProductPtr &product,
     foreach (Artifact *artifact, addedArtifacts)
         foreach (const QString &ft, artifact->fileTags)
             artifactsPerFileTag[ft] += artifact;
-    product->applyRules(artifactsPerFileTag, m_engine, m_observer);
+    product->applyRules(artifactsPerFileTag);
 
     // parents of removed artifacts must update their transformers
     foreach (Artifact *removedArtifact, artifactsToRemove)
         foreach (Artifact *parent, removedArtifact->parents)
             product->project->addToArtifactsThatMustGetNewTransformers(parent);
-    product->project->updateNodesThatMustGetNewTransformer(m_engine, m_observer);
+    product->project->updateNodesThatMustGetNewTransformer();
 
     // delete all removed artifacts physically from the disk
     foreach (Artifact *artifact, artifactsToRemove) {
diff --git a/src/lib/buildgraph/buildgraph.h b/src/lib/buildgraph/buildgraph.h
index 7547a095a..25dd664d5 100644
--- a/src/lib/buildgraph/buildgraph.h
+++ b/src/lib/buildgraph/buildgraph.h
@@ -47,9 +47,9 @@
 #include <QVector>
 
 namespace qbs {
-
 namespace Internal {
 class ProgressObserver;
+class RulesEvaluationContext;
 class ScriptEngine;
 class Transformer;
 
@@ -68,8 +68,7 @@ public:
     Artifact *lookupArtifact(const QString &filePath) const;
     Artifact *createArtifact(const SourceArtifactConstPtr &sourceArtifact);
     void insertArtifact(Artifact *n);
-    void applyRules(ArtifactsPerFileTagMap &artifactsPerFileTag, ScriptEngine *engine,
-                    ProgressObserver *observer);
+    void applyRules(ArtifactsPerFileTagMap &artifactsPerFileTag);
 
     WeakPointer<BuildProject> project;
     ResolvedProductPtr rProduct;
@@ -96,14 +95,16 @@ class BuildProject : public PersistentObject
     friend class BuildProjectLoader;
     friend class BuildProjectResolver;
 public:
-    BuildProject(BuildGraph *bg);
+    BuildProject();
     ~BuildProject();
 
     void store() const;
     static QString deriveBuildGraphFilePath(const QString &buildDir, const QString projectId);
     QString buildGraphFilePath() const;
 
-    BuildGraph *buildGraph() const;
+    void setEvaluationContext(RulesEvaluationContext *evalContext);
+    RulesEvaluationContext *evaluationContext() const { return m_evalContext; }
+
     ResolvedProjectPtr resolvedProject() const;
     QSet<BuildProductPtr> buildProducts() const;
     bool dirty() const;
@@ -115,7 +116,7 @@ public:
     void insertFileDependency(Artifact *artifact);
     void rescueDependencies(const BuildProjectPtr &other);
     void removeArtifact(Artifact *artifact);
-    void updateNodesThatMustGetNewTransformer(ScriptEngine *engine, ProgressObserver *observer);
+    void updateNodesThatMustGetNewTransformer();
     void removeFromArtifactsThatMustGetNewTransformers(Artifact *a) {
         m_artifactsThatMustGetNewTransformers -= a;
     }
@@ -128,11 +129,10 @@ private:
     void store(PersistentPool &pool) const;
     void addBuildProduct(const BuildProductPtr &product);
     void setResolvedProject(const ResolvedProjectPtr &resolvedProject);
-    void updateNodeThatMustGetNewTransformer(Artifact *artifact, ScriptEngine *engine,
-                                             ProgressObserver *observer);
+    void updateNodeThatMustGetNewTransformer(Artifact *artifact);
 
 private:
-    BuildGraph *m_buildGraph;
+    RulesEvaluationContext *m_evalContext;
     ResolvedProjectPtr m_resolvedProject;
     QSet<BuildProductPtr> m_buildProducts;
     ArtifactList m_dependencyArtifacts;
@@ -154,54 +154,24 @@ private:
 class BuildGraph
 {
 public:
-    class EngineInitializer
-    {
-    public:
-        EngineInitializer(BuildGraph *bg);
-        ~EngineInitializer();
-
-    private:
-        BuildGraph *buildGraph;
-    };
-
-    BuildGraph();
-    ~BuildGraph();
-
-    void setEngine(ScriptEngine *engine);
-    ScriptEngine *engine() { return m_engine; }
-
-    void setProgressObserver(ProgressObserver *observer);
-    ProgressObserver *observer() const { return m_progressObserver; }
-
     static bool findPath(Artifact *u, Artifact *v, QList<Artifact*> &path);
     static void connect(Artifact *p, Artifact *c);
     static void loggedConnect(Artifact *u, Artifact *v);
     static bool safeConnect(Artifact *u, Artifact *v);
     static void removeGeneratedArtifactFromDisk(Artifact *artifact);
-
-    static void setupScriptEngineForProduct(ScriptEngine *scriptEngine,
-                                            const ResolvedProductConstPtr &product,
-                                            RuleConstPtr rule, QScriptValue targetObject);
     static void disconnect(Artifact *u, Artifact *v);
+    static void setupScriptEngineForProduct(ScriptEngine *engine,
+            const ResolvedProductConstPtr &product, const RuleConstPtr &rule,
+            QScriptValue targetObject);
 
