[Concepts] Constraint Enforcement & Diagnostics
Part of the C++20 concepts implementation effort.
- Associated constraints (requires clauses, currently) are now enforced when instantiating/specializing templates and when considering partial specializations and function overloads.
- Elaborated diagnostics give helpful insight as to why the constraints were not satisfied.
Phabricator: D41569
diff --git a/clang/test/CXX/temp/temp.constr/temp.constr.constr/partial-specializations.cpp b/clang/test/CXX/temp/temp.constr/temp.constr.constr/partial-specializations.cpp
new file mode 100644
index 0000000..47bd2a5
--- /dev/null
+++ b/clang/test/CXX/temp/temp.constr/temp.constr.constr/partial-specializations.cpp
@@ -0,0 +1,67 @@
+// RUN: %clang_cc1 -std=c++2a -fconcepts-ts -x c++ -verify %s
+
+namespace class_templates
+{
+ template<typename T, typename U> requires sizeof(T) >= 4 // expected-note {{because 'sizeof(char) >= 4' (1 >= 4) evaluated to false}}
+ struct is_same { static constexpr bool value = false; };
+
+ template<typename T> requires sizeof(T*) >= 4 && sizeof(T) >= 4
+ struct is_same<T*, T*> { static constexpr bool value = true; };
+
+ static_assert(!is_same<char*, char*>::value);
+ static_assert(!is_same<short*, short*>::value);
+ static_assert(is_same<int*, int*>::value);
+ static_assert(is_same<char, char>::value); // expected-error {{constraints not satisfied for class template 'is_same' [with T = char, U = char]}}
+
+ template<typename T>
+ struct A { using type = typename T::type; }; // expected-error{{type 'int *' cannot be used prior to '::' because it has no members}}
+
+ template<typename T>
+ struct B {};
+
+ template<typename T> requires A<T>::type // expected-note{{in instantiation of template class 'class_templates::A<int *>' requested here}}
+ // expected-note@-1{{while substituting template arguments into constraint expression here}}
+ struct B<T*> {};
+
+ template<typename T> requires T{} // expected-error{{atomic constraint must be of type 'bool' (found 'int')}}
+ struct B<T**> {};
+
+ static_assert((B<int**>{}, true)); // expected-note{{while checking constraint satisfaction for class template partial specialization 'B<int *>' required here}}
+ // expected-note@-1{{while checking constraint satisfaction for class template partial specialization 'B<int>' required here}}
+ // expected-note@-2{{during template argument deduction for class template partial specialization 'B<T *>' [with T = int *]}}
+ // expected-note@-3{{during template argument deduction for class template partial specialization 'B<T **>' [with T = int]}}
+ // expected-note@-4 2{{in instantiation of template class 'class_templates::B<int **>' requested here}}
+}
+
+namespace variable_templates
+{
+ template<typename T, typename U> requires sizeof(T) >= 4
+ constexpr bool is_same_v = false;
+
+ template<typename T> requires sizeof(T*) >= 4 && sizeof(T) >= 4
+ constexpr bool is_same_v<T*, T*> = true;
+
+ static_assert(!is_same_v<char*, char*>);
+ static_assert(!is_same_v<short*, short*>);
+ static_assert(is_same_v<int*, int*>);
+
+ template<typename T>
+ struct A { using type = typename T::type; }; // expected-error{{type 'int *' cannot be used prior to '::' because it has no members}}
+
+ template<typename T>
+ constexpr bool v1 = false;
+
+ template<typename T> requires A<T>::type // expected-note{{in instantiation of template class 'variable_templates::A<int *>' requested here}}
+ // expected-note@-1{{while substituting template arguments into constraint expression here}}
+ constexpr bool v1<T*> = true;
+
+ template<typename T> requires T{} // expected-error{{atomic constraint must be of type 'bool' (found 'int')}}
+ constexpr bool v1<T**> = true;
+
+ static_assert(v1<int**>); // expected-note{{while checking constraint satisfaction for variable template partial specialization 'v1<int *>' required here}}
+ // expected-note@-1{{while checking constraint satisfaction for variable template partial specialization 'v1<int>' required here}}
+ // expected-note@-2{{during template argument deduction for variable template partial specialization 'v1<T *>' [with T = int *]}}
+ // expected-note@-3{{during template argument deduction for variable template partial specialization 'v1<T **>' [with T = int]}}
+ // expected-error@-4{{static_assert failed due to requirement 'v1<int **>'}}
+
+}
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