QL: Add module expressions and module aliases

ql/src/codeql_ql/ast/Ast.qll

@@ -203,6 +203,11 @@ class Module extends TModule, AstNode, ModuleMember {
   AstNode getAMember() {
     toGenerated(result) = mod.getChild(_).(Generated::ModuleMember).getChild(_)
   }
+
+  /** Gets the module expression that this module is an alias for, if any. */
+  ModuleExpr getAlias() {
+    toGenerated(result) = mod.getAFieldOrChild().(Generated::ModuleAliasBody).getChild()
+  }
 }
 
 /**
@@ -624,3 +629,38 @@ class AddExpr extends TAddExpr, BinOpExpr {
 
   FunctionSymbol getOperator() { result = addexpr.getChild().getValue() }
 }
+
+/** A module expression. */
+class ModuleExpr extends TModuleExpr, AstNode {
+  Generated::ModuleExpr me;
+
+  ModuleExpr() { this = TModuleExpr(me) }
+
+  /**
+   * Gets the name of this module expression. For example, the name of
+   *
+   * ```ql
+   * Foo::Bar
+   * ```
+   *
+   * is `Bar`.
+   */
+  string getName() {
+    result = me.getName().getValue()
+    or
+    not exists(me.getName()) and result = me.getChild().(Generated::SimpleId).getValue()
+  }
+
+  /**
+   * Gets the qualifier of this module expression. For example, the qualifier of
+   *
+   * ```ql
+   * Foo::Bar::Baz
+   * ```
+   *
+   * is `Foo::Bar`.
+   */
+  ModuleExpr getQualifier() { result = TModuleExpr(me.getChild()) }
+
+  final override string toString() { result = this.getName() }
+}

ql/src/codeql_ql/ast/internal/AstNodes.qll

@@ -26,7 +26,8 @@ newtype TAstNode =
   TAsExpr(Generated::AsExpr asExpr) or
   TNegation(Generated::Negation neg) or
   TAddExpr(Generated::AddExpr addexp) or
-  TLiteral(Generated::Literal lit)
+  TLiteral(Generated::Literal lit) or
+  TModuleExpr(Generated::ModuleExpr me)
 
 class TFormula = TDisjunction or TConjunction or TComparisonFormula or TQuantifier or TNegation;
 
@@ -80,6 +81,8 @@ Generated::AstNode toGenerated(AST::AstNode n) {
   n = TLiteral(result)
   or
   n = TAsExpr(result)
+  or
+  n = TModuleExpr(result)
 }
 
 class TPredicate = TCharPred or TClasslessPredicate or TClassPredicate;