C#: Implement ContentSet

Author: hvitved

csharp/ql/lib/semmle/code/csharp/dataflow/FlowSummary.qll

@@ -144,7 +144,7 @@ private class SummarizedCallableDefaultClearsContent extends Impl::Public::Summa
   }
 
   // By default, we assume that all stores into arguments are definite
-  override predicate clearsContent(ParameterPosition pos, DataFlow::Content content) {
+  override predicate clearsContent(ParameterPosition pos, DataFlow::ContentSet content) {
     exists(SummaryComponentStack output, SummaryComponent target |
       this.propagatesFlow(_, output, _) and
       output.drop(_) =

csharp/ql/lib/semmle/code/csharp/dataflow/internal/DataFlowPublic.qll

@@ -252,3 +252,23 @@ class ElementContent extends Content, TElementContent {
 
   override Location getLocation() { result instanceof EmptyLocation }
 }
+
+/**
+ * An entity that represents a set of `Content`s.
+ *
+ * The set may be interpreted differently depending on whether it is
+ * stored into (`getAStoreContent`) or read from (`getAReadContent`).
+ */
+class ContentSet instanceof Content {
+  /** Gets a content that may be stored into when storing into this set. */
+  Content getAStoreContent() { result = this }
+
+  /** Gets a content that may be read from when reading from this set. */
+  Content getAReadContent() { result = this }
+
+  /** Gets a textual representation of this content set. */
+  string toString() { result = super.toString() }
+
+  /** Gets the location of this content set. */
+  Location getLocation() { result = super.getLocation() }
+}

csharp/ql/lib/semmle/code/csharp/frameworks/system/Collections.qll

@@ -54,7 +54,7 @@ private class SystemCollectionsIEnumerableClearFlow extends SummarizedCallable {
     this.hasName("Clear")
   }
 
-  override predicate clearsContent(ParameterPosition pos, DataFlow::Content content) {
+  override predicate clearsContent(ParameterPosition pos, DataFlow::ContentSet content) {
     pos.isThisParameter() and
     content instanceof DataFlow::ElementContent
   }

csharp/ql/lib/semmle/code/csharp/frameworks/system/Text.qll

@@ -32,7 +32,7 @@ private class SystemTextStringBuilderClearFlow extends SummarizedCallable {
     this = any(SystemTextStringBuilderClass s).getAMethod("Clear")
   }
 
-  override predicate clearsContent(ParameterPosition pos, DataFlow::Content content) {
+  override predicate clearsContent(ParameterPosition pos, DataFlow::ContentSet content) {
     pos.isThisParameter() and
     content instanceof DataFlow::ElementContent
   }