AST: add LhsExpr

ql/src/codeql_ruby/ast/Pattern.qll

@@ -14,6 +14,21 @@ class Pattern extends AstNode {
   Variable getAVariable() { result = range.getAVariable() }
 }
 
+/**
+ * A "left-hand-side" expression.
+ * ```rb
+ * var = 1
+ * var += 1
+ * E = 1
+ * foo.bar = 1
+ * foo[0] = 1
+ * rescue E => var
+ * ```
+ */
+class LhsExpr extends Pattern, Expr {
+  override LhsExpr::Range range;
+}
+
 /** A simple variable pattern. */
 class VariablePattern extends Pattern {
   override VariablePattern::Range range;

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

@@ -310,7 +310,7 @@ module RescueClause {
   class Range extends Expr::Range, @rescue {
     final override Generated::Rescue generated;
 
-    final Expr getException(int n) { result = generated.getExceptions().getChild(n) }
+    final LhsExpr getException(int n) { result = generated.getExceptions().getChild(n) }
 
     final Expr getVariableExpr() { result = generated.getVariable() }
 

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

@@ -246,7 +246,7 @@ module AssignOperation {
 
     final override string getOperator() { result = generated.getOperator() }
 
-    final override Expr getLhs() { result = generated.getLeft() }
+    final override LhsExpr getLhs() { result = generated.getLeft() }
 
     final override Expr getRhs() { result = generated.getRight() }
   }

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

@@ -1,6 +1,7 @@
 private import codeql_ruby.AST
 private import TreeSitter
 private import codeql_ruby.ast.internal.AST
+private import codeql_ruby.ast.internal.Expr
 private import codeql_ruby.ast.internal.Variable
 private import codeql_ruby.ast.internal.Method
 private import codeql.Locations
@@ -58,8 +59,12 @@ module Pattern {
   }
 }
 
+module LhsExpr {
+  abstract class Range extends Pattern::Range, Expr::Range { }
+}
+
 module VariablePattern {
-  class Range extends Pattern::Range, @token_identifier {
+  class Range extends LhsExpr::Range, @token_identifier {
     override Generated::Identifier generated;
 
     string getVariableName() { result = generated.getValue() }