 private:
-    void initEngine();
-    void cleanupEngine();
-
-    ProgressObserver *m_progressObserver;
-    ScriptEngine *m_engine;
-    unsigned int m_initEngineCalls;
-    QScriptValue m_scope;
-    QScriptValue m_prepareScriptScope;
-
-    friend class EngineInitializer;
+    BuildGraph();
 };
 
 class RulesApplicator
 {
 public:
-    RulesApplicator(BuildProduct *product, ArtifactsPerFileTagMap &artifactsPerFileTag,
-                    ScriptEngine *engine, ProgressObserver *observer);
+    RulesApplicator(BuildProduct *product, ArtifactsPerFileTagMap &artifactsPerFileTag);
     void applyAllRules();
     void applyRule(const RuleConstPtr &rule);
 
@@ -211,13 +181,12 @@ private:
     Artifact *createOutputArtifact(const RuleArtifactConstPtr &ruleArtifact,
             const ArtifactList &inputArtifacts);
     QString resolveOutPath(const QString &path) const;
-
+    RulesEvaluationContext *evalContext() const;
+    ScriptEngine *engine() const;
     QScriptValue scope() const;
 
     BuildProduct * const m_buildProduct;
     ArtifactsPerFileTagMap &m_artifactsPerFileTag;
-    ScriptEngine * const m_engine;
-    ProgressObserver * const m_observer;
 
     RuleConstPtr m_rule;
     TransformerPtr m_transformer;
@@ -227,17 +196,16 @@ class BuildProjectResolver
 {
 public:
     BuildProjectPtr resolveProject(const ResolvedProjectPtr &resolvedProject,
-                                     BuildGraph *buildgraph, ProgressObserver *observer = 0);
+                                   RulesEvaluationContext *evalContext);
 
 private:
     BuildProductPtr resolveProduct(const ResolvedProductPtr &rProduct);
 
-    BuildGraph *buildGraph() const { return m_project->buildGraph(); }
-    ScriptEngine *engine() const { return buildGraph()->engine(); }
+    RulesEvaluationContext *evalContext() const;
+    ScriptEngine *engine() const;
     QScriptValue scope() const;
 
     BuildProjectPtr m_project;
-    ProgressObserver *m_observer;
     QHash<ResolvedProductPtr, BuildProductPtr> m_productCache;
 };
 
@@ -253,8 +221,9 @@ public:
         bool discardLoadedProject;
     };
 
-    LoadResult load(const QString &projectFilePath, BuildGraph *bg, const QString &buildRoot,
-                    const QVariantMap &cfg, const QStringList &loaderSearchPaths);
+    LoadResult load(const QString &projectFilePath, RulesEvaluationContext *evalContext,
+                    const QString &buildRoot, const QVariantMap &cfg,
+                    const QStringList &loaderSearchPaths);
 
 private:
     void onProductRemoved(const BuildProductPtr &product);
@@ -263,8 +232,7 @@ private:
     void removeArtifactAndExclusiveDependents(Artifact *artifact,
                                               QList<Artifact*> *removedArtifacts = 0);
 
-    ScriptEngine *m_engine;
-    ProgressObserver *m_observer;
+    RulesEvaluationContext *m_evalContext;
     LoadResult m_result;
 };
 
diff --git a/src/lib/buildgraph/buildgraph.pri b/src/lib/buildgraph/buildgraph.pri
index 2290df847..45d34ffec 100644
--- a/src/lib/buildgraph/buildgraph.pri
+++ b/src/lib/buildgraph/buildgraph.pri
@@ -15,7 +15,8 @@ SOURCES += \
     $$PWD/inputartifactscanner.cpp \
     $$PWD/artifactvisitor.cpp \
     $$PWD/artifactcleaner.cpp \
-    $$PWD/cycledetector.cpp
+    $$PWD/cycledetector.cpp \
+    $$PWD/rulesevaluationcontext.cpp
 
