Create ExtensionMethodAccess class

java/ql/lib/semmle/code/java/ControlFlowGraph.qll

@@ -550,12 +550,23 @@ private module ControlFlowGraphImpl {
       or
       index = 0 and result = this.(RValue).getQualifier() and not result instanceof TypeAccess
       or
-      exists(Call e | e = this |
+      exists(Call e | e = this and not e instanceof ExtensionMethodAccess |
         index = -1 and result = e.getQualifier() and not result instanceof TypeAccess
         or
         result = e.getArgument(index)
       )
       or
+      exists(ExtensionMethodAccess e | e = this |
+        // the actual qualifier of the expression method access
+        index = -1 and result.(Expr).isNthChildOf(this, index)
+        or
+        // the extension receiver
+        index = 0 and result = e.getQualifier()
+        or
+        // the arguments
+        result = e.getArgument(index)
+      )
+      or
       exists(StringTemplateExpr e | e = this | result = e.getComponent(index))
       or
       index = 0 and result = this.(ClassExpr).getExpr()

java/ql/lib/semmle/code/java/Expr.qll

@@ -1957,6 +1957,22 @@ class MethodAccess extends Expr, Call, @methodaccess {
   override string getAPrimaryQlClass() { result = "MethodAccess" }
 }
 
+/**
+ * An invocation of a Kotlin `ExtensionMethod`.
+ *
+ * The syntactical qualifier of an extension method is its receiver (arg 0),
+ * whereas the actual arguments begin at index 1.
+ */
+class ExtensionMethodAccess extends MethodAccess {
+  ExtensionMethodAccess() { this.getMethod() instanceof ExtensionMethod }
+
+  override Expr getQualifier() { result.isNthChildOf(this, 0) }
+
+  override Expr getAnArgument() { result.getIndex() >= 1 and result.getParent() = this }
+
+  override Expr getArgument(int index) { result = super.getArgument(index + 1) }
+}
+
 /** A type access is a (possibly qualified) reference to a type. */
 class TypeAccess extends Expr, Annotatable, @typeaccess {
   /** Gets the qualifier of this type access, if any. */