[clang] [Clang] Substitute non dependent concepts in constraints (PR #163827)

[Younan Zhang via cfe-commits]

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@@ -4487,6 +4487,109 @@ ExprResult Sema::SubstConstraintExprWithoutSatisfaction(
   return Instantiator.TransformExpr(E);
 }
 
+ExprResult Sema::SubstConceptTemplateArguments(
+    const ConceptSpecializationExpr *CSE, const Expr *ConstraintExpr,
+    const MultiLevelTemplateArgumentList &MLTAL) {
+  TemplateInstantiator Instantiator(*this, MLTAL, SourceLocation(),
+                                    DeclarationName());
+  auto *ArgsAsWritten = CSE->getTemplateArgsAsWritten();
+  TemplateArgumentListInfo SubstArgs(ArgsAsWritten->getLAngleLoc(),
+                                     ArgsAsWritten->getRAngleLoc());
+
+  Sema::InstantiatingTemplate Inst(
+      *this, ArgsAsWritten->arguments().front().getSourceRange().getBegin(),
+      Sema::InstantiatingTemplate::ConstraintNormalization{},
+      CSE->getNamedConcept(),
+      ArgsAsWritten->arguments().front().getSourceRange());
+
+  if (Instantiator.TransformConceptTemplateArguments(
+          ArgsAsWritten->getTemplateArgs(),
+          ArgsAsWritten->getTemplateArgs() +
+              ArgsAsWritten->getNumTemplateArgs(),
+          SubstArgs))
+    return true;
+
+  llvm::SmallVector<TemplateArgument, 4> NewArgList;
+  NewArgList.reserve(SubstArgs.arguments().size());
+  for (const auto &ArgLoc : SubstArgs.arguments())
+    NewArgList.push_back(ArgLoc.getArgument());
+
+  MultiLevelTemplateArgumentList MLTALForConstraint =
+      getTemplateInstantiationArgs(
+          CSE->getNamedConcept(),
+          CSE->getNamedConcept()->getLexicalDeclContext(),
+          /*Final=*/false,
+          /*Innermost=*/NewArgList,
+          /*RelativeToPrimary=*/true,
+          /*Pattern=*/nullptr,
+          /*ForConstraintInstantiation=*/true);
+
+  struct ConstraintExprTransformer : TreeTransform<ConstraintExprTransformer> {
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zyn0217 wrote:

Can we have an explanation as to why we need a TreeTransform here, and it would be better to have an example too.

https://github.com/llvm/llvm-project/pull/163827