[clang] [Clang] Implement CWG2900 (PR #224291)

[Corentin Jabot via cfe-commits]

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@@ -234,31 +234,39 @@ class NonTypeOrVarTemplateParmDecl {
   const NamedDecl *Template;
 };
 
-/// If the given expression is of a form that permits the deduction
-/// of a non-type template parameter, return the declaration of that
-/// non-type template parameter.
+/// If the given expression is of a form that names a non-type template
+/// parameter, return the declaration of that parameter. A null \p Depth
+/// accepts a parameter at any depth.
 static NonTypeOrVarTemplateParmDecl
-getDeducedNTTParameterFromExpr(const Expr *E, unsigned Depth) {
+getNTTParameterFromExpr(const Expr *E, UnsignedOrNone Depth) {
   // If we are within an alias template, the expression may have undergone
   // any number of parameter substitutions already.
   E = unwrapExpressionForDeduction(E);
   if (const auto *DRE = dyn_cast<DeclRefExpr>(E))
     if (const auto *NTTP = dyn_cast<NonTypeTemplateParmDecl>(DRE->getDecl()))
-      if (NTTP->getDepth() == Depth)
+      if (!Depth || NTTP->getDepth() == *Depth)
         return NTTP;
 
   // A pack-index-template-name is not deducible.
   if (const auto *DTI = dyn_cast<DependentTemplateIdExpr>(E))
     if (!DTI->getTemplateName().getAsPackIndexingTemplate() &&
-        DTI->getParameter()->getDepth() == Depth)
+        (!Depth || DTI->getParameter()->getDepth() == *Depth))
       return DTI->getParameter();
 
   return nullptr;
 }
 
+QualType Sema::getTypeOfConstantTemplateParameter(const TemplateArgument &A,
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cor3ntin wrote:

The type of the parameter gets deduced from its value/argument

https://github.com/llvm/llvm-project/pull/224291