C++: add isVla predicated to ArrayType

cpp/downgrades/0f0a390468a5eb43d1dc72937c028070b106bf53/upgrade.properties

@@ -0,0 +1,3 @@
+description: Add a new predicate `isVla()` to the `ArrayType` class
+compatibility: full
+type_is_vla.rel: delete

cpp/ql/lib/change-notes/2025-04-14-variable-length-arrays.md

@@ -0,0 +1,4 @@
+---
+category: feature
+---
+* Added the `isVla()` predicate to the `ArrayType` class. This allows queries to identify variable-length arrays (VLAs).

cpp/ql/lib/semmle/code/cpp/Type.qll

@@ -1369,6 +1369,11 @@ class ArrayType extends DerivedType {
   override predicate isDeeplyConst() { this.getBaseType().isDeeplyConst() } // No such thing as a const array type
 
   override predicate isDeeplyConstBelow() { this.getBaseType().isDeeplyConst() }
+
+  /**
+   * Holds if this array is a variable-length array (VLA).
+   */
+  predicate isVla() { type_is_vla(underlyingElement(this)) }
 }
 
 /**

cpp/ql/lib/semmlecode.cpp.dbscheme

@@ -2178,6 +2178,8 @@ variable_vla(
     int decl: @stmt_vla_decl ref
 );
 
+type_is_vla(unique int type_id: @derivedtype ref)
+
 if_initialization(
     unique int if_stmt: @stmt_if ref,
     int init_id: @stmt ref