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[clang][Sema] Simplify err_init_conversion_failed diagnostic message for const variables #82109

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[clang][Sema] Simplify err_init_conversion_failed diagnostic message for const variables #82109

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[clang][Sema] Simplify err_init_conversion_failed diagnostic message …
agentcooper Feb 17, 2024
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agentcooper Feb 17, 2024
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2 changes: 1 addition & 1 deletion clang/include/clang/Basic/DiagnosticSemaKinds.td
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Original file line number Diff line number Diff line change
Expand Up @@ -2204,7 +2204,7 @@ def err_destructor_template : Error<

// C++ initialization
def err_init_conversion_failed : Error<
"cannot initialize %select{a variable|a parameter|template parameter|"
"cannot initialize %select{a constant|a variable|a parameter|template parameter|"
"return object|statement expression result|an "
"exception object|a member subobject|an array element|a new value|a value|a "
"base class|a constructor delegation|a vector element|a block element|a "
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22 changes: 16 additions & 6 deletions clang/lib/Sema/SemaInit.cpp
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Expand Up @@ -9804,12 +9804,22 @@ bool InitializationSequence::Diagnose(Sema &S,

case FK_ConversionFailed: {
QualType FromType = OnlyArg->getType();
PartialDiagnostic PDiag = S.PDiag(diag::err_init_conversion_failed)
<< (int)Entity.getKind()
<< DestType
<< OnlyArg->isLValue()
<< FromType
<< Args[0]->getSourceRange();

// NOTE: need to be in sync with err_init_conversion_failed
const auto TotalSpecialKinds = 1;

PartialDiagnostic PDiag = S.PDiag(diag::err_init_conversion_failed);
if (Entity.getKind() == InitializedEntity::EK_Variable &&
DestType.isConstQualified()) {
QualType NonConstDestType = DestType;
NonConstDestType.removeLocalConst();
PDiag << 0 /* a constant */
<< NonConstDestType;
} else {
PDiag << (TotalSpecialKinds + (int)Entity.getKind()) << DestType;
}
PDiag << OnlyArg->isLValue() << FromType << Args[0]->getSourceRange();
Comment on lines +9808 to +9821
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@AaronBallman AaronBallman Jan 16, 2025

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How about something along these lines (with comments)?

PartialDiagnostic PDiag = S.PDiag(diag::err_init_conversion_failed);
{
  llvm::SaveAndRestore _(DestType);
  unsigned EKind = (unsigned)Entity.getKind() + 1;
  if (Entity.getKind() == InitializedEntity::EK_Variable &&
        DestType.isConstQualified()) {
    EKind = 0;
    DestType.removeLocalConst();
  }

  PDiag << EKind << DestType << ...;
}
S.HandleFunctionTypeMismatch(PDiag, ...);


S.HandleFunctionTypeMismatch(PDiag, FromType, DestType);
S.Diag(Kind.getLocation(), PDiag);
emitBadConversionNotes(S, Entity, Args[0]);
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2 changes: 1 addition & 1 deletion clang/test/SemaCXX/constant-expression-cxx11.cpp
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Expand Up @@ -901,7 +901,7 @@ static_assert((Derived*)(Base*)pb1 == (Derived*)pok2, "");

// Core issue 903: we do not perform constant evaluation when checking for a
// null pointer in C++11. Just check for an integer literal with value 0.
constexpr Base *nullB = 42 - 6 * 7; // expected-error {{cannot initialize a variable of type 'Base *const' with an rvalue of type 'int'}}
constexpr Base *nullB = 42 - 6 * 7; // expected-error {{cannot initialize a constant of type 'Base *' with an rvalue of type 'int'}}
constexpr Base *nullB1 = 0;
static_assert((Bottom*)nullB == 0, "");
static_assert((Derived*)nullB1 == 0, "");
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11 changes: 11 additions & 0 deletions clang/test/SemaCXX/err_init_conversion_failed.cpp
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Expand Up @@ -59,3 +59,14 @@ void test_15() {
// expected-error-re@-1{{cannot initialize a member subobject of type 'void (template_test::S::*)(const int &){{( __attribute__\(\(thiscall\)\))?}}' with an rvalue of type 'void (template_test::S::*)(int){{( __attribute__\(\(thiscall\)\))?}}': type mismatch at 1st parameter ('const int &' vs 'int')}}
}
}

void test_16() {
const int a = (void)0;
// expected-error@-1{{cannot initialize a constant of type 'int'}}

int* const c = (void)0;
// expected-error@-1{{cannot initialize a constant of type 'int *'}}

const int* b = (void)0;
// expected-error@-1{{cannot initialize a variable of type 'const int *'}}
}