AST: add SetterMethodCall as instance of LhsExpr

ql/src/codeql_ruby/ast/Call.qll

@@ -7,6 +7,8 @@ private import internal.Call
 class Call extends Expr {
   override Call::Range range;
 
+  Call() { range.isNormal() }
+
   override string getAPrimaryQlClass() { result = "Call" }
 
   /**
@@ -93,6 +95,19 @@ class MethodCall extends Call {
   final Block getBlock() { result = range.getBlock() }
 }
 
+/**
+ * A call to a setter method.
+ * ```rb
+ * self.foo = 10
+ * a[0] = 10
+ * ```
+ */
+class SetterMethodCall extends LhsExpr {
+  final override SetterMethodCall::Range range;
+
+  final override string getAPrimaryQlClass() { result = "SetterMethodCall" }
+}
+
 /**
  * An element reference; a call to the `[]` method.
  * ```rb

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

@@ -1,6 +1,7 @@
 private import codeql_ruby.AST
 private import codeql_ruby.ast.internal.AST
 private import codeql_ruby.ast.internal.Expr
+private import codeql_ruby.ast.internal.Pattern
 private import codeql_ruby.ast.internal.TreeSitter
 private import codeql_ruby.ast.internal.Variable
 
@@ -8,6 +9,12 @@ module Call {
   abstract class Range extends Expr::Range {
     abstract Expr getArgument(int n);
 
+    final predicate isSetter() { this instanceof LhsExpr }
+
+    final predicate isNormal() {
+      not isSetter() or generated.getParent() instanceof AssignOperation
+    }
+
     override predicate child(string label, AstNode::Range child) {
       label = "getArgument" and child = getArgument(_)
     }
@@ -111,6 +118,30 @@ module ElementReference {
   }
 }
 
+module SetterMethodCall {
+  class Range extends LhsExpr::Range {
+    private MethodCall::Range range;
+
+    Range() { this = range }
+
+    final Expr getReceiver() { result = range.getReceiver() }
+
+    final Expr getArgument(int n) { result = range.getArgument(n) }
+
+    final string getMethodName() { result = range.getMethodName() }
+
+    final override string toString() { result = range.toString() }
+
+    final override predicate child(string label, AstNode::Range child) {
+      super.child(label, child)
+      or
+      label = "getReceiver" and child = getReceiver()
+      or
+      label = "getArgument" and child = getArgument(_)
+    }
+  }
+}
+
 module YieldCall {
   class Range extends Call::Range, @yield {
     final override Generated::Yield generated;