C++: Handle requires clauses and type template type constraints

cpp/downgrades/6f169f1c65aaf527a856823b84d74865d1475125/upgrade.properties

@@ -0,0 +1,6 @@
+description: Support requires clauses and type constraints
+compatibility: full
+fun_requires.rel: delete
+var_requires.rel: delete
+type_requires.rel: delete
+type_template_type_constraint.rel: delete

cpp/ql/lib/change-notes/2024-12-26-requires-clause.md

@@ -0,0 +1,7 @@
+---
+category: feature
+---
+* New predicates `getARequiresClause`, `getTemplateRequiresClause` and `getFunctionRequiresClause` were added to the `FunctionDeclarationEntry` class, which yield the requires clauses when the entry represents a function template declaration with requires clauses.
+* A new predicate `getRequiresClause` was added to the `TypeDeclarationEntry` class, which yields the requires clause when the entry represents a class template declaration with a requires clause.
+* A new predicate `getRequiresClause` was added to the `VariableDeclarationEntry` class, which yields the requires clause when the entry represents a variable template declaration with a requires clause.
+* A new predicate `getTypeConstraint` was added to the `TypeTemplateParameter` class, which yields the type constraint of the parameter if it exists.

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

@@ -715,6 +715,27 @@ class FunctionDeclarationEntry extends DeclarationEntry, @fun_decl {
    * specification.
    */
   predicate isNoExcept() { fun_decl_empty_noexcept(underlyingElement(this)) }
+
+  /**
+   * Gets a requires clause if this declaration is a template with such a clause.
+   */
+  Expr getARequiresClause() { fun_requires(underlyingElement(this), _, unresolveElement(result)) }
+
+  /**
+   * Gets the requires clause that appears after the template argument list if this
+   * declaration is a template with such a clause.
+   */
+  Expr getTemplateRequiresClause() {
+    fun_requires(underlyingElement(this), 1, unresolveElement(result))
+  }
+
+  /**
+   * Gets the requires clause that appears after the declarator if this declaration
+   * is a template with such a clause.
+   */
+  Expr getFunctionRequiresClause() {
+    fun_requires(underlyingElement(this), 2, unresolveElement(result))
+  }
 }
 
 /**

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

@@ -59,6 +59,13 @@ class TypeTemplateParameter extends UserType, TemplateParameterImpl {
   override string getAPrimaryQlClass() { result = "TypeTemplateParameter" }
 
   override predicate involvesTemplateParameter() { any() }
+
+  /**
+   * Get the type constraint of this type template parameter.
+   */
+  Expr getTypeConstraint() {
+    type_template_type_constraint(underlyingElement(this), unresolveElement(result))
+  }
 }
 
 /**

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

@@ -129,4 +129,9 @@ class TypeDeclarationEntry extends DeclarationEntry, @type_decl {
    * class or typedef.
    */
   predicate isTopLevel() { type_decl_top(underlyingElement(this)) }
+
+  /**
+   * Gets the requires clause if this declaration is a template with such a clause.
+   */
+  Expr getRequiresClause() { type_requires(underlyingElement(this), unresolveElement(result)) }
 }

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

@@ -278,6 +278,11 @@ class VariableDeclarationEntry extends DeclarationEntry, @var_decl {
 
   /** Holds if this declaration is a template specialization. */
   predicate isSpecialization() { var_specialized(underlyingElement(this)) }
+
+  /**
+   * Gets the requires clause if this declaration is a template with such a clause.
+   */
+  Expr getRequiresClause() { var_requires(underlyingElement(this), unresolveElement(result)) }
 }
 
 /**

cpp/ql/lib/semmlecode.cpp.dbscheme

@@ -480,6 +480,20 @@ fun_decl_typedef_type(
     int typedeftype_id: @usertype ref
 );
 
+/*
+case @fun_requires.kind of
+  1 = @template_attached
+| 2 = @function_attached
+;
+*/
+
+#keyset[id, kind]
+fun_requires(
+    int id: @fun_decl ref,
+    int kind: int ref,
+    int constraint: @expr ref
+);
+
 param_decl_bind(
     unique int id: @var_decl ref,
     int index: int ref,
@@ -501,6 +515,10 @@ var_decl_specifiers(
     string name: string ref
 )
 is_structured_binding(unique int id: @variable ref);
+var_requires(
+    unique int id: @var_decl ref,
+    int constraint: @expr ref
+);
 
 type_decls(
     unique int id: @type_decl,
@@ -511,6 +529,10 @@ type_def(unique int id: @type_decl ref);
 type_decl_top(
     unique int type_decl: @type_decl ref
 );
+type_requires(
+    unique int id: @type_decl ref,
+    int constraint: @expr ref
+);
 
 namespace_decls(
     unique int id: @namespace_decl,
@@ -790,6 +812,11 @@ nontype_template_parameters(
     int id: @expr ref
 );
 
+type_template_type_constraint(
+    int id: @usertype ref,
+    int constraint: @expr ref
+);
+
 mangled_name(
     unique int id: @declaration ref,
     int mangled_name : @mangledname,