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[Clang] Handle ?: operator in fold expression #164019

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[Clang] Handle ?: operator in fold expression #164019

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[Clang] Handle ?: operator in fold expression
azmat-y Oct 17, 2025
457c556
Merge branch 'main' into users/azmat-y/clang-frontend/fold-expr
azmat-y Nov 6, 2025
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3 changes: 3 additions & 0 deletions clang/lib/Sema/SemaExpr.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -8966,6 +8966,9 @@ ExprResult Sema::ActOnConditionalOp(SourceLocation QuestionLoc,
commonExpr = MatExpr.get();
}

if (commonExpr->getDependence() & ExprDependence::UnexpandedPack)
return ExprError();

opaqueValue = new (Context) OpaqueValueExpr(commonExpr->getExprLoc(),
commonExpr->getType(),
commonExpr->getValueKind(),
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2 changes: 1 addition & 1 deletion clang/lib/Sema/SemaTemplateVariadic.cpp
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Expand Up @@ -1510,7 +1510,7 @@ static void CheckFoldOperand(Sema &S, Expr *E) {
E = E->IgnoreImpCasts();
auto *OCE = dyn_cast<CXXOperatorCallExpr>(E);
if ((OCE && OCE->isInfixBinaryOp()) || isa<BinaryOperator>(E) ||
isa<AbstractConditionalOperator>(E)) {
isa<AbstractConditionalOperator>(E) || isa<RecoveryExpr>(E)) {
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@erichkeane erichkeane Nov 12, 2025

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You can't really do this I think? RecoveryExpr isn't always generated/always valid.

It seems to me that we shouldn't have created the RecoveryExpr here (or done the return ExprError) unless we had diagnosed

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@azmat-y azmat-y Nov 30, 2025

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IIUC the frontend produces a RecoveryExpr on semantic errors that prevent forming well formed statements. In that case should it be always generated in case of semantic errors? Can you point an example where it is not always generated.

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@Sirraide Sirraide Nov 30, 2025

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IIUC the frontend produces a RecoveryExpr on semantic errors that prevent forming well formed statements. In that case should it be always generated in case of semantic errors? Can you point an example where it is not always generated.

RecoveryExprs are only created if they’re enabled by some flag (-frecovery-ast iirc), otherwise, you just get ExprError():

llvm-project/clang/lib/Sema/SemaExpr.cpp

Lines 21591 to 21594 in f42e58f

ExprResult Sema::CreateRecoveryExpr(SourceLocation Begin, SourceLocation End,
ArrayRef<Expr *> SubExprs, QualType T) {
if (!Context.getLangOpts().RecoveryAST)
return ExprError();

S.Diag(E->getExprLoc(), diag::err_fold_expression_bad_operand)
<< E->getSourceRange()
<< FixItHint::CreateInsertion(E->getBeginLoc(), "(")
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5 changes: 5 additions & 0 deletions clang/test/SemaCXX/fold_expr_typo.cpp
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Expand Up @@ -12,3 +12,8 @@ template <typename... U> struct A {
foo<T>((... + static_cast<U>(1))); // expected-error {{expression contains unexpanded parameter pack 'T'}}
}
};

template <typename ... T>
void foo(T... Params) {
(Params ?: 1, ...); // expected-error {{expression not permitted as operand of fold expression}}
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@erichkeane erichkeane Nov 12, 2025

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This feels like it is in desperate need of notes or better source locations.

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@azmat-y azmat-y Nov 30, 2025

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Sorry for the late response, I've been busy with college and such. Do you mean the test itself? Or the diagnostic? g++ diagnostic shows the caret on the conditional operator, should we do something similar here?

}