Enable evaluation cache for module validation

After the modules have been merged and all Probes have run, the cache
can be enabled, preventing unnecessary re-evaluation of properties
accessed in the validation script.

Output of qbs_benchmarker on Linux using qbs itself as the test project:
========== Performance data for Resolving ==========
    Old instruction count: 1817936584
    New instruction count: 1696757221
    Relative change: -7 %
    Old peak memory usage: 2714982 Bytes
    New peak memory usage: 2743848 Bytes
    Relative change: +1 %

This does not technically fix the bug mentioned below, but alleviates
the pain caused by it.

Task-number: QBS-1033
Change-Id: Ib0041067ff82a2f4b1818e6f76259d544e5184bd
Reviewed-by: Joerg Bornemann <joerg.bornemann@qt.io>

1 files changed, 14 insertions, 0 deletions

diff --git a/src/lib/corelib/language/evaluator.h b/src/lib/corelib/language/evaluator.h
index 3701935d3..2c12abb34 100644
--- a/src/lib/corelib/language/evaluator.h
+++ b/src/lib/corelib/language/evaluator.h
@@ -95,6 +95,20 @@ private:
     mutable QHash<FileContextConstPtr, QScriptValue> m_fileScopeMap;
 };
 
+class EvalCacheEnabler
+{
+public:
+    EvalCacheEnabler(Evaluator *evaluator) : m_evaluator(evaluator)
+    {
+        m_evaluator->setCachingEnabled(true);
+    }
+
+    ~EvalCacheEnabler() { m_evaluator->setCachingEnabled(false); }
+
+private:
+    Evaluator * const m_evaluator;
+};
+
 } // namespace Internal
 } // namespace qbs