[Clang] Added explanation why is_constructible evaluated to false.

clang/include/clang/Basic/DiagnosticSemaKinds.td

@@ -1765,7 +1765,8 @@ def err_user_defined_msg_constexpr : Error<
 // Type traits explanations
 def note_unsatisfied_trait : Note<"%0 is not %enum_select<TraitName>{"
                                   "%TriviallyRelocatable{trivially relocatable}|"
-                                  "%TriviallyCopyable{trivially copyable}"
+                                  "%TriviallyCopyable{trivially copyable}|"
+                                  "%Constructible{constructible with provided types}"
                                   "}1">;
 
 def note_unsatisfied_trait_reason
@@ -1785,7 +1786,9 @@ def note_unsatisfied_trait_reason
            "%UserProvidedAssign{has a user provided %select{copy|move}1 "
            "assignment operator}|"
            "%UnionWithUserDeclaredSMF{is a union with a user-declared "
-           "%sub{select_special_member_kind}1}"
+           "%sub{select_special_member_kind}1}|"
+           "%FunctionType{is a function type}|"
+           "%CVVoidType{is a cv void type}"
            "}0">;
 
 def warn_consteval_if_always_true : Warning<

clang/lib/Sema/SemaTypeTraits.cpp

@@ -21,6 +21,7 @@
 #include "clang/Sema/Overload.h"
 #include "clang/Sema/Sema.h"
 #include "clang/Sema/SemaHLSL.h"
+#include "llvm/Support/raw_ostream.h"
 
 using namespace clang;
 
@@ -1941,6 +1942,7 @@ static std::optional<TypeTrait> StdNameToTypeTrait(StringRef Name) {
       .Case("is_trivially_relocatable",
             TypeTrait::UTT_IsCppTriviallyRelocatable)
       .Case("is_trivially_copyable", TypeTrait::UTT_IsTriviallyCopyable)
+      .Case("is_constructible", TypeTrait::TT_IsConstructible)
       .Default(std::nullopt);
 }
 
@@ -1977,8 +1979,14 @@ static ExtractedTypeTraitInfo ExtractTypeTraitFromExpression(const Expr *E) {
     Trait = StdNameToTypeTrait(Name);
     if (!Trait)
       return std::nullopt;
-    for (const auto &Arg : VD->getTemplateArgs().asArray())
-      Args.push_back(Arg.getAsType());
+    for (const auto &Arg : VD->getTemplateArgs().asArray()) {
+      if (Arg.getKind() == TemplateArgument::ArgKind::Pack) {
+        for (const auto &InnerArg : Arg.pack_elements())
+          Args.push_back(InnerArg.getAsType());
+      }
+      if (Arg.getKind() == TemplateArgument::ArgKind::Type)
+        Args.push_back(Arg.getAsType());
+    }
     return {{Trait.value(), std::move(Args)}};
   }
 
@@ -2159,6 +2167,26 @@ static void DiagnoseNonTriviallyCopyableReason(Sema &SemaRef,
   }
 }
 
+static void DiagnoseNonConstructibleReason(Sema &SemaRef, SourceLocation Loc,
+                                           QualType T) {
+  SemaRef.Diag(Loc, diag::note_unsatisfied_trait)
+      << T << diag::TraitName::Constructible;
+
+  if (T->isFunctionType())
+    SemaRef.Diag(Loc, diag::note_unsatisfied_trait_reason)
+        << diag::TraitNotSatisfiedReason::FunctionType;
+
+  if (T->isVoidType())
+    SemaRef.Diag(Loc, diag::note_unsatisfied_trait_reason)
+        << diag::TraitNotSatisfiedReason::CVVoidType;
+
+  const CXXRecordDecl *D = T->getAsCXXRecordDecl();
+  if (!D || D->isInvalidDecl() || !D->hasDefinition())
+    return;
+
+  SemaRef.Diag(D->getLocation(), diag::note_defined_here) << D;
+}
+
 static void DiagnoseNonTriviallyCopyableReason(Sema &SemaRef,
                                                SourceLocation Loc, QualType T) {
   SemaRef.Diag(Loc, diag::note_unsatisfied_trait)
@@ -2195,6 +2223,9 @@ void Sema::DiagnoseTypeTraitDetails(const Expr *E) {
   case UTT_IsTriviallyCopyable:
     DiagnoseNonTriviallyCopyableReason(*this, E->getBeginLoc(), Args[0]);
     break;
+  case TT_IsConstructible:
+    DiagnoseNonConstructibleReason(*this, E->getBeginLoc(), Args[0]);
+    break;
   default:
     break;
   }

