Merge pull request #21360 from microsoft/unbreak-changes

C++: Provide `BarrierGuard` API without a `Unit` column when instantiating non-parameterized `BarrierGuard`s

Author: MathiasVP

cpp/ql/lib/change-notes/2026-02-24-barrier-guards.md

@@ -0,0 +1,4 @@
+---
+category: breaking
+---
+* CodeQL version 2.24.2 accidentially introduced a syntactical breaking change to `BarrierGuard<...>::getAnIndirectBarrierNode` and `InstructionBarrierGuard<...>::getAnIndirectBarrierNode`. These breaking changes have now been reverted so that the original code compiles again.

cpp/ql/lib/semmle/code/cpp/ir/dataflow/internal/DataFlowUtil.qll

@@ -2641,7 +2641,54 @@ module BarrierGuard<guardChecksSig/3 guardChecks> {
     exists(unit)
   }
 
-  import ParameterizedBarrierGuard<Unit, guardChecks/4>
+  private module P = ParameterizedBarrierGuard<Unit, guardChecks/4>;
+
+  predicate getABarrierNode = P::getABarrierNode/0;
+
+  /**
+   * Gets an indirect expression node with indirection index `indirectionIndex` that is
+   * safely guarded by the given guard check.
+   *
+   * For example, given the following code:
+   * ```cpp
+   * int* p;
+   * // ...
+   * *p = source();
+   * if(is_safe_pointer(p)) {
+   *   sink(*p);
+   * }
+   * ```
+   * and the following barrier guard check:
+   * ```ql
+   * predicate myGuardChecks(IRGuardCondition g, Expr e, boolean branch) {
+   *   exists(Call call |
+   *     g.getUnconvertedResultExpression() = call and
+   *     call.getTarget().hasName("is_safe_pointer") and
+   *     e = call.getAnArgument() and
+   *     branch = true
+   *   )
+   * }
+   * ```
+   * implementing `isBarrier` as:
+   * ```ql
+   * predicate isBarrier(DataFlow::Node barrier) {
+   *   barrier = DataFlow::BarrierGuard<myGuardChecks/3>::getAnIndirectBarrierNode(1)
+   * }
+   * ```
+   * will block flow from `x = source()` to `sink(x)`.
+   *
+   * NOTE: If a non-indirect expression is tracked, use `getABarrierNode` instead.
+   */
+  Node getAnIndirectBarrierNode(int indirectionIndex) {
+    result = P::getAnIndirectBarrierNode(indirectionIndex, _)
+  }
+
+  /**
+   * Gets an indirect expression node that is safely guarded by the given guard check.
+   *
+   * See `getAnIndirectBarrierNode/1` for examples.
+   */
+  Node getAnIndirectBarrierNode() { result = getAnIndirectBarrierNode(_) }
 }
 
 private module InstrWithParam<ParamSig P> {
@@ -2752,7 +2799,20 @@ module InstructionBarrierGuard<instructionGuardChecksSig/3 instructionGuardCheck
     exists(unit)
   }
 
-  import ParameterizedInstructionBarrierGuard<Unit, instructionGuardChecks/4>
+  private module P = ParameterizedInstructionBarrierGuard<Unit, instructionGuardChecks/4>;
+
+  predicate getABarrierNode = P::getABarrierNode/0;
+
+  /**
+   * Gets an indirect node with indirection index `indirectionIndex` that is
+   * safely guarded by the given guard check.
+   */
+  Node getAnIndirectBarrierNode(int indirectionIndex) {
+    result = P::getAnIndirectBarrierNode(indirectionIndex, _)
+  }
+
+  /** Gets an indirect node that is safely guarded by the given guard check. */
+  Node getAnIndirectBarrierNode() { result = getAnIndirectBarrierNode(_) }
 }
 
 /**

cpp/ql/test/library-tests/dataflow/ir-barrier-guards/test.ql

@@ -15,7 +15,10 @@ predicate instructionGuardChecks(IRGuardCondition gc, Instruction checked, boole
 module BarrierGuard = DataFlow::InstructionBarrierGuard<instructionGuardChecks/3>;
 
 predicate indirectBarrierGuard(DataFlow::Node node, string s) {
-  node = BarrierGuard::getAnIndirectBarrierNode(_) and
+  // This any(...) could technically be removed, but it helps us verify that we don't
+  // accidentially change the API of this predicate (for instance, by having
+  // the column be a unit parameter).
+  node = BarrierGuard::getAnIndirectBarrierNode(any(int indirectionIndex)) and
   if node.isGLValue()
   then s = "glval<" + node.getType().toString().replaceAll(" ", "") + ">"
   else s = node.getType().toString().replaceAll(" ", "")