[clang] [Clang][RFC] Intrododuce a builtin to determine the structure binding size (PR #131515)

[Younan Zhang via cfe-commits]

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@@ -4160,6 +4160,54 @@ static bool CheckVecStepTraitOperandType(Sema &S, QualType T,
   return false;
 }
 
+static ExprResult BuildStructuredBindingSizeTraitImpl(Sema &S, QualType T,
+                                                      Expr *E,
+                                                      TypeSourceInfo *TInfo,
+                                                      SourceLocation Loc,
+                                                      SourceRange ArgRange) {
+  assert(!!E != !!TInfo);
+  assert(!T->isDependentType());
+  std::optional<unsigned> Size =
+      S.GetDecompositionElementCount(T, ArgRange.getBegin());
+  if (!Size) {
+    return S.Diag(Loc, diag::err_arg_is_not_destructurable) << T << ArgRange;
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zyn0217 wrote:

Looking closer I'm surprised a SemaDiagnosticBuilder could be implicitly converted to ExprResult. Is that due to the implicit operator bool()?

https://github.com/llvm/llvm-project/pull/131515