[clang] [clang] Use getDefaultArgRange instead of getDefaultArg to retrieve the (PR #79296)

[Haojian Wu via cfe-commits]

https://github.com/hokein created https://github.com/llvm/llvm-project/pull/79296

source location in AliasTemplateDeductionGuideTransform.

I don't have a reproducible testcase, but this should be a safe and non-functional change. We have checked the `hasDefaultArg` before calling getDefaultArg(), but `hasDefaultArg` allows unparsed/uninstantiated default arg which is prohibited in getDefaultArg().

Since we're only interested in the source location, we switch to use getDefaultArgRange() API.

Context: I hit the "!hasUninstantiatedDefaultArg()" assertion inside the getDefaultArg when reusing the "transformFunctionTypeParam" for type alias CTAD implementation (https://github.com/llvm/llvm-project/pull/77890/commits/f0919914f828daf705f89317081946359f00971a).

>From 034810c714dcbebc26b6d6d50c4396c318849327 Mon Sep 17 00:00:00 2001
From: Haojian Wu <hokein.wu at gmail.com>
Date: Wed, 24 Jan 2024 14:55:03 +0100
Subject: [PATCH] [clang] Use getDefaultArgRange instead of getDefaultArg to
 retrieve the source location in AliasTemplateDeductionGuideTransform.

I don't have a reproducible testcase, but this should be a safe and non-functional change.
We have checked the `hasDefaultArg` before calling getDefaultArg(), but `hasDefaultArg`
allows unparsed/uninstantiated default arg which is prohibited in getDefaultArg().

Since we're only interested in the source location, we switch to use getDefaultArgRange() API.

Context: I hit the "!hasUninstantiatedDefaultArg()" assertion inside the
getDefaultArg when reusing the "transformFunctionTypeParam" for
implementing type alias CTAD.
---
 clang/lib/Sema/SemaTemplate.cpp | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/clang/lib/Sema/SemaTemplate.cpp b/clang/lib/Sema/SemaTemplate.cpp
index 9bfa71dc8bcf1db..a5d2afdf4a0bab8 100644
--- a/clang/lib/Sema/SemaTemplate.cpp
+++ b/clang/lib/Sema/SemaTemplate.cpp
@@ -2588,7 +2588,7 @@ struct ConvertConstructorToDeductionGuideTransform {
       // placeholder to indicate there is a default argument.
       QualType ParamTy = NewDI->getType();
       NewDefArg = new (SemaRef.Context)
-          OpaqueValueExpr(OldParam->getDefaultArg()->getBeginLoc(),
+          OpaqueValueExpr(OldParam->getDefaultArgRange().getBegin(),
                           ParamTy.getNonLValueExprType(SemaRef.Context),
                           ParamTy->isLValueReferenceType()   ? VK_LValue
                           : ParamTy->isRValueReferenceType() ? VK_XValue