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 +57,34 @@ 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. */
+  private Getter getFirstGetter() {
+    if exists(this.getGetter())
+    then result = this.getGetter()
+    else result = this.getOverridee().getFirstGetter()
+  }
+
+  /** Gets the target accessor of this declaration when used in a read context, if any. */
+  Accessor getReadTarget() { result = this.getFirstGetter() }
+
+  /** Gets the target `set` accessor of this declaration, if any. */
+  private Setter getFirstSetter() {
+    if exists(this.getSetter())
+    then result = this.getSetter()
+    else result = this.getOverridee().getFirstSetter()
+  }
+
+  /** Gets the target accessor of this declaration when used in a write context, if any. */
+  Accessor getWriteTarget() {
+    result = this.getFirstSetter()
+    or
+    result =
+      any(Getter g |
+        g = this.getFirstGetter() and
+        g.getAnnotatedReturnType().isRef()
+      )
+  }
+
   override DeclarationWithGetSetAccessors getOverridee() {
     result = DeclarationWithAccessors.super.getOverridee()
   }

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

@@ -762,20 +762,12 @@ 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().getReadTarget()
   }
 
   override Accessor getWriteTarget() {
     this instanceof AssignableWrite and
-    exists(Property p | p = this.getProperty() |
-      result = p.getSetter()
-      or
-      result =
-        any(Getter g |
-          g = p.getGetter() and
-          g.getAnnotatedReturnType().isRef()
-        )
-    )
+    result = this.getProperty().getWriteTarget()
   }
 
   override Expr getArgument(int i) {
@@ -806,20 +798,12 @@ 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().getReadTarget()
   }
 
   override Accessor getWriteTarget() {
     this instanceof AssignableWrite and
-    exists(Indexer i | i = this.getIndexer() |
-      result = i.getSetter()
-      or
-      result =
-        any(Getter g |
-          g = i.getGetter() and
-          g.getAnnotatedReturnType().isRef()
-        )
-    )
+    result = this.getIndexer().getWriteTarget()
   }
 
   override Expr getArgument(int i) {