 HEADERS += \
     $$PWD/automoc.h\
@@ -35,4 +36,5 @@ HEADERS += \
     $$PWD/artifactvisitor.h \
     $$PWD/artifactcleaner.h \
     $$PWD/cycledetector.h \
-    $$PWD/forward_decls.h
+    $$PWD/forward_decls.h \
+    $$PWD/rulesevaluationcontext.h
diff --git a/src/lib/buildgraph/executor.cpp b/src/lib/buildgraph/executor.cpp
index 9d055c85f..df63aa111 100644
--- a/src/lib/buildgraph/executor.cpp
+++ b/src/lib/buildgraph/executor.cpp
@@ -34,6 +34,7 @@
 #include "cycledetector.h"
 #include "executorjob.h"
 #include "inputartifactscanner.h"
+#include "rulesevaluationcontext.h"
 
 #include <buildgraph/transformer.h>
 #include <language/language.h>
@@ -87,13 +88,15 @@ private:
 
 Executor::Executor(QObject *parent)
     : QObject(parent)
-    , m_engine(0)
+    , m_evalContext(new RulesEvaluationContext)
     , m_progressObserver(0)
     , m_state(ExecutorIdle)
 {
     m_inputArtifactScanContext = new InputArtifactScannerContext(&m_scanResultCache);
     m_autoMoc = new AutoMoc;
     m_autoMoc->setScanResultCache(&m_scanResultCache);
+    foreach (ExecutorJob *job, findChildren<ExecutorJob *>())
+        job->setMainThreadScriptEngine(m_evalContext->engine());
 }
 
 Executor::~Executor()
@@ -133,7 +136,6 @@ void Executor::build(const QList<BuildProductPtr> &productsToBuild)
 void Executor::doBuild(const QList<BuildProductPtr> &productsToBuild)
 {
     Q_ASSERT(m_buildOptions.maxJobCount > 0);
-    Q_ASSERT(m_engine);
     Q_ASSERT(m_state == ExecutorIdle);
     m_leaves.clear();
     m_productsToBuild = productsToBuild;
@@ -143,10 +145,8 @@ void Executor::doBuild(const QList<BuildProductPtr> &productsToBuild)
     QSet<BuildProject *> projects;
     foreach (const BuildProductConstPtr &buildProduct, productsToBuild)
         projects << buildProduct->project;
-    foreach (BuildProject * const project, projects) {
-        project->buildGraph()->setEngine(m_engine);
-        project->buildGraph()->setProgressObserver(m_progressObserver);
-    }
+    foreach (BuildProject * const project, projects)
+        project->setEvaluationContext(m_evalContext);
 
     initializeArtifactsState();
     setState(ExecutorRunning);
@@ -170,7 +170,7 @@ void Executor::doBuild(const QList<BuildProductPtr> &productsToBuild)
     // prepare products
     const QProcessEnvironment systemEnvironment = QProcessEnvironment::systemEnvironment();
     foreach (BuildProductPtr product, m_productsToBuild)
-        product->rProduct->setupBuildEnvironment(m_engine, systemEnvironment);
+        product->rProduct->setupBuildEnvironment(m_evalContext->engine(), systemEnvironment);
 
     // find the root nodes
     m_roots.clear();
@@ -196,16 +196,6 @@ void Executor::doBuild(const QList<BuildProductPtr> &productsToBuild)
     }
 }
 
