[clang] [Clang][Sema] Refactor collection of multi-level template argument lists (PR #106585)

[Younan Zhang via cfe-commits]

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@@ -317,7 +317,8 @@ struct ConvertConstructorToDeductionGuideTransform {
     }
 
     if (NestedPattern)
-      OuterInstantiationArgs = SemaRef.getTemplateInstantiationArgs(Template);
+      OuterInstantiationArgs = SemaRef.getTemplateInstantiationArgs(
+          /*D=*/nullptr, Template->getDeclContext());
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zyn0217 wrote:

What's happening here? Why do we want to pass in a null `Decl` and its DeclContext here?

https://github.com/llvm/llvm-project/pull/106585