clang/test/SemaCXX/type-traits-unsatisfied-diags-std.cpp

@@ -20,6 +20,14 @@ struct is_trivially_copyable {
 
 template <typename T>
 constexpr bool is_trivially_copyable_v = __is_trivially_copyable(T);
+
+template <typename... Args>
+struct is_constructible {
+    static constexpr bool value = __is_constructible(Args...);
+};
+
+template <typename... Args>
+constexpr bool is_constructible_v = __is_constructible(Args...);
 #endif
 
 #ifdef STD2
@@ -44,6 +52,17 @@ using is_trivially_copyable  = __details_is_trivially_copyable<T>;
 
 template <typename T>
 constexpr bool is_trivially_copyable_v = __is_trivially_copyable(T);
+
+template <typename... Args>
+struct __details_is_constructible{
+    static constexpr bool value = __is_constructible(Args...);
+};
+
+template <typename... Args>
+using is_constructible  = __details_is_constructible<Args...>;
+
+template <typename... Args>
+constexpr bool is_constructible_v = __is_constructible(Args...);
 #endif
 
 
@@ -73,6 +92,15 @@ using is_trivially_copyable  = __details_is_trivially_copyable<T>;
 
 template <typename T>
 constexpr bool is_trivially_copyable_v = is_trivially_copyable<T>::value;
+
+template <typename... Args>
+struct __details_is_constructible : bool_constant<__is_constructible(Args...)> {};
+
+template <typename... Args>
+using is_constructible  = __details_is_constructible<Args...>;
+
+template <typename... Args>
+constexpr bool is_constructible_v = is_constructible<Args...>::value;
 #endif
 
 }
@@ -100,6 +128,17 @@ static_assert(std::is_trivially_copyable_v<int&>);
 // expected-note@-1 {{because it is a reference type}}
 
 
+static_assert(std::is_constructible<int, int>::value);
+
+static_assert(std::is_constructible<void>::value);
+// expected-error-re@-1 {{static assertion failed due to requirement 'std::{{.*}}is_constructible<void>::value'}} \
+// expected-note@-1 {{'void' is not constructible with provided types}} \
+// expected-note@-1 {{because it is a cv void type}}
+static_assert(std::is_constructible_v<void>);
+// expected-error@-1 {{static assertion failed due to requirement 'std::is_constructible_v<void>'}} \
+// expected-note@-1 {{'void' is not constructible with provided types}} \
+// expected-note@-1 {{because it is a cv void type}}
+
 namespace test_namespace {
     using namespace std;
     static_assert(is_trivially_relocatable<int&>::value);
@@ -119,6 +158,15 @@ namespace test_namespace {
     // expected-error@-1 {{static assertion failed due to requirement 'is_trivially_copyable_v<int &>'}} \
     // expected-note@-1 {{'int &' is not trivially copyable}} \
     // expected-note@-1 {{because it is a reference type}}
+
+    static_assert(is_constructible<void>::value);
+    // expected-error-re@-1 {{static assertion failed due to requirement '{{.*}}is_constructible<void>::value'}} \
+    // expected-note@-1 {{'void' is not constructible with provided types}} \
+    // expected-note@-1 {{because it is a cv void type}}
+    static_assert(is_constructible_v<void>);
+    // expected-error@-1 {{static assertion failed due to requirement 'is_constructible_v<void>'}} \
+    // expected-note@-1 {{'void' is not constructible with provided types}} \
+    // expected-note@-1 {{because it is a cv void type}}
 }
 