-void Executor::setEngine(ScriptEngine *engine)
-{
-    if (m_engine == engine)
-        return;
-
-    m_engine = engine;
-    foreach (ExecutorJob *job, findChildren<ExecutorJob *>())
-        job->setMainThreadScriptEngine(engine);
-}
-
 void Executor::setBuildOptions(const BuildOptions &buildOptions)
 {
     m_buildOptions = buildOptions;
@@ -577,8 +567,7 @@ void Executor::addExecutorJobs(int jobNumber)
 {
     for (int i = 1; i <= jobNumber; i++) {
         ExecutorJob *job = new ExecutorJob(this);
-        if (m_engine)
-            job->setMainThreadScriptEngine(m_engine);
+        job->setMainThreadScriptEngine(m_evalContext->engine());
         job->setObjectName(QString(QLatin1String("J%1")).arg(i));
         m_availableJobs.append(job);
         connect(job, SIGNAL(error(QString)), this, SLOT(onProcessError(QString)));
@@ -606,7 +595,7 @@ void Executor::runAutoMoc()
         foreach (const ResolvedModuleConstPtr &m, product->rProduct->modules) {
             if (m->name == "qt/core") {
                 autoMocApplied = true;
-                m_autoMoc->apply(product, m_engine, m_progressObserver);
+                m_autoMoc->apply(product);
                 break;
             }
         }
diff --git a/src/lib/buildgraph/executor.h b/src/lib/buildgraph/executor.h
index 918045308..7ddb66b9e 100644
--- a/src/lib/buildgraph/executor.h
+++ b/src/lib/buildgraph/executor.h
@@ -46,8 +46,8 @@ class AutoMoc;
 class ExecutorJob;
 class InputArtifactScannerContext;
 class ProgressObserver;
+class RulesEvaluationContext;
 class ScanResultCache;
-class ScriptEngine;
 
 class Executor : public QObject
 {
@@ -58,7 +58,6 @@ public:
 
     void build(const QList<BuildProductPtr> &productsToBuild);
 
-    void setEngine(ScriptEngine *engine);
     void setBuildOptions(const BuildOptions &buildOptions);
     void setProgressObserver(ProgressObserver *observer) { m_progressObserver = observer; }
 
@@ -96,7 +95,7 @@ private:
     void cancelJobs();
     void setupProgressObserver(bool mocWillRun);
 
