Merge pull request #18483 from jketema/extractor-fixes

C++: Fix types of struct/union templates and fix assumptions on proxy classes

Author: jketema

cpp/downgrades/a01d8f91b8d49259e509b574962dec90719f69a6/old.dbscheme

@@ -0,0 +1,3 @@
+description: Improve user types and proxy classes
+compatibility: full
+usertypes.rel: run usertypes.qlo

cpp/downgrades/a01d8f91b8d49259e509b574962dec90719f69a6/semmlecode.cpp.dbscheme

@@ -0,0 +1,10 @@
+class UserType extends @usertype {
+  string toString() { none() }
+}
+
+bindingset[kind]
+int getKind(int kind) { if kind in [15, 16, 17] then result = 6 else result = kind }
+
+from UserType usertype, string name, int kind
+where usertypes(usertype, name, kind)
+select usertype, name, getKind(kind)

cpp/downgrades/a01d8f91b8d49259e509b574962dec90719f69a6/upgrade.properties

@@ -0,0 +1,6 @@
+---
+category: feature
+---
+* A new predicate `getDecltype`was added to the `ProxyClass` class, which yields the decltype for the proxy class.
+* Template classes that are of `struct` type are now also instances of the `Struct` class.
+* Template classes that are of `union` type are now also instances of the `Union` class.

cpp/downgrades/a01d8f91b8d49259e509b574962dec90719f69a6/usertypes.ql

@@ -869,7 +869,7 @@ class AbstractClass extends Class {
  * `FullClassTemplateSpecialization`.
  */
 class TemplateClass extends Class {
-  TemplateClass() { usertypes(underlyingElement(this), _, 6) }
+  TemplateClass() { usertypes(underlyingElement(this), _, [15, 16, 17]) }
 
   /**
    * Gets a class instantiated from this template.
@@ -1076,13 +1076,19 @@ class VirtualBaseClass extends Class {
 }
 
 /**
- * The proxy class (where needed) associated with a template parameter, as
- * in the following code:
- * ```
+ * The proxy class (where needed) associated with a template parameter or a
+ * decltype, as in the following code:
+ * ```cpp
  * template <typename T>
  * struct S : T { // the type of this T is a proxy class
  *   ...
  * };
+ *
+ * template <typename T>
+ * concept C =
+ *   decltype(std::span{std::declval<T&>()})::extent
+ *     != std::dynamic_extent;
+ *   // the type of decltype(std::span{std::declval<T&>()}) is a proxy class
  * ```
  */
 class ProxyClass extends UserType {
@@ -1093,10 +1099,13 @@ class ProxyClass extends UserType {
   /** Gets the location of the proxy class. */
   override Location getLocation() { result = this.getTemplateParameter().getDefinitionLocation() }
 
-  /** Gets the template parameter for which this is the proxy class. */
+  /** Gets the template parameter for which this is the proxy class, if any. */
   TypeTemplateParameter getTemplateParameter() {
     is_proxy_class_for(underlyingElement(this), unresolveElement(result))
   }
+
+  /** Gets the decltype for which this is the proxy class, if any. */
+  Decltype getDecltype() { is_proxy_class_for(underlyingElement(this), unresolveElement(result)) }
 }
 
 // Unpacks "array of ... of array of t" into t.

cpp/ql/lib/change-notes/2025-01-13-struct-proxy.md

@@ -20,7 +20,7 @@ import semmle.code.cpp.Class
  * ```
  */
 class Struct extends Class {
-  Struct() { usertypes(underlyingElement(this), _, 1) or usertypes(underlyingElement(this), _, 3) }
+  Struct() { usertypes(underlyingElement(this), _, [1, 3, 15, 17]) }
 
   override string getAPrimaryQlClass() { result = "Struct" }
 

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

@@ -52,9 +52,7 @@ deprecated class TemplateParameter = TypeTemplateParameter;
  * ```
  */
 class TypeTemplateParameter extends UserType, TemplateParameterImpl {
-  TypeTemplateParameter() {
-    usertypes(underlyingElement(this), _, 7) or usertypes(underlyingElement(this), _, 8)
-  }
+  TypeTemplateParameter() { usertypes(underlyingElement(this), _, [7, 8]) }
 
   override string getAPrimaryQlClass() { result = "TypeTemplateParameter" }
 

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

@@ -406,10 +406,7 @@ class IntegralOrEnumType extends Type {
     isIntegralType(underlyingElement(this), _)
     or
     // Enum type
-    (
-      usertypes(underlyingElement(this), _, 4) or
-      usertypes(underlyingElement(this), _, 13)
-    )
+    usertypes(underlyingElement(this), _, [4, 13])
   }
 }
 

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

@@ -13,10 +13,7 @@ private import semmle.code.cpp.internal.ResolveClass
  * ```
  */
 class TypedefType extends UserType {
-  TypedefType() {
-    usertypes(underlyingElement(this), _, 5) or
-    usertypes(underlyingElement(this), _, 14)
-  }
+  TypedefType() { usertypes(underlyingElement(this), _, [5, 14]) }
 
   /**
    * Gets the base type of this typedef type.