AST: add ElementReference

ql/src/codeql_ruby/ast/Call.qll

@@ -83,6 +83,18 @@ class Call extends Expr {
   final Block getBlock() { result = range.getBlock() }
 }
 
+/**
+ * An element reference; a call to the `[]` method.
+ * ```rb
+ * a[0]
+ * ```
+ */
+class ElementReference extends Call, @element_reference {
+  final override ElementReference::Range range;
+
+  final override string getAPrimaryQlClass() { result = "ElementReference" }
+}
+
 /**
  * A call to `yield`.
  * ```rb

ql/src/codeql_ruby/ast/internal/AST.qll

@@ -49,8 +49,6 @@ module AstNode {
       or
       this instanceof Generated::Array
       or
-      this instanceof Generated::ElementReference
-      or
       this instanceof Generated::Complex
       or
       this instanceof Generated::Character

ql/src/codeql_ruby/ast/internal/Call.qll

@@ -13,7 +13,7 @@ module Call {
 
     abstract Block getBlock();
 
-    final override string toString() { result = "call to " + this.getMethodName() }
+    override string toString() { result = "call to " + this.getMethodName() }
   }
 
   private class IdentifierCallRange extends Call::Range, @token_identifier {
@@ -71,6 +71,22 @@ module Call {
   }
 }
 
+module ElementReference {
+  class Range extends Call::Range, @element_reference {
+    final override Generated::ElementReference generated;
+
+    final override Expr getReceiver() { result = generated.getObject() }
+
+    final override string getMethodName() { result = "[]" }
+
+    final override string toString() { result = "...[...]" }
+
+    final override Expr getArgument(int n) { result = generated.getChild(n) }
+
+    final override Block getBlock() { none() }
+  }
+}
+
 module YieldCall {
   class Range extends Call::Range, @yield {
     final override Generated::Yield generated;