[clang] [Clang] Defer the instantiation of explicit-specifier until constraint checking completes (PR #70548)

[Younan Zhang via cfe-commits]

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@@ -3553,6 +3553,56 @@ static unsigned getPackIndexForParam(Sema &S,
   llvm_unreachable("parameter index would not be produced from template");
 }
 
+// if `Specialization` is a `CXXConstructorDecl` or `CXXConversionDecl`
+// we try to instantiate and update its explicit specifier after constraint
+// checking.
+static Sema::TemplateDeductionResult
+tryInstantiateExplicitSpecifier(Sema &S, FunctionDecl *Specialization,
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zyn0217 wrote:

nit: Do you think we should make this function a (private) member of `Sema` instead of a static function?

https://github.com/llvm/llvm-project/pull/70548