Merge pull request #4405 from tamasvajk/feature/lazy-flow

C#: Improve data flow summary for System.Lazy<>

Author: tamasvajk

csharp/ql/src/semmle/code/csharp/dataflow/LibraryTypeDataFlow.qll

@@ -718,6 +718,13 @@ class SystemLazyFlow extends LibraryTypeDataFlow, SystemLazyClass {
       sink = TCallableFlowSinkReturn() and
       sinkAp = AccessPath::property(this.getValueProperty())
     )
+    or
+    preservesValue = false and
+    c = this.getValueProperty().getGetter() and
+    source = TCallableFlowSourceQualifier() and
+    sourceAp = AccessPath::empty() and
+    sink = TCallableFlowSinkReturn() and
+    sinkAp = AccessPath::empty()
   }
 }
 

csharp/ql/test/library-tests/dataflow/library/LibraryTypeDataFlow.expected

@@ -442,6 +442,7 @@ callableFlow
 | System.Int32.TryParse(string, NumberStyles, IFormatProvider, out int) | argument 0 -> return | false |
 | System.Int32.TryParse(string, out int) | argument 0 -> argument 1 | false |
 | System.Int32.TryParse(string, out int) | argument 0 -> return | false |
+| System.Lazy<>.get_Value() | qualifier -> return | false |
 | System.Linq.Enumerable.Aggregate<TSource, TAccumulate, TResult>(IEnumerable<TSource>, TAccumulate, Func<TAccumulate, TSource, TAccumulate>, Func<TAccumulate, TResult>) | argument 1 -> parameter 0 of argument 2 | true |
 | System.Linq.Enumerable.Aggregate<TSource, TAccumulate, TResult>(IEnumerable<TSource>, TAccumulate, Func<TAccumulate, TSource, TAccumulate>, Func<TAccumulate, TResult>) | output from argument 2 -> parameter 0 of argument 3 | true |
 | System.Linq.Enumerable.Aggregate<TSource, TAccumulate, TResult>(IEnumerable<TSource>, TAccumulate, Func<TAccumulate, TSource, TAccumulate>, Func<TAccumulate, TResult>) | output from argument 3 -> return | true |