[clang] [clang][Sema] Fix crash when diagnosing candidates with parameter packs (PR #93079)

[kadir çetinkaya via cfe-commits]

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@@ -11298,8 +11298,9 @@ static void DiagnoseBadConversion(Sema &S, OverloadCandidate *Cand,
   Expr *FromExpr = Conv.Bad.FromExpr;
   QualType FromTy = Conv.Bad.getFromType();
   QualType ToTy = Conv.Bad.getToType();
-  SourceRange ToParamRange =
-      !isObjectArgument ? Fn->getParamDecl(I)->getSourceRange() : SourceRange();
+  SourceRange ToParamRange;
+  if (!isObjectArgument && I < Fn->getNumParams())
+    ToParamRange = Fn->getParamDecl(I)->getSourceRange();
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kadircet wrote:

> Though I don't think solving this is complicated

sorry I guess I didn't convey full context in my previous message when I just said "it requires propagating extra information in the bad conversion about the parameter location".  `Fn` in this context is the template decl itself, hence the packs in the parameters are dependent. hence we can't simply ask how many expansions are there.

https://github.com/llvm/llvm-project/pull/93079