[clang] Use getDefaultArgRange instead of getDefaultArg to retrieve the

[hokein]

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.

[llvmbot]

@llvm/pr-subscribers-clang

Author: Haojian Wu (hokein)

Changes

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 (f091991).

---

Full diff: https://github.com/llvm/llvm-project/pull/79296.diff

1 Files Affected:

• (modified) clang/lib/Sema/SemaTemplate.cpp (+1-1)

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

[sam-mccall]

Sorry for missing this!

Would be nice to have a testcase but I see it's hard to get into the crashing state (maybe even not possible via clang).
Seems worthwhile to be robust to such conditions and getDefaultArgRange appears less fragile.

[hokein]

Sorry for missing this!

Would be nice to have a testcase but I see it's hard to get into the crashing state (maybe even not possible via clang). Seems worthwhile to be robust to such conditions and getDefaultArgRange appears less fragile.

This fix was needed for the initial type-alias CTAD implementation, we don't need it anymore in the new implementation :)

We could drop this change, but I think it is worth having it, it is an improvement, and make the code more robust.