Merge pull request #19329 from github/idrissrio/designated-initializer

C++: add predicate to distinguish designator-based initializations

cpp/downgrades/2e2d805ef93d060b813403cb9b51dc72455a4c68/aggregate_array_init.ql

@@ -0,0 +1,11 @@
+class Expr extends @expr {
+  string toString() { none() }
+}
+
+class AggregateLiteral extends Expr, @aggregateliteral {
+  override string toString() { none() }
+}
+
+from AggregateLiteral aggregate, Expr initializer, int element_index, int position
+where aggregate_array_init(aggregate, initializer, element_index, position, _)
+select aggregate, initializer, element_index, position

cpp/downgrades/2e2d805ef93d060b813403cb9b51dc72455a4c68/aggregate_field_init.ql

@@ -0,0 +1,15 @@
+class Expr extends @expr {
+  string toString() { none() }
+}
+
+class AggregateLiteral extends Expr, @aggregateliteral {
+  override string toString() { none() }
+}
+
+class MemberVariable extends @membervariable {
+  string toString() { none() }
+}
+
+from AggregateLiteral aggregate, Expr initializer, MemberVariable field, int position
+where aggregate_field_init(aggregate, initializer, field, position, _)
+select aggregate, initializer, field, position

cpp/downgrades/2e2d805ef93d060b813403cb9b51dc72455a4c68/upgrade.properties

@@ -0,0 +1,4 @@
+description: add `hasDesignator` predicate to `ArrayOrVectorAggregateLiteral` and `ClassAggregateLiteral`
+compatibility: backwards
+aggregate_array_init.rel: run aggregate_array_init.qlo
+aggregate_field_init.rel: run aggregate_field_init.qlo

cpp/ql/lib/change-notes/2025-04-15-field-array-designator.md

@@ -0,0 +1,4 @@
+---
+category: feature
+---
+* Introduced `hasDesignator()` predicates to distinguish between designated and positional initializations for both struct/union fields and array elements.

cpp/ql/lib/semmle/code/cpp/exprs/Literal.qll

@@ -213,7 +213,24 @@ class ClassAggregateLiteral extends AggregateLiteral {
   Expr getFieldExpr(Field field, int position) {
     field = classType.getAField() and
     aggregate_field_init(underlyingElement(this), unresolveElement(result), unresolveElement(field),
-      position)
+      position, _)
+  }
+
+  /**
+   * Holds if the `position`-th initialization of `field` in this aggregate initializer
+   * uses a designated (e.g., `.x = ...`) rather than a positional initializer.
+   *
+   * For example, in:
+   * ```c
+   * struct S { int x, y; };
+   * struct S s = { .x = 1, 2 };
+   * ```
+   * - `.x = 1` is a designated initializer, therefore `hasDesignator(x, 0)` holds.
+   * - `2` is a positional initializer for `s.y`, therefore `hasDesignator(y, 1)` does not hold.
+   */
+  predicate hasDesignator(Field field, int position) {
+    field = classType.getAField() and
+    aggregate_field_init(underlyingElement(this), _, unresolveElement(field), position, true)
   }
 
   /**
@@ -304,7 +321,24 @@ class ArrayOrVectorAggregateLiteral extends AggregateLiteral {
    * - `a.getElementExpr(0, 2)` gives `789`.
    */
   Expr getElementExpr(int elementIndex, int position) {
-    aggregate_array_init(underlyingElement(this), unresolveElement(result), elementIndex, position)
+    aggregate_array_init(underlyingElement(this), unresolveElement(result), elementIndex, position,
+      _)
+  }
+
+  /**
+   * Holds if the `position`-th initialization of the array element at `elementIndex`
+   * in this aggregate initializer uses a designated (e.g., `[0] = ...`) rather than
+   * a positional initializer.
+   *
+   * For example, in:
+   * ```c
+   * int x[] = { [0] = 1, 2 };
+   * ```
+   * - `[0] = 1` is a designated initializer, therefore `hasDesignator(0, 0)` holds.
+   * - `2` is a positional initializer for `x[1]`, therefore `hasDesignator(1, 1)` does not hold.
+   */
+  predicate hasDesignator(int elementIndex, int position) {
+    aggregate_array_init(underlyingElement(this), _, elementIndex, position, true)
   }
 
   /**

cpp/ql/lib/semmlecode.cpp.dbscheme

@@ -2039,7 +2039,8 @@ aggregate_field_init(
     int aggregate: @aggregateliteral ref,
     int initializer: @expr ref,
     int field: @membervariable ref,
-    int position: int ref
+    int position: int ref,
+    boolean is_designated: boolean ref
 );
 
 /**
@@ -2051,7 +2052,8 @@ aggregate_array_init(
     int aggregate: @aggregateliteral ref,
     int initializer: @expr ref,
     int element_index: int ref,
-    int position: int ref
+    int position: int ref,
+    boolean is_designated: boolean ref
 );
 
 @ctorinit = @ctordirectinit

cpp/ql/lib/upgrades/0f0a390468a5eb43d1dc72937c028070b106bf53/aggregate_array_init.ql

@@ -0,0 +1,11 @@
+class Expr extends @expr {
+  string toString() { none() }
+}
+
+class AggregateLiteral extends Expr, @aggregateliteral {
+  override string toString() { none() }
+}
+
+from AggregateLiteral aggregate, Expr initializer, int element_index, int position
+where aggregate_array_init(aggregate, initializer, element_index, position)
+select aggregate, initializer, element_index, position, false

cpp/ql/lib/upgrades/0f0a390468a5eb43d1dc72937c028070b106bf53/aggregate_field_init.ql

@@ -0,0 +1,15 @@
+class Expr extends @expr {
+  string toString() { none() }
+}
+
+class AggregateLiteral extends Expr, @aggregateliteral {
+  override string toString() { none() }
+}
+
+class MemberVariable extends @membervariable {
+  string toString() { none() }
+}
+
+from AggregateLiteral aggregate, Expr initializer, MemberVariable field, int position
+where aggregate_field_init(aggregate, initializer, field, position)
+select aggregate, initializer, field, position, false

cpp/ql/lib/upgrades/0f0a390468a5eb43d1dc72937c028070b106bf53/upgrade.properties

@@ -0,0 +1,4 @@
+description: add `hasDesignator` predicate to `ArrayOrVectorAggregateLiteral` and `ClassAggregateLiteral`
+compatibility: backwards
+aggregate_array_init.rel: run aggregate_array_init.qlo
+aggregate_field_init.rel: run aggregate_field_init.qlo