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Improve diagnostics for EvaluateAsConstantExpr (#6956)

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Initialize the `Diag` field `EvalResult` to get notes from clang when
`EvaluateAsConstantExpr` fails, then emit them using clang's diagnostic
infrastructure.

Also set valid source locations in a couple places, otherwise clang's
diagnostics code crashes.
This commit is contained in:
Nicholas Bishop
2026-03-24 19:40:09 +00:00
committed by GitHub
parent e0c6800ab3
commit f9e1806c4a
3 changed files with 21 additions and 13 deletions
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toolchain/check/cpp/constant.cpp
+12 -9
View File
@@ -5,6 +5,7 @@
#include "toolchain/check/cpp/constant.h"
#include "toolchain/check/cpp/import.h"
#include "toolchain/check/cpp/location.h"
#include "toolchain/check/cpp/type_mapping.h"
#include "toolchain/check/eval.h"
#include "toolchain/check/member_access.h"
@@ -226,7 +227,7 @@ auto EvalCppCall(Context& context, SemIR::LocId loc_id,
context.ast_context(), /*QualifierLoc=*/clang::NestedNameSpecifierLoc(),
/*TemplateKWLoc=*/clang::SourceLocation(), function_decl,
/*RefersToEnclosingVariableOrCapture=*/false,
/*NameLoc=*/clang::SourceLocation(), function_decl->getType(),
/*NameLoc=*/GetCppLocation(context, loc_id), function_decl->getType(),
clang::VK_LValue);
// Cast to a function pointer type.
@@ -253,18 +254,20 @@ auto EvalCppCall(Context& context, SemIR::LocId loc_id,
auto* call_expr = clang::CallExpr::Create(
context.ast_context(), implicit_cast_expr, arg_exprs,
function_decl->getCallResultType(), clang::VK_PRValue,
/*RParenLoc=*/clang::SourceLocation(), clang::FPOptionsOverride());
/*RParenLoc=*/GetCppLocation(context, loc_id),
clang::FPOptionsOverride());
// Evaluate the expr as a constant and map that to Carbon constant.
clang::SmallVector<clang::PartialDiagnosticAt> notes;
clang::Expr::EvalResult eval_result;
eval_result.Diag = &notes;
if (!call_expr->EvaluateAsConstantExpr(eval_result, context.ast_context())) {
// TODO: improve this diagnostic with information from `eval_result`.
CARBON_DIAGNOSTIC(CppConstexprEval, Error,
"failed to evaluate {0:consteval|constexpr} function "
"call as a constant",
Diagnostics::BoolAsSelect);
context.emitter().Emit(loc_id, CppConstexprEval,
function_decl->isConsteval());
context.clang_sema().Diag(call_expr->getBeginLoc(),
clang::diag::err_invalid_consteval_call)
<< function_decl << function_decl->isConsteval();
for (const auto& note : notes) {
context.clang_sema().Diag(note.first, note.second);
}
return SemIR::ErrorInst::ConstantId;
}