-    ScriptEngine *m_engine;
+    RulesEvaluationContext *m_evalContext;
     BuildOptions m_buildOptions;
     ProgressObserver *m_progressObserver;
     QList<ExecutorJob*> m_availableJobs;
diff --git a/src/lib/buildgraph/rulesevaluationcontext.cpp b/src/lib/buildgraph/rulesevaluationcontext.cpp
new file mode 100644
index 000000000..9c5db3643
--- /dev/null
+++ b/src/lib/buildgraph/rulesevaluationcontext.cpp
@@ -0,0 +1,116 @@
+/****************************************************************************
+**
+** Copyright (C) 2012 Digia Plc and/or its subsidiary(-ies).
+** Contact: http://www.qt-project.org/legal
+**
+** This file is part of the Qt Build Suite.
+**
+** Commercial License Usage
+** Licensees holding valid commercial Qt licenses may use this file in
+** accordance with the commercial license agreement provided with the
+** Software or, alternatively, in accordance with the terms contained in
+** a written agreement between you and Digia.  For licensing terms and
+** conditions see http://qt.digia.com/licensing.  For further information
+** use the contact form at http://qt.digia.com/contact-us.
+**
+** GNU Lesser General Public License Usage
+** Alternatively, this file may be used under the terms of the GNU Lesser
+** General Public License version 2.1 as published by the Free Software
+** Foundation and appearing in the file LICENSE.LGPL included in the
+** packaging of this file.  Please review the following information to
+** ensure the GNU Lesser General Public License version 2.1 requirements
+** will be met: http://www.gnu.org/licenses/old-licenses/lgpl-2.1.html.
+**
+** In addition, as a special exception, Digia gives you certain additional
+** rights.  These rights are described in the Digia Qt LGPL Exception
+** version 1.1, included in the file LGPL_EXCEPTION.txt in this package.
+**
+****************************************************************************/
+#include "rulesevaluationcontext.h"
+
+#include "artifact.h"
+#include "buildgraph.h"
+#include "command.h"
+#include "transformer.h"
+#include <language/language.h>
+#include <language/scriptengine.h>
+#include <logging/translator.h>
+#include <tools/error.h>
+#include <tools/fileinfo.h>
+#include <tools/progressobserver.h>
+
+#include <QVariant>
+
+namespace qbs {
+namespace Internal {
+
+RulesEvaluationContext::RulesEvaluationContext()
+    : m_engine(new ScriptEngine), m_observer(0), m_initScopeCalls(0)
+{
+    m_prepareScriptScope = m_engine->newObject();
+    ProcessCommand::setupForJavaScript(m_prepareScriptScope);
+    JavaScriptCommand::setupForJavaScript(m_prepareScriptScope);
+}
+
+RulesEvaluationContext::~RulesEvaluationContext()
+{
+    delete m_engine;
+}
+
+void RulesEvaluationContext::initializeObserver(const QString &description, int maximumProgress)
+{
+    if (m_observer)
+        m_observer->initialize(description, maximumProgress);
+}
+
+void RulesEvaluationContext::incrementProgressValue()
+{
+    if (m_observer)
+        m_observer->incrementProgressValue();
+}
+
+void RulesEvaluationContext::checkForCancelation()
+{
+    if (m_observer && m_observer->canceled())
+        throw Error(Tr::tr("Build canceled."));
+}
+
+void RulesEvaluationContext::initScope()
+{
+    if (m_initScopeCalls++ > 0)
+        return;
+
+    m_engine->setProperty("lastSetupProject", QVariant());
+    m_engine->setProperty("lastSetupProduct", QVariant());
+
+    m_engine->clearImportsCache();
+    m_engine->pushContext();
+    m_scope = m_engine->newObject();
+    m_scope.setPrototype(m_prepareScriptScope);
+    m_engine->currentContext()->pushScope(m_scope);
+}
+
+void RulesEvaluationContext::cleanupScope()
+{
+    Q_ASSERT(m_initScopeCalls > 0);
+    if (--m_initScopeCalls > 0)
+        return;
+
+    m_scope = QScriptValue();
+    m_engine->currentContext()->popScope();
+    m_engine->popContext();
+}
+
+RulesEvaluationContext::Scope::Scope(RulesEvaluationContext *evalContext)
+    : m_evalContext(evalContext)
+{
+    evalContext->initScope();
+}
+
+RulesEvaluationContext::Scope::~Scope()
+{
+    m_evalContext->cleanupScope();
+}
+
+} // namespace Internal
+} // namespace qbs
diff --git a/src/lib/buildgraph/rulesevaluationcontext.h b/src/lib/buildgraph/rulesevaluationcontext.h
new file mode 100644
index 000000000..2395cc34f
--- /dev/null
+++ b/src/lib/buildgraph/rulesevaluationcontext.h
@@ -0,0 +1,81 @@
+/****************************************************************************
+**
+** Copyright (C) 2012 Digia Plc and/or its subsidiary(-ies).
+** Contact: http://www.qt-project.org/legal
+**
+** This file is part of the Qt Build Suite.
+**
+** Commercial License Usage
+** Licensees holding valid commercial Qt licenses may use this file in
+** accordance with the commercial license agreement provided with the
+** Software or, alternatively, in accordance with the terms contained in
+** a written agreement between you and Digia.  For licensing terms and
+** conditions see http://qt.digia.com/licensing.  For further information
+** use the contact form at http://qt.digia.com/contact-us.
+**
+** GNU Lesser General Public License Usage
+** Alternatively, this file may be used under the terms of the GNU Lesser
+** General Public License version 2.1 as published by the Free Software
+** Foundation and appearing in the file LICENSE.LGPL included in the
+** packaging of this file.  Please review the following information to
+** ensure the GNU Lesser General Public License version 2.1 requirements
+** will be met: http://www.gnu.org/licenses/old-licenses/lgpl-2.1.html.
+**
+** In addition, as a special exception, Digia gives you certain additional
+** rights.  These rights are described in the Digia Qt LGPL Exception
+** version 1.1, included in the file LGPL_EXCEPTION.txt in this package.
+**
+****************************************************************************/
+#ifndef QBS_RULESEVALUATIONCONTEXT_H
+#define QBS_RULESEVALUATIONCONTEXT_H
+
+#include <language/forward_decls.h>
+
+#include <QScriptValue>
+
+namespace qbs {
+namespace Internal {
+class ProgressObserver;
+class ScriptEngine;
+
+class RulesEvaluationContext
+{
+public:
+    RulesEvaluationContext();
+    ~RulesEvaluationContext();
+
+    class Scope
+    {
+    public:
+        Scope(RulesEvaluationContext *evalContext);
+        ~Scope();
+
+    private:
+        RulesEvaluationContext * const m_evalContext;
+    };
+
+    ScriptEngine *engine() const { return m_engine; }
+    QScriptValue scope() const { return m_scope; }
+
+    void setObserver(ProgressObserver *observer) { m_observer = observer; }
+    void initializeObserver(const QString &description, int maximumProgress);
+    void incrementProgressValue();
+    void checkForCancelation();
+
+private:
+    friend class Scope;
+
+    void initScope();
+    void cleanupScope();
+
+    ScriptEngine * const m_engine;
+    ProgressObserver *m_observer;
+    unsigned int m_initScopeCalls;
+    QScriptValue m_scope;
+    QScriptValue m_prepareScriptScope;
+};
+
+} // namespace Internal
+} // namespace qbs
+
+#endif // QBS_RULESEVALUATIONCONTEXT_H