Fix false positives in RULE-15-1-4 for class template constructors

Delegating constructors of uninstantiated class templates are not modelled as delegating,
so all members were reported as uninitialized. Skip the template and rely on the instantiations.

Author: castler

change_notes/2026-10-20-fix-fp-rule-15-1-4-template-constructors.md

@@ -0,0 +1,2 @@
+- `RULE-15-1-4` - `NonStaticMemberNotInitBeforeUse.ql`:
+  - Remove false positives for constructors of uninstantiated class templates, where delegating constructors are not modelled as such. The instantiations are still checked.

cpp/misra/src/rules/RULE-15-1-4/NonStaticMemberNotInitBeforeUse.ql

@@ -116,6 +116,9 @@ class IncompleteConstructor extends Constructor, IncompleteInitialization {
     not getDeclaringType() instanceof Union and
     this.getDeclaringType().hasDefinition() and
     not this.isDeleted() and
+    // Constructors of uninstantiated class templates cannot be analysed reliably, because for
+    // instance a delegating constructor is not modelled as such. The instantiations are checked.
+    not this.getDeclaringType() instanceof TemplateClass and
     // Delegating constructors do not need to initialize members
     not any(ConstructorDelegationInit init) = this.getAnInitializer() and
     // exclude defaulted move and copy constructors.

cpp/misra/test/rules/RULE-15-1-4/NonStaticMemberNotInitBeforeUse.expected

@@ -24,3 +24,4 @@
 | test.cpp:267:18:267:18 | a | Aggregate variable does not initialize non-static data member $@ (and 9 more). | test.cpp:262:43:262:45 | m10 | m10 |
 | test.cpp:290:18:290:18 | a | Aggregate variable does not initialize non-static data member $@ (and 1 more). | test.cpp:285:9:285:10 | m1 | m1 |
 | test.cpp:290:18:290:18 | a | Aggregate variable does not initialize non-static data member $@ (and 1 more). | test.cpp:286:11:286:12 | m2 | m2 |
+| test.cpp:318:3:318:3 | TemplateMemberUninit | Constructor does not initialize non-static data member $@. | test.cpp:322:7:322:8 | m2 | m2 |

cpp/misra/test/rules/RULE-15-1-4/test.cpp

@@ -302,4 +302,52 @@ union UnionWithConstructor {
   // Union constructors should still be required to initialize one member, but
   // this is not implemented.
   UnionWithConstructor() {} // NON_COMPLIANT[False negative]
-};
+};
+template <typename T> class TemplateAllInit {
+public:
+  TemplateAllInit(T value) : m1(value), m2(0) {} // COMPLIANT
+  TemplateAllInit(const TemplateAllInit &) = delete;
+
+private:
+  T m1;
+  int m2;
+};
+
+template <typename T> class TemplateMemberUninit {
+public:
+  TemplateMemberUninit(T value) : m1(value) {} // NON_COMPLIANT
+
+private:
+  T m1;
+  int m2;
+};
+
+template <typename T> class TemplateOutOfLineInit {
+public:
+  TemplateOutOfLineInit(T value);
+
+private:
+  T m1;
+  int m2;
+};
+
+template <typename T>
+TemplateOutOfLineInit<T>::TemplateOutOfLineInit(T value)
+    : m1(value), m2(0) {} // COMPLIANT
+
+template <typename T> class TemplateDelegating {
+public:
+  TemplateDelegating() : TemplateDelegating(0) {}   // COMPLIANT
+  TemplateDelegating(T value) : m1(value), m2(0) {} // COMPLIANT
+
+private:
+  T m1;
+  int m2;
+};
+
+void instantiateTemplates() {
+  TemplateAllInit<int> a(1);
+  TemplateMemberUninit<int> b(1);
+  TemplateOutOfLineInit<int> c(1);
+  TemplateDelegating<int> d;
+}