Skip to content

[Clang] Added explanation why is_constructible evaluated to false. #143309

New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

Sign up for GitHub

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

Merged
merged 9 commits into from
Jun 13, 2025
Merged

[Clang] Added explanation why is_constructible evaluated to false. #143309

Show file tree
Hide file tree
Changes from 1 commit
Commits
Show all changes
9 commits
Select commit Hold shift + click to select a range
ed1f379
Fixed problem when std::is_xxx_v<> tries to get Argument as type when…
egorshamshura Jun 8, 2025
ef79556
Updated DiagnoseNonTriviallyCopyableReason, changed tests to current …
egorshamshura Jun 9, 2025
cb89df9
Fixed problems, updated DiagnoseNonConstructibleReason and tests
egorshamshura Jun 10, 2025
bd3cefd
Merge branch 'main' into explain-is-constructible
egorshamshura Jun 10, 2025
172cee8
Fixed tests
egorshamshura Jun 11, 2025
bd3cfca
Removed incomplete type check. Added check for incomplete array type …
egorshamshura Jun 12, 2025
bd1e468
Changed Baz to cwg1890-Baz in cwg18xx.cpp
egorshamshura Jun 12, 2025
124e9f1
Fixed some problems, changed behavior on void types, updated test
egorshamshura Jun 12, 2025
e18073b
Added curley brackets, changed assert to llvm_unreachable
egorshamshura Jun 12, 2025
File filter

Filter by extension

Filter by extension
Conversations
Failed to load comments.
Loading
Jump to
Jump to file
Failed to load files.
Loading
Diff view
Diff view
7 changes: 5 additions & 2 deletions clang/include/clang/Basic/DiagnosticSemaKinds.td
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -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
Expand All @@ -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<
Expand Down
35 changes: 33 additions & 2 deletions clang/lib/Sema/SemaTypeTraits.cpp
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -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;

Expand Down Expand Up @@ -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);
}

Expand Down Expand Up @@ -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());
Copy link
Collaborator

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

IS this a valid assumption here (that this is a type?). Presumably this could be an NTTP pack as well...

Though getAsType would assert for us?

Copy link
Contributor Author

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

getAsType would assert for us

}
if (Arg.getKind() == TemplateArgument::ArgKind::Type)
Copy link
Collaborator

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

Suggested change
if (Arg.getKind() == TemplateArgument::ArgKind::Type)
else if (Arg.getKind() == TemplateArgument::ArgKind::Type)

Copy link
Contributor Author

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

Fixed

Args.push_back(Arg.getAsType());
}
Copy link
Collaborator

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

If the kind is neither, we should probably do SOMETHING about it, even if it is just an assert.

Copy link
Contributor Author

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

Added assert

return {{Trait.value(), std::move(Args)}};
}

Expand Down Expand Up @@ -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)
Copy link
Contributor

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

I think what would be useful here is to try to run overload resolution again on all the arguments,
and show the errors - https://compiler-explorer.com/z/aMG1nEoz1

You can look at how static bool EvaluateBooleanTypeTrait works (in the same file).

I think that by calling InitializationSequence::Diagnose we would get super useful diagnostics.

We don't have a good way to turn the errors that would be produced into notes, though @AaronBallman @erichkeane @Sirraide - but maybe emitting errors is good enough as a first approach

Copy link
Member

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

We don't have a good way to turn the errors that would be produced into notes

I’m working on something diagnostics-related right now that would allow nesting errors but it’s not finished yet. Because of how that works though it should be straight-forward to add the nesting later, so just emitting the errors for now should be fine imo.

Copy link
Contributor Author

@egorshamshura egorshamshura Jun 9, 2025 •
edited
Loading

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

Thanks for your advice @cor3ntin (and also can i ping you?). I have tried to use InitializationSequence::Diagnose. However I'm dealing with some issues.

  1. InitializationSequence::Diagnose does not emit any diagnostic. It correctly returns true or false, but nothing appears in console. Although the FailureKind in InitializationSequence is defined correctly.
  2. After InitializationSequence::Diagnose I can not use SemaRef.Diag. Nothing is being written to the console. However I can write in llvm::errs manually.
    So, can you please help me understand what I'm doing wrong? I have uploaded the latest update.

Copy link
Contributor Author

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

Well, I figured it out! SFINAETrap was the problem. So now it works as expected.

<< 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)
Expand Down Expand Up @@ -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;
}
Expand Down
72 changes: 72 additions & 0 deletions clang/test/SemaCXX/type-traits-unsatisfied-diags-std.cpp
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -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
Expand All @@ -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


Expand Down Expand Up @@ -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

}
Expand Down Expand Up @@ -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);
Expand All @@ -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}}
}


Expand All @@ -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'}} \
Expand Down Expand Up @@ -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}}
}
}
44 changes: 44 additions & 0 deletions clang/test/SemaCXX/type-traits-unsatisfied-diags.cpp
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -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}}
}
Loading