C#: Use the first getter/setter when calling a property (override can apply to only a getter or a setter).

Author: michaelnebel

csharp/ql/lib/semmle/code/csharp/Property.qll

@@ -57,6 +57,20 @@ class DeclarationWithGetSetAccessors extends DeclarationWithAccessors, TopLevelE
   /** Gets the `set` accessor of this declaration, if any. */
   Setter getSetter() { result = this.getAnAccessor() }
 
+  /** Gets the target `get` accessor of this declaration, if any. */
+  Getter getFirstGetter() {
+    if exists(this.getGetter())
+    then result = this.getGetter()
+    else result = this.getOverridee().getFirstGetter()
+  }
+
+  /** Gets the target `set` accessor of this declaration, if any. */
+  Setter getFirstSetter() {
+    if exists(this.getSetter())
+    then result = this.getSetter()
+    else result = this.getOverridee().getFirstSetter()
+  }
+
   override DeclarationWithGetSetAccessors getOverridee() {
     result = DeclarationWithAccessors.super.getOverridee()
   }

csharp/ql/lib/semmle/code/csharp/exprs/Call.qll

@@ -762,11 +762,11 @@ class AccessorCall extends Call, QualifiableExpr, @call_access_expr {
  */
 class PropertyCall extends AccessorCall, PropertyAccessExpr {
   override Accessor getReadTarget() {
-    this instanceof AssignableRead and result = this.getProperty().getGetter()
+    this instanceof AssignableRead and result = this.getProperty().getFirstGetter()
   }
 
   override Accessor getWriteTarget() {
-    this instanceof AssignableWrite and result = this.getProperty().getSetter()
+    this instanceof AssignableWrite and result = this.getProperty().getFirstSetter()
   }
 
   override Expr getArgument(int i) {
@@ -797,11 +797,11 @@ class PropertyCall extends AccessorCall, PropertyAccessExpr {
  */
 class IndexerCall extends AccessorCall, IndexerAccessExpr {
   override Accessor getReadTarget() {
-    this instanceof AssignableRead and result = this.getIndexer().getGetter()
+    this instanceof AssignableRead and result = this.getIndexer().getFirstGetter()
   }
 
   override Accessor getWriteTarget() {
-    this instanceof AssignableWrite and result = this.getIndexer().getSetter()
+    this instanceof AssignableWrite and result = this.getIndexer().getFirstSetter()
   }
 
   override Expr getArgument(int i) {