From 8393b40b59083b4feff88d086105b6954020aa03 Mon Sep 17 00:00:00 2001
From: Mathias Vorreiter Pedersen <mathiasvp@github.com>
Date: Wed, 27 May 2026 17:13:48 +0200
Subject: [PATCH] C++: Use the new extensionals to map template functions and
 classes to their fully templated versions.

---
 .../semmle/code/cpp/dataflow/ExternalFlow.qll | 70 ++++++++++++++++++-
 1 file changed, 68 insertions(+), 2 deletions(-)

diff --git a/cpp/ql/lib/semmle/code/cpp/dataflow/ExternalFlow.qll b/cpp/ql/lib/semmle/code/cpp/dataflow/ExternalFlow.qll
index 5bab7dd00f2..4ec2f2f3997 100644
--- a/cpp/ql/lib/semmle/code/cpp/dataflow/ExternalFlow.qll
+++ b/cpp/ql/lib/semmle/code/cpp/dataflow/ExternalFlow.qll
@@ -277,11 +277,44 @@ private predicate isClassConstructedFrom(Class c, Class templateClass) {
 }
 
 /** Gets the fully templated version of `f`. */
-private Class getFullyTemplatedClass(Class c) {
+private Class getFullyTemplatedClassOld(Class c) {
   not c.isFromUninstantiatedTemplate(_) and
   isClassConstructedFrom(c, result)
 }
 
+private TemplateClass getOriginalClassTemplate(TemplateClass tc) {
+  result = tc.getOriginalTemplate()
+  or
+  not exists(tc.getOriginalTemplate()) and
+  result = tc
+}
+
+/** Gets the fully templated version of `f`. */
+private Class getFullyTemplatedClassNew(Class c) {
+  not c.isFromUninstantiatedTemplate(_) and
+  exists(Class mid |
+    c.isConstructedFrom(mid)
+    or
+    not c.isConstructedFrom(_) and c = mid
+  |
+    result = getOriginalClassTemplate(mid)
+    or
+    not mid instanceof TemplateClass and mid = result
+  )
+}
+
+/** Gets the fully templated version of `c`. */
+private Class getFullyTemplatedClass(Class c) {
+  // The `Class::getOriginalTemplate` predicate was introduced in CodeQL
+  // version 2.25.6 and the upgrade script leaves the
+  // `class_template_generated_from` extensionals empty if the database
+  // was generated with an older extractor. So we use the old implementation
+  // if the `class_template_generated_from` extensional is empty.
+  if class_template_generated_from(_, _)
+  then result = getFullyTemplatedClassNew(c)
+  else result = getFullyTemplatedClassOld(c)
+}
+
 /**
  * Holds if `f` is an instantiation of a function template `templateFunc`, or
  * holds with `f = templateFunc` if `f` is not an instantiation of any function
@@ -298,7 +331,7 @@ private predicate isFunctionConstructedFrom(Function f, Function templateFunc) {
 }
 
 /** Gets the fully templated version of `f`. */
-Function getFullyTemplatedFunction(Function f) {
+private Function getFullyTemplatedFunctionOld(Function f) {
   not f.isFromUninstantiatedTemplate(_) and
   (
     exists(Class c, Class templateClass, int i |
@@ -312,6 +345,39 @@ Function getFullyTemplatedFunction(Function f) {
   )
 }
 
+private TemplateFunction getOriginalFunctionTemplate(TemplateFunction tf) {
+  result = tf.getOriginalTemplate()
+  or
+  not exists(tf.getOriginalTemplate()) and
+  result = tf
+}
+
+/** Gets the fully templated version of `f`. */
+private Function getFullyTemplatedFunctionNew(Function f) {
+  not f.isFromUninstantiatedTemplate(_) and
+  exists(Function mid |
+    f.isConstructedFrom(mid)
+    or
+    not f.isConstructedFrom(_) and f = mid
+  |
+    result = getOriginalFunctionTemplate(mid)
+    or
+    not mid instanceof TemplateFunction and mid = result
+  )
+}
+
+/** Gets the fully templated version of `f`. */
+Function getFullyTemplatedFunction(Function f) {
+  // The `Function::getOriginalTemplate` predicate was introduced in CodeQL
+  // version 2.25.6 and the upgrade script leaves the
+  // `function_template_generated_from` extensionals empty if the database
+  // was generated with an older extractor. So we use the old implementation
+  // if the `function_template_generated_from` extensional is empty.
+  if function_template_generated_from(_, _)
+  then result = getFullyTemplatedFunctionNew(f)
+  else result = getFullyTemplatedFunctionOld(f)
+}
+
 /** Prefixes `const` to `s` if `t` is const, or returns `s` otherwise. */
 bindingset[s, t]
 private string withConst(string s, Type t) {