C++: Add getTemplateClass to DeductionGuide

cpp/ql/lib/change-notes/2024-08-01-deduction-guide.md

@@ -0,0 +1,4 @@
+---
+category: feature
+---
+* A `getTemplateClass` predicate was added to the `DeductionGuide` class to get the class template for which the deduction guide is a guide.

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

@@ -898,4 +898,11 @@ class UserDefinedLiteral extends Function {
  */
 class DeductionGuide extends Function {
   DeductionGuide() { functions(underlyingElement(this), _, 8) }
+
+  /**
+   * Gets the class template for which this is a deduction guide.
+   */
+  TemplateClass getTemplateClass() {
+    deduction_guide_for_class(underlyingElement(this), unresolveElement(result))
+  }
 }

cpp/ql/lib/semmlecode.cpp.dbscheme

@@ -409,6 +409,11 @@ function_defaulted(unique int id: @function ref);
 
 function_prototyped(unique int id: @function ref)
 
+deduction_guide_for_class(
+    int id: @function ref,
+    int class_template: @usertype ref
+)
+
 member_function_this_type(
     unique int id: @function ref,
     int this_type: @type ref

cpp/ql/lib/upgrades/9629fc87dab7dbed0771bf5ce22bce4d7f943b52/upgrade.properties

@@ -0,0 +1,2 @@
+description: Add relation between deduction guides and class templates
+compatibility: partial