 
@@ -139,6 +187,15 @@ concept C2 = std::is_trivially_copyable_v<T>; // #concept4
 
 template <C2 T> void g2();  // #cand4
 
+template <typename... Args>
+requires std::is_constructible<Args...>::value void f3();  // #cand5
+
+template <typename... Args>
+concept C3 = std::is_constructible_v<Args...>; // #concept6
+
+template <C3 T> void g3();  // #cand6
+
+
 void test() {
     f<int&>();
     // expected-error@-1 {{no matching function for call to 'f'}} \
@@ -169,5 +226,20 @@ void test() {
     // expected-note@#concept4 {{because 'std::is_trivially_copyable_v<int &>' evaluated to false}} \
     // expected-note@#concept4 {{'int &' is not trivially copyable}} \
     // expected-note@#concept4 {{because it is a reference type}}
+
+    f3<void>();
+    // expected-error@-1 {{no matching function for call to 'f3'}} \
+    // expected-note@#cand5 {{candidate template ignored: constraints not satisfied [with Args = <void>]}} \
+    // expected-note-re@#cand5 {{because '{{.*}}is_constructible<void>::value' evaluated to false}} \
+    // expected-note@#cand5 {{'void' is not constructible with provided types}} \
+    // expected-note@#cand5 {{because it is a cv void type}}
+
+    g3<void>();
+    // expected-error@-1 {{no matching function for call to 'g3'}} \
+    // expected-note@#cand6 {{candidate template ignored: constraints not satisfied [with T = void]}} \
+    // expected-note@#cand6 {{because 'void' does not satisfy 'C3'}} \
+    // expected-note@#concept6 {{because 'std::is_constructible_v<void>' evaluated to false}} \
+    // expected-note@#concept6 {{'void' is not constructible with provided types}} \
+    // expected-note@#concept6 {{because it is a cv void type}}
 }
 }

clang/test/SemaCXX/type-traits-unsatisfied-diags.cpp

@@ -290,3 +290,47 @@ static_assert(__is_trivially_copyable(S12));
 // expected-note@-1 {{'S12' is not trivially copyable}} \
 // expected-note@#tc-S12 {{'S12' defined here}}
 }
+
+namespace constructible {
+
+struct S1 { // #c-S1
+    S1(int);
+};
+static_assert(__is_constructible(S1, int, float));
+// expected-error@-1 {{static assertion failed due to requirement '__is_constructible(constructible::S1, int, float)'}} \
+// expected-note@-1 {{'S1' is not constructible with provided types}} \
+// expected-note@#c-S1 {{'S1' defined here}}
+
+struct S2 { // #c-S2
+    S2(int, float, double);
+};
+static_assert(__is_constructible(S2, float));
+// expected-error@-1 {{static assertion failed due to requirement '__is_constructible(constructible::S2, float)'}} \
+// expected-note@-1 {{'S2' is not constructible with provided types}} \
+// expected-note@#c-S2 {{'S2' defined here}}
+
+static_assert(__is_constructible(void));
+// expected-error@-1 {{static assertion failed due to requirement '__is_constructible(void)'}} \
+// expected-note@-1 {{'void' is not constructible with provided types}} \
+// expected-note@-1 {{because it is a cv void type}}
+
+static_assert(__is_constructible(const void));
+// expected-error@-1 {{static assertion failed due to requirement '__is_constructible(const void)'}} \
+// expected-note@-1 {{'const void' is not constructible with provided types}} \
+// expected-note@-1 {{because it is a cv void type}}
+
+static_assert(__is_constructible(volatile void));
+// expected-error@-1 {{static assertion failed due to requirement '__is_constructible(volatile void)'}} \
+// expected-note@-1 {{'volatile void' is not constructible with provided types}} \
+// expected-note@-1 {{because it is a cv void type}}
+
+static_assert(__is_constructible(int ()));
+// expected-error@-1 {{static assertion failed due to requirement '__is_constructible(int ())'}} \
+// expected-note@-1 {{'int ()' is not constructible with provided types}} \
+// expected-note@-1 {{because it is a function type}}
+
+static_assert(__is_constructible(void (int, float)));
+// expected-error@-1 {{static assertion failed due to requirement '__is_constructible(void (int, float))'}} \
+// expected-note@-1 {{'void (int, float)' is not constructible with provided types}} \
+// expected-note@-1 {{because it is a function type